Association between the HOXA1 A218G polymorphism and increased head circumference in patients with autism

Retinal Thinning in Adults with Autism Spectrum Disorder

Since the retina shares its embryological origin with the central nervous system, optical coherence tomography (OCT), an imaging technique frequently employed in ophthalmology to analyze the macula and intraretinal layer thicknesses and volumes, has recently become increasingly important in psychiatric research. We examined 34 autistic and 31 neurotypical adults (NT) using OCT. Autistic adults had reduced overall macular and outer nuclear layer (ONL) thickness and volume compared to NT. Both macular and ONL thickness showed significant inverse associations with the severity of autistic symptoms measured with the Social Responsiveness Scale 2 (SRS-2). Longitudinal studies across different age groups are required to clarify whether retinal changes may represent a possible trait marker.

Role of HOXA1-4 in the development of genetic and malignant diseases

The HOXA genes, belonging to the HOX family, encompass 11 members (HOXA1-11) and exert critical functions in early embryonic development, as well as various adult processes. Furthermore, dysregulation of HOXA genes is implicated in genetic diseases, heart disease, and various cancers. In this comprehensive overview, we primarily focused on the HOXA1-4 genes and their associated functions and diseases. Emphasis was placed on elucidating the impact of abnormal expression of these genes and highlighting their significance in maintaining optimal health and their involvement in the development of genetic and malignant diseases. Furthermore, we delved into their regulatory mechanisms, functional roles, and underlying biology and explored the therapeutic potential of targeting HOXA1-4 genes for the treatment of malignancies. Additionally, we explored the utility of HOXA1-4 genes as biomarkers for monitoring cancer recurrence and metastasis.

Neuroimaging genetics approaches to identify new biomarkers for the early diagnosis of autism spectrum disorder

Autism-spectrum disorders (ASDs) are developmental disabilities that manifest in early childhood and are characterized by qualitative abnormalities in social behaviors, communication skills, and restrictive or repetitive behaviors. To explore the neurobiological mechanisms in ASD, extensive research has been done to identify potential diagnostic biomarkers through a neuroimaging genetics approach. Neuroimaging genetics helps to identify ASD-risk genes that contribute to structural and functional variations in brain circuitry and validate biological changes by elucidating the mechanisms and pathways that confer genetic risk. Integrating artificial intelligence models with neuroimaging data lays the groundwork for accurate diagnosis and facilitates the identification of early diagnostic biomarkers for ASD. This review discusses the significance of neuroimaging genetics approaches to gaining a better understanding of the perturbed neurochemical system and molecular pathways in ASD and how these approaches can detect structural, functional, and metabolic changes and lead to the discovery of novel biomarkers for the early diagnosis of ASD.

TRIM32 Deficiency Impairs the Generation of Pyramidal Neurons in Developing Cerebral Cortex

Excitatory-inhibitory imbalance (E/I) is a fundamental mechanism underlying autism spectrum disorders (ASD). TRIM32 is a risk gene genetically associated with ASD. The absence of TRIM32 causes impaired generation of inhibitory GABAergic interneurons, neural network hyperexcitability, and autism-like behavior in mice, emphasizing the role of TRIM32 in maintaining E/I balance, but despite the description of TRIM32 in regulating proliferation and differentiation of cultured mouse neural progenitor cells (NPCs), the role of TRIM32 in cerebral cortical development, particularly in the production of excitatory pyramidal neurons, remains unknown. The present study observed that TRIM32 deficiency resulted in decreased numbers of distinct layer-specific cortical neurons and decreased radial glial cell (RGC) and intermediate progenitor cell (IPC) pool size. We further demonstrated that TRIM32 deficiency impairs self-renewal of RGCs and IPCs as indicated by decreased proliferation and mitosis. A TRIM32 deficiency also affects or influences the formation of cortical neurons. As a result, TRIM32-deficient mice showed smaller brain size. At the molecular level, RNAseq analysis indicated reduced Notch signalling in TRIM32-deficient mice. Therefore, the present study indicates a role for TRIM32 in pyramidal neuron generation. Impaired generation of excitatory pyramidal neurons may explain the hyperexcitability observed in TRIM32-deficient mice.

Bosley-Salih-Alorainy syndrome in patients from India

Bi-allelic HOXA1 pathogenic variants clinically manifest as two distinct syndromes, Bosley-Salih-Alorainy syndrome (BSAS) and Athabascan brainstem dysgenesis syndrome, mainly reported in two different populations from Saudi Arabia and southwest North America, respectively. Here we report two siblings of Indian origin with BSAS phenotype caused by a novel homozygous exon 2 HOXA1 pathogenic variants.

Genetics of structural and functional brain changes in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurological and developmental disorder characterized by social impairment and restricted interactive and communicative behaviors. It may occur as an isolated disorder or in the context of other neurological, psychiatric, developmental, and genetic disorders. Due to rapid developments in genomics and imaging technologies, imaging genetics studies of ASD have evolved in the last few years. Increased risk for ASD diagnosis is found to be related to many specific single-nucleotide polymorphisms, and the study of genetic mechanisms and noninvasive imaging has opened various approaches that can help diagnose ASD at the nascent level. Identifying risk genes related to structural and functional changes in the brain of ASD patients provide a better understanding of the disease's neuropsychiatry and can help identify targets for therapeutic intervention that could be useful for the clinical management of ASD patients.

Segregated expressions of autism risk genes Cdh11 and Cdh9 in autism-relevant regions of developing cerebellum

Results of recent genome-wide association studies (GWAS) and whole genome sequencing (WGS) highlighted type II cadherins as risk genes for autism spectrum disorders (ASD). To determine whether these cadherins may be linked to the morphogenesis of ASD-relevant brain regions, in situ hybridization (ISH) experiments were carried out to examine the mRNA expression profiles of two ASD-associated cadherins, Cdh9 and Cdh11, in the developing cerebellum. During the first postnatal week, both Cdh9 and Cdh11 were expressed at high levels in segregated sub-populations of Purkinje cells in the cerebellum, and the expression of both genes was declined as development proceeded. Developmental expression of Cdh11 was largely confined to dorsal lobules (lobules VI/VII) of the vermis as well as the lateral hemisphere area equivalent to the Crus I and Crus II areas in human brains, areas known to mediate high order cognitive functions in adults. Moreover, in lobules VI/VII of the vermis, Cdh9 and Cdh11 were expressed in a complementary pattern with the Cdh11-expressing areas flanked by Cdh9-expressing areas. Interestingly, the high level of Cdh11 expression in the central domain of lobules VI/VII was correlated with a low level of expression of the Purkinje cell marker calbindin, coinciding with a delayed maturation of Purkinje cells in the same area. These findings suggest that these two ASD-associated cadherins may exert distinct but coordinated functions to regulate the wiring of ASD-relevant circuits in the cerebellum.

Bio-collections in autism research

Autism spectrum disorder (ASD) is a group of complex neurodevelopmental disorders with diverse clinical manifestations and symptoms. In the last 10 years, there have been significant advances in understanding the genetic basis for ASD, critically supported through the establishment of ASD bio-collections and application in research. Here, we summarise a selection of major ASD bio-collections and their associated findings. Collectively, these include mapping ASD candidate genes, assessing the nature and frequency of gene mutations and their association with ASD clinical subgroups, insights into related molecular pathways such as the synapses, chromatin remodelling, transcription and ASD-related brain regions. We also briefly review emerging studies on the use of induced pluripotent stem cells (iPSCs) to potentially model ASD in culture. These provide deeper insight into ASD progression during development and could generate human cell models for drug screening. Finally, we provide perspectives concerning the utilities of ASD bio-collections and limitations, and highlight considerations in setting up a new bio-collection for ASD research.

Autism genetics: Methodological issues and experimental design

Autism is a complex neuropsychiatric disorder of developmental origin, where multiple genetic and environmental factors likely interact resulting in a clinical continuum between "affected" and "unaffected" individuals in the general population. During the last two decades, relevant progress has been made in identifying chromosomal regions and genes in linkage or association with autism, but no single gene has emerged as a major cause of disease in a large number of patients. The purpose of this paper is to discuss specific methodological issues and experimental strategies in autism genetic research, based on fourteen years of experience in patient recruitment and association studies of autism spectrum disorder in Italy.

Neuroimaging endophenotypes in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that has a strong genetic basis, and is heterogeneous in its etiopathogenesis and clinical presentation. Neuroimaging studies, in concert with neuropathological and clinical research, have been instrumental in delineating trajectories of development in children with ASD. Structural neuroimaging has revealed ASD to be a disorder with general and regional brain enlargement, especially in the frontotemporal cortices, while functional neuroimaging studies have highlighted diminished connectivity, especially between frontal-posterior regions. The diverse and specific neuroimaging findings may represent potential neuroendophenotypes, and may offer opportunities to further understand the etiopathogenesis of ASD, predict treatment response, and lead to the development of new therapies.

Overweight and Obesity in a Sample of Children With Autism Spectrum Disorder

OBJECTIVE

To determine the prevalence of overweight/obese status in children with autism spectrum disorders (ASD), identify associated characteristics, and develop a model to predict weight status.

METHODS

The prevalence of overweight and obesity was determined in 2769 children with ASD enrolled in the Autism Speaks Autism Treatment Network, a collaboration of 17 academic centers, and compared with a national sample matched for age, sex, and race. Associations in the ASD sample between weight status and demographic and clinical variables, such as age, race, head circumference, and adaptive functioning, were tested using ordinal logistic regression. The accuracy of a final model that predicted weight status based on early life variables was evaluated in a validation sample.

RESULTS

The prevalence of overweight and obesity were 33.9% and 18.2%, respectively; ASD was associated with a higher risk of obesity (but not overweight) relative to the national sample (odds ratio [OR], 1.16; 95% confidence interval [CI], 1.05-1.28; P = .003). In the adjusted analysis, overweight/obese status was significantly associated with Hispanic ethnicity (OR, 1.99; 95% CI, 1.37-2.89), parental high school education (OR, 1.56; 95% CI, 1.09-2.21), high birth weight (OR, 1.56; 95% CI, 1.11-2.18), macrocephaly (OR, 4.01; 95% CI, 2.96-5.43), and increased somatic symptoms (OR, 1.41; 95% CI, 1.01-1.95). A prediction model designed to have high sensitivity predicted low risk of overweight/obesity accurately, but had low positive predictive value.

CONCLUSIONS

The prevalence of obesity in children with ASD was greater than a national sample. Independent associations with increased weight status included known risk factors and macrocephaly and increased level of somatic symptoms. A model based on early life variables accurately predicted low risk of overweight/obesity.

YAP regulates the expression of Hoxa1 and Hoxc13 in mouse and human oral and skin epithelial tissues

Yes-associated protein (YAP) is a Hippo signaling transcriptional coactivator that plays pivotal roles in stem cell proliferation, organ size control, and tumor development. The downstream targets of YAP have been shown to be highly context dependent. In this study, we used the embryonic mouse tooth germ as a tool to search for the downstream targets of YAP in ectoderm-derived tissues. Yap deficiency in the dental epithelium resulted in a small tooth germ with reduced epithelial cell proliferation. We compared the gene expression profiles of embryonic day 14.5 (E14.5) Yap conditional knockout and YAP transgenic mouse tooth germs using transcriptome sequencing (RNA-Seq) and further confirmed the differentially expressed genes using real-time PCR and in situ hybridization. We found that YAP regulates the expression of Hoxa1 and Hoxc13 in oral and dental epithelial tissues as well as in the epidermis of skin during embryonic and adult stages. Sphere formation assay suggested that Hoxa1 and Hoxc13 are functionally involved in YAP-regulated epithelial progenitor cell proliferation, and chromatin immunoprecipitation (ChIP) assay implies that YAP may regulate Hoxa1 and Hoxc13 expression through TEAD transcription factors. These results provide mechanistic insights into abnormal YAP activities in mice and humans.

A critical review of the research on the extreme male brain theory and digit ratio (2D:4D)

Boys are more likely than girls to be diagnosed with an autism spectrum disorder (ASD). The extreme male brain (EMB) theory of ASD suggests that fetal testosterone (FT) exposure may underlie sex differences in autistic traits. A link between the organizational effects of FT on the brain and ASD is often drawn based on research using digit ratio (2D:4D), a putative biomarker, without a full survey of the findings. This paper critically and quantitatively reviews the research on the relationship between 2D:4D and ASD as well as autism spectrum, empathizing, and systemizing measures in neurotypical populations. Overall, there is some support for the EMB theory in all four areas, particularly the 2D:4D-ASD relationship. Recommendations for future research are provided.

Autism genetics

Autism spectrum disorder (ASD) is a severe neuropsychiatric disease with strong genetic underpinnings. However, genetic contributions to autism are extremely heterogeneous, with many different loci underlying the disease to a different extent in different individuals. Moreover, the phenotypic expression (i.e., "penetrance") of these genetic components is also highly variable, ranging from fully penetrant point mutations to polygenic forms with multiple gene-gene and gene-environment interactions. Furthermore, many genes involved in ASD are also involved in intellectual disability, further underscoring their lack of specificity in phenotypic expression. We shall hereby review current knowledge on the genetic basis of ASD, spanning genetic/genomic syndromes associated with autism, monogenic forms due to copy number variants (CNVs) or rare point mutations, mitochondrial forms, and polygenic autisms. Finally, the recent contributions of genome-wide association and whole exome sequencing studies will be highlighted.

Mass spectrometry as a tool for studying autism spectrum disorder

Autism spectrum disorders (ASDs) are increasing in incidence but have an incompletely understood etiology. Tools for uncovering clues to the cause of ASDs and means for diagnoses are valuable to the field. Mass Spectrometry (MS) has been a useful method for evaluating differences between individuals with ASDs versus matched controls. Different biological substances can be evaluated using MS, including urine, blood, saliva, and hair. This technique has been used to evaluate relatively unsupported hypotheses based on introduction of exogenous factors, such as opiate and heavy metal excretion theories of ASDs. MS has also been used to support disturbances in serotonin-related molecules, which have been more consistently observed in ASDs. Serotonergic system markers, markers for oxidative stress, cholesterol system disturbances, peptide hypo-phosphorylation and methylation have been measured using MS in ASDs, although further analyses with larger numbers of subjects are needed (as well as consideration of behavioral data). Refinements in MS and data analysis are ongoing, allowing for the possibility that future studies examining body fluids and specimens from ASD subjects could continue to yield novel insights. This review summarizes MS investigations that have been conducted to study ASD to date and provides insight into future promising applications for this technique, with focus on proteomic studies.

Head circumference and height abnormalities in autism revisited: the role of pre- and perinatal risk factors

Pre/perinatal risk factors and body growth abnormalities have been studied frequently as early risk markers in autism spectrum disorder (ASD), yet their interrelatedness in ASD has received very little research attention. This is surprising, given that pre/perinatal risk factors can have a substantial impact on growth trajectories in the first years of life. We aimed to determine which pre/perinatal factors were more prevalent in ASD children and if these factors differentially influenced body growth in ASD and control children. A total of 96 ASD and 163 control children matched for gender participated. Data of growth of head size and body length during the first 13 months of life were collected. Data on pre/perinatal risk factors were retrospectively collected through standardized questionnaires. Results indicated that after matching for SES, prematurity/low birth weight and being first born were more prevalent in the ASD versus the control group. In addition, with increasing age children with ASD tended to have a proportionally smaller head circumference compared to their height. However, the effect of prematurity/low birth weight on head growth corrected for height was significantly different in ASD and control children: premature/low birth weight control children showed a disproportionate larger head circumference in relation to height during their first year of life, whereas this effect was absent in premature/low birth weight ASD children. This may suggest that the etiology of abnormal growth is potentially different in ASD and control children: where abnormal growth in control children is related to suboptimal conditions in the uterus, abnormal growth in ASD may be more strongly related to the causal factors that also increase the risk for ASD. However, prospective studies measuring growth and ASD characteristics in both premature/low birth weight and a terme children are necessary to support this conclusion.

A genome-wide association study of autism incorporating autism diagnostic interview-revised, autism diagnostic observation schedule, and social responsiveness scale

Efforts to understand the causes of autism spectrum disorders (ASDs) have been hampered by genetic complexity and heterogeneity among individuals. One strategy for reducing complexity is to target endophenotypes, simpler biologically based measures that may involve fewer genes and constitute a more homogenous sample. A genome-wide association study of 2,165 participants (mean age = 8.95 years) examined associations between genomic loci and individual assessment items from the Autism Diagnostic Interview-Revised, Autism Diagnostic Observation Schedule, and Social Responsiveness Scale. Significant associations with a number of loci were identified, including KCND2 (overly serious facial expressions), NOS2A (loss of motor skills), and NELL1 (faints, fits, or blackouts). These findings may help prioritize directions for future genomic efforts.

Allelic variation within the putative autism spectrum disorder risk gene homeobox A1 and cerebellar maturation in typically developing children and adolescents

Homeobox A1 (HOXA1) has been proposed as a candidate gene for autism spectrum disorder (ASD) as it regulates embryological patterning of hind-brain structures implicated in autism neurobiology. In line with this notion, a nonsynonymous single nucleotide polymorphism within a highly conserved domain of HOXA1--A218G (rs10951154)--has been linked to both ASD risk, and cross-sectional differences in superior posterior lobar cerebellar anatomy in late adulthood. Despite evidence for early onset and developmentally dynamic cerebellar involvement in ASD, little is known of the relationship between A218G genotype and maturation of the cerebellum over early development. We addressed this issue using 296 longitudinally acquired structural magnetic resonance imaging brain scans from 116 healthy individuals between 5 and 23 years of age. Mixed models were used to compare the relationship between age and semi-automated measures of cerebellar volume in A-homozygotes (AA) and carriers of the G allele (Gcar). Total cerebellar volume increased between ages of 5 and 23 years in both groups. However, this was accelerated in the Gcar relative to the AA group (Genotype-by-age interaction term, P = 0.03), and driven by genotype-dependent differences in the rate of bilateral superior posterior lobar volume change with age (P = 0.002). Resultantly, although superior posterior lobar volume did not differ significantly between genotype groups at age 5 (P = 0.9), by age 23 it was 12% greater in Gcar than AA (P = 0.002). Our results suggest that common genetic variation within this putative ASD risk gene has the capacity to modify the development of cerebellar systems implicated in ASD neurobiology.

Autism risk assessment in siblings of affected children using sex-specific genetic scores

Background

The inheritance pattern in most cases of autism is complex. The risk of autism is increased in siblings of children with autism and previous studies have indicated that the level of risk can be further identified by the accumulation of multiple susceptibility single nucleotide polymorphisms (SNPs) allowing for the identification of a higher-risk subgroup among siblings. As a result of the sex difference in the prevalence of autism, we explored the potential for identifying sex-specific autism susceptibility SNPs in siblings of children with autism and the ability to develop a sex-specific risk assessment genetic scoring system.

Methods

SNPs were chosen from genes known to be associated with autism. These markers were evaluated using an exploratory sample of 480 families from the Autism Genetic Resource Exchange (AGRE) repository. A reproducibility index (RI) was proposed and calculated in all children with autism and in males and females separately. Differing genetic scoring models were then constructed to develop a sex-specific genetic score model designed to identify individuals with a higher risk of autism. The ability of the genetic scores to identify high-risk children was then evaluated and replicated in an independent sample of 351 affected and 90 unaffected siblings from families with at least 1 child with autism.

Results

We identified three risk SNPs that had a high RI in males, two SNPs with a high RI in females, and three SNPs with a high RI in both sexes. Using these results, genetic scoring models for males and females were developed which demonstrated a significant association with autism (P = 2.2 × 10^-6 and 1.9 × 10^-5, respectively).

Conclusions

Our results demonstrate that individual susceptibility associated SNPs for autism may have important differential sex effects. We also show that a sex-specific risk score based on the presence of multiple susceptibility associated SNPs allow for the identification of subgroups of siblings of children with autism who have a significantly higher risk of autism.

An integrated meta-analysis of two variants in HOXA1/HOXB1 and their effect on the risk of autism spectrum disorders

Background

HOXA1 and HOXB1 have been strongly posed as candidate genes for autism spectrum disorders (ASD) given their important role in the development of hindbrain. The A218G (rs10951154) in HOXA1 and the insertion variant in HOXB1 (nINS/INS, rs72338773) were of special interest for ASD but with inconclusive results. Thus, we conducted a meta-analysis integrating case-control and transmission/disequilibrium test (TDT) studies to clearly discern the effect of these two variants in ASD.

Methods and Findings

Multiple electronic databases were searched to identify studies assessing the A218G and/or nINS/INS variant in ASD. Data from case-control and TDT studies were analyzed in an allelic model using the Catmap software. A total of 10 and 7 reports were found to be eligible for meta-analyses of A218G and nINS/INS variant, respectively. In overall meta-analysis, the pooled OR for the 218G allele and the INS allele was 0.97 (95% CI = 0.76-1.25, P_{heterogeneity} = 0.029) and 1.14 (95% CI = 0.97-1.33, P_{heterogeneity} = 0.269), respectively. No significant association was also identified between these two variants and ASD risk in stratified analysis. Further, cumulative meta-analysis in chronologic order showed the inclination toward null-significant association for both variants with continual adding studies. Additionally, although the between-study heterogeneity regarding the A218G is not explained by study design, ethnicity, and sample size, the sensitive analysis indicated the stability of the result.

Conclusions

This meta-analysis suggests the HOXA1 A218G and HOXB1 nINS/INS variants may not contribute significantly to ASD risk.

Israeli children with autism spectrum disorder are not macrocephalic

The prevalence of macrocephaly in autism spectrum disorder is reported to be much higher than in the general population, 12% to 37%. Progressive macrocephaly is even considered a warning sign for the development of autism. We evaluated the prevalence of an abnormal head circumference in children with autism in Israel and compared it with the head circumferences of children with developmental language disorder and children with normal development. We did not find a higher prevalence of macrocephaly among Israeli children with autism spectrum disorder (4.4%). Although children with autism spectrum disorder had a significantly higher rate of a head circumference above the 75th percentile compared with children with developmental language disorder, it was not significantly different compared with normal controls. We conclude that there is no increased prevalence of macrocephaly in Israeli children with autism; this can be attributed to a different genetic background.

Morphological features in children with autism spectrum disorders: a matched case-control study

This study was designed to examine morphological features in a large group of children with autism spectrum disorder versus normal controls. Amongst 421 patients and 1,007 controls, 224 matched pairs were created. Prevalence rates and odds ratios were analyzed by conditional regression analysis, McNemar test or paired t-test matched pairs. Morphological abnormalities were significantly more prevalent in patients with autism than in the normal control group and 48 morphological features distinguished patients from controls. Our findings show that morphological features are associated with autism. Exploring potential underlying genetic mechanisms of this association might lead to a better understanding of autism.

Decreased serum arylesterase activity in autism spectrum disorders

The PON1 gene, previously found associated with autism spectrum disorders (ASDs), encodes a serum protein responsible for the detoxification of organophosphates (OPs) and able to exert several enzymatic activities. PON1 arylesterase, but not diazoxonase activity, was significantly decreased in 174 ASD patients compared to 175 first-degree relatives and 144 controls (P=2.65×10⁻¹⁶). First degree relatives displayed intermediate activities, closer to patient than to control levels. Differences between patients, first-degree relatives and controls were especially evident among 164 Italians compared to 329 Caucasian-Americans, because arylesterase activity was significantly higher in Italian controls, compared to Caucasian-American controls (P=2.84×10⁻¹⁶). Arylesterase activity and PON protein concentrations were not significantly correlated, supporting a functional inhibition of arylesterase activity in ASD patients over quantitative changes in protein amounts. Serum arylesterase activity, in combination with PON1 genotypes at two single nucleotide polymorphisms (SNPs) known to influence protein amounts (rs705379: C-108T) and substrate specificity (rs662: Q192R), was able to discriminate ASD patients from controls with elevated sensitivity and specificity, depending on genotype and ethnic group. Serum arylesterase activity and genotyping at these two SNPs could thus represent an informative biochemical/genetic test, able to aid clinicians in estimating autism risk in ethnic groups with higher baseline arylesterase activity levels.

Family-based association study of ITGB3 in autism spectrum disorder and its endophenotypes

The integrin-β 3 gene (ITGB3), located on human chromosome 17q21.3, was previously identified as a quantitative trait locus (QTL) for 5-HT blood levels and has been implicated as a candidate gene for autism spectrum disorder (ASD). We performed a family-based association study in 281 simplex and 12 multiplex Caucasian families. ITGB3 haplotypes are significantly associated with autism (HBAT, global P=0.038). Haplotype H3 is largely over-transmitted to the affected offspring and doubles the risk of an ASD diagnosis (HBAT P=0.005; odds ratio (OR)=2.000), at the expense of haplotype H1, which is under-transmitted (HBAT P=0.018; OR=0.725). These two common haplotypes differ only at rs12603582 located in intron 11, which reaches a P-value of 0.072 in single-marker FBAT analyses. Interestingly, rs12603582 is strongly associated with pre-term delivery in our ASD patients (P=0.008). On the other hand, it is SNP rs2317385, located at the 5' end of the gene, that significantly affects 5-HT blood levels (Mann-Whitney U-test, P=0.001; multiple regression analysis, P=0.010). No gene-gene interaction between ITGB3 and SLC6A4 has been detected. In conclusion, we identify a significant association between a common ITGB3 haplotype and ASD. Distinct markers, located toward the 5' and 3' ends of the gene, seemingly modulate 5-HT blood levels and autism liability, respectively. Our results also raise interest into ITGB3 influences on feto-maternal immune interactions in autism.

Normal variation in fronto-occipital circuitry and cerebellar structure with an autism-associated polymorphism of CNTNAP2

Recent genetic studies have implicated a number of candidate genes in the pathogenesis of Autism Spectrum Disorder (ASD). Polymorphisms of CNTNAP2 (contactin-associated like protein-2), a member of the neurexin family, have already been implicated as a susceptibility gene for autism by at least 3 separate studies. We investigated variation in white and grey matter morphology using structural MRI and diffusion tensor imaging. We compared volumetric differences in white and grey matter and fractional anisotropy values in control subjects characterised by genotype at rs7794745, a single nucleotide polymorphism in CNTNAP2. Homozygotes for the risk allele showed significant reductions in grey and white matter volume and fractional anisotropy in several regions that have already been implicated in ASD, including the cerebellum, fusiform gyrus, occipital and frontal cortices. Male homozygotes for the risk alleles showed greater reductions in grey matter in the right frontal pole and in FA in the right rostral fronto-occipital fasciculus compared to their female counterparts who showed greater reductions in FA of the anterior thalamic radiation. Thus a risk allele for autism results in significant cerebral morphological variation, despite the absence of overt symptoms or behavioural abnormalities. The results are consistent with accumulating evidence of CNTNAP2's function in neuronal development. The finding suggests the possibility that the heterogeneous manifestations of ASD can be aetiologically characterised into distinct subtypes through genetic-morphological analysis.

Candidate gene study of HOXB1 in autism spectrum disorder

BACKGROUND

HOXB1 plays a major role in brainstem morphogenesis and could partly determine the cranial circumference in conjunction with HOXA1. In our sample, HOXA1 alleles significantly influence head growth rates both in autistic patients and in population controls. An initial report, suggesting that HOXB1 could confer autism vulnerability in interaction with HOXA1, was not confirmed by five small association studies.

METHODS

Our sample includes 269 autistic individuals, belonging to 219 simplex and 28 multiplex families. A mutational analysis of the two exons and flanking intronic sequences of the HOXB1 gene was carried out in 84 autistic patients by denaturing high performance liquid chromatography, followed by DNA sequencing. Identified rare variants were then searched by a restriction analysis in 236 autistic patients and 325-345 controls. Case-control and family-based association studies were performed on two common variants in 169 Italian patients versus 184 Italian controls and in 247 trios.

RESULTS

We identified three common polymorphisms, rs72338773 [c.82insACAGCGCCC (INS/nINS)], rs12939811 [c.309A>T (Q103H)], and rs7207109 [c.450G>A (A150A)] and three rare variants, namely IVS1+63G>A, rs35115415 [c.702G>A (V234V)] and c.872_873delinsAA (S291N). SNPs rs72338773 and rs12939811 were not associated with autism, using either a case-control (alleles, exact P = 0.13) or a family-based design [transmission/disequilibrium test (TDT)chi2 = 1.774, P = 0.183]. The rare variants, all inherited from one of the parents, were present in two Italian and in two Caucasian-American families. Autistic probands in two families surprisingly inherited a distinct rare variant from each parent. The IVS1+63A allele was present in 3/690 control chromosomes, whereas rare alleles at rs35115415 and c.872_873delinsAA (S291N) were not found in 662 and 650 control chromosomes, respectively. The INS-T309 allele influenced head size, but its effect appears more modest and shows no interaction with HOXA1 alleles. The INS-T309 allele is also associated with more severe stereotypic behaviours, according to ADI-R scores (N = 60 patients, P < 0.01).

CONCLUSIONS

HOXB1 mutations do not represent a common cause of autism, nor do HOXB1 common variants play important roles in autism vulnerability. HOXB1 provides minor, albeit detectable contributions to head circumference in autistic patients, with HOXA1 displaying more prominent effects. HOXB1 variants may modulate the clinical phenotype, especially in the area of stereotypic behaviours.

Altered calcium homeostasis in autism-spectrum disorders: evidence from biochemical and genetic studies of the mitochondrial aspartate/glutamate carrier AGC1

Autism is a severe developmental disorder, whose pathogenetic underpinnings are still largely unknown. Temporocortical gray matter from six matched patient-control pairs was used to perform post-mortem biochemical and genetic studies of the mitochondrial aspartate/glutamate carrier (AGC), which participates in the aspartate/malate reduced nicotinamide adenine dinucleotide shuttle and is physiologically activated by calcium (Ca(2+)). AGC transport rates were significantly higher in tissue homogenates from all six patients, including those with no history of seizures and with normal electroencephalograms prior to death. This increase was consistently blunted by the Ca(2+) chelator ethylene glycol tetraacetic acid; neocortical Ca(2+) levels were significantly higher in all six patients; no difference in AGC transport rates was found in isolated mitochondria from patients and controls following removal of the Ca(2+)-containing postmitochondrial supernatant. Expression of AGC1, the predominant AGC isoform in brain, and cytochrome c oxidase activity were both increased in autistic patients, indicating an activation of mitochondrial metabolism. Furthermore, oxidized mitochondrial proteins were markedly increased in four of the six patients. Variants of the AGC1-encoding SLC25A12 gene were neither correlated with AGC activation nor associated with autism-spectrum disorders in 309 simplex and 17 multiplex families, whereas some unaffected siblings may carry a protective gene variant. Therefore, excessive Ca(2+) levels are responsible for boosting AGC activity, mitochondrial metabolism and, to a more variable degree, oxidative stress in autistic brains. AGC and altered Ca(2+) homeostasis play a key interactive role in the cascade of signaling events leading to autism: their modulation could provide new preventive and therapeutic strategies.

HOXA1 A218G polymorphism is associated with smaller cerebellar volume in healthy humans

BACKGROUND AND PURPOSE

The Homeobox A1 (HOXA1) gene plays a critical role during development of the hindbrain in mice. Little is currently known about the relation between this gene and human brain development. The HOXA1 A218G polymorphism has been found to be associated with autism and larger head circumference in autistic patients. Similar effects were revealed also in healthy children but not in adult controls. The aim of this study was to investigate the role of the A218G polymorphism on the hindbrain structure of healthy adults.

METHODS

Healthy persons from two independent groups underwent 3-dimensional high resolution magnetic resonance (MR) exam. Group A was made of 80 persons (27 G allele carriers and 53 non-carriers) and Group B of 72 (26 carriers and 46 non-carriers). Statistical parametric mapping 2 (SPM2) were used to perform voxel-based analysis of the gray matter (GM) of the hindbrain in carriers and non. Significance threshold was set at .05 with small volume correction using a cerebellar mask.

RESULTS

In Group A, G carriers exhibited decreased GM volume in the superior posterior and anterior lobe of the cerebellum bilaterally. In Group B, decreased GM volume were found across the entire left cerebellar cortex.

CONCLUSIONS

These data suggest that the HOXA1 A218G polymorphism may affect cerebellar development in humans.

Genes related to sex steroids, neural growth, and social-emotional behavior are associated with autistic traits, empathy, and Asperger syndrome

Genetic studies of autism spectrum conditions (ASC) have mostly focused on the "low functioning" severe clinical subgroup, treating it as a rare disorder. However, ASC is now thought to be relatively common ( approximately 1%), and representing one end of a quasi-normal distribution of autistic traits in the general population. Here we report a study of common genetic variation in candidate genes associated with autistic traits and Asperger syndrome (AS). We tested single nucleotide polymorphisms in 68 candidate genes in three functional groups (sex steroid synthesis/transport, neural connectivity, and social-emotional responsivity) in two experiments. These were (a) an association study of relevant behavioral traits (the Empathy Quotient (EQ), the Autism Spectrum Quotient (AQ)) in a population sample (n=349); and (b) a case-control association study on a sample of people with AS, a "high-functioning" subgroup of ASC (n=174). 27 genes showed a nominally significant association with autistic traits and/or ASC diagnosis. Of these, 19 genes showed nominally significant association with AQ/EQ. In the sex steroid group, this included ESR2 and CYP11B1. In the neural connectivity group, this included HOXA1, NTRK1, and NLGN4X. In the socio-responsivity behavior group, this included MAOB, AVPR1B, and WFS1. Fourteen genes showed nominally significant association with AS. In the sex steroid group, this included CYP17A1 and CYP19A1. In the socio-emotional behavior group, this included OXT. Six genes were nominally associated in both experiments, providing a partial replication. Eleven genes survived family wise error rate (FWER) correction using permutations across both experiments, which is greater than would be expected by chance. CYP11B1 and NTRK1 emerged as significantly associated genes in both experiments, after FWER correction (P<0.05). This is the first candidate-gene association study of AS and of autistic traits. The most promising candidate genes require independent replication and fine mapping.

Infant head growth in male siblings of children with and without autism spectrum disorders

Previous research has indicated that children with autism exhibit accelerated head growth (HG) in infancy, although the timing of acceleration varies between studies. We examined infant HG trajectory as a candidate autism endophenotype by studying sibling pairs. We retrospectively obtained serial head orbitofrontal circumference measurements of: a) 48 sibling pairs in which one (n = 28) or both (n = 20) sibs were affected by an autism spectrum disorder (ASD); and b) 85 control male sibling pairs. Rate of HG of ASD subjects was slightly accelerated compared to controls, but the magnitude of difference was below the limit of reliability of standard measurement methods. Sibling intra class correlation for rate of HG was highly statistically significant; the magnitude was significantly stronger among autism-affected families (ICC = .63) than among controls (ICC = .26), p < .01. Infant HG trajectory appears familial—possibly endophenotypic—but was not a reliable marker of autism risk among siblings of ASD probands in this sample.

Involvement of the PRKCB1 gene in autistic disorder: significant genetic association and reduced neocortical gene expression

Protein kinase C enzymes play an important role in signal transduction, regulation of gene expression and control of cell division and differentiation. The fsI and betaII isoenzymes result from the alternative splicing of the PKCbeta gene (PRKCB1), previously found to be associated with autism. We performed a family-based association study in 229 simplex and 5 multiplex families, and a postmortem study of PRKCB1 gene expression in temporocortical gray matter (BA41/42) of 11 autistic patients and controls. PRKCB1 gene haplotypes are significantly associated with autism (P<0.05) and have the autistic endophenotype of enhanced oligopeptiduria (P<0.05). Temporocortical PRKCB1 gene expression was reduced on average by 35 and 31% for the PRKCB1-1 and PRKCB1-2 isoforms (P<0.01 and <0.05, respectively) according to qPCR. Protein amounts measured for the PKCbetaII isoform were similarly decreased by 35% (P=0.05). Decreased gene expression characterized patients carrying the 'normal' PRKCB1 alleles, whereas patients homozygous for the autism-associated alleles displayed mRNA levels comparable to those of controls. Whole genome expression analysis unveiled a partial disruption in the coordinated expression of PKCbeta-driven genes, including several cytokines. These results confirm the association between autism and PRKCB1 gene variants, point toward PKCbeta roles in altered epithelial permeability, demonstrate a significant downregulation of brain PRKCB1 gene expression in autism and suggest that it could represent a compensatory adjustment aimed at limiting an ongoing dysreactive immune process. Altogether, these data underscore potential PKCbeta roles in autism pathogenesis and spur interest in the identification and functional characterization of PRKCB1 gene variants conferring autism vulnerability.

A high-density SNP genome-wide linkage scan in a large autism extended pedigree

We performed a high-density, single nucleotide polymorphism (SNP), genome-wide scan on a six-generation pedigree from Utah with seven affected males, diagnosed with autism spectrum disorder. Using a two-stage linkage design, we first performed a nonparametric analysis on the entire genome using a 10K SNP chip to identify potential regions of interest. To confirm potentially interesting regions, we eliminated SNPs in high linkage disequilibrium (LD) using a principal components analysis (PCA) method and repeated the linkage results. Three regions met genome-wide significance criteria after controlling for LD: 3q13.2-q13.31 (nonparametric linkage (NPL), 5.58), 3q26.31-q27.3 (NPL, 4.85) and 20q11.21-q13.12 (NPL, 5.56). Two regions met suggestive criteria for significance 7p14.1-p11.22 (NPL, 3.18) and 9p24.3 (NPL, 3.44). All five chromosomal regions are consistent with other published findings. Haplotype sharing results showed that five of the affected subjects shared more than a single chromosomal region of interest with other affected subjects. Although no common autism susceptibility genes were found for all seven autism cases, these results suggest that multiple genetic loci within these regions may contribute to the autism phenotype in this family, and further follow-up of these chromosomal regions is warranted.

Polymorphisms of coding trinucleotide repeats of homeogenes in neurodevelopmental psychiatric disorders

OBJECTIVES

Autism (MIM#209850) and schizophrenia (MIM#181500) are both neurodevelopmental psychiatric disorders characterized by a highly genetic component. Homeogenes and forkhead genes encode transcription factors, which have been involved in brain development and cell differentiation. Thus, they are relevant candidate genes for psychiatric disorders. Genetic studies have reported an association between autism and DLX2, HOXA1, EN2, ARX, and FOXP2 genes whereas only three studies of EN2, OTX2, and FOXP2 were performed on schizophrenia. Interestingly, most of these candidate genes contain trinucleotide repeats coding for polyamino acid stretch in which instability can be the cause of neurodevelopmental disorders. Our goal was to identify variations of coding trinucleotide repeats in schizophrenia, autism, and idiopathic mental retardation.

METHODS

We screened the coding trinucleotide repeats of OTX1, EN1, DLX2, HOXA1, and FOXP2 genes in populations suffering from schizophrenia (247 patients), autism (98 patients), and idiopathic mental retardation (56 patients), and compared them with control populations (112 super controls and 202 healthy controls).

RESULTS

Novel deletions and insertions of coding trinucleotide repeats were found in the DLX2, HOXA1, and FOXP2 genes. Most of these variations were detected in controls and no difference in their distribution was observed between patient and control groups. Two different polymorphisms in FOXP2 were, however, found only in autistic patients and the functional consequences of these variations of repeats have to be characterized and correlated to particular clinical features.

CONCLUSION

This study did not identify specific disease risk variants of trinucleotide repeats in OTX1, EN1, DLX2, HOXA1, and FOXP2 candidate genes in neurodevelopmental psychiatric disorders.

What's new in autism?

This review on autism spectrum disorder (ASD) focusses on recent insights in the clinical picture, such as continuity of the phenotype and the concept of broader phenotype, on epidemiology and on clinical issues relevant to physicians, including new methods for early screening and diagnosis, psychiatric and somatic co-morbidity, and the expansion of so-called complementary and alternative treatments. ASD is a disorder with mainly genetic causes and recent insights show that a variety of genetic mechanisms may be involved, i.e. single gene disorders, copy number variations and polygenic mechanisms. Technological advances in genetics have lead to a number of promising findings, which, together with other lines of fundamental research, suggest that ASD may be a disorder of connectivity in the brain, at least in a subgroup of patients. It is possible that part of the genetic load in autism actually reflects gene-environment interaction, but there is no evidence for purely environmental causes in a substantial number of cases. Clinical research suggests that ASD may be a multi-system disorder in at least a subgroup of subjects, affecting the gastro-intestinal (GI) tract, the immune system and perhaps other systems. Behavioural treatments remain the cornerstone of management, and are mainly aimed at stimulation of the domains of impaired development and reducing secondary behaviours. These treatments are constantly being refined, but the main progress in this area may be the increase of research on effectiveness.

Current developments in the genetics of autism: from phenome to genome

Despite compelling evidence from twin and family studies indicating a strong genetic involvement in the etiology of autism, the unequivocal detection of autism susceptibility genes remains an elusive goal. The purpose of this review is to evaluate the current state of autism genetics research, with attention focused on new techniques and analytic approaches. We first present a brief overview of evidence for the genetic basis of autism, followed by an appraisal of linkage and candidate gene study findings and consideration of new analytic approaches to the study of complex psychiatric conditions, namely, genome-wide association studies, assessment of structural variation within the genome, and the incorporation of endophenotypes in genetic analysis.

Autistic phenotypes and genetic testing: state-of-the-art for the clinical geneticist

Autism spectrum disorders represent a group of developmental disorders with strong genetic underpinnings. Several cytogenetic abnormalities or de novo mutations able to cause autism have recently been uncovered. In this study, the literature was reviewed to highlight genotype-phenotype correlations between causal gene mutations or cytogenetic abnormalities and behavioural or morphological phenotypes. Based on this information, a set of practical guidelines is proposed to help clinical geneticists pursue targeted genetic testing for patients with autism whose clinical phenotype is suggestive of a specific genetic or genomic aetiology.

Intersubjectivity, affective neuroscience, and the neurobiology of autistic spectrum disorders: a systematic review

Intersubjectivity is an approach to the study of social interaction viewed from a perspective which rejects the view that reducing any such analysis to study at the level of the individual is adequate to address the issues of social functioning. It also stresses the view that social processes cannot be reduced to cognitive ones - most of the important questions in the study of developmental psychopathology deal with issues which have commonality with many other species and are patent well before the ontological emergence of 'cognitive' abilities. In this paper we review the evidence in this area, and discuss a range of issues relevant to autistic spectrum disorders. We focus in particular on social interaction; the role of the Intrinsic Motive Formation and recent work on mirror neurons in autism; genetic and teratogenic factors in the genesis of autism; and the role of a number of biological factors in pathogenesis - tryptophan; vitamin B12; sterol metabolism; glutamate and GABA; and the Fragile-X expansion.

Advances in behavioral genetics: mouse models of autism

Autism is a neurodevelopmental syndrome with markedly high heritability. The diagnostic indicators of autism are core behavioral symptoms, rather than definitive neuropathological markers. Etiology is thought to involve complex, multigenic interactions and possible environmental contributions. In this review, we focus on genetic pathways with multiple members represented in autism candidate gene lists. Many of these pathways can also be impinged upon by environmental risk factors associated with the disorder. The mouse model system provides a method to experimentally manipulate candidate genes for autism susceptibility, and to use environmental challenges to drive aberrant gene expression and cell pathology early in development. Mouse models for fragile X syndrome, Rett syndrome and other disorders associated with autistic-like behavior have elucidated neuropathology that might underlie the autism phenotype, including abnormalities in synaptic plasticity. Mouse models have also been used to investigate the effects of alterations in signaling pathways on neuronal migration, neurotransmission and brain anatomy, relevant to findings in autistic populations. Advances have included the evaluation of mouse models with behavioral assays designed to reflect disease symptoms, including impaired social interaction, communication deficits and repetitive behaviors, and the symptom onset during the neonatal period. Research focusing on the effect of gene-by-gene interactions or genetic susceptibility to detrimental environmental challenges may further understanding of the complex etiology for autism.

The neurobiology of autism

Improving clinical tests are allowing us to more precisely classify autism spectrum disorders and diagnose them at earlier ages. This raises the possibility of earlier and potentially more effective therapeutic interventions. To fully capitalize on this opportunity, however, will require better understanding of the neurobiological changes underlying this devastating group of developmental disorders. It is becoming clear that the normal trajectory of neurodevelopment is altered in autism, with aberrations in brain growth, neuronal patterning and cortical connectivity. Changes to the structure and function of synapses and dendrites have also been strongly implicated in the pathology of autism by morphological, genetic and animal modeling studies. Finally, environmental factors are likely to interact with the underlying genetic profile, and foster the clinical heterogeneity seen in autism spectrum disorders. In this review we attempt to link the molecular pathways altered in autism to the neurodevelopmental and clinical changes that characterize the disease. We focus on signaling molecules such as neurotrophin, Reelin, PTEN and hepatocyte growth factor, neurotransmitters such as serotonin and glutamate, and synaptic proteins such as neurexin, SHANK and neuroligin. We also discuss evidence implicating oxidative stress, neuroglial activation and neuroimmunity in autism.

Transmission disequilibrium study of an oligodendrocyte and myelin glycoprotein gene allele in 431 families with an autistic proband

Autistic disorder is a neurodevelopmental disorder where genetic factors play an important role. We previously described an association between a subgroup of French autistic patients and an allele of a non-synonymous single nucleotide polymorphism (nsSNP: OMGP62 G>A or rs11080149) in the gene coding for the oligodendrocyte and myelin glycoprotein (OMG), located at 7Mb from the marker D17S250, linked to autism in two independent genome scan studies. We report a study on 431 families with 1 affected child from different origins: French Canada (n=262), Italy (n=123) and United States (n=46). We analyzed the transmission of the rs11080149 alleles from parents to their affected children. There was a preferential transmission of the G allele from parents to affected children (p=0.0017) in the overall sample. Paternal and maternal transmission rates were both skewed. Taking into account our previous results obtained in a French group of patients, where we observed an association with allele A, a direct role of this polymorphism is improbable in autism. The associations observed in Japanese and French patients, the linkage studies and the present work speak in favor of the existence of a susceptibility gene for autism in the NF1 locus.

Clinical, morphological, and biochemical correlates of head circumference in autism

BACKGROUND

Head growth rates are often accelerated in autism. This study is aimed at defining the clinical, morphological, and biochemical correlates of head circumference in autistic patients.

METHODS

Fronto-occipital head circumference was measured in 241 nonsyndromic autistic patients, 3 to 16 years old, diagnosed according to DSM-IV criteria. We assessed 1) clinical parameters using the Autism Diagnostic Observation Schedule, Autism Diagnostic Interview-Revised, Vineland Adaptive Behavioral Scales, intelligence quotient measures, and an ad hoc clinical history questionnaire; 2) height and weight; 3) serotonin (5-HT) blood levels and peptiduria.

RESULTS

The distribution of cranial circumference is significantly skewed toward larger head sizes (p < .00001). Macrocephaly (i.e., head circumference >97th percentile) is generally part of a broader macrosomic endophenotype, characterized by highly significant correlations between head circumference, weight, and height (p < .001). A head circumference >75th percentile is associated with more impaired adaptive behaviors and with less impairment in IQ measures and motor and verbal language development. Surprisingly, larger head sizes are significantly associated with a positive history of allergic/immune disorders both in the patient and in his/her first-degree relatives.

