Role In Autism Research Articles

Insights into the structure and function of the extracellular domain of alpha‐neurexin by single particle EM and surface plasmon resonance

Neurexins are a family of presynaptic cell‐adhesion membrane proteins that are important for synapse maintenance through contact with the postsynaptic neuroligin molecules. Several studies have indicated that mutations in these genes may play an important role in autism and mental retardation. Each neurexin gene contains two promoters corresponding to the α‐and β‐neurexins. While the extracellular domain of β ‐neurexin contains only a single LNS/LG domain, α ‐neurexin consists of six LNS/LG domains, including the β ‐neurexin domain, separated by three EGF domains. To investigate the conformation of the extracellular domain of α ‐neurexin we imaged purified protein using negative‐stain EM. Raw particle EM images suggest that the LNS/LG domains of α ‐neurexin exist in a mixture of different conformations. Additional experiments to obtain class averages and to investigate the effect of calcium and ligands on conformation are ongoing. Using surface plasmon resonance (SPR) we report a rank order of specificity for α ‐neurexin binding to the different neuroligins. Furthermore, we are using mutagenesis and SPR to help us understand the contribution of the different LNS/LG domains of α‐neurexin to neuroligin binding.This work was supported by: USPHS Grant R37 GM‐18360 and NIEHS to PT, and the Pharmacology Training Grant

DNA Methylation Signatures within the Human Brain

DNA methylation is a heritable modification of genomic DNA central to development, imprinting, transcriptional regulation, chromatin structure, and overall genomic stability. Aberrant DNA methylation of individual genes is a hallmark of cancer and has been shown to play an important role in neurological disorders such as Rett syndrome. Here, we asked whether normal DNA methylation might distinguish individual brain regions. We determined the quantitative DNA methylation levels of 1,505 CpG sites representing 807 genes with diverse functions, including proliferation and differentiation, previously shown to be implicated in human cancer. We initially analyzed 76 brain samples representing cerebral cortex (n=35), cerebellum (n=34), and pons (n=7), along with liver samples (n=3) from 43 individuals. Unsupervised hierarchical analysis showed clustering of 33 of 35 cerebra distinct from the clustering of 33 of 34 cerebella, 7 of 7 pons, and all 3 livers. By use of comparative marker selection and permutation testing, 156 loci representing 118 genes showed statistically significant differences--a >or=17% absolute change in DNA methylation (P<.004)--among brain regions. These results were validated for all six genes tested in a replicate set of 57 samples. Our data suggest that DNA methylation signatures distinguish brain regions and may help account for region-specific functional specialization.

Are There Enhanced MBP Autoantibodies in Autism?

Autoantibodies to central nervous system antigens, such as myelin basic protein (MBP), may play a role in autism. We measured autoantibody titers to MBP in children with autism, both classic onset and regressive onset forms, controls (healthy age- and gender-matched) and individuals with Tourette syndrome via enzyme-linked immunosorbent assays. We found a significant difference in autoantibody titers to MBP, not accounted for by age or medication, between Tourette and classic autism (both significantly lower) when compared to regressive autism, but not when compared to controls. Autoantibody responses against MBP are unlikely to play a pathogenic role in autism.

How Relevant are GFAP Autoantibodies in Autism and Tourette Syndrome?

Controversy exists over the role of autoantibodies to central nervous system antigens in autism and Tourette Syndrome. We investigated plasma autoantibody titers to glial fibrillary acidic protein (GFAP) in children with classic onset (33) and regressive onset (26) autism, controls (25, healthy age- and gender-matched) and individuals with Tourette Syndrome (24) by enzyme-linked immunosorbent assays. We found a significant difference in autoantibody titers to GFAP, not accounted for by age, between the Tourette (significantly lower) and regressive autism groups. However, no differences were found between: classic/regressive; classic/controls; classic/Tourette; regressive/controls; or controls/Tourette. Autoantibody responses against GFAP are unlikely to play a pathogenic role in autism or Tourette Syndrome.

