The chronic inflammatory process that is damaging the brains of autistic children has an undeniable autoimmune component. The second editorial on this site on the causes of autism

(Link to the first editorial: https://wp.me/pbW3AH-1DO -Link to the third editorial of this series: https://wp.me/pbW3AH-1Tx)

Based on the logic enlightened by scientific publications that have accumulated over decades, this series of editorials aims to offer the reader a path to identifying the etiology (cause) of autism—a condition whose annual cost, including direct and indirect expenses, could exceed 460 billion dollars in the U.S. by 2025 (https://pubmed.ncbi.nlm.nih.gov/26183723/).

The previous editorial brought together clinical and scientific data that identify the inflammatory nature of the pathological process causing autistic behavior. It is, therefore, unquestionably excluded (through a simple laboratory test, such as measuring the circulating levels of the enzyme Neuronal Specific Enolase – NSE) the hypothesis that autistic children would be just “neuroatypical” individuals. This term mistakenly regards them as “different” and not as carriers of deficits of an organic nature (carriers of a physical illness). In this sense, it is worth remembering that up to 60% of autistic people have a cognitive impairment (https://www.cdc.gov/mmwr/volumes/72/ss/ss7202a1.htm).

The release of NSE into circulation by damaged neuronal cells is eloquent enough to define autism as a neurological disease (with pathologic features consistent with chronic encephalitis). Persistent denial of this fact only hinders the development and timely application of early and effective treatment—a right of the affected children and their parents. With autism acknowledged as a neurological disorder, pinpointing its fundamental cause would enable preventive strategies and stop the ongoing autism epidemic, which is in the best interest of society (including the medical community). As will be seen in the next Editorial, the autism epidemic can no longer be regarded as merely apparent or as a result of “better diagnostics and awareness” (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6242891/), which led to the coining of the expression “Autism Spectrum Disorders” (ASD) instead of “autism”. In fact, how can one possibly believe that a simple pre-existing behavioral disorder, whose prevalence allegedly is not increasing worldwide (just being better “perceived” or “detected”), could be expected to generate an annual cost of more than 460 billion dollars by 2025 in the USA alone (https://pubmed.ncbi.nlm.nih.gov/26183723/)?

An inflammatory process that affects the brain (encephalitis) can, for example, be caused by viral or bacterial infections or even by the aggression of the immune system (autoimmune encephalitis). In addition, there is a fundamental fact regarding autism (which will be reviewed in subsequent editorials on this site): the chronic encephalitis characterizing this condition can be caused by the presence of aluminum in the nervous tissue (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10180736/), triggering an autoimmune process directed against neural proteins (antigens).

This Second Editorial focuses on the chronic autoimmune aggression present in individuals with autism (chronic encephalitis). The avalanche of scientific data demonstrating the presence of an autoimmune process in this condition contrasts with the view that autism is a simple behavioral disorder (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5373490/). As we will see in subsequent editorials, in line with the renowned “Principle of Parsimony,” which inspired modern statistics, one must identify the primary triggering factor of this autoimmune aggression, around which several secondary factors contributing to its progression and maintenance gravitate. That principle is used, for example, in daily medical practice to establish a single diagnosis (the most likely one), as opposed to the improbability of multiple diagnoses co-occurring in a single patient. When identifying the diagnosis of a disease, i.e., the single cause of a constellation of clinical and laboratory manifestations, it is essential to pursue the most straightforward explanation (ideally the only one) for all manifestations.

Thus, just as it is improbable that a patient will present with two diseases that begin simultaneously without any pathophysiological relationship between them, it is also unlikely that the pieces of the pathophysiological puzzle of autism will not fit together perfectly around an overriding causal factor.

Likewise, all the discoveries reported in autism, including its condition of chronic encephalitis, the autoimmune features, the predisposing genetic factors, and mainly, the exponential growth of its incidence and prevalence that has occurred in the last 40 to 50 years, must be grouped and arranged around a primary cause, much like the process of assembling the pieces of a jigsaw puzzle. Again, it is emphasized here that without identifying this primary cause, there is no way to stop the pathological (inflammatory, autoimmune, neurodegenerative) process that characterizes autism or to implement its prevention.

The statement that “autism has multiple causes that occur in various combinations” or that it is “a highly complex and heterogeneous biological disorder” (https://www.biologicalpsychiatryjournal.com/article/S0006-3223(16)32739-1/) contradicts the Principle of Parsimony (or “Occam’s Razor”). Such statements only serve to evade the search for the primary cause of this humanitarian, social, and economic tragedy while its prevalence continues to rise rapidly without preventive measures to counter it. On the contrary, in this series of editorials, we seek to equate the diversity of pathophysiological findings related to autism with the various clinical and laboratory manifestations found in a patient to identify a single primary cause—comparatively, a single diagnosis as opposed to multiple diagnoses.

On the other hand, the statement that “a person with autism is born with autism” (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5501015/) disregards the currently undisputed fact that many children develop the first manifestations of autism after the first year of life, following a perfectly normal initial psychomotor development (“regressive autism” – which was speculatively denied for a long time) (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4949854/).

However, regressive autism does exist (https://goldencaretherapy.com/regressive-autism – 2021):

“Regressive autism, also known as late-onset autism, involves a period of typical development followed by a loss of previously acquired skills or a noticeable decline in social and communication abilities. This regression usually occurs between 15 and 30 months of age and can be sudden or gradual.”

The following example was taken from a text written a few years ago. At that time (2017), the author was trying to argue against the reality of the existence of cases of regressive autism (https://www.thetransmitter.org/spectrum/rethinking-regression-autism/):

“…a talkative, curious 2-year-old suddenly withdraws. He grows indifferent to the sound of his name. He begins to speak less than before or stops entirely. He turns from playing with people to playing with things, from exploring many objects and activities to obsessing over a few. He loses many of the skills he had mastered and starts to rock, spin, walk on his toes or flap his hands. It’s often at this point that his terrified parents seek answers from experts.”

