To investigate the underlying phenotypic constructs in autism spectrum disorders (ASD) and to identify genetic loci that are linked to these empirically derived factors.
Exploratory factor analysis was applied to two datasets with 28 selected Autism Diagnostic Interview-Revised (ADI-R) algorithm items. The first dataset was from the Autism Genome Project (AGP) phase I (1,236 ASD subjects from 618 families); the second was from the AGP phase II (804 unrelated ASD subjects). Variables derived from the factor analysis were then used as quantitative traits in genome-wide variance components linkage analyses.
Six factors, joint attention, social interaction and communication, non-verbal communication, repetitive sensory-motor behaviour, peer interaction, and compulsion/restricted interests, were retained for both datasets. There was good agreement between the factor loading patterns from the two datasets. All factors showed familial aggregation. Suggestive evidence for linkage was obtained for the joint attention factor on 11q23. Genome-wide significant evidence for linkage was obtained for the repetitive sensory-motor behaviour factor on 19q13.3.
This study demonstrates that the underlying phenotypic constructs based on the ADI-R algorithm items are replicable in independent datasets; and the empirically derived factors are suitable and informative in genetic studies of ASD.
autism; ADI-R; factor analysis; linkage analysis; quantitative trait
Autism is a neurodevelopmental disorder with increasing evidence of heterogeneous genetic etiology including de novo and inherited copy number variants (CNVs). We performed array comparative genomic hybridization using a custom Agilent 1 M oligonucleotide array intended to cover 197 332 unique exons in RefSeq genes; 98% were covered by at least one probe and 95% were covered by three or more probes with the focus on detecting relatively small CNVs that would implicate a single protein-coding gene. The study group included 99 trios from the Simons Simplex Collection. The analysis identified and validated 55 potentially pathogenic CNVs, categorized as de novo autosomal heterozygous, inherited homozygous autosomal, complex autosomal and hemizygous deletions on the X chromosome of probands. Twenty percent (11 of 55) of these CNV calls were rare when compared with the Database of Genomic Variants. Thirty-six percent (20 of 55) of the CNVs were also detected in the same samples in an independent analysis using the 1 M Illumina single-nucleotide polymorphism array. Findings of note included a common and sometimes homozygous 61 bp exonic deletion in SLC38A10, three CNVs found in lymphoblast-derived DNA but not present in whole-blood derived DNA and, most importantly, in a male proband, an exonic deletion of the TMLHE (trimethyllysine hydroxylase epsilon) that encodes the first enzyme in the biosynthesis of carnitine. Data for CNVs present in lymphoblasts but absent in fresh blood DNA suggest that these represent clonal outgrowth of individual B cells with pre-existing somatic mutations rather than artifacts arising in cell culture. GEO accession number GSE23765 (http://www.ncbi.nlm.nih.gov/geo/, date last accessed on 30 August 2011). Genboree accession: http://genboree.org/java-bin/gbrowser.jsp?refSeqId=1868&entryPointId=chr17&from=53496072&to=53694382&isPublic=yes, date last accessed on 30 August 2011.
A promoter-linked insertion/deletion polymorphism of the serotonin transporter gene (SLC6A4) has been implicated in autism spectrum disorders (ASDs) in numerous family-based association studies. However, the results of these investigations have been inconsistent in that both the long and short alleles have been shown to be over-transmitted to affected offspring. In order to further elucidate the relationship between the 5-HTTLPR variant and autism risk, we undertook a thorough study of parent-of-origin effects, maternal genotype effects, and offspring genotype effects in a sample of affected offspring from the Autism Genetic Resource Exchange (AGRE). Both the overall autism phenotype and measures of autism behaviors from the Autism Diagnostic Interview-Revised (Lord et al, 1994) were considered. We found evidence of over-transmission (risk allele short, p=0.012), maternal effects (risk allele long, p=0.035), and parent-of-origin effects (risk allele short from mother, p=0.018) of the 5-HTTLPR variant in the AGRE sample. Population-specific and gender-specific effects were also explored as associations may be heterogeneous across populations and sexes. Parent-of-origin effects of the variant were associated with maternally-inherited copies of the short allele that resulted in more impaired overall level of language (p=0.04). Our study was conducted to further investigate the 5-HTTLPR risk variants by identifying allelic associations that may be population-specific, phenotype-specific, or conferred by maternal or parent-of-origin effects. In light of conflicting observations from previous studies, these are just a few of the possible explanations that deserve attention.
Autism; 5-HTTLPR; maternal effects; parent-of-origin effects; association
Maternal 15q11-q13 duplication is the most common copy number variant in autism, accounting for ∼1-3% of cases. The 15q11-q13 region is subject to epigenetic regulation and genomic copy number losses and gains cause genomic disorders in a parent-of-origin-specific manner. One 15q11-q13 locus encodes the GABAA receptor β3 subunit gene (GABRB3), which has been implicated by several studies in both autism and absence epilepsy, and the co-morbidity of epilepsy in autism is well established. We report that maternal transmission of a GABRB3 signal peptide variant (P11S), previously implicated in childhood absence epilepsy, is associated with autism. Analysis of wild-type and mutant β3 subunit-containing α1β3γ2 GABAA receptors demonstrates reduced whole cell current and decreased β3 subunit protein on the cell surface due to impaired intracellular β3 subunit processing. We thus provide the first evidence for association between a specific GABAA receptor defect and autism, direct evidence that this defect causes synaptic dysfunction that is autism-relevant, and the first maternal risk effect in the 15q11-q13 autism duplication region linked to a coding variant.
autism; GABRB3; epilepsy; GABAA receptor; imprinting; mutation
Autism spectrum disorder is a severe early onset neurodevelopmental disorder with high heritability but significant heterogeneity. Traditional genome-wide approaches to test for an association of common variants with autism susceptibility risk have met with limited success. However, novel methods to identify moderate risk alleles in attainable sample sizes are now gaining momentum.
In this study, we utilized publically available genome-wide association study data from the Autism Genome Project and annotated the results (P <0.001) for expression quantitative trait loci present in the parietal lobe (GSE35977), cerebellum (GSE35974) and lymphoblastoid cell lines (GSE7761). We then performed a test of enrichment by comparing these results to simulated data conditioned on minor allele frequency to generate an empirical P-value indicating statistically significant enrichment of expression quantitative trait loci in top results from the autism genome-wide association study.
Our findings show a global enrichment of brain expression quantitative trait loci, but not lymphoblastoid cell line expression quantitative trait loci, among top single nucleotide polymorphisms from an autism genome-wide association study. Additionally, the data implicates individual genes SLC25A12, PANX1 and PANX2 as well as pathways previously implicated in autism.
These findings provide supportive rationale for the use of annotation-based approaches to genome-wide association studies.
Autism; annotation; cerebellum; enrichment; expression quantitative trait (eQTL); GWAS; LCL; pannexin; parietal; SLC25A12
Mounting evidence suggests that genetic risks for mental disorders often interact with the social environment, but most studies still ignore environmental moderation of genetic influences. We tested interactions between maternal parenting and the variable number tandem repeat (VNTR) polymorphism in the 3′ untranslated region (UTR) of the dopamine transporter gene in the child to increase understanding of gene-environment interactions involving early parenting. Participants were part of a 9-year longitudinal study of 4–6-year-old children who met criteria for attention-deficit/hyperactivity disorder (ADHD) and demographically matched controls. Maternal parenting was observed during standard mother-child interactions in wave 1. The child’s conduct disorder (CD) symptoms 5–8 years later were measured using separate structured diagnostic interviews of the mother and youth. Controlling for ADHD symptoms and child disruptive behavior during the mother-child interaction, there was a significant inverse relation between levels of both positive and negative parenting at 4–6 years and the number of later CD symptoms, but primarily among children with two copies of the 9-repeat allele of the VNTR. The significant interaction with negative parenting was replicated in parent and youth reports of CD symptoms separately.
gene-environment interaction; dopamine transporter gene; maternal parenting; conduct disorder
Polymorphism of the dopamine transporter genotype (DAT1) confers a small but significant susceptibility to Attention Deficit Hyperactivity Disorder (ADHD). We examined whether the volume of the head of caudate, a striatal structure with high DAT expression that is important for inhibitory function, differs by DAT1 in a children diagnosed with the disorder relative to age and IQ matched controls.
Volume of the head of caudate was delineated in the right and left hemisphere and compared between 7–13 year old children with and without ADHD (Combined type) who were carriers of two (10/10) or one (9/10) copy of the 10-repeat DAT1 allele.
Caudate volumes were overall smaller 10/10 than 9/10 children, particularly in the left than right hemisphere. While DAT1 effects did not vary by ADHD diagnosis, overall caudate volumes were smaller in ADHD relative to control children.
Altered caudate development associated with 10-repeat homozygosity of DAT1 may contribute susceptibility to ADHD.
Brain; structure; VNTR; polymorphism; striatal
Variations in the serotonin transporter gene (5HTTLPR) and biased processing of face-emotion displays both have been implicated in the transmission of depression risk, but little is known about developmental influences on these relationships. Within a community sample of adolescents, we examine whether 5HTTLPR genotype moderates the link between maternal depressive history and errors in face-emotion labeling. When controlling for current levels of depression and anxiety among youth, a two-way interaction between maternal depressive history and 5HTTLPR genotype was detected. Specifically, adolescents whose mothers reported a depressive history and who had a low expressing genotype made more errors in classifying emotional faces when compared with adolescents with an intermediate or high expressing genotype, with or without maternal depression history. These findings highlight the complex manner in which maternal depression and genetic risk may interact to predict individual differences in social information processing, as it is moderated by the 5HTTLPR genotype.
intergenerational transmission; depression; 5HT; adolescence; face processing; G X E
Restricted and repetitive behavior (RRB) is a group of heterogeneous maladaptive behaviors. RRB is one of the key diagnostic features of autism spectrum disorders (ASDs) and also commonly observed in Prader–Willi syndrome (PWS). In this study, we assessed RRB using the Repetitive Behavior Scale-Revised (RBS-R) in two ASD samples (University of Illinois at Chicago [UIC] and University of Florida [UF]) and one PWS sample. We compared the RBS-R item endorsements across three ASD cohorts (UIC, UF and an ASD sample from Lam, The Repetitive Behavior Scale-Revised: independent validation and the effect of subject variables, PhD thesis, 2004), and a PWS sample. We also compared the mean RBS-R subscale/sum scores across the UIC, UF and PWS samples; across the combined ASD (UIC + UF), PWS-deletion and PWS-disomy groups; and across the combined ASD sample, PWS subgroup with a Social Communication Questionnaire (SCQ) score ≥15, and PWS subgroup with a SCQ score <15. Despite the highly heterogeneous nature, the three ASD samples (UIC, UF and Lam’s) showed a similar pattern of the RBS-R endorsements, and the mean RBS-R scores were not different between the UIC and UF samples. However, higher RRB was noted in the ASD sample compared with the PWS sample, as well as in the PWS subgroup with a SCQ score ≥15 compared with the PWS subgroup with a SCQ score <15. Study limitations include a small sample size, a wide age range of our participants, and not controlling for potential covariates. A future replication study using a larger sample and further investigation into the genetic bases of overlapping ASD and RRB phenomenology are needed, given the higher RRB in the PWS subgroup with a SCQ score ≥15.
RRB; ASD; PWS; RBS-R
Inheriting two (10/10) relative to one (9/10) copy of the 10-repeat allele of the dopamine transporter genotype (DAT1) is associated with Attention Deficit Hyperactivity Disorder, a childhood disorder marked by poor executive function. We examined whether functional anatomy underlying working memory, a component process of executive function, differed by DAT1 in 7-12 year-old typically developing children. 10/10 and 9/10 carriers performed a verbal n-back task in two functional magnetic resonance imaging (fMRI) runs varying in working memory load, high (2-back vs. 1-back) and low (1-back vs. 0-back). Performance accuracy was superior in 9/10 than 10/10 carriers in the high but not low load runs. Examination of each run separately revealed that frontal-striatal-parietal regions were more activated in 9/10 than 10/10 carriers in the high load run; the groups did not differ in the low load run. Examination of load effects revealed a DAT1 X Load interaction in the right hemisphere in the caudate, our a priori region of interest. Exploratory analysis at a more liberal threshold revealed this interaction in other basal ganglia regions (putamen, and substantial nigra/subthalamic nuclei – SN/STN) and in medial parietal cortex (left precuneus). The striatal and parietal regions were more activated in 9/10 carriers under high than low load, and DAT1 differences (9/10 > 10/10) were evident only under high load. In contrast, SN/STN tended to be more activated in 10/10 carriers under low than high load and DAT1 differences (10/10 > 9/10) were evident only under low load. Thus, 10-repeat homozygosity of DAT1 was associated with reduced performance and a lack of increased basal ganglia involvement under higher working memory demands.
caudate; fMRI; N-back; functional polymorphism; DAT1; executive function
Polymorphisms in the 3′ UTR variable number tandem repeat (VNTR) of exon 15 of the dopamine transporter gene (DAT1) have been linked to attention-deficit hyperactivity disorder (ADHD); moreover, variability in DAT1 3′UTR genotype may contribute to both heterogeneity of the ADHD phenotype and differences in response to stimulant medications. The impact of this VNTR on neuronal function in individuals with ADHD remains unclear despite evidence that the polymorphisms influence dopamine transporter expression. Thus, we used event-related functional magnetic resonance imaging to examine the impact of DAT1 3′UTR genotype on brain activation during response inhibition in unmedicated children and adolescents with ADHD. Twenty-one youth with ADHD who were homozygous for the 10-repeat (10R) allele of the DAT1 3′UTR and 12 youth who were carriers of the 9-repeat (9R) allele were scanned while they performed a Go/No-Go task. Response inhibition was modeled by contrasting activation during correct No-Go trials versus correct Go trials. Participants who were homozygous for the DAT1 3′UTR 10R allele and those who had a single 9R allele did not differ on percent of trials with successful inhibition, which was the primary measure of inhibitory control. Yet, youth with the DAT1 3′UTR 10R/10R genotype had significantly greater inhibitory control-related activation than those with one 9R allele in the left striatum, right dorsal premotor cortex, and bilaterally in the temporoparietal cortical junction. These findings provide preliminary evidence that neural activity related to inhibitory control may differ as a function of DAT1 3′UTR genotype in youth with ADHD.
The most common chromosomal abnormalities associated with autism are 15q11–q13 duplications. Maternally derived or inherited duplications of 15q pose a substantial risk for an autism phenotype, while paternally derived duplications may be incompletely penetrant or result in other neurodevelopmental problems. Therefore, the determination of maternal versus paternal origin of this duplication is important for early intervention therapies and for appropriate genetic counseling to the families. We adapted a previous single-reaction tube assay (high-resolution melting curve analysis) to determine the parent of origin of 15q duplications in 28 interstitial duplication 15q samples, one family and two isodicentric subjects. Our method distinguished parent origin in 92% of the independent samples as well as in the familial inherited duplication and in the two isodicentric samples. This method accurately determines parental origin of the duplicated segment and measures the dosage of these alleles in the sample. In addition, it can be performed on samples where parental DNA is not available for microsatellite analysis. The development of this single-tube assay will make it easier for genetic testing laboratories to provide parent-of-origin information and will provide important information to clinical geneticists about autism risk in these individuals.
SLC25A12 was previously identified by a linkage-directed association analysis in autism. In this study, we investigated the relationship between three SLC25A12 single nucleotide polymorphisms (SNPs) (rs2056202, rs908670 and rs2292813) and restricted repetitive behavior (RRB) traits in autism spectrum disorders (ASDs), based on a positive correlation between the G allele of rs2056202 and an RRB subdomain score on the Autism Diagnostic Interview-Revised (ADI-R).
We used the Repetitive Behavior Scale-Revised (RBS-R) as a quantitative RRB measure, and conducted linear regression analyses for individual SNPs and a previously identified haplotype (rs2056202-rs2292813). We examined associations in our University of Illinois at Chicago-University of Florida (UIC-UF) sample (179 unrelated individuals with an ASD), and then attempted to replicate our findings in the Simons Simplex Collection (SSC) sample (720 ASD families).
In the UIC-UF sample, three RBS-R scores (ritualistic, sameness, sum) had positive associations with the A allele of rs2292813 (p = 0.006-0.012) and with the rs2056202-rs2292813 haplotype (omnibus test, p = 0.025-0.040). The SSC sample had positive associations between the A allele of rs2056202 and four RBS-R scores (stereotyped, sameness, restricted, sum) (p = 0.006-0.010), between the A allele of rs908670 and three RBS-R scores (stereotyped, self-injurious, sum) (p = 0.003-0.015), and between the rs2056202-rs2292813 haplotype and six RBS-R scores (stereotyped, self-injurious, compulsive, sameness, restricted, sum)(omnibus test, p = 0.002-0.028). Taken together, the A alleles of rs2056202 and rs2292813 were consistently and positively associated with RRB traits in both the UIC-UF and SSC samples, but the most significant SNP with phenotype association varied in each dataset.
This study confirmed an association between SLC25A12 and RRB traits in ASDs, but the direction of the association was different from that in the initial study. This could be due to the examined SLC25A12 SNPs being in linkage disequilibrium with another risk allele, and/or genetic/phenotypic heterogeneity of the ASD samples across studies.
This study was conducted to examine the relationship between whole blood serotonin level and behavioral symptoms in 78 subjects with autism. No significant associations were found between serotonin level and the primary behavioral outcome measures. However, a significant inverse relationship between serotonin level and self-injury was demonstrated.
autism; serotonin; repetitive behavior; self-injury; aggression
To determine the effect of serotonin transporter polymorphism promoter region (5-HTTPLR) genotypic variation (low, intermediate, and high expression groups) on response to escitalopram treatment of children and adolescents with Autism Spectrum Disorders (ASDs).
The study used a forced titration, open label design, with genotype blind until study completion. Participants were children and adolescents aged 4 to 17 years of age with a confirmed ASD (Autistic Disorder, Asperger’s Disorder, or Pervasive Developmental Disorder, Not Otherwise Specified).
There was an interaction between genotype group and time on the Aberrant Behavior Checklist Irritability Subscale (primary outcome variable) (linear MMLE = −4.84, Z = −2.89, SE = 1.67, p = 0.004). Examination of baseline to last-observation carried forward scores revealed that a genotype grouping based on a previous study of platelet 5-HT uptake revealed less response in the genotype group that had S/S genotype for 5-HTTLPR and did not have a diplotype in intron 1 previously shown to be associated with increased platelet 5-HT uptake.
This genotype-blind, prospective pharmacogenetic study found the group of subjects with associated with the lowest platelet 5-HT uptake from previous study had the smallest reduction in ABC-Irritability scores after open label treatment with escitalopram. Replication is necessary to confirm these findings.
Many children with Autism Spectrum Disorders have problems with anxiety, obsessions, compulsions, and insisting that things stay the same. When other interventions are not adequately helping the child deal with these difficulties, sometimes medication is considered a treatment option.
Serotonin is inactivated when it is taken back into nerve cells by a protein called the serotonin transporter. Escitalopram blocks this protein. We wanted to know if variation in the gene that produces the protein target for escitalopram would be related to response to this treatment.
autistic disorder; escitalopram; pharmacogenetics; open label; drug treatment
The dopamine transporter locus (DAT1) has been studied as a risk factor for attention-deficit/hyperactivity disorder (ADHD) and in pharmacogenetic studies of stimulant response. Several prospective studies have reported an association between the homozygous 9 repeat allele of the DAT1 3′ untranslated region (UTR) variable number tandem repeat (VNTR) (DAT1 3′) and decreased efficacy of methylphenidate (MPH). We hypothesized that children with the 9/9 genotype would display higher rates of specific stimulant side effects. Data on adverse events and DAT1 3′ genotypes were combined from two, double-blind, placebo-controlled, crossover studies of MPH conducted in child psychiatric outpatient clinics in Montreal and Washington, D.C. There were 177 participants, 5–16 years old (mean age = 8.99, standard deviation [SD] = 2), with ADHD. Parents completed the Stimulant Side Effect Scale (SERS) after a week of placebo and a week of MPH treatment. Principal components analysis of the SERS resulted in three factors: Emotionality, Somatic Complaints, and Over-focused. Children with the 9/9 genotype displayed higher scores on the Emotionality factor during placebo than children with the 9/10 and the 10/10 genotype, and their Emotionality scores increased further during MPH treatment (F[2,151] = 3.24, p < 0.05). Children with the 10/10 genotype displayed a significant increase in Somatic Complaint factor scores during MPH treatment relative to the other genotype groups (F[2,150] = 3.4, p < 0.05). These data provide suggestive evidence that DAT1 variants are differentially associated with specific stimulant side effects. Children with the 9/10 genotype displayed less severe stimulant side-effect ratings than either of the homozygous groups, who each displayed increased susceptibility to different types of adverse events. Preliminary evidence suggests that pharmacogenetic analysis using DAT1 variants shows promise for identifying individuals at increased or decreased risk for poor tolerability.
As one of the major glutathione conjugation enzymes, GSTM1 detoxifies a number of drugs and xenobiotics. Its expression and activity have been shown to correlate both with cancer risks and drug resistance. Through a genome-wide association study, we identified a significant association between HapMap SNP rs366631 and GSTM1 expression. In this study, utilizing lymphoblastoid cell lines derived from International HapMap Consortium CEU and YRI populations, we designed and performed site-specific genotyping assays for both rs366631 and a highly homologous GSTM1 upstream site. Copy number variation (CNV) assays were performed for three different regions of the GSTM1 gene. We demonstrated that HapMap SNP rs366631 is a non-polymorphic site. The false genotyping call arises from sequence homology, a common GSTM1 region deletion and a non-specific genotyping platform used to identify the SNP. However, the HapMap call for rs366631 genotype is an indicator of GSTM1 upstream region deletion. Furthermore, this upstream deletion can be used as a marker of GSTM1 gene deletion. Using a novel GSTM1 CNV assay, we showed a population-specific CNV in this region upstream of the gene. More than 75% of the Caucasian (CEU) samples exhibit GSTM1 deletion and none contain two copies of GSTM1. In contrast, up to 25% of African (YRI) samples were found to have two copies of GSTM1. In conclusion, HapMap rs366631 is a pseudo-SNP that can be used as a GSTM1 deletion marker. Both the pseudo-SNP allele frequency and GSTM1 upstream region CNV show population-specific patterns between CEU and YRI samples.
Elevated platelet serotonin (5-HT) is found in a subset of children with autism and in some of their first-degree relatives. Indices of the platelet serotonin system, including whole blood serotonin (5-HT), 5-HT binding affinity for the serotonin transporter (Km), 5-HT uptake (Vmax), and lysergic acid diethylamide (LSD) receptor binding, were previously studied in twenty-four first-degree relatives of probands with autism, half of whom were selected for elevated whole blood 5-HT levels. All subjects were then genotyped for selected polymorphisms at the SLC6A4, HTR7, HTR2A, ITGB3, and TPH1 loci. Previous studies allowed an a priori prediction of SLC6A4 haplotypes that separated the subjects into three groups that showed significantly different 5-HT binding affinity (Km, p = 0.005) and 5-HT uptake rate (Vmax, p = 0.046). Genotypes at four individual polymorphisms in SLC6A4 were not associated with platelet 5-HT indices. Haplotypes at SLC6A4 and individual genotypes of polymorphisms at SLC6A4, HTR7, HTR2A, ITGB3, and TPH1 showed no significant association with whole blood 5-HT. Haplotype analysis of two polymorphisms in TPH1 revealed a nominally significant association with whole blood 5-HT (p = 0.046). These initial studies of indices of the 5-HT system with several SNPs at loci in this system generate hypotheses for testing in other samples.
Autism; serotonin; binding; platelet; genetic; association
The oxytocin receptor gene (OXTR) has been studied in autism because of the role of oxytocin (OT) in social cognition. Linkage has also been demonstrated to the region of OXTR in a large sample. Two single nucleotide polymorphisms (SNPs) and a haplotype constructed from them in OXTR have been associated with autism in the Chinese Han population. We tested whether these associations replicated in a Caucasian sample with strictly defined autistic disorder.
We genotyped the two previously associated SNPs (rs2254298, rs53576) in 57 Caucasian autism trios. Probands met clinical, ADI-R, and ADOS criteria for autistic disorder.
Significant association was detected at rs2254298 (p = 0.03) but not rs53576. For rs2254298, overtransmission of the G allele to probands with autistic disorder was found which contrasts with the overtransmission of A previously reported in the Chinese Han sample. In both samples, G was more frequent than A. However, in our Caucasian autism trios and the CEU Caucasian HapMap samples the frequency of A was less than that reported in the Chinese Han and Chinese in Bejing HapMap samples. The haplotype test of association did not reveal excess transmission from parents to affected offspring.
These findings provide support for association of OXTR with autism in a Caucasian population. Overtransmission of different alleles in different populations may be due to a different pattern of linkage disequilibrium between the marker rs2254298 and an as yet undetermined susceptibility variant in OXTR.
A child with autism and mild microcephaly was found to have a de novo 3.3 Mb microdeletion on chromosome 1p34.2p34.3. The hypothesis is tested that this microdeletion contains one or more genes that underlie the autism phenotype in this child and in other children with autism spectrum disorders.
To search for submicroscopic chromosomal rearrangements in the child, array comparative genomic hybridisation (aCGH) was performed using a 19 K whole genome human bacterial artificial chromosome (BAC) array and the Illumina 610-Quad BeadChip microarray. Ingenuity pathway analysis (IPA) was used to construct functional biological networks to identify candidate autism genes. To identify putative functional variants in candidate genes, mutation screening was performed using polymerase chain reaction (PCR) based Sanger sequencing in 512 unrelated autism patients and 462 control subjects.
A de novo 3.3 Mb deletion containing ∼43 genes in chromosome 1p34.2p34.3 was identified and subsequently confirmed using fluorescence in situ hybridization (FISH). Literature review and bioinformatics analyses identified Regulating Synaptic Membrane Exocytosis 3 (RIMS3) as the most promising autism candidate gene. Mutation screening of this gene in autism patients identified five inherited coding variants, including one (p.E177A) that segregated with the autism phenotype in a sibship, was predicted to be deleterious, and was absent in 1161 controls.
This case report and mutation screening data suggest that RIMS3 is an autism causative or contributory gene. Functional studies of RIMS3 variants such as p.E177A should provide additional insight into the role of synaptic proteins in the pathophysiology of autism.
autism; microcephaly; mental retardation; copy number variants; synapse; molecular genetics; neurosciences; psychiatry
Reports identified the neuronal glutamate transporter gene, SLC1A1 (OMIM 133550, chromosome 9p24), as a positional and functional candidate gene for obsessive–compulsive disorder (OCD). The presence of obsessions and compulsions similar to OCD in autism, the identification of this region in a genome-wide linkage analysis of individuals with autism spectrum disorders (ASDs), and the hypothesized role of glutamate in ASDs make SLC1A1 a candidate gene for ASD as well. To test for association between SLC1A1 and autism, we typed three single nucleotide polymorphisms (SNPs, rs301430, rs301979, rs301434) previously associated with OCD in 86 strictly defined trios with autism. Family-Based Association Tests (FBAT) with additive and recessive models were used to check for association. Additionally, an rs301430–rs301979 haplotype identified for OCD was investigated. FBAT revealed nominally significant association between autism and one SNP under a recessive model. The G allele of rs301979 was undertransmitted (equivalent to overtransmission of the C allele under a dominant model) to individuals with autism (Z = −2.47, P = 0.01). The G allele was also undertransmitted in the T–G haplotype under the recessive model (Z = −2.41, P = 0.02). Both findings were also observed in the male-only sample. However, they did not withstand correction for multiple comparisons.
autism; SLC1A1; OCD; association
Although genetic factors are known to be important in addiction, no candidate genes have yet been consistently linked to drug use or abuse. Brain-derived neurotrophic factor (BDNF), which has been implicated in the behavioral response to psychomotor stimulants and potentiates neurotransmitters that are strongly linked to addiction, is a logical candidate gene to study. Using a drug challenge approach, we tested for association between BDNF G196A (val66met) genotype and subjective responses to amphetamine (AMPH). Healthy volunteers participated in a double-blind, crossover design in which they received placebo, 10 mg, and 20 mg oral d-amphetamine in random order. Subjective and physical responses to ingestion of AMPH were measured at thirty minute intervals after drug ingestion. Each subject was genotyped for the BDNF G196A polymorphism and grouped and analyzed accordingly. The effects of AMPH on ratings of arousal, energy, and heart rate were compared in subjects with the val/val genotype (N = 67) and the subjects with either the val/met or met/met genotypes (N = 32). AMPH produced less pronounced self-ratings of arousal and energy, yet higher increases in heart rate, in the val/met and met/met compared to the val/val group. These results suggest that BDNF is related to the subjective and physical response to low doses of AMPH.
brain-derived neurotrophic factor (BDNF); amphetamine (AMPH); polymorphism; drug response; addiction
One genetic mechanism known to be associated with autism spectrum disorders (ASD) is chromosomal abnormalities. The identification of copy number variants (CNV) i.e. microdeletions and microduplications that are undetectable at the level of traditional cytogenetic analysis allows the potential association of submicroscopic chromosomal imbalances and human disease.
We performed array comparative genomic hybridization (aCGH) utilizing a 19K whole genome tiling path bacterial artificial chromosome (BAC) microarray on 397 unrelated subjects with autism spectrum disorder (ASD). Common CNV were excluded using a control group comprised of 372 individuals from the NIMH Genetics Initiative Control samples. Confirmation studies were performed on all remaining CNV using FISH (Fluorescence In Situ Hybridization), microsatellite analysis and/or quantitative PCR analysis.
A total of 51 CNV were confirmed in 46 ASD subjects. Three maternal interstitial duplications of 15q11-q13 known to be associated with ASD were identified. The other 48 CNV ranged in size from 189 kb to 5.5 Mb and contained from 0 to ~40 RefSeq genes. Seven CNV were de novo and 44 were inherited.
51 autism-specific CNV were identified in 46/397 ASD patients using a 19K BAC microarray for an overall rate of 11.6%. These microdeletions and microduplications cause gene dosage imbalance in 272 genes many of which could be considered as candidate genes for autism.
autism; array comparative genomic hybridization; microdeletions; microduplications
The essential contribution of the antidepressant-sensitive serotonin (5-HT) transporter SERT (which is encoded by the SLC6A4 gene) to platelet 5-HT stores suggests an important role of this transporter in platelet function. Here, using SERT-deficient mice, we have established a role for constitutive SERT expression in efficient ADP- and thrombin-triggered platelet aggregation. Additionally, using pharmacological blockers of SERT and the vesicular monoamine transporter (VMAT), we have identified a role for ongoing 5-HT release and SERT activity in efficient human platelet aggregation. We have also demonstrated that fibrinogen, an activator of integrin αIIbβ3, enhances SERT activity in human platelets and that integrin αIIbβ3 interacts directly with the C terminus of SERT. Consistent with these findings, knockout mice lacking integrin β3 displayed diminished platelet SERT activity. Conversely, HEK293 cells engineered to express human SERT and an activated form of integrin β3 exhibited enhanced SERT function that coincided with elevated SERT surface expression. Our results support an unsuspected role of αIIbβ3/SERT associations as well as αIIbβ3 activation in control of SERT activity in vivo that may have broad implications for hyperserotonemia, cardiovascular disorders, and autism.