Immunizations and Autism: A Review of the Literature

Because of a temporal correlation between the first notable signs and symptoms of autism and the routine childhood vaccination schedule, many parents have become increasingly concerned regarding the possible etiologic role vaccines may play in the development of autism. In particular, some have suggested an association between the Measles-Mumps-Rubella vaccine and autism. Our literature review found very few studies supporting this theory, with the overwhelming majority showing no causal association between the Measles-Mumps-Rubella vaccine and autism. The vaccine preservative thimerosal has alternatively been hypothesized to have a possible causal role in autism. Again, no convincing evidence was found to support this claim, nor for the use of chelation therapy in autism. With decreasing uptake of immunizations in children and the inevitable occurrence of measles outbreaks, it is important that clinicians be aware of the literature concerning vaccinations and autism so that they may have informed discussions with parents and caregivers.

Cerebellar contributions to autism spectrum disorders

The pathophysiology of autism appears to encompass a number of different brain structures and systems. However, the most consistent site of neural abnormality in autism is the cerebellum. Postmortem investigations have reported a variety of anomalies, most notably a reduction in the number of Purkinje neurons. Additionally, structural neuroimaging studies have shown volumetric changes in the cerebellum, including decreases in gray matter and increases in white matter. Emerging evidence for cerebellar abnormality in autism was paralleled by a revolution in our understanding of normal cerebellar function and cerebellar connectivity, such that the importance of elucidating the contributions of the cerebellum to autism is now clear. In fact, recent brain-behavior correlation studies suggest that cerebellar abnormality may play a more central role in autism than previously thought. At present, it is crucial that we increase our understanding of cerebellar functioning in autism, and functional neuroimaging studies are just beginning to reveal the possible role(s) of cerebellar dysfunction in this disorder. In this review, evidence for cerebellar anatomic and functional abnormality in autism will be delineated. This will be followed by consideration of the implications of cerebellar abnormality in autism. Two major questions will be addressed: (1) how might dysfunction of the cerebellum impact the development of connectivity between the cerebellum and other brain systems, and (2) how might cerebellar dysfunction impact behavior and the symptoms of autism. The paper concludes with a discussion of how cerebellar abnormalities might inform our understanding of the etiology of autism spectrum disorders.

Lack of Evidence for Association of the Serotonin Transporter Gene SLC6A4 with Autism

The serotonin transporter (5-HTT) has long been considered likely to play a role in autism. Hyperserotonemia has been consistently found in a proportion of autistic patients, and the use of selective serotonin reuptake inhibitors (SSRIs) can have a positive effect in treating some symptoms of autism. Specific variants of the 5-HTT gene, SLC6A4, especially the insertion-deletion 5-HTTLPR promoter locus, have been found to modulate its expression and transporter function. We examined the transmission of the short or long allele of 5-HTTLPR locus to affected individuals, using a large cohort of 352 families. In addition, we screened five single nucleotide polymorphisms (SNPs) in the 5' region of SLC6A4 previously reported to be positively associated with autism, as well as 4 additional SNPs also in the 5' region. No association of the 5-HTTLPR locus with autism was found. Furthermore, no evidence for association of any of the nine SNPs covering the SLC6A4 gene, or any of their haplotypes, was observed in our study. Using obsessive-compulsive behaviors (OCB), severe OCBs or rigid-compulsive subsets of our cohort gave the same negative results. SLC6A4 variants do not appear to be significantly involved in the liability to autism.

Executive Functioning in Children with an Autism Spectrum Disorder: Can We Differentiate Within the Spectrum?

The aim of this study was to investigate whether children with high-functioning autism (HFA), Asperger's syndrome (AS), and pervasive developmental disorder not otherwise specified (PDDNOS) can be differentiated from each other and from normal controls on their neurocognitive executive functioning (EF) profile. Children with HFA and AS showed the most EF deficits. The EF profile of the PDDNOS group was more disturbed that the normal control group, but was less disturbed than the profile of the HFA and AS groups. Little difference was found between the three PDD subtypes with respect to EF. This study supports the view that executive dysfunctioning plays an important role in autism. The usefulness of a distinction between different PDD subtypes was not demonstrated.

Assessment of metallothionein and antibodies to metallothionein in normal and autistic children having exposure to vaccine‐derived thimerosal

Allergic autoimmune reaction after exposure to heavy metals such as mercury may play a causal role in autism, a developmental disorder of the central nervous system. As metallothionein (MT) is the primary metal-detoxifying protein in the body, we conducted a study of the MT protein and antibodies to metallothionein (anti-MT) in normal and autistic children whose exposure to mercury was only from thimerosal-containing vaccines. Laboratory analysis by immunoassays revealed that the serum level of MT did not significantly differ between normal and autistic children. Furthermore, autistic children harboured normal levels of anti-MT, including antibodies to isoform MT-I (anti-MT-I) and MT-II (anti-MT-II), without any significant difference between normal and autistic children. Our findings indicate that because autistic children have a normal profile of MT and anti-MT, the mercury-induced autoimmunity to MT may not be implicated in the pathogenesis of autism.

Do other methyl‐binding proteins play a role in autism?

Do other methyl‐binding proteins play a role in autism?

Neurochemical correlates of autistic disorder: A review of the literature

Review of neurochemical investigations in autistic disorder revealed that a wide array of transmitter systems have been studied, including serotonin, dopamine, norepinephrine, acetylcholine, oxytocin, endogenous opioids, cortisol, glutamate, and gamma-aminobutyric acid (GABA). These studies have been complicated by the fact that autism is a very heterogeneous disorder which often presents with comorbid behavioral problems. In addition, many of these studies employed very small samples and inappropriate control groups, making it difficult to draw conclusions with confidence. Overall, serotonin appears to have the most empirical evidence for a role in autism, but this requires further investigation and replication. There is little support for the notion that a dysfunction of norepinephrine or the endogenous opioids are related to autism. The role of dopaminergic functioning has not been compelling thus far, though conflicting findings on central dopamine turnover require further study. Promising new areas of study may include possible dysfunction of the cholinergic system, oxytocin, and amino acid neurotransmitters. Implications for pharmacotherapy are briefly discussed for each neurotransmitter system with brief research examples. Review of this work emphasizes the need for future studies to control for subject variables, such as race, sex, pubertal status, and distress associated with blood draws, which can affect measures of neurochemical function. In addition, research in neurochemistry must continue to work in concert with other subspecialties to form a more comprehensive and theory-based approach to the neurobiological correlates of autistic disorder.

Risk Factors for Autism: Perinatal Factors, Parental Psychiatric History, and Socioeconomic Status

Research suggests that heredity and early fetal development play a causal role in autism. This case-control study explored the association between perinatal factors, parental psychiatric history, socioeconomic status, and risk of autism. The study was nested within a cohort of all children born in Denmark after 1972 and at risk of being diagnosed with autism until December 1999. Prospectively recorded data were obtained from nationwide registries in Denmark. Cases totaled 698 children with a diagnosis of autism; each case was individually matched by gender, birth year, and age to 25 controls. Analyses by conditional logistic regression produced risk ratios and 95% confidence intervals. Adjusted analyses showed that the risk of autism was associated with breech presentation (risk ratio (RR) = 1.63, 95% confidence interval (CI): 1.18, 2.26), low Apgar score at 5 minutes (RR = 1.89, 95% CI: 1.10, 3.27), gestational age at birth <35 weeks (RR = 2.45, 95% CI: 1.55, 3.86), and parental psychiatric history (schizophrenia-like psychosis: RR = 3.44, 95% CI: 1.48, 7.95; affective disorder: RR = 2.91, 95% CI: 1.65, 5.14). Analyses showed no statistically significant association between risk of autism and weight for gestational age, parity, number of antenatal visits, parental age, or socioeconomic status. Results suggest that prenatal environmental factors and parental psychopathology are associated with the risk of autism. These factors seem to act independently.