…and parents do not usually find assertive answers consistent with scientific logic—only speculations. This is due to the lack of an integrated and rational presentation of the pathophysiological features already documented in various studies. Such a gap is precisely the objective that inspired these consecutive editorials, which should also explain the existence of regressive autism.

Contrary to attempts to deny its existence, the reality of regressive autism has been recognized for many years in scientific publications, where the authors point it out as “intriguing” (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4949854/), thus acknowledging that they do not know how to explain it:

“The occurrence of developmental regression in autism spectrum disorder (ASD) is one of the most puzzling phenomena of this disorder.”

“To date, the causes of regression in autism are unknown.”

In this editorial, we review the direct impact of this autoimmune aggression on the access of a vitally important nutrient to the central nervous system (CNS): vitamin B9 (or “folate”: methylfolate and folinic acid—the latter also called leucovorin). Specific genetic polymorphisms (genes with a structure different from the standard conformation) make a significant fraction of the child population particularly susceptible to a reduction in the supply of folates to the CNS.

Autoimmune aggression towards the brain in autistic children is confirmed through repeated publications beginning in the 1980s and subsequently reviewed by several authors (https://www.sciencedirect.com/science/article/pii/S1750946720300581; https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2018.00405/full#B90; https://psychiatryonline.org/doi/10.1176/appi.focus.24022004; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8955336/; https://www.nature.com/articles/npp2016158; https://psychiatryonline.org/doi/10.1176/appi.focus.24022004;

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6242891/; https://pubmed.ncbi.nlm.nih.gov/15223250/;

https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2018.00405/full#B153).

The evidence suggesting that chronic encephalitis in autistic individuals involves an autoimmune attack against brain tissue can be arranged as follows:

(I) Generation of autoantibodies targeting neural antigens;

(II) Generation of autoantibodies not specifically targeting neural antigens;

(III) Correlation between circulating autoantibody levels and the severity of autism;

(IV) Presence of lymphocytes infiltrating the brain of individuals with autism;

(V) Th17 immune response (induced by interleukin 17-producing helper lymphocytes, typical in autoimmune conditions) has been observed in autistic individuals;

(VI) Mitigation of autistic symptoms through corticosteroid or immunoglobulin therapy;

(VII) Occurrence of autoimmune or immune-mediated disorders as comorbidities in autism;

(VIII) Elevated prevalence of autoimmune diseases among consanguineous relatives (a family history of autoimmune disorders increases autism risk);

(IX) Similar to classic autoimmune diseases, the benefits of cholecalciferol administration are also observed in autism;

(X) Evidence pieces show genetic resistance to the immunoregulatory effects of cholecalciferol (or “vitamin” D, which inhibits Th17 activity) in autism

Below is the presentation of each group of publications.

(I) Generation of autoantibodies targeting neural antigens.

The immune system of individuals with autism generates a wide variety of autoantibodies targeting neural antigens (https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2018.00405/full#B90; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6952169/), with reactivity directed against various regions of the CNS and different populations of neurons. Together with the other published data listed below, the production of autoantibodies cannot be considered merely an epiphenomenon of the process causing autism; rather, it should be regarded as a cardinal factor in the inflammatory process harmful to the CNS (an epiphenomenon would be a phenomenon associated with a lesional process without a causal relationship to it).

According to the Principle of Parsimony, the primary cause of autism must explain both the broad repertoire of autoantibodies produced and the variety of neural regions and cells affected. As mentioned in the introduction to this Editorial, the primary cause around which aggravating factors gravitate will be identified in a future Editorial, applying the causality criteria established by Austin Bradford Hill in 1965 and widely recognized since then.

Singh et al. first identified the presence of autoantibodies directed against CNS proteins in autistic individuals in 1988. They found antibodies against neuron axon filament protein (NAFP) in the blood of 10 out of 15 children with autism (https://pubmed.ncbi.nlm.nih.gov/3144935/). Anti-myelin basic protein (MBP) antibodies were identified in individuals with ASD in 1993 (https://pubmed.ncbi.nlm.nih.gov/7682457/)—a finding that was replicated in 1998 (https://pubmed.ncbi.nlm.nih.gov/9756729/) and again in 2006 (https://pubmed.ncbi.nlm.nih.gov/16181614/). The presence of anti-NAFP antibodies was also confirmed in 1998 (https://pubmed.ncbi.nlm.nih.gov/9756729/). In 2013, significantly elevated levels of anti-MBP antibodies were confirmed compared to healthy controls (https://pubmed.ncbi.nlm.nih.gov/23726766/). The same study demonstrated significantly elevated levels of anti-myelin-associated glycoprotein (“anti-MAG”) antibodies compared to healthy controls. The same study also demonstrated the link between these autoantibodies and autism severity:

“Patients with severe autism had significantly higher serum anti-MBP and anti-MAG auto-antibodies than children with mild to moderate autism, P = 0.047 and P < 0.001, respectively (Tables 1 and 2).”

Other studies have demonstrated a significant increase in the incidence of anti-NAFP and anti-glial fibrillary acidic protein (GFAP) in autistic individuals, but not in individuals with mental retardation (https://www.sciencedirect.com/science/article/abs/pii/S0887899497000453).

More recent studies have found autoantibodies targeting regions of the prefrontal cortex, caudate, putamen, cerebellum, and cingulate gyrus of the brain (https://pubmed.ncbi.nlm.nih.gov/16842863/) and hypothalamus (https://pubmed.ncbi.nlm.nih.gov/17804536/) in children with ASD.

As the authors of this latest study conclude:

“While the potential role of these autoantibodies in autism is currently unknown, their presence suggests a loss of self-tolerance to one or more neural antigens during early childhood.”

Similarly, in another study published in 2009 (https://pubmed.ncbi.nlm.nih.gov/18706993/), researchers found that 21% of plasma samples from children with ASD were highly immunoreactive against primate Golgi neurons. These inhibitory interneurons are located in the granular layer of the cerebellum. They use the neurotransmitter gamma-aminobutyric acid (GABA) to modulate excitatory synapses, enabling a balance between excitation and inhibition. In contrast, this immunoreactivity was not observed when plasma obtained from age-matched, typically developing controls was used. A later study found that autoreactivity also targeted other GABAergic interneurons distributed throughout the neocortex and in many subcortical regions, including the superficial layers of the cortex (https://pubmed.ncbi.nlm.nih.gov/21521495/). Other authors found that immunoreactivity directed at Golgi neurons and other interneurons correlates with the severity of behavioral and emotional changes in autistic children (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3313674/; https://pubmed.ncbi.nlm.nih.gov/21420487/;https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3039058/; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4111628/; https://pubmed.ncbi.nlm.nih.gov/22226851). In line with the results of these studies, alterations in the structure of the cerebellum and in the composition of the cerebellar neuron population are among the most consistent abnormalities in autism (https://pubmed.ncbi.nlm.nih.gov/11468308/).

Contrary to what was previously thought, immune system cells routinely penetrate the CNS, even in the absence of inflammation, to perform immunological surveillance. Local presentation of antigens to produce antibodies and the proliferation of lymphocyte clones occur even in the noninflamed nervous system (https://www.nature.com/articles/nn.3161). In neuroinflammation, the barriers that separate the brain from circulation are disrupted, thus increasing the transit of cells and macromolecules between these compartments. (https://www.mdpi.com/1422-0067/24/16/12699). The penetration of autoantibodies directed against GABAergic neurons may, therefore, reduce the number or activity of these inhibitory cells. This may contribute to the imbalance between excitation and inhibition—an imbalance that has long been suggested as a determinant of the disturbance of sensory, memory, social, and emotional systems found in autism (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6748642/).

Glial cells (which help shield, support, and nourish neurons) have long been known to multiply (through a process called mitosis). Contrary to older concepts, the generation of new neurons has also been demonstrated in the adult human CNS for over a quarter of a century, although not through mitosis. Newly formed neurons arise from the multiplication of cells located around the cavities and channels through which cerebrospinal fluid circulates—the “subependymal” layer. The term “ependyma” is used to indicate the layer of cells that lines the internal cavities of the brain (ventricles), while the “subependymal” region denotes the area adjacent to the ventricles. The cells in this region can be classified into two types: neural stem cells and neural progenitor cells, the latter of which are derived from neural stem cells. When they multiply, both lead to the formation of new neurons (neurogenesis) and two types of glial cells: astrocytes and oligodendrocytes, which constitute the “macroglia”. They participate in the formation and maturation of the neural system, not only in the embryonic and fetal phases but also after birth, and the production of new neurons continue even in elderly individuals. These newly formed neurons (“neuroblasts”) are capable of migrating from the subependymal region to various regions of the CNS, supporting the neural cell population and function of these regions (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6782600/; https://www.jneurosci.org/content/22/3/612.short; https://www.nature.com/articles/nm1198_1313; https://www.sciencedirect.com/science/article/pii/S2214854X20300133).

Neurogenesis is probably involved in the processes of skill acquisition in childhood, such as speech (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3844860/). On the other hand, the normal development of the nervous system during the postnatal period requires the elimination of an excess of connections (synapses) between neurons through a process called “synaptic pruning” (https://www.science.org/doi/abs/10.1126/science.1202529). This process is inhibited in the brains of individuals with autism (https://www.nature.com/articles/mp2016103).

A high serum level of autoantibodies generated against human neural progenitor cells has been identified in patients with autism (https://pubmed.ncbi.nlm.nih.gov/23838310/). On the other hand, serum from autism patients suppresses the differentiation and maturation of neural progenitor cells in culture, demonstrating an autoimmune event that may be one of the mechanisms of neurodevelopmental impairment in this condition, involving the inhibition of neurogenesis (https://pubmed.ncbi.nlm.nih.gov/19526302/; https://pubmed.ncbi.nlm.nih.gov/19526302/; https://pubmed.ncbi.nlm.nih.gov/23838310/).

On the other hand, excessive microglial activation, as part of the mechanism involved in the inflammation that affects the autistic brain (https://www.sciencedirect.com/science/article/abs/pii/S0022395620308785), can alter the execution of the neural pruning process by these cells. This may lead to an excess of excitatory synapses to the detriment of inhibitory synapses (https://www.sciencedirect.com/science/article/abs/pii/S0168010215001625), thus contributing, also through this mechanism, to a hyperexcitation potentially underlying the hyperactivity found in autistic individuals.

Contributing to this imbalance is the production of autoantibodies directed against serotonin receptors in the autistic brain (https://pubmed.ncbi.nlm.nih.gov/2578670/; https://pubmed.ncbi.nlm.nih.gov/1375597/). Serotonin is a neurotransmitter of fundamental importance for emotional behavior, and the impairment of serotonergic activity can alter attention and emotional reactions to external stimuli (https://www.sciencedirect.com/science/article/abs/pii/S1569733910700904), as seen in autistic behavior (https://www.sciencedirect.com/science/article/abs/pii/S0890856713003080). The antibodies directed against the serotonin receptor in an autistic child reached values of 600 and 980 fmol/ml of serum in two samples collected one month apart. These levels are much higher than the levels of antibodies directed against the nicotinic receptors of the neurotransmitter acetylcholine, found in a disease classically recognized as autoimmune (myasthenia gravis), in which serum autoantibody titers reach maximum values of 45 fmol/ml, resulting in a reduction in skeletal muscle strength (https://pubmed.ncbi.nlm.nih.gov/2578670/).

Among the autoantibodies directed against brain cells found in the serum of autistic children are also antibodies against myelin-associated basic glycoprotein (anti-MAG) (https://pubmed.ncbi.nlm.nih.gov/22898564/; https://pubmed.ncbi.nlm.nih.gov/23726766/), anti-myelin basic protein (anti-MBP) (https://pubmed.ncbi.nlm.nih.gov/23726766/), and anti-ganglioside M1 antibodies (the most abundant glycosphingolipid component of neuronal membranes). The highest levels of these autoantibodies are found in more severe cases of autism (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3104945/).

Other specific brain autoantibodies, such as anti-myelin basic protein antibodies (https://pubmed.ncbi.nlm.nih.gov/15223250/), anti-myelin-associated glycoprotein antibodies, and anti-ganglioside M1 antibodies (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3104945/), have been observed in autistic children.

(II) Generation of autoantibodies not specifically targeting neural antigens.

The antinuclear antibody (ANA) is composed of antibodies directed against structures (antigens) located in the nucleus and cytoplasm of cells, such as proteins, nucleic acids (DNA, RNA), and protein-nucleic acid complexes. For decades, its presence in the circulation has been considered fundamental for diagnosing autoimmune diseases (https://ard.bmj.com/content/73/1/17.short; https://www.sciencedirect.com/science/article/abs/pii/S2173574310700496). Its production by the cells of an individual’s immune system (also in children) indicates that an autoimmune disease may be present or developing, such as systemic lupus erythematosus (SLE), scleroderma (localized or systemic), mixed connective tissue disease (with mixed features of SLE, and polymyositis), rheumatoid arthritis, juvenile rheumatoid arthritis, Sjögren’s syndrome, polymyositis and dermatomyositis (https://my.clevelandclinic.org/health/diagnostics/14897-antinuclear-antibody-test-in-children; https://www.researchgate.net/publication/333705452_Pattern_and_Frequency_of_Anti-nuclear_Antibody_Positivity_in_Paediatric_Rheumatic_Diseases).

As would be expected in the case of the participation of autoimmune mechanisms in autism, a positive result on the ANA test has been found in autistic children, associated with the severity of autistic manifestations and the presence of electroencephalographic alterations (https://pubmed.ncbi.nlm.nih.gov/19135624/).

Antiphospholipid antibodies are autoantibodies that target proteins bound to phospholipids (fundamental lipid structures in cell membranes) (https://pt.khanacademy.org/science/ap-biology/cell-structure-and-function/plasma-membranes/a/structure-of-the-plasma-membrane#:~:text=v%C3%AAm%20dos%20carboidratos.-,Fosfolip%C3%ADdios,t%C3%AAm%20regi%C3%B5es%20hidrof%C3%ADlicas%20e%20hidrof%C3%B3bicas). The presence of these antibodies leads to antiphospholipid antibody syndrome (APS—a multisystem autoimmune disease—https://pubmed.ncbi.nlm.nih.gov/36849186/). The result is an increased risk of thrombotic events, pregnancy morbidity, and several other autoimmune and inflammatory complications (https://pubmed.ncbi.nlm.nih.gov/36849186/). Although it was initially described in the context of lupus (SLE), APS is also found to be dissociated from SLE with similar frequency (https://pubmed.ncbi.nlm.nih.gov/36849186/). In addition to SLE, diseases such as thrombocytopenia, hemolytic anemia, heart valve disease, pulmonary hypertension, microangiopathic nephropathy, skin ulcers, livedo reticularis, refractory migraine, cognitive dysfunction, and atherosclerosis are associated with APS (https://www.ncbi.nlm.nih.gov/books/NBK459442/). Supporting the involvement of autoimmune mechanisms in autism, elevated levels of antiphospholipid autoantibodies (anti-cardiolipin, anti-β2-glycoprotein 1, and anti-phosphoserine) have been found in individuals with autism and are associated with the severity of behavioral changes (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3794552/).

Anti-endothelial cell antibodies are a heterogeneous group of antibodies directed against the cells lining blood vessels. Since their discovery in the 1970s, these autoantibodies have been identified in several conditions characterized by vascular inflammation, including SLE, APS, systemic vasculitis, rheumatoid arthritis, systemic scleroderma, and organ transplant rejection (https://www.sciencedirect.com/science/article/abs/pii/S1568997216302798). Similar to what occurs with ANA and antiphospholipid antibodies, the presence of higher levels of circulating anti-endothelial cell antibodies has a direct relationship to the severity of behavioral changes in people with autism (https://www.sciencedirect.com/science/article/pii/S1726490115000969?via%3Dihub).

The detection of antimitochondrial antibodies (AMA) is used to diagnose the autoimmune disease called primary biliary cholangitis. It may also occur in other autoimmune diseases, such as Sjögren’s syndrome, systemic sclerosis (or scleroderma), polymyositis/dermatomyositis, juvenile idiopathic arthritis, SLE, and autoimmune hepatitis (https://link.springer.com/article/10.1007/s12016-021-08904-y; https://www.sciencedirect.com/science/article/pii/S2589909022000065: https://www.sciencedirect.com/science/article/abs/pii/S0889857X05702970). Anti-double-stranded DNA antibodies are considered highly specific markers of SLE (https://www.nature.com/articles/s41584-020-0480-7) and lupoid autoimmune hepatitis (https://www.nature.com/articles/s41584-021-00573-7). The presence of AMA (https://jneuroinflammation.biomedcentral.com/articles/10.1186/1742-2094-7-80; https://pubmed.ncbi.nlm.nih.gov/24837704/), anti-double-stranded DNA antibodies and ANA (https://pubmed.ncbi.nlm.nih.gov/24837704/) and anti-nucleosome antibodies (https://pubmed.ncbi.nlm.nih.gov/24708718/) have also been documented in the serum of autistic individuals (nucleosomes are structural units that form chromosomes and are composed of two spirals of DNA wrapped around a protein disc consisting of four pairs of proteins called histones). The anti-nucleosome antibody test is considered highly sensitive and specific for the diagnosis of SLE (https://pubmed.ncbi.nlm.nih.gov/20374326/). This indicates that the autoimmunity found in autism, which is part of the inflammatory process described in the first editorial of this series, may not only be organ-specific in many cases. In other words, it may not be solely directed against the brain or CNS of the autistic individual but rather a condition in which the immune system attacks other organs or systems.