CONCLUSIONS

Our study demonstrates the existence of a macrosomic endophenotype in autism and points toward pathogenetic links with immune dysfunctions that we speculate either lead to or are associated with increased cell cycle progression and/or decreased apoptosis.

Clinical characterization of the HOXA1 syndrome BSAS variant

BACKGROUND

The Bosley-Salih-Alorainy syndrome (BSAS) variant of the congenital human HOXA1 syndrome results from autosomal recessive truncating HOXA1 mutations. We describe the currently recognized spectrum of ocular motility, inner ear malformations, cerebrovascular anomalies, and cognitive function.

METHODS

We examined nine affected individuals from five consanguineous Saudi Arabian families, all of whom harbored the same I75-I76insG homozygous mutation in the HOXA1 gene. Patients underwent complete neurologic, neuro-ophthalmologic, orthoptic, and neuropsychological examinations. Six individuals had CT, and six had MRI of the head.

RESULTS

All nine individuals had bilateral Duane retraction syndrome (DRS) type 3, but extent of abduction and adduction varied between eyes and individuals. Eight patients were deaf with the common cavity deformity of the inner ear, while one patient had normal hearing and skull base development. Six had delayed motor milestones, and two had cognitive and behavioral abnormalities meeting Diagnostic and Statistical Manual of Mental Disorders-IV criteria for autism spectrum disorder. MRI of the orbits, extraocular muscles, brainstem, and supratentorial brain appeared normal. All six appropriately studied patients had cerebrovascular malformations ranging from unilateral internal carotid artery hypoplasia to bilateral agenesis.

CONCLUSIONS

This report extends the Bosley-Salih-Alorainy syndrome phenotype and documents the clinical variability resulting from identical HOXA1 mutations within an isolated ethnic population. Similarities between this syndrome and thalidomide embryopathy suggest that the teratogenic effects of early thalidomide exposure in humans may be due to interaction with the HOX cascade.

HOXA1 gene variants influence head growth rates in humans

We previously described a significant association between the HOXA1 G218 allele and increased head circumference in autism [Conciatori et al. (2004); Biol Psychiatry 55:413-419]. The present study reveals identical effects also in normal children. HOXA1 A218G alleles and sex explain as much as 10.9 and 6.8% of the variance in head circumference in 142 pediatric controls and in 191 autistic children, aged 3-16 years (F = 6.777, 3 and 141 df, P < 0.001 and F = 5.588, 3 and 190 df, P < 0.01, respectively). Instead, no association is found in 183 adult controls and in 35 pediatric fragile-X patients. Therefore HOXA1 A218G alleles significantly influence head growth rates, but not final head size, in normal human development. This influence does not differ between normal and autistic children, whereas the lack of FMRP seemingly overwhelms HOXA1 effects in fragile-X patients.

Case-control and family-based association studies of candidate genes in autistic disorder and its endophenotypes: TPH2 and GLO1

Background

The TPH2 gene encodes the enzyme responsible for serotonin (5-HT) synthesis in the Central Nervous System (CNS). Stereotypic and repetitive behaviors are influenced by 5-HT, and initial studies report an association of TPH2 alleles with childhood-onset obsessive-compulsive disorder (OCD) and with autism. GLO1 encodes glyoxalase I, the enzyme which detoxifies α-oxoaldehydes such as methylglyoxal in all living cells. The A111E GLO1 protein variant, encoded by SNP C419A, was identifed in autopsied autistic brains and proposed to act as an autism susceptibility factor. Hyperserotoninemia, macrocephaly, and peptiduria represent some of the best-characterized endophenotypes in autism research.

Methods

Family-based and case-control association studies were performed on clinical samples drawn from 312 simplex and 29 multiplex families including 371 non-syndromic autistic patients and 156 unaffected siblings, as well as on 171 controls. TPH2 SNPs rs4570625 and rs4565946 were genotyped using the TaqMan assay; GLO1 SNP C419A was genotyped by PCR and allele-specific restriction digest. Family-based association analyses were performed by TDT and FBAT, case-control by χ², endophenotypic analyses for 5-HT blood levels, cranial circumference and urinary peptide excretion rates by ANOVA and FBAT.

Results

TPH2 alleles and haplotypes are not significantly associated in our sample with autism (rs4570625: TDT P = 0.27, and FBAT P = 0.35; rs4565946: TDT P = 0.45, and FBAT P = 0.55; haplotype P = 0.84), with any endophenotype, or with the presence/absence of prominent repetitive and stereotyped behaviors (motor stereotypies: P = 0.81 and 0.84, verbal stereotypies: P = 0.38 and 0.73 for rs4570625 and rs4565946, respectively). Also GLO1 alleles display no association with autism (191 patients vs 171 controls, P = 0.36; TDT P = 0.79, and FBAT P = 0.37), but unaffected siblings seemingly carry a protective gene variant marked by the A419 allele (TDT P < 0.05; patients vs unaffected siblings TDT and FBAT P < 0.00001).

Conclusion

TPH2 gene variants are unlikely to contribute to autism or to the presence/absence of prominent repetitive behaviors in our sample, although an influence on the intensity of these behaviors in autism cannot be excluded. GLO1 gene variants do not confer autism vulnerability in this sample, but allele A419 apparently carries a protective effect, spurring interest into functional correlates of the C419A SNP.

Head circumference and height in autism: a study by the Collaborative Program of Excellence in Autism

Data from 10 sites of the NICHD/NIDCD Collaborative Programs of Excellence in Autism were combined to study the distribution of head circumference and relationship to demographic and clinical variables. Three hundred thirty-eight probands with autism-spectrum disorder (ASD) including 208 probands with autism were studied along with 147 parents, 149 siblings, and typically developing controls. ASDs were diagnosed, and head circumference and clinical variables measured in a standardized manner across all sites. All subjects with autism met ADI-R, ADOS-G, DSM-IV, and ICD-10 criteria. The results show the distribution of standardized head circumference in autism is normal in shape, and the mean, variance, and rate of macrocephaly but not microcephaly are increased. Head circumference tends to be large relative to height in autism. No site, gender, age, SES, verbal, or non-verbal IQ effects were present in the autism sample. In addition to autism itself, standardized height and average parental head circumference were the most important factors predicting head circumference in individuals with autism. Mean standardized head circumference and rates of macrocephaly were similar in probands with autism and their parents. Increased head circumference was associated with a higher (more severe) ADI-R social algorithm score. Macrocephaly is associated with delayed onset of language. Although mean head circumference and rates of macrocephaly are increased in autism, a high degree of variability is present, underscoring the complex clinical heterogeneity of the disorder. The wide distribution of head circumference in autism has major implications for genetic, neuroimaging, and other neurobiological research.