Evaluation of the chromosome 2q37.3 geneCENTG2as an autism susceptibility gene

Autism is a highly heritable neurodevelopmental syndrome with a complex genetic etiology for which no disease genes have yet been definitively identified. We ascertained three subjects with autism spectrum disorders and chromosome 2q37.3 terminal deletions, and refined the deletion breakpoint regions using polymorphism mapping and fluorescence in situ hybridization (FISH) probes. We then genotyped polymorphic markers downstream from the breakpoint region in a sample of autism affected sibling pair families. Both the chromosomal breakpoints and linkage analyses focused our attention on the gene centaurin gamma-2 (CENTG2), an attractive candidate gene based also on its function and pattern of expression. We therefore assessed CENTG2 for its involvement in autism by (1) screening its exons for variants in 199 autistic and 160 non-autistic individuals, and (2) genotyping and assessing intra-genic polymorphisms for linkage and linkage disequilibrium (LD). The exon screen revealed a Ser --> Gly substitution in one proband, an Arg --> Gly substitution in another, and a number of additional variants unique to the autism families. No unique variants were found in the control subjects. The genotyping produced strong evidence for linkage from two intronic polymorphisms, with a maximum two-point HLOD value of 3.96 and a posterior probability of linkage (PPL) of 51%. These results were contradicted, however, by substantially weaker evidence for linkage from multi-point analyses and by no evidence of LD. We conclude, therefore, that 2q37.3 continues to be a region of interest for autism susceptibility, and that CENTG2 is an intriguing candidate gene that merits further scrutiny for its role in autism.

7. Language disorders and autism

Early diagnosis of language disorders and autism is important, and early intervention for autism and some language disorders makes a difference. Developmental surveillance of children to detect these disorders should be a routine part of medical practice. The persistence and pervasiveness of communication and socialising deficits differentiate children with autism from those with specific developmental language disorders. Hearing and vision assessment is essential in any communication disorder. Interventions, targeted to identified areas of need, should encompass communication enhancement, behavioural therapy, educational modification, parent education and family support. Pharmacological interventions have an important but discrete role in autism, but there are no magic bullets. It is important to remember that the normal childhood illnesses occur in children with developmental disorders. Parents should be directed to reliable websites on the Internet, and given information and books to read as well as phone numbers of relevant services (eg, autism associations). There is a need for increased government financial support for early intervention programs.

Autistic disorder and viral infections

Autistic disorder (autism) is a behaviorally defined developmental disorder with a wide range of behaviors. Although the etiology of autism is unknown, data suggest that autism results from multiple etiologies with both genetic and environmental contributions, which may explain the spectrum of behaviors seen in this disorder. One proposed etiology for autism is viral infection very early in development. The mechanism, by which viral infection may lead to autism, be it through direct infection of the central nervous system (CNS), through infection elsewhere in the body acting as a trigger for disease in the CNS, through alteration of the immune response of the mother or offspring, or through a combination of these, is not yet known. Animal models in which early viral infection results in behavioral changes later in life include the influenza virus model in pregnant mice and the Borna disease virus model in newborn Lewis rats. Many studies over the years have presented evidence both for and against the association of autism with various viral infections. The best association to date has been made between congenital rubella and autism; however, members of the herpes virus family may also have a role in autism. Recently, controversy has arisen as to the involvement of measles virus and/or the measles, mumps, rubella (MMR) vaccine in the development of autism. Biological assays lend support to the association between measles virus or MMR and autism whereas epidemiologic studies show no association between MMR and autism. Further research is needed to clarify both the mechanisms whereby viral infection early in development may lead to autism and the possible involvement of the MMR vaccine in the development of autism.

Behavioral and cellular consequences of increasing serotonergic activity during brain development: a role in autism?

The hypothesis explored in this review is that the high levels of serotonin in the blood seen in some autistic children (the so-called hyperserotonemia of autism) may lead to some of the behavioral and cellular changes also observed in the disorder. At early stages of development, when the blood–brain Barrier is not yet fully formed, the high levels of serotonin in the blood can enter the brain of a developing fetus and cause loss of serotonin terminals through a known negative feedback function of serotonin during development. The loss of serotonin innervation persists throughout subsequent development and the symptoms of autism appear. A review of the basic scientific literature on prenatal treatments affecting serotonin is given, in support of this hypothesis, with an emphasis on studies using the serotonin agonist, 5-methoxytryptamine (5-MT).In work using 5-MT to mimic hyperserotonemia, Sprague-Dawley rats are treated from gestational day 12 until postnatal 20. In published reports, these animals have been found to have a significant loss of serotonin terminals, decreased metabolic activity in cortex, changes in columnar development in cortex, changes in serotonin receptors, and “autistic-like” behaviors. In preliminary cellular findings given in this review, the animals have also been found to have cellular changes in two relevant brain regions: 1. Central nucleus of the amygdala, a brain region involved in fear-responding, where an increase in calcitonin gene related peptide (CGRP) was found 2. Paraventricular nucleus of the hypothalamus, a brain region involved in social memory and bonding, where a decrease in oxytocin was found. Both of these cellular changes could result from loss of serotonin innervation, possibly due to loss of terminal outgrowth from the same cells of the raphe nuclei. Thus, increased serotonergic activity during development could damage neurocircuitry involved in emotional responding to social stressors and may have relevance to the symptoms of autism.

Oxidative stress in autism: Increased lipid peroxidation and reduced serum levels of ceruloplasmin and transferrin - the antioxidant proteins

Autism is a neurological disorder of childhood with poorly understood etiology and pathology. We compared lipid peroxidation status in the plasma of children with autism, and their developmentally normal non-autistic siblings by quantifying the levels of malonyldialdehyde, an end product of fatty acid oxidation. Lipid peroxidation was found to be elevated in autism indicating that oxidative stress is increased in this disease. Levels of major antioxidant proteins namely, transferrin (iron–binding protein) and ceruloplasmin (copper–binding protein) in the serum, were significantly reduced in autistic children as compared to their developmentally normal non-autistic siblings. A striking correlation was observed between reduced levels of these proteins and loss of previously acquired language skills in children with autism. These results indicate altered regulation of transferrin and ceruloplasmin in autistic children who lose acquired language skills. It is suggested that such changes may lead to abnormal iron and copper metabolism in autism, and that increased oxidative stress may have pathological role in autism.

Obstetric Complications May Join With Other Factors to Lead to Autism

Back to table of contents Previous article Next article Clinical & Research NewsFull AccessObstetric Complications May Join With Other Factors to Lead to AutismJoan Arehart-TreichelJoan Arehart-TreichelSearch for more papers by this authorPublished Online:20 Aug 2004https://doi.org/10.1176/pn.39.16.0390028bCertainly genes play a causative role in autism, ample evidence has revealed. However, perinatal complications or certain variables, such as older maternal age, may also be culprits, studies of the past 30 years have suggested. Nonetheless, findings regarding perinatal complications have been inconsistent and often contradictory because of variations in sample size, data quality, control groups, and so forth.Thus, Australian researchers decided to use centralized resources in Western Australia to conduct a large population-based study on possible perinatal factors contributing to autism. As they reported in the June Archives of General Psychiatry, they have found what previous studies have generally found—mothers of individuals with autism are more likely to have experienced difficulties during pregnancy, labor, and delivery than mothers of persons without autism.The investigation, headed by Emma Glasson, Ph.D., a research fellow in the School of Population Health at the University of Western Australia, included 2,259 subjects—465 individuals born in Western Australia between 1980 and 1995 and diagnosed with autism spectrum disorder, 481 siblings of the autism subjects, and 1,313 controls randomly selected across the same birth years as the autism subjects.Perinatal information collected about each of the subjects at the time of birth was retrieved from the Maternal and Child Health Research Database of Western Australia, and obstetric information for each of the three groups of subjects was then compared. In fact, as the researchers pointed out in their report, their study was “unique for incorporating the largest number of autistic cases born in a geographic region, using obstetric data collected at the time of birth, comparing cases with a large population-based control group, and comparing cases with siblings.”Compared with the control subjects, the researchers found, autism subjects had significantly greater frequencies of threatened miscarriage, epidural caudal anesthesia use, labor induction, and a labor duration of less than one hour. They were significantly more likely to have experienced fetal distress, to have been delivered by an elective or emergency cesarean section, or to have had an Apgar score of less than 6 at one minute.Further, autism subjects were more likely to be firstborn compared with control subjects and had significantly older parents than control subjects. In fact, older maternal age emerged as one of the strongest findings of this study, and the effect was incremental in that younger mothers had the lowest risk for having a child with autism and older mothers had the highest risk. In other words, the risk of mothers 35 years or older of having a child with autism was increased threefold compared with mothers younger than 20 years.When data on perinatal complications for the siblings of autism subjects were examined and compared, siblings were found generally to have experienced fewer complications than autism subjects, but more than control subjects.The researchers concluded that perinatal complications do appear to play a role in the causation of autism, although it seems that no particular factor is at fault. But how might perinatal difficulties be linked to autism? It could be by interacting with autism susceptibility genes. This possibility, in fact, could explain why siblings of autism subjects, who presumably possess some of the genes for autism but not as many as the autism subjects, have fewer obstetric complications than autism subjects, yet more than control subjects.“The increased prevalence of obstetric complications among autism cases is most likely due to the underlying genetic factors or an interaction of these factors with the environment,” the researchers suggested.An abstract of the study, “Perinatal Factors and the Development of Autism,” is posted online at<http://archpsyc.amaassn.org/cgi/content/abstract/61/6/618>.▪ Arch Gen Psychiatry 2004 61 618 ISSUES NewArchived

Autoantibody repertoires to brain tissue in autism nuclear families

The hypothesis of an immune dysfunction in autism spectrum disorders has previously been put forward without, however, compelling evidence of a direct relation to its etiology or pathogenesis. To further understand if autoimmunity could play a significant role in autism, we analyzed autoantibody repertoires to brain tissue extract in the plasma of 171 autism children, their parents, and 54 controls, by quantitative immunoblotting. Multiparametric analysis revealed significant differences between patients and controls, and showed that one single reactivity in Section 32 of the blot had the most power to discriminate between these samples. Family correlation coefficients and heritability estimates did not provide any evidence that this reactivity was genetically determined. While the molecular weight of the target protein suggested that it might be an isoform of Myelin Basic Protein (MBP), inhibition assays with human MBP argued against this hypothesis. The study evidences the widespread occurrence of autoreactivities to brain tissue in autism patients, which may represent the immune system's neuroprotective response to a previous brain injury occurred during neurodevelopment. The molecular identification of the target protein in Section 32 will contribute to the understanding of the role of immune responses against brain antigens in autistic patients.

Mutation screening of X-chromosomal neuroligin genes: no mutations in 196 autism probands.

Autism, a childhood neuropsychiatric disorder with a strong genetic component, is currently the focus of considerable attention within the field of human genetics as well many other medical-related disciplines. A recent study has implicated two X-chromosomal neuroligin genes, NLGN3 and NLGN4, as having an etiological role in autism, having identified a frameshift mutation in one gene and a substitution mutation in the other, segregating in multiplex autism spectrum families (Jamain et al. [2003: Nat Genet 34:27-29]). The function of neuroligin as a trigger for synapse formation would suggest that such mutations would likely result in some form of pathological manifestation. Our own study, screening a larger sample of 196 autism probands, failed to identify any mutations that would affect the coding regions of these genes. Our findings suggest that mutations in these two genes are infrequent in autism.