Again, following the Principle of Parsimony, according to which the simplest and most comprehensive explanation should be considered the most likely for any phenomenon (including any disease), the search for the primary determining cause of autism must necessarily identify as causal a factor that can explain not only the aggression against the CNS but also the autoimmune aggression directed at other organs and systems.

(III) Correlation between circulating autoantibody levels and the severity of autism

Autoantibody levels have been identified as markers of the activity and severity of autoimmune diseases (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC209428/).

Corroborating the participation of the autoimmune phenomenon in the pathophysiology of autism, this correlation (direct relationship) has been documented in autistic children (https://www.sciencedirect.com/science/article/pii/S1726490115000969?via%3Dihub; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3794552/; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3039058/; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3104945/; https://pubmed.ncbi.nlm.nih.gov/22226851; https://pubmed.ncbi.nlm.nih.gov/19135624/).

(IV) Presence of lymphocytes infiltrating the brain of individuals with autism

Lymphocyte accumulation is present in tissues and organs affected by autoimmune diseases. In association with inflammation and the production of autoantibodies, this finding (found in biopsies or autopsies under the microscope) is considered the hallmark of autoimmune diseases (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2832720/; https://pathology.jhu.edu/autoimmune/damage).

Similarly, lymphocytic infiltrates have been demonstrated in the brains of individuals with autism (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7210715/). Together with the evidence of an active brain inflammatory process (chronic encephalitis: first Editorial in this series) and the repertoire of antibodies produced against brain tissue listed here, the presence of autoreactive lymphocytes infiltrating the nervous tissue of autistic individuals completes the characterization of the triad classically considered the hallmark of autoimmune aggression involved in the pathophysiological mechanism of autism.

On the other hand, the discovery of active lymphatic vessels connecting the CNS to the lymphatic system (https://www.nature.com/articles/npp2016158; https://pubmed.ncbi.nlm.nih.gov/26077718/) indicates a possible communication channel through which autoimmune aggression may act in the autistic brain and in other autoimmune neurological diseases.

(V) The Th17 immune response (induced by interleukin 17-producing helper lymphocytes, typical in autoimmune conditions – https://link.springer.com/article/10.1007/s00281-019-00733-8) has been observed in autistic individuals (https://link.springer.com/article/10.1186/s13229-021-00472-4).

(VI) Mitigation of autistic symptoms through corticosteroid or immunoglobulin therapy

One of the most classic characteristics of autoimmune diseases is the vigorous response to the therapeutic use of drugs considered to be the most potent immunosuppressants and anti-inflammatories: glucocorticoids (https://pubmed.ncbi.nlm.nih.gov/11457656/). That also occurs in autoimmune diseases that affect the nervous system (https://pubmed.ncbi.nlm.nih.gov/11430999/), such as multiple sclerosis (https://pubmed.ncbi.nlm.nih.gov/23229226/). The core features of autism similarly respond to corticosteroid treatment (https://link.springer.com/article/10.1186/1471-2377-14-70; https://pubmed.ncbi.nlm.nih.gov/32168067/; https://www.scielo.br/j/jped/a/PBQNCqJ5L4cyqLXF5hyCxQy/?lang=en#), revealing an autoimmune mechanism involved in the pathophysiology of autism.

Likewise, autoimmune diseases may respond to immunoglobulin therapy when other therapeutic approaches fail (https://pubmed.ncbi.nlm.nih.gov/37062358/), as widely reported (https://ameripharmaspecialty.com/ivig-and-autoimmune-diseases/). As further evidence of the involvement of autoimmune mechanisms in autism, the same effect has been reported on the manifestations of this disorder (https://pubmed.ncbi.nlm.nih.gov/30097568/; https://www.mdpi.com/2075-4426/11/6/488).

(VII) Occurrence of autoimmune or immune-mediated disorders as comorbidities in autism

Allergies, asthma, atopic dermatitis, allergic rhinitis, urticaria, type 1 diabetes, inflammatory bowel disease (Crohn’s disease), and psoriasis are comorbidities of autism; that is, they are found in individuals with autism at a higher prevalence than in the general population or in individuals without autism (https://pubmed.ncbi.nlm.nih.gov/23726766/; https://jlb.onlinelibrary.wiley.com/doi/epdf/10.1189/jlb.1205707; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10619695/; https://pubmed.ncbi.nlm.nih.gov/22511918/; https://www.sciencedirect.com/science/article/abs/pii/S1750946712001018; https://www.scirp.org/journal/paperinformation?paperid=78725; https://pubmed.ncbi.nlm.nih.gov/37939694/). The presence of atopic dermatitis is associated not only with a greater likelihood of autism but also with the greater severity of the autistic condition (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10619695/), suggesting a common causal factor for these two conditions.

(VIII) Elevated prevalence of autoimmune diseases among consanguineous relatives (a family history of autoimmune disorders increases autism risk)

This group of evidence demonstrates that children who have family members with autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, celiac disease, ulcerative colitis, type 1 diabetes, hypothyroidism, Hashimoto’s thyroiditis, psoriasis, and rheumatic fever, are more likely to develop autism (https://pubmed.ncbi.nlm.nih.gov/19135624/; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5373490/; https://pubmed.ncbi.nlm.nih.gov/25981892/; https://jamanetwork.com/journals/jamapediatrics/article-abstract/485932; https://pubmed.ncbi.nlm.nih.gov/14595086/; https://pubmed.ncbi.nlm.nih.gov/10385847/; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3115699/; https://pubmed.ncbi.nlm.nih.gov/19581261/; https://pubmed.ncbi.nlm.nih.gov/16598435/; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9025211/).

Children whose parents have autoimmune diseases may have a 50% higher risk of developing autism (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3115699/).

(IX) Similar to classic autoimmune diseases, the benefits of cholecalciferol administration are also observed in autism

“Vitamin” D (cholecalciferol, whose pre-active form is calcidiol or calcifediol and whose active form is calcitriol) has a structure similar to that of steroid hormones (estrogen, progesterone, testosterone, and cortisol). Like steroid hormones, it is derived from cholesterol, has receptors in the cell nucleus, and acts by modifying genetic activity—it modulates the activity of thousands of genes (https://www.mdpi.com/2073-4425/14/9/1691; https://www.sciencedirect.com/science/article/pii/S0039128X23000995). With nuclear receptors present in almost all, if not all, nucleated cells (https://www.sciencedirect.com/science/article/abs/pii/S0003986112001324; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9325172/), as well as in cell membranes (https://pubmed.ncbi.nlm.nih.gov/17341182/), “vitamin” D (actually a hormone or a steroid hormone precursor) has pleiotropic (multiple) effects on the human organism. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4045445/; https://www.sciencedirect.com/science/article/abs/pii/B9780323913867000064). Due to its multiple benefits for human health, to the fact that it is produced by exposing the skin to sunlight during the daytime hours that are mistakenly regarded as inappropriate (https://www.grassrootshealth.net/blog/shadow-can-tell-right-time-make-vitamin-d/), and to the confinement typical of modern urban life (https://link.springer.com/article/10.1186/s12889-017-4436-z; https://www.sciencedirect.com/science/article/abs/pii/B9780323913867000064), the deficiency of this pre-steroid hormone (“vitamin” D) has reached epidemic proportions (https://go.gale.com/ps/i.do?id=GALE%7CA592138121&sid=googleScholar&v=2.1&it=r&linkaccess=abs&issn=15228606&p=AONE&sw=w&userGroupName=anon%7E84477f50&aty=open-web-entry; https://academic.oup.com/nutritionreviews/article-abstract/81/10/1290/7071638?redirectedFrom=PDF&login=false; https://www.scielo.br/j/abem/a/78X5HHQSwzZtc435P9CsjCg/?lang=en). This deficiency has profound consequences for pre- and postnatal brain development that can extend throughout an individual’s lifespan (https://pubs.rsc.org/en/content/articlehtml/2023/fo/d3fo00166k).

Low vitamin D levels (masked by underestimated laboratory reference values) (https://www.grassrootshealth.net/wp-content/uploads/2017/05/dip_with_numbers_nmol_051317.pdf; https://www.mdpi.com/2072-6643/16/11/1666), “recommended” supplementation doses lower than those actually needed (https://www.mdpi.com/2227-9067/1/2/208), and genetic resistance to its effects (https://pubmed.ncbi.nlm.nih.gov/33897704/) have contributed to an increasing incidence of a wide variety of diseases, including multiple sclerosis, rheumatoid arthritis, inflammatory bowel diseases (Crohn’s disease, ulcerative colitis), celiac disease, uveitis, dermatological diseases, ankylosing spondylitis, fibromyalgia, diabetes, hypertension, tuberculosis, COVID-19, and cancer (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6032242/; https://link.springer.com/article/10.1007/s00223-019-00577-2; https://www.pnas.org/doi/abs/10.1073/pnas.1200072109; https://www.nature.com/articles/s41430-020-0661-0; https://apcz.umk.pl/QS/article/view/54077; https://www.sciencedirect.com/science/article/abs/pii/S0039625721001685; https://www.nature.com/articles/nrcardio.2009.135; https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2023.950465/full; https://pubmed.ncbi.nlm.nih.gov/11115787/; https://www.sciencedirect.com/science/article/abs/pii/S0009898114003921; https://www.sciencedirect.com/science/article/abs/pii/S0304395913005411).

As Wacker and Holick highlighted in their 2012 publication (https://www.mdpi.com/2072-6643/5/1/111):

“Vitamin D, the sunshine vitamin, has received a lot of attention recently as a result of a meteoric rise in the number of publications showing that vitamin D plays a crucial role in a plethora of physiological functions and associating vitamin D deficiency with many acute and chronic illnesses including disorders of calcium metabolism, autoimmune diseases, some cancers, type 2 diabetes mellitus, cardiovascular disease and infectious diseases.”

Patients with autoimmune diseases treated safely with high doses of vitamin D (https://www.mdpi.com/2072-6643/14/8/1575/review_report) may have polymorphisms (SNPs) affecting any combination of the nine genes that vitamin D requires to produce various biological effects, such as regulating the immune system (https://pubmed.ncbi.nlm.nih.gov/33897704/). Evidently, these genetic polymorphisms can cause resistance to the effects of vitamin D, impairing tolerance to autoantigens (https://pmc.ncbi.nlm.nih.gov/articles/PMC6712894/).

The fundamental roles of this steroid hormone (in the forms of calcidiol and calcitriol) in regulating and enhancing the immune system https://www.sciencedirect.com/science/article/abs/pii/S1471489210000378; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2861286/; https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2023.1186635/full), as well as in the functions of the CNS (https://academic.oup.com/jbmrplus/article/5/1/e10419/7486306?login=false), are relevant to the present presentation.

As Eyles highlights in his article (https://www.mdpi.com/2072-6643/5/1/111):

“There is now also good evidence linking gestational and/or neonatal vitamin D deficiency with an increased risk of neurodevelopmental disorders, such as schizophrenia and autism, and adult vitamin D deficiency with certain degenerative conditions.”

Similar to its advantages in autoimmune diseases (https://www.nature.com/articles/ncprheum0855; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2998156/), vitamin D supplementation also offers benefits for autism. In a recent umbrella review (2024)—a systematic analysis of various systematic reviews and meta-analyses on a specific topic—Jiang and colleagues (https://www.tandfonline.com/doi/full/10.2147/NDS.S470462#abstract) conclude:

“Based on rigorous analysis, we found that vitamin D deficiency early in life is a risk factor for the development of ASD and that vitamin D supplementation improves the core symptoms of ASD. Our study concludes that vitamin D supplementation is beneficial for individuals with autism, that vitamin D deficiency early in embryonic life increases the risk of ASD, and that our study supports the idea that prevention begins with vitamin D supplementation early in life.”

(X) Evidence pieces show genetic resistance to the immunoregulatory effects of cholecalciferol (or “vitamin” D, which inhibits Th17 activity) in autism

As is the case in autoimmune diseases in general, in which genetic polymorphisms related to vitamin D activity (https://www.cell.com/heliyon/fulltext/S2405-8440(24)03731-9) can cause resistance to its biological effects (including limiting its role in regulating the immune system) (https://pubmed.ncbi.nlm.nih.gov/33897704/), similar polymorphisms affecting the same genes have also been described in autism (https://www.mdpi.com/2076-3425/7/9/115; https://onlinelibrary.wiley.com/doi/abs/10.1002/aur.2279; https://www.sciencedirect.com/science/article/abs/pii/S0378111916303614; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6207492/; https://www.sciencedirect.com/science/article/abs/pii/S037837821500119X).

Guerine and collaborators (https://onlinelibrary.wiley.com/doi/abs/10.1002/aur.2279) even observed a correlation between a specific polymorphism (SNP) in the vitamin D receptor (VDR) gene and the severity of autism:

“Finally, a strong gene-dose association of FokI (T) allele with both higher Childhood Autism Rating Scale score (Pc = 0.01) and, particularly, with hyperactivity behavior (Pc = 0.006) emerged in ASD children.”

These genetic polymorphisms, capable of causing resistance to the effects of vitamin D, indicate that administering higher doses (capable of compensating for the level of resistance), such as those used in psoriasis and vitiligo, can restore the immunomodulatory effects of vitamin D in autism as well. (https://pubmed.ncbi.nlm.nih.gov/24494059/).

In autism, autoimmunity damages the pathway that allows vitamin B9 to enter the Central Nervous System, leading to further harm to nerve cells.

Folate (or vitamin B9), whose natural forms are methylfolate (or methyltetrahydrofolate, the active form) and folinic acid (or D,L-leucovorin, or 5-formyl tetrahydrofolate), is a B-complex vitamin essential for normal CNS development and physiology. Abnormalities in folate levels (low CNS levels despite normal serum levels) and in folate-related pathways (genetic polymorphisms affecting enzymes involved in its metabolism) have been identified in children with autism, characterizing a condition known as cerebral folate deficiency syndrome (“CFD” – also found in schizophrenia and in other neurodevelopmental disorders) (https://pmc.ncbi.nlm.nih.gov/articles/PMC8622150/); https://www.degruyter.com/document/doi/10.1515/cclm-2012-0543/html).

The nervous system requires higher concentrations of folate than those found in the blood. To reach the nervous tissue, folates must cross the barriers that separate the blood from the CNS: the blood-brain barrier and the blood-cerebrospinal fluid barrier. To this end, the transport of folate to the CNS is essentially mediated by two highly specific systems (https://pubmed.ncbi.nlm.nih.gov/32200980/):

(1) A high-affinity transport mechanism (in which folate is transferred to nervous tissue at an energy expenditure) called the “folate receptor alpha”; this is the primary mechanism for folate transfer to the brain, capable of pumping folate to levels three times higher than those in the blood. Transport occurs through a mechanism called potocytosis, where the receptor-bound folate is internalized and then recycled back to the cell membrane.

(2) A transport mechanism that allows folates to be passively transferred to the CNS through the “reduced folate carrier” without using energy. This secondary system can only equalize brain folate levels with those in the blood. In other words, the concentrations of folate in the blood and the CNS are maintained in balance when this transport system is the sole option available.

What would be a third transporter mechanism (“proton-coupled”) actually functions as part of the mechanism mediated by the folate receptor alpha at the level of the blood-liquor barrier (https://pubmed.ncbi.nlm.nih.gov/19074442/).

Autistic children have high levels of autoantibodies directed against neurons, and the concentration of these antibodies directly correlates with the severity of their neuropsychiatric condition (https://pubmed.ncbi.nlm.nih.gov/22226851/). Several studies have shown that among autistic children, 70% have the antibody directed against the folate receptor (https://pubmed.ncbi.nlm.nih.gov/22230883/; https://pubmed.ncbi.nlm.nih.gov/20668945/).

Depending on the type of antibody produced, folate receptors are blocked or destroyed. The former block the folate-binding pocket, while binding antibodies can attach to other sites on the protein structure of the folate receptor alpha, followed by the attraction of the complement cascade, activation of cytokines, and finally destruction of the antigen-antibody complex (https://pubmed.ncbi.nlm.nih.gov/27068282/). The brain then becomes dependent on the second category of folate transporter (reduced folate transporter) to obtain a minimum level of folate, which is insufficient for the biological needs of neural cells. This condition (characterized by normal blood folate levels and reduced levels in cerebrospinal fluid – or “CSF”) has been termed “Cerebral Folate Deficiency” (CFD) syndrome and has also been found in other neurological and neuropsychiatric disorders, such as Rett syndrome, psychosis, refractory (intractable) schizophrenia, schizoaffective disorders, treatment-resistant major depression in adults, spastic-ataxic syndrome, and intractable epilepsy among young children (https://pubmed.ncbi.nlm.nih.gov/27068282/).

CFD results in impairment of the metabolic pathways used in the synthesis of nucleic acids (and therefore inhibition of neurogenesis—the formation of new neurons from stem cells residing in the CNS) (https://www.sciencedirect.com/science/article/pii/S2405844021021745). It also affects methylation processes, which are crucial for regulating gene expression, and hinders protective mechanisms against the damaging impacts of free radicals—cellular waste that must be continuously removed to prevent nerve cell damage (https://doi.org/10.1016/j.spen.2020.100835).

An important consequence of CFD is reduced glutathione synthesis. Glutathione is an important endogenous antioxidant that plays a crucial role in protecting cells against exogenous (such as heavy metals) and endogenous toxins, particularly in the CNS (https://pubmed.ncbi.nlm.nih.gov/22528835/). Abnormalities in reduced glutathione (GSH) metabolism result in oxidative damage to cellular DNA, proteins, and lipids. GSH abnormalities and markers of oxidative damage have been documented postmortem in brain regions involved in speech, emotion, and social behavior in individuals with autism (https://doi.org/10.1016/j.spen.2020.100835). In fact, methylation and redox abnormalities are so prevalent in autism that it has been proposed that their biomarkers be used for the diagnosis of ASD (https://doi.org/10.1016/j.spen.2020.100835).

Furthermore, the folate receptor alpha has functions independent of its role as a folate transporter; it also plays a role in maintaining the repertoire of stem cells from which new neurons must constantly originate (neurogenesis) both in prenatal life and throughout an individual’s lifespan (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5268765/). Its destruction by the antibodies found in high levels in autistic children, therefore, also compromises the recovery capacity of nervous tissue damaged by the inflammatory process that characterizes this condition.

Cerebral folate deficiency syndrome identified in autism can be treated with high doses of oral folinic acid (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7477301/). Folic acid supplementation is contraindicated and, if used, may aggravate CSF methylfolate deficiency (https://pubmed.ncbi.nlm.nih.gov/24494987/; https://pubmed.ncbi.nlm.nih.gov/20668945/). Elevated serum folate levels result in the transfer of this vitamin across the BBB via the “reduced folate transporter”. Elevated (supraphysiological) serum levels then provide restoration of the CNS’s own higher (physiological) concentrations.

In 2013, Frye et al. found that antibodies directed against the folate receptor alpha were present in 75% of children with autism when both blocking and binding antibodies were considered, with 29% being positive for both types of antibodies (https://pubmed.ncbi.nlm.nih.gov/22230883). Administration of folinic acid (leucovorin) at a dose of 2 mg per kg per day (maximum dose of 50 mg per day) provided improvements in communication, language, attention, and stereotypic behaviors in treated children compared to non-supplemented controls with ASD (https://pubmed.ncbi.nlm.nih.gov/22230883). This therapeutic approach was reviewed in 2020 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7477301/), and the authors recommended gradually increasing the dose over the first 2 weeks to avoid a possible transient increase in agitation occasionally reported by parents. However, they themselves did not observe such a side effect; on the contrary, they found an improvement in excitement and agitation after approximately nine weeks of treatment. These results indicate that among autistic individuals who produce antibodies against the folate receptor alpha, some of the autistic manifestations may result from, or be aggravated by, cerebral folate deficiency syndrome, which can be corrected by administering high doses of folinic acid.

The presence of polymorphisms affecting the gene for an enzyme that plays a key role in folate metabolism (methylenetetrahydrofolate reductase, MTHFR) occurs in a significant percentage of the population (https://www.racgp.org.au/afp/2016/april/mthfr-genetic-testing-controversy-and-clinical-imp).

The presence of the C677T variant of the MTHFR gene, in particular, constitutes a risk factor for autism (https://journals.lww.com/psychgenetics/abstract/2009/08000/aberrations_in_folate_metabolic_pathway_and.2.aspx) and may interact with polymorphisms affecting other genes related to folate metabolism (such as the 19-base pair deletion polymorphism of the enzyme dihydrofolate reductase (DHFR) and the G80A SNP affecting the reduced folate carrier gene) to increase the risk of autism (https://pubmed.ncbi.nlm.nih.gov/17597297/). Evidently, these polymorphisms may exacerbate cerebral folate deficiency syndrome, particularly when they occur in association. The identification of a polymorphism affecting the DHFR gene as another risk factor for autism (https://pubmed.ncbi.nlm.nih.gov/17597297/) further emphasizes the need to avoid folic acid supplementation in autistic children, since the metabolism (reduction) of this synthetic folate requires DHFR activity.

MTHFR requires vitamin B2 (riboflavin), which acts as its cofactor (https://www.ncbi.nlm.nih.gov/books/NBK6145/). In turn, riboflavin deficiency may result from genetic factors prevalent in the general population (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1918332/), potentially representing an additional factor that contributes to susceptibility to autism. Thus, administering supraphysiological doses of riboflavin may prove to be beneficial.

In conclusion of this second Editorial, the evidence accumulated over the last decades makes clear the fundamental participation of autoimmune mechanisms in the pathophysiology of chronic encephalitis associated with autism (characterized in the first Editorial). The triad considered the “hallmark” of an autoimmune disease (inflammation, autoantibody production, and lymphocytic infiltration) is present in autism. In the next Editorial, we will see that the statement that “the origin of autoimmunity in autism is unknown” (https://pubmed.ncbi.nlm.nih.gov/22226851/ – page 465) is no longer supported.

Leia as postagens pelo índice mensal: