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Abstract: Serotoninergic dysfunction is highly implicated in autism. Serotonin transporter gene (SLC6A4) that regulates synaptic serotonin level has been investigated as a candidate gene for autism, but consensus opinion on possible association is still lacking. Converging evidences of platelet-hyperserotoninemia in ∼25% of the patients, betterment of ritualistic behavior on administration of SSRI and linkage to chromosome 17q11 harboring SLC6A4, supports the hypothesis that SLC6A4 polymorphisms may contribute towards autism pathology. Our recent report on 5-HTTLPR marker represents the first study on genetic association of SLC6A4 with autism in the Indian population. Further analysis involving additional markers may reinforce the earlier hypothesis. So in the present study, we have investigated the association of a VNTR of 17 bp at intron2 (STin2) and an SNP at 3′UTR (HTT-3′UTR-SNP) of the gene with autism using family and population-based approaches. We have genotyped 421 individuals (93 autistic subjects, their parents and 160 controls) and consistent with other publications, family-based association studies using individual markers (STin2 and HTT-3′UTR-SNP) have not revealed any preferential allelic transmission to the probands. However, the interesting finding of strong linkage disequilibrium (LD) between the markers and significant disease-specific distortion in the distribution of HTT-3′UTR-SNP genotypes (T1χ 2 =5.19, P =0.02; OR=2.89, 95% CI=1.13–7.41) and the specific haplotypes of the two markers (LRS=11.85, p c =0.02), with higher frequencies of T/T genotype and 10-T haplotype in autistic cases suggests that either these markers or nearby markers of SLC6A4 that are in LD, may pose a risk towards autism in the Eastern Indian population. [Copyright &y& Elsevier]

Abstract: Involvement of reelin with Autism spectrum disorder (ASD) has been implicated through several biochemical as well as genetic studies. Reelin is an extracellular signaling protein, which plays a significant role in cytoarchitