Common genetic variants on 5p14.1 associate with autism spectrum disorders

Autism spectrum disorders (ASDs) represent a group of childhood neurodevelopmental and neuropsychiatric disorders characterized by deficits in verbal communication, impairment of social interaction, and restricted and repetitive patterns of interests and behaviour. To identify common genetic risk factors underlying ASDs, here we present the results of genome-wide association studies on a cohort of 780 families (3,101 subjects) with affected children, and a second cohort of 1,204 affected subjects and 6,491 control subjects, all of whom were of European ancestry. Six single nucleotide polymorphisms between cadherin 10 (CDH10) and cadherin 9 (CDH9)-two genes encoding neuronal cell-adhesion molecules-revealed strong association signals, with the most significant SNP being rs4307059 (P = 3.4 x 10(-8), odds ratio = 1.19). These signals were replicated in two independent cohorts, with combined P values ranging from 7.4 x 10(-8) to 2.1 x 10(-10). Our results implicate neuronal cell-adhesion molecules in the pathogenesis of ASDs, and represent, to our knowledge, the first demonstration of genome-wide significant association of common variants with susceptibility to ASDs.

Examination of association of genes in the serotonin system to autism

Autism is characterized as one of the pervasive developmental disorders, a spectrum of often severe behavioral and cognitive disturbances of early development. The high heritability of autism has driven multiple efforts to identify genetic variation that increases autism susceptibility. Numerous studies have suggested that variation in peripheral and central metabolism of serotonin (5-hydroxytryptamine) may play a role in the pathophysiology of autism. We screened 403 autism families for 45 single nucleotide polymorphisms in ten serotonin pathway candidate genes. Although genome-wide linkage scans in autism have provided support for linkage to various loci located within the serotonin pathway, our study does not provide strong evidence for linkage to any specific gene within the pathway. The most significant association (p = 0.0002; p = 0.02 after correcting for multiple comparisons) was found at rs1150220 (HTR3A) located on chromosome 11 ( approximately 113 Mb). To test specifically for multilocus effects, multifactor dimensionality reduction was employed, and a significant two-way interaction (p value = 0.01) was found between rs10830962, near MTNR1B (chromosome11; 92,338,075 bp), and rs1007631, near SLC7A5 (chromosome16; 86,413,596 bp). These data suggest that variation within genes on the serotonin pathway, particularly HTR3A, may have modest effects on autism risk.

Autism in African American families: clinical-phenotypic findings

Unlike other complex diseases, the study of autism has been almost exclusively limited to Caucasian families. This study represents a first effort to examine clinical and phenotypic findings in individuals with autism from African American families. Drawing from an ongoing genetic study of autism we compared African American (N = 46, mean age = 118 months) and Caucasian (N = 298, mean age = 105 months) groups on autism symptoms and developmental language symptoms. The African American group showed greater delays in language but did not differ from the Caucasian group on core autism symptoms. These findings, while suggestive of a more severe phenotype, may reflect an ascertainment bias. Nonetheless, we believe that more studies of racial-ethnic groups should be conducted with several goals in mind including strengthening recruiting strategies to include more ethnic-racial groups and more thoughtful evaluation of phenotypic traits. Such considerations will aid greatly in the search for genetic variants in autism.

Multifactor dimensionality reduction-phenomics: a novel method to capture genetic heterogeneity with use of phenotypic variables

Complex human diseases do not have a clear inheritance pattern, and it is expected that risk involves multiple genes with modest effects acting independently or interacting. Major challenges for the identification of genetic effects are genetic heterogeneity and difficulty in analyzing high-order interactions. To address these challenges, we present MDR-Phenomics, a novel approach based on the multifactor dimensionality reduction (MDR) method, to detect genetic effects in pedigree data by integration of phenotypic covariates (PCs) that may reflect genetic heterogeneity. The P value of the test is calculated using a permutation test adjusted for multiple tests. To validate MDR-Phenomics, we compared it with two MDR-based methods: (1) traditional MDR pedigree disequilibrium test (PDT) without consideration of PCs (MDR-PDT) and (2) stratified phenotype (SP) analysis based on PCs, with use of MDR-PDT with a Bonferroni adjustment (SP-MDR). Using computer simulations, we examined the statistical power and type I error of the different approaches under several genetic models and sampling scenarios. We conclude that MDR-Phenomics is more powerful than MDR-PDT and SP-MDR when there is genetic heterogeneity, and the statistical power is affected by sample size and the number of PC levels. We further compared MDR-Phenomics with conditional logistic regression (CLR) for testing interactions across single or multiple loci with consideration of PC. The results show that CLR with PC has only slightly smaller power than does MDR-Phenomics for single-locus analysis but has considerably smaller power for multiple loci. Finally, by applying MDR-Phenomics to autism, a complex disease in which multiple genes are believed to confer risk, we attempted to identify multiple gene effects in two candidate genes of interest--the serotonin transporter gene (SLC6A4) and the integrin beta 3 gene (ITGB3) on chromosome 17. Analyzing four markers in SLC6A4 and four markers in ITGB3 in 117 white family triads with autism and using sex of the proband as a PC, we found significant interaction between two markers--rs1042173 in SLC6A4 and rs3809865 in ITGB3.

Investigation of potential gene–gene interactions between apoe and reln contributing to autism risk

BACKGROUND

Several candidate gene studies support RELN as susceptibility gene for autism. Given the complex inheritance pattern of autism, it is expected that gene-gene interactions will exist. A logical starting point for examining potential gene-gene interactions is to evaluate the joint effects of genes involved in a common biological pathway. RELN shares a common biological pathway with APOE, and Persico et al. have observed transmission distortion of the APOE-2 allele in autism families.

OBJECTIVE

We evaluated RELN and APOE for joint effects in autism susceptibility.

METHODS

A total of 470 Caucasian autism families were analyzed (265 multiplex; 168 trios with no family history; 37 positive family history but only one sampled affected). These families were genotyped for 11 RELN polymorphisms, including the 5' untranslated region repeat previously associated with autism, as well as for the APOE functional allele. We evaluated single locus allelic and genotypic association with the pedigree disequilibrium test and geno-PDT, respectively. Multilocus effects were evaluated using the extended version of the multifactorial dimensionality reduction method.

RESULTS

For the single locus analyses, there was no evidence for an effect of APOE in our data set. Evidence for association with RELN (rs2,073,559; trio subset P=0.07 PDT; P=0.001 geno-PDT; overall geno-PDT P=0.05), however, was found. For multilocus geno-PDT analysis, the joint genotype of APOE and RELN rs2,073,559 was highly significant (trio subset, global P=0.0001), probably driven by the RELN single locus effect. Using the extended version of the multifactorial dimensionality reduction method to detect multilocus effects, there were no statistically significant associations for any of the n-locus combinations involving RELN or APOE in the overall or multiplex subset. In the trio subset, 1-locus and 2-locus models selected only markers in RELN as best models for predicting autism case status.

CONCLUSION

Thus, we conclude that there is no main effect of APOE in our autism data set, nor is there any evidence for a joint effect of APOE with RELN. RELN, however, remains a good candidate for autism susceptibility.

A comparison of repetitive behaviors in Aspergers Disorder and high functioning autism

In this study we compared 33 IQ and age matched pairs of individuals with Aspergers Disorder (ASP) and high functioning autism (HFA) on measures of repetitive behavior. On the Repetitive Behavior Scale-Revised (RBS-R), the ASP and HFA groups showed no differences in RBS-R Intensity score (severity) score or Frequency score (number of problems present). This suggests that the two groups are similar with respect to the intensity or severity of repetitive behaviors and the presence of repetitive behaviors. At the item level there were no differences on scales typically associated with autism (Stereotyped Behavior) and ASP (Restricted Interests). Similarly, there were no differences between the groups on the Aberrant Behavior Checklist Stereotypy scale. These findings add to the body of literature showing that HFA and ASP fail to differ with respect to repetitive behaviors. The implications of the findings for neurobiologic and genetic studies are discussed.

Dissecting the locus heterogeneity of autism: significant linkage to chromosome 12q14

Autism is a common neurodevelopmental disorder with a significant genetic component and locus heterogeneity. To date, 12 microsatellite genome screens have been performed using various data sets of sib-pair families (parents and affected children) resulting in numerous regions of potential linkage across the genome. However, no universal region or consistent candidate gene from these regions has emerged. The use of large, extended pedigrees is a recognized powerful approach to identify significant linkage results, as these families potentially contain more potential linkage information than sib-pair families. A genome-wide linkage analysis was performed on 26 extended autism families (65 affected, 184 total individuals). Each family had two to four affected individuals comprised of either avuncular or cousin pairs. For analysis, we used a high-density single-nucleotide polymorphism genotyping assay, the Affymetrix GeneChip Human Mapping 10K array. Two-point analysis gave peak heterogeneity limit of detection (HLOD) of 2.82 at rs2877739 on chromosome 14q. Suggestive linkage evidence (HLOD>2) from a two-point analysis was also found on chromosomes 1q, 2q, 5q, 6p,11q and 12q. Chromosome 12q was the only region showing significant linkage evidence by multipoint analysis with a peak HLOD=3.02 at rs1445442. In addition, this linkage evidence was enhanced significantly in the families with only male affected (multipoint HLOD=4.51), suggesting a significant gender-specific effect in the etiology of autism. Chromosome-wide haplotype analyses on chromosome 12 localized the potential autism gene to a 4 cM region shared among the affected individuals across linked families. This novel linkage peak on chromosome 12q further supports the hypothesis of substantial locus heterogeneity in autism.

Factor analysis of the aberrant behavior checklist in individuals with autism spectrum disorders

Exploratory factor analysis (varimax and promax rotations) of the aberrant behavior checklist-community version (ABC) in 275 individuals with Autism spectrum disorder (ASD) identified four- and five-factor solutions which accounted for >70% of the variance. Confirmatory factor analysis (Lisrel 8.7) revealed indices of moderate fit for the five-factor solution. Our results suggest that the factor structure of the ABC is robust within an ASD sample. Both solutions yielded a three items self-injury factor. Stratifying on this factor, we identified significant differences between the high- and low-self injury groups on ABC subscales. The emergence of a self-injury factor, while not suggestive of a new subscale, warrants further exploration as a tool that could help dissect relevant neurobiobehavioral groups in ASD.

The relationship between restrictive and repetitive behaviors in individuals with autism and obsessive compulsive symptoms in parents

This study investigated the relationship between repetitive behaviors in individuals with autism and obsessive-compulsive behaviors in parents. We hypothesized that repetitive behaviors in probands with autism would be associated with increased obsessive-compulsive behaviors in parents in sporadic families (1 known case of autism per family and no known history of autism). Parents with clinically significant Y-BOCS scores were more likely to have a family history of obsessive-compulsive disorder. The empirically derived Autism Diagnostic Interview-R (ADI-R) factor, Insistence on Sameness, was positively correlated with obsessive-compulsive behaviors in parents. Further, when probands were grouped on the basis of parental Y-BOCS scores (clinically significant versus non-clinically significant), probands whose parents had clinically significant Y-BOCS scores had higher ADI-R Insistence on Sameness factor scores. The findings of the current study of sporadic families extend previous work that has shown an association between restrictive/repetitive behaviors in probands with autism and obsessive-compulsive features in parents.

Investigation of autism and GABA receptor subunit genes in multiple ethnic groups

Autism is a neurodevelopmental disorder of complex genetics, characterized by impairment in social interaction and communication, as well as repetitive behavior. Multiple lines of evidence, including alterations in levels of GABA and GABA receptors in autistic patients, indicate that the GABAergic system, which is responsible for synaptic inhibition in the adult brain, may be involved in autism. Previous studies in our lab indicated association of noncoding single nucleotide polymorphisms (SNPs) within a GABA receptor subunit gene on chromosome 4, GABRA4, and interaction between SNPs in GABRA4 and GABRB1 (also on chromosome 4), within Caucasian autism patients. Studies of genetic variation in African-American autism families are rare. Analysis of 557 Caucasian and an independent population of 54 African-American families with 35 SNPs within GABRB1 and GABRA4 strengthened the evidence for involvement of GABRA4 in autism risk in Caucasians (rs17599165, p=0.0015; rs1912960, p=0.0073; and rs17599416, p=0.0040) and gave evidence of significant association in African-Americans (rs2280073, p=0.0287 and rs16859788, p=0.0253). The GABRA4 and GABRB1 interaction was also confirmed in the Caucasian dataset (most significant pair, rs1912960 and rs2351299; p=0.004). Analysis of the subset of families with a positive history of seizure activity in at least one autism patient revealed no association to GABRA4; however, three SNPs within GABRB1 showed significant allelic association; rs2351299 (p=0.0163), rs4482737 (p=0.0339), and rs3832300 (p=0.0253). These results confirmed our earlier findings, indicating GABRA4 and GABRB1 as genes contributing to autism susceptibility, extending the effect to multiple ethnic groups and suggesting seizures as a stratifying phenotype.

An Analysis Paradigm for Investigating Multi-locus Effects in Complex Disease: Examination of Three GABAA Receptor Subunit Genes on 15q11-q13 as Risk Factors for Autistic Disorder

Gene-gene interactions are likely involved in many complex genetic disorders and new statistical approaches for detecting such interactions are needed. We propose a multi-analytic paradigm, relying on convergence of evidence across multiple analysis tools. Our paradigm tests for main and interactive effects, through allele, genotype and haplotype association. We applied our paradigm to genotype data from three GABAA receptor subunit genes (GABRB3, GABRA5, and GABRG3) on chromosome 15 in 470 Caucasian autism families. Previously implicated in autism, we hypothesized these genes interact to contribute to risk. We detected no evidence of main effects by allelic (PDT, FBAT) or genotypic (genotype-PDT) association at individual markers. However, three two-marker haplotypes in GABRG3 were significant (HBAT). We detected no significant multi-locus associations using genotype-PDT analysis or the EMDR data reduction program. However, consistent with the haplotype findings, the best single locus EMDR model selected a GABRG3 marker. Further, the best pairwise genotype-PDT result involved GABRB3 and GABRG3, and all multi-locus EMDR models also selected GABRB3 and GABRG3 markers. GABA receptor subunit genes do not significantly interact to contribute to autism risk in our overall data set. However, the consistency of results across analyses suggests that we have defined a useful framework for evaluating gene-gene interactions.

Lack of association between autism and SLC25A12

OBJECTIVE

Autism has a strong, complex genetic component, most likely involving several genes. Multiple genomic screens have shown evidence suggesting linkage to chromosome 2q31-q33, which includes the SLC25A12 gene. Recently, an association between autism risk and two single nucleotide polymorphisms (SNPs) in SLC25A12 was reported. This study aimed to test for association in SLC25A12 in an independent data set of 327 families with autistic offspring.

METHOD

The authors analyzed two SNPs that were significant in the previous study group, as well as seven additional SNPs within the gene. Association analyses for individual SNPs as well as haplotypes were performed.

RESULTS

There was no evidence of an association between SLC25A12 and autism.

CONCLUSIONS

These results suggest that SLC25A12 is not a major contributor to autism risk in these families.

Identification of significant association and gene-gene interaction of GABA receptor subunit genes in autism

Autism is a common neurodevelopmental disorder with a significant genetic component. Existing research suggests that multiple genes contribute to autism and that epigenetic effects or gene-gene interactions are likely contributors to autism risk. However, these effects have not yet been identified. Gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the adult brain, has been implicated in autism etiology. Fourteen known autosomal GABA receptor subunit genes were studied to look for the genes associated with autism and their possible interactions. Single-nucleotide polymorphisms (SNPs) were screened in the following genes: GABRG1, GABRA2, GABRA4, and GABRB1 on chromosome 4p12; GABRB2, GABRA6, GABRA1, GABRG2, and GABRP on 5q34-q35.1; GABRR1 and GABRR2 on 6q15; and GABRA5, GABRB3, and GABRG3 on 15q12. Intronic and/or silent mutation SNPs within each gene were analyzed in 470 white families with autism. Initially, SNPs were used in a family-based study for allelic association analysis--with the pedigree disequilibrium test and the family-based association test--and for genotypic and haplotypic association analysis--with the genotype-pedigree disequilibrium test (geno-PDT), the association in the presence of linkage (APL) test, and the haplotype family-based association test. Next, with the use of five refined independent marker sets, extended multifactor-dimensionality reduction (EMDR) analysis was employed to identify the models with locus joint effects, and interaction was further verified by conditional logistic regression. Significant allelic association was found for markers RS1912960 (in GABRA4; P = .01) and HCV9866022 (in GABRR2; P = .04). The geno-PDT found significant genotypic association for HCV8262334 (in GABRA2), RS1912960 and RS2280073 (in GABRA4), and RS2617503 and RS12187676 (in GABRB2). Consistent with the allelic and genotypic association results, EMDR confirmed the main effect at RS1912960 (in GABRA4). EMDR also identified a significant two-locus gene-gene effect model involving RS1912960 in GABRA4 and RS2351299 in GABRB1. Further support for this two-locus model came from both the multilocus geno-PDT and the APL test, which indicated a common genotype and haplotype combination positively associated with disease. Finally, these results were also consistent with the results from the conditional logistic regression, which confirmed the interaction between GABRA4 and GABRB1 (odds ratio = 2.9 for interaction term; P = .002). Through the convergence of all analyses, we conclude that GABRA4 is involved in the etiology of autism and potentially increases autism risk through interaction with GABRB1. These results support the hypothesis that GABA receptor subunit genes are involved in autism, most likely via complex gene-gene interactions.

Analysis of the RELN gene as a genetic risk factor for autism

Several genome-wide screens have indicated the presence of an autism susceptibility locus within the distal long arm of chromosome 7 (7q). Mapping at 7q22 within this region is the candidate gene reelin (RELN). RELN encodes a signaling protein that plays a pivotal role in the migration of several neuronal cell types and in the development of neural connections. Given these neurodevelopmental functions, recent reports that RELN influences genetic risk for autism are of significant interest. The total data set consists of 218 Caucasian families collected by our group, 85 Caucasian families collected by AGRE, and 68 Caucasian families collected at Tufts University were tested for genetic association of RELN variants to autism. Markers included five single-nucleotide polymorphisms (SNPs) and a repeat in the 5'-untranslated region (5'-UTR). Tests for association in Duke and AGRE families were also performed on four additional SNPs in the genes PSMC2 and ORC5L, which flank RELN. Family-based association analyses (PDT, Geno-PDT, and FBAT) were used to test for association of single-locus markers and multilocus haplotypes with autism. The most significant association identified from this combined data set was for the 5'-UTR repeat (PDT P-value=0.002). These analyses show the potential of RELN as an important contributor to genetic risk in autism.

Ordered-subset analysis of savant skills in autism for 15q11-q13

Autism is a complex disorder characterized by genetic and phenotypic heterogeneity. Analysis of phenotypically homogeneous subtypes has been used to both confirm and narrow potential autism linkage regions such as the chromosomal region 15q11-q13. Increased evidence for linkage in this region had been found in a subgroup of 21 autism families (total families = 94) stratified based on a savant skill factor (SSF) from the Autism Diagnostic Interview, Revised (ADI-R). We examined the savant phenotypic finding in our sample of 91 multiplex autism families. Using two-point parametric analysis in stratification with a cutoff point of a savant skill score of 0.16, our families failed to demonstrate linkage to 15q11-q13. In addition, ordered subset analysis (OSA) using SSF as a covariate also failed to show evidence for linkage. Our findings do not support savant skills as an informative phenotypic subset for linkage in our sample.

Repetitive behaviors in autism: relationships with associated clinical features

Relationships between repetitive behaviors (RBs) and associated clinical features (i.e., cognitive and adaptive functioning levels, sleep problems, medication use, and other behavioral problems) were examined in two groups (High nonverbal IQ > or = 97 versus Low nonverbal IQ < or = 56) of children with autism spectrum disorders (n = 14; mean age = 10 years, 7 months). For the group as a whole, nonverbal cognitive ability (NVIQ) (as measured by the Leiter-R), adaptive functioning level, the presence of sleep problems, and three scales of the Aberrant Behavior Checklist (ABC) (Irritability, Lethargy, and Hyperactivity) were highly correlated with total RB scores on the Repetitive Behavior Scale-Revised (RBS-R). After controlling for NVIQ, adaptive level, sleep problems, and two scales of the ABC (Irritability and Lethargy) were not significantly associated with RB scores. However, there remained a significant positive correlation between the presence of RBs and the Hyperactivity scale of the ABC. Parent ratings of their stress levels and the presence of RBs in their children were highly correlated. The relationship between RBs and associated clinical features in autism is complex and future studies should control for cognitive ability when examining the direct and indirect relationships of these variables with RBs.

Accelerated head growth in early development of individuals with autism

Macrocephaly is one of the most consistent physical findings reported in autistic individuals. Previous studies attempted to determine if macrocephaly is associated with risk for autism. This study hypothesizes that an abnormal acceleration in head growth during early development, rather than macrocephaly, is associated with autism risk. To investigate this hypothesis, head circumference data were examined in 251 individuals from 82 multiplex (at least two individuals with autism) and 113 sporadic (no family history) families with autism. This examination included longitudinal measurements for 79 individuals. Nineteen percent of the original 251 individuals were found to have macrocephaly (head circumference >97%). Abnormal acceleration in head growth was defined as an increase of 25 or more percentile points in head circumference between two consecutive measurements. Thirty-five percent of individuals with multiple head circumference records had an abnormal increase in head circumference. Furthermore, autistic individuals with accelerated head growth in early childhood displayed higher levels of adaptive functioning and less social impairment. This study confirms the presence of abnormal acceleration in head growth during the first and second months of life in a subgroup of autistic individuals.

Analysis of the autism chromosome 2 linkage region: GAD1 and other candidate genes

Autism has a strong and complex genetic component, involving several genes. Genomic screens, including our own, have shown suggestive evidence for linkage over a 20-30 cM region on chromosome 2q31-q33. Two subsequent reports showed that the linkage evidence increased in the subset of families with phrase speech delay (PSD), defined as onset of phrase speech later than 3 years of age. To further investigate the linkage in the presumptive candidate region, microsatellite markers in a 2 cM grid covering the interval from 164 to 203 cM were analyzed in 110 multiplex (2 or more sampled autism patients) families. A maximum heterogeneity LOD (HLOD) score of 1.54 was detected at D2S1776 (173 cM) in the overall dataset (dominant model), increasing to 1.71 in the PSD subset. While not conclusive, these data continue to provide suggestive evidence for linkage, particularly considering replication by multiple independent groups. Positive LOD scores extended over the entire region, continuing to define a broad candidate interval. Association studies were performed on several functional candidates mapping within the region. These included GAD1, encoding GAD67, whose levels are reduced in autopsy brain material from autistic subjects, and STK17B, ABI2, CTLA4, CD28, NEUROD1, PDE1A, HOXD1 and DLX2. We found no evidence for significant allelic association between autism and any of these candidates, suggesting that they do not play a major role in the genetics of autism or that substantial allelic heterogeneity at any one of these loci dilutes potential disease-allele association.

No association between the APOE gene and autism

Autism is a neurodevelopmental disorder characterized by stereotypic and repetitive behavior and interests, together with social and communicative deficiencies. The results of several genomic screens suggest the presence of an autism susceptibility locus on chromosome 19p13.2-q13.4. The apolipoprotein E (APOE) gene on chromosome 19 encodes for a protein, apoE, whose different isoforms (E2, E3, E4) influence neuronal growth. APOE participates in lipid transport and metabolism, repair, growth, and maintenance of axons and myelin during neuronal development. The APOE protein competes with the Reelin protein for VLDL/APOER2 receptor binding. Several studies have reported evidence for an association between autism and the Reelin gene. Based on these data we tested for association between APOE and autism using family-based association methods in a data set of 322 autism families. Three promoter, one intronic, and one 3' UTR single nucleotide polymorphisms (SNPs) in the APOE gene (-491a/t, -427c/t, -219g/t, 113c/g, and 5361c/t) as well as the APOE functional polymorphism (E2, E3, E4) were examined and failed to reveal significant evidence that autism is associated with APOE.

Factor analysis of restricted and repetitive behaviors in autism using the Autism Diagnostic Interview-R

The current study examined the factor structure of restricted and repetitive behaviors (RRB) in children with autism. Factor extraction procedures of 12 items from the Autism Diagnostic Interview-Revised (ADI-R) were applied in N = 207 individuals with autism. Two interpretable factors were identified: Factor 1--repetitive sensory motor actions and Factor 2--resistance to change. There was a significant negative correlation between an index of level of adaptive functioning and Factor 1. Intraclass correlations were not significant for either factor in a subset of families with two or more siblings with autism (multiplex). No differences in scores were apparent for either factor when multiplex families and families containing only one affected individual with autism (singleton) were compared. RRB in autism are represented by two distinct factors which may reflect two separate groups within autism. Defining subgroups within autism will allow for reduction of clinical heterogeneity and enhance our ability to dissect the genetic etiology of this complex disorder.

Fine mapping of autistic disorder to chromosome 15q11-q13 by use of phenotypic subtypes

Autistic disorder (AutD) is a complex genetic disease. Available evidence suggests that several genes contribute to the underlying genetic risk for the development of AutD. However, both etiologic heterogeneity and genetic heterogeneity confound the discovery of AutD-susceptibility genes. Chromosome 15q11-q13 has been identified as a strong candidate region on the basis of both the frequent occurrence of chromosomal abnormalities in that region and numerous suggestive linkage and association findings. Ordered-subset analysis (OSA) is a novel statistical method to identify a homogeneous subset of families that contribute to overall linkage at a given chromosomal location and thus to potentially help in the fine mapping and localization of the susceptibility gene within a chromosomal area. For the present analysis, a factor that represents insistence on sameness (IS)--derived from a principal-component factor analysis using data on 221 patients with AutD from the repetitive behaviors/stereotyped patterns domain in the Autism Diagnostic Interview-Revised--was used as a covariate in OSA. Analysis of families sharing high scores on the IS factor increased linkage evidence for the 15q11-q13 region, at the GABRB3 locus, from a LOD score of 1.45 to a LOD score of 4.71. These results narrow our region of interest on chromosome 15 to an area surrounding the gamma-aminobutyric acid-receptor subunit genes, in AutD, and support the hypothesis that the analysis of phenotypic homogeneous subtypes may be a powerful tool for the mapping of disease-susceptibility genes in complex traits.

Identification of MeCP2 mutations in a series of females with autistic disorder

Rett disorder and autistic disorder are both pervasive developmental disorders. Recent studies indicate that at least 80% of Rett Disorder cases are caused by mutations in the methyl-CpG-binding protein 2 (MeCP2) gene. Since there is some phenotypic overlap between autistic disorder and Rett disorder, we analyzed 69 females clinically diagnosed with autistic disorder for the presence of mutations in the MeCP2 gene. Two autistic disorder females were found to have de novo mutations in the MeCP2 gene. These data provide additional evidence of variable expression in the Rett disorder phenotype and suggest MeCP2 testing may be warranted for females presenting with autistic disorder.

Behavioral comparisons in autistic individuals from multiplex and singleton families

Autistic disorder (AD) is a complex neurodevelopmental disorder. The role of genetics in AD etiology is well established, and it is postulated that anywhere from 2 to 10 genes could be involved. As part of a larger study to identify these genetic effects we have ascertained a series of AD families: Sporadic (SP, 1 known AD case per family and no known history of AD) and multiplex (MP, > or = 2 cases per family). The underlying etiology of both family types is unknown. It is possible that MP families may constitute a unique subset of families in which the disease phenotype is more likely due to genetic factors. Clinical differences between the two family types could represent underlying genetic heterogeneity. We examined ADI-R data for 69 probands from MP families and 88 from SP families in order to compare and contrast the clinical phenotypes for each group as a function of verbal versus nonverbal status. Multivariate analysis controlling for covariates of age at examination, gender, and race (MANCOVA) revealed no differences between either the verbal or nonverbal MP and SP groups for the three ADI-R area scores: social interaction, communication, and restricted/repetitive interests or behaviors. These data failed to find clinical heterogeneity between MP and SP family types. This supports previous work that indicated that autism features are not useful as tools to index genetic heterogeneity. Thus, although there may be different underlying etiologic mechanisms in the SP and MP probands, there are no distinct behavioral patterns associated with probands from MP families versus SP families. These results suggests the possibility that common etiologic mechanisms, either genetic and/or environmental, could underlie all of AD.

Association analysis of chromosome 15 gabaa receptor subunit genes in autistic disorder

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the brain, acting via the GABAA receptors. The GABAA receptors are comprised of several different homologous subunits, forming a group of receptors that are both structurally and functionally diverse. Three of the GABAA receptor subunit genes (GABRB3, GABRA5 and GABRG3) form a cluster on chromosome 15q11-q13, in a region that has been genetically associated with autistic disorder (AutD). Based on these data, we examined 16 single nucleotide polymorphisms (SNPs) located within GABRB3, GABRA5 and GABRG3 for linkage disequilibrium (LD) in 226 AutD families (AutD patients and parents). Genotyping was performed using either OLA (oligonucleotide ligation assay), or SSCP (single strand conformation polymorphism) followed by DNA sequencing. We tested for LD using the Pedigree Disequilibrium Test (PDT). PDT results gave significant evidence that AutD is associated with two SNPs located within the GABRG3 gene (exon5_539T/C, p=0.02 and intron5_687T/C, p=0.03), suggesting that the GABRG3 gene or a gene nearby contributes to genetic risk in AutD.

Phenotypic homogeneity provides increased support for linkage on chromosome 2 in autistic disorder

Autistic disorder (AutD) is a neurodevelopmental disorder characterized by significant disturbances in social, communicative, and behavioral functioning. A two-stage genomic screen analysis of 99 families with AutD revealed suggestive evidence for linkage to chromosome 2q (D2S116 nonparametric sib-pair LOD score [MLS] 1.12 at 198 cM). In addition, analysis of linkage disequilibrium for D2S116 showed an allele-specific P value of <.01. Recently, linkage to the same region of 2q was reported in an independent genome screen. This evidence for linkage increased when analysis was restricted to the subset of patients with AutD who had delayed onset (>36 mo) of phrase speech (PSD). We similarly classified our data set of 82 sib pairs with AutD, identifying 45 families with AutD and PSD. Analysis of this PSD subset increased our support for linkage to 2q (MLS 2.86 and HLOD 2.12 for marker D2S116). These data support evidence for a gene on chromosome 2 contributing to risk of AutD, and they suggest that phenotypic homogeneity increases the power to find susceptibility genes for AutD.

Genomic screen and follow-up analysis for autistic disorder

Autistic disorder (AutD) is a neurodevelopmental disorder characterized by significant impairment in social, communicative, and behavioral functioning. A genetic basis for AutD is well established with as many as 10 genes postulated to contribute to its underlying etiology. We have completed a genomic screen and follow-up analysis to identify potential AutD susceptibility loci. In stage one of the genome screen, 52 multiplex families (two or more AutD affected individuals/family) were genotyped with 352 genetic markers to yield an approximately 10 centimorgan (cM) grid, inclusive of the X chromosome. The selection criterion for follow-up of interesting regions was a maximum heterogeneity lod score (MLOD) or a maximum nonparametric sib pair lod score (MLS) of at least 1.0. Eight promising regions were identified on chromosomes 2, 3, 7, 15, 18, 19, and X. In the stage two follow-up study we analyzed an additional 47 multiplex families (total=99 families). Regions on chromosomes 2, 3, 7, 15, 19, and X remained interesting (MLOD> or =1.0) in stage two analysis. The peak lod score regions on chromosomes 2, 7, 15, 19, and X overlap previously reported peak linkage areas. The region on chromosome 3 is unique.

No association between the WNT2 gene and autistic disorder

Autistic disorder is a pervasive neurodevelopmental disorder characterized by deficits in language and social communication, as well as stereotyped patterns of behavior. Peak LOD scores from several genomic screening efforts indicate the presence of an autistic disorder susceptibility locus within the distal long arm of human chromosome 7 (7q31-q35). Wassink et al. [2001: Am J Med Genet 105:406-413] reported that WNT2, located at 7q31, influences genetic risk in autistic disorder. These findings were enhanced when examined in a subset of families with severe language impairment. WNT genes encode secreted growth factor-like proteins that participate in growth regulation, differentiation, and tumorigenesis. We tested for genetic association of two WNT2 variants in an independent data set of 135 singleton and 82 multiplex families. No significant association was found between autistic disorder and the WNT2 genotypes in either the overall data set or in the language-impaired subset of families. However, differences in allele frequencies of the 3' UTR single nucleotide polymorphism between the present population and that of Wassink et al. may account for the inability to detect association between WNT2 and autistic disorder in the present data set. We also screened the two reported autistic disorder mutations previously detected by Wassink et al. We did not identify any activating mutation in the coding region of the WNT2 gene. Thus, we conclude that activating mutations of the WNT2 gene are not a major contributor to the development of autistic disorder in these data.

De novo partial duplication of chromosome 7p in a male with autistic disorder

We describe a de novo partial duplication of 7p in a 25-year-old male with autistic disorder (AD). High-resolution chromosome analysis revealed an extra segment added to the proximal short arm of chromosome 7. The G-band pattern was consistent with an inverted duplication of 7p11.2-p14.1. Fluorescent in situ hybridization (FISH), using a whole chromosome 7 DNA probe (Cytocell, Inc., UK), confirmed that the extra chromosome material is derived from chromosome 7, indicating that the patient is partially trisomic for a region of the short arm of chromosome 7. Partial duplication of the short arm of chromosome 7 is uncommon with little more than 30 cases in the literature. This is the first report of an individual with a 7p duplication who also has AD.

Female with autistic disorder and monosomy X (Turner syndrome): parent-of-origin effect of the X chromosome

We have ascertained and examined a patient with autistic disorder (AD) and monosomy X (Turner syndrome). The patient met Diagnostic and Statistical Manual of Mental Disorders (DSM-IV)/International Classification of Diseases (ICD-10) criteria for AD verified by the Autism Diagnostic Interview-Revised. The patient exhibited both social and verbal deficits and manifested the classical physical features associated with monosomy X. Skuse et al. [1997: Nature 387:705-708] reported three such cases of AD and monosomy X in their study of Turner syndrome and social cognition. They observed that monosomy X females with a maternally inherited X chromosome had reduced social cognition when compared with monosomy X females with a paternally inherited X chromosome. All three cases of AD and monosomy X were maternally inherited. Based on their data, they suggested that there was a gene for social cognition on the X chromosome that is imprinted and not expressed when the X chromosome is of maternal origin. Thus, we conducted parent-of-origin studies in our AD/monosomy X patient by genotyping X chromosome markers in the patient and her family. We found that the patient's X chromosome was of maternal origin. These findings represent the fourth documented case of maternal inheritance of AD and monosomy X and provide further support for the hypothesis that parent-of-origin of the X chromosome influences social cognition.

Three probands with autistic disorder and isodicentric chromosome 15

We have identified three unrelated probands with autistic disorder (AD) and isodicentric chromosomes that encompass the proximal region of 15q11.2. All three probands met the Diagnostic and Statistical Manual of Mental Disorders, fourth edition [DSM-IV; American Psychiatric Association, 1994], and International Classification of Diseases ( ICD-10) diagnostic criteria for AD, confirmed with the Autism Diagnostic Interview -Revised (ADI-R). Chromosome analysis revealed the following karyotypes: 47,XX,+idic(15)(q11.2), 47,XX, +idic(15) (q11.2), and 47,XY,+idic(15)(q11.2). Haplotype analysis of genotypic maker data in the probands and their parents showed that marker chromosomes in all three instances were of maternal origin. Comparison of the clinical findings of the three AD probands with case reports in the published literature (N = 20) reveals a clustering of physical and developmental features. Specifically, these three probands and the majority of reported probands in the literature exhibited hypotonia (n = 13), seizures (n = 13), and delayed gross motor development (n = 13). In addition, clustering of the following clinical signs was seen with respect to exhibited speech delay (n = 13), lack of social reciprocity (n = 11), and stereotyped behaviors (n = 12). Collectively, these data provide further evidence for the involvement of chromosome 15 in AD as well as present preliminary data suggesting a clustering of clinical features in AD probands with proximal 15q anomalies.

Genetic studies in autistic disorder and chromosome 15

Autistic disorder (AD) is a developmental disorder affecting social interactions, communication, and behavior. AD is a disease of complex genetic architecture. It is postulated that several genes contribute to the underlying etiology of AD. Chromosome 15 is of particular interest due to numerous reports of AD in the presence of chromosomal abnormalities, located mainly in the 15q11-q13 region. There are also a number of plausible candidate genes in this area, including the gamma-aminobutyric acidA (GABA(A)) receptor gene complex. We have undertaken a study of this region of chromosome 15 in a data set of 63 multiplex families (with 2 or more AD affected individuals per family). We found evidence in support of linkage to the 15q11-q13 region, as well as evidence of increased recombination in this region. These findings provide further support for the involvement of chromosome 15q11-q13 in the genetic etiology of AD.

Analysis of linkage disequilibrium in gamma-aminobutyric acid receptor subunit genes in autistic disorder

Autistic disorder (AD) is a neurodevelopmental disorder characterized by abnormalities in behavior, communication, and social interactions and functioning. Recently, Cook et al. reported significant linkage disequilibrium with an AD susceptibility locus and a marker, GABRB3 155CA-2, in the gamma-aminobutyric acid(A) (GABA(A)) receptor beta3-subunit gene on chromosome 15q11-q13. This linkage disequilibrium was detected using a multiallelic version of the transmission/disequilibrium test (TDT) in a sample of nuclear families having at least one child with autistic disorder. In an attempt to replicate this finding we tested for linkage disequilibrium with this marker, as well as with three additional markers in and around the GABA(A) receptor beta3-subunit gene, in an independent, clinically comparable set of AD families. Unlike Cook et al., we failed to detect significant linkage disequilibrium between GABRB3 155CA-2 and AD in our sample. We did, however, find suggestive evidence for linkage disequilibrium with a marker, GABRB3, approximately 60 kb beyond the 3' end of beta3-subunit gene. This finding lends support for previous reports implicating the involvement of genes in this region with AD. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:43-48, 2000

Genetic studies of autistic disorder and chromosome 7

Genome-wide scans have suggested that a locus on 7q is involved in the etiology of autistic disorder (AD). We have identified an AD family in which three sibs inherited from their mother a paracentric inversion in the chromosome 7 candidate region (inv(7)(q22-q31.2)). Clinically, the two male sibs have AD, while the female sib has expressive language disorder. The mother carries the inversion, but does not express AD. Haplotype data on the family suggest that the chromosomal origin of the inversion was from the children's maternal grandfather. Based on these data, we have genotyped 76 multiplex (>/=2 AD affecteds/family) families for markers in this region of 7q. Two-point linkage analysis yielded a maximum heterogeneity lod score of 1.47 and maximum lod score (MLS) of 1.03 at D7S495. Multipoint MLS and NPL analyses resulted in peak scores of 1.77 at D7S2527 and 2.01 at D7S640. Examination of affected sibpairs revealed significant paternal (P = 0.007), but not maternal (P = 0. 75), identity-by-descent sharing at D7S640. Significant linkage disequilibrium was detected with paternal (P = 0.02), but not maternal (P = 0.15), transmissions at D7S1824 in multiplex and singleton families. There was also evidence for an increase in recombination in the region (D7S1817 to D7S1824) in the AD families versus non-AD families (P = 0.03, sex-averaged; and P = 0.01, sex-specific). These results provide further evidence for the presence of an AD locus on chromosome 7q, as well as provide evidence suggesting that this locus may be paternally expressed.

An interim report on the development of the Psychological Trauma and Resources Scales

The William S. Hall Psychiatric Institute Psychological Trauma and Psychological Resources Scales is a preliminary measure for the assessment of psychological trauma and psychological health from a developmental perspective. This three-part article (1) discusses the various rationales leading to the development of the scales, (2) provides a factor-analysis of responses of 336 college students, and (3) addresses current (N = 37) and planned efforts to establish reliability and validity of a more refined version.

Group intervention with second graders at risk for behavioral problems: a pilot study

A 7-session-group intervention with four successfully adapting children and two with emerging behavior problems was conducted. Pre-posttest data showed reductions in teachers' ratings of externalizing behavior for each of the target children.

Race and gender differences in the treatment of psychiatric disorders in young adolescents

OBJECTIVE

Most children and adolescents with mental illness remain untreated. Evidence suggests that race is a factor in the referral of children for treatment. This study examines race and gender differences in treatment of adolescent psychiatric disorders.

METHOD

During a two-stage, school-based, epidemiological study of depression, data were collected on 478 adolescents. Instruments included the Schedule for Affective Disorders and Schizophrenia for School-Age Children and the Children's Global Assessment Scale.

RESULTS

Twenty-two percent of the sample had contact with professionals during the prior year, including 56% of adolescents with a psychiatric diagnosis. Significant odds ratios (ORs) were found between all diagnoses and treatment. Trends for undertreatment of females and African-Americans were evident in univariable and multivariable models. The OR (0.34) for African-American females was significant in the multivariable model. African-Americans were significantly more likely to receive only one or two treatment contacts.

CONCLUSION

Data suggest race and gender differences in the treatment of adolescent psychiatric disorders. Possible explanations include referral bias, low cultural competence of mental health professionals, and cultural differences in the expression and tolerance of symptoms and help-seeking behaviors. Further study of factors influencing treatment decisions is needed.

Case study: fluoxetine in the multimodal treatment of a preschool child with selective mutism

Selective mutism is a rare disorder with poor treatment outcome. The current study describes the successful treatment of selective mutism in a preschool-age girl, using a comprehensive multifaceted therapeutic approach. The components of this intervention reflect a conceptualization of selective mutism that emphasizes anxiety as a core feature but also focuses on associated factors such as oppositional behaviors.

A guided bibliography of the selective mutism (elective mutism) literature

This guided bibliography of 122 articles on selective mutism covers nearly all of the English language publications on the topic. Index Medicus and Psychological Abstracts were the major source documents for the citations.

Behavior problems in preschool children: a pilot study

Behavior problems in 20 preschool children (13 boys, 7 girls) referred to a diagnostic nursery were assessed using parents' ratings. The patterns of behavior problems reported in 4- and 5-yr.-olds parallel those noted for older clinic-referred children (i.e., internalizing difficulties in girls, externalizing difficulties in boys). The most salient behavior problems for 3-yr.-olds involved aggression. Correlations between children's behavior problems and an index of parents' experienced stress were moderate (.44 to .64).

Whole-blood serotonin and cognitive functioning in autistic individuals and their first-degree relatives

The relationship between cognitive-intellectual abilities and whole-blood serotonin (5-hydroxytryptamine; 5-HT) in 18 autistic probands and their first-degree relatives (n = 21 parents, n = 13 siblings) was investigated. Whole-blood 5-HT was significantly negatively associated with verbal-expressive/symbolic abilities for the entire sample. The proportion of variance in cognitive-intellectual performances attributable to whole-blood 5-HT was substantial in the context of variance attributable to familial classification. The relationship between verbal-expressive abilities and whole-blood 5-HT, adjusted for race and familial classification, was noteworthy. Simple correlations between 5-HT and cognitive-intellectual performances were conducted. However, bias related to covariance attributable to race seriously limits such findings. The issue of bias and its relevance to previous research is discussed further.

Calcium release from pituitary secretory granules: modulation by thiols, disulfides, and dihydropyridine calcium channel blockers

The distribution of calcium in isolated bovine pituitary secretory granules was studied by atomic absorption. The total granule calcium (in 26 preparations) averaged 14.5 nmol/mg protein, or 21.2 +/- 1.6% of the total pituitary homogenate calcium. Incubation of granules with KCl resulted in calcium release (78% at 15 mM and 100% at 50 mM, for example). Calcium release was also pH dependent, with greater release at acidic pH values; it was not influenced by either 500 microM strontium or 500 microM lanthanum. Release was augmented by reduced glutathione (GSH), with significant release observable at thiol levels as low as 10 microM. In addition to GSH, cysteine also stimulated release; mercaptoethanol and dithiothreitol were less potent. Interestingly, the disulfides cystine and oxidized glutathione also stimulated calcium release. Since the latter compounds are known to inhibit hormone release from granules, calcium and protein release appear to be regulated independently. A number of dihydropyridines were tested as potential blockers of calcium release from granules. Nimodipine inhibited basal calcium release at high concentrations and potently inhibited GSH-stimulated calcium release, with an apparent Ki in the 10-20 nM range; it also inhibited K(+)-stimulated release but to a lesser extent. Nimodipine, however, did not significantly influence protein or hormone release. GSH-stimulated calcium release was also inhibited by nifedipine, and this inhibition was qualitatively and quantitatively similar to that by nimodipine. Nisoldipine and nitrendipine, however, displayed no significant inhibition. In summary, it appears that the release of secretory granule calcium in vitro is independent of protein release. Thiols and some disulfides stimulate calcium release, and its inhibition by dihydropyridines suggests that granule membranes may contain specific ion channels. The role of granule calcium in the cell remains to be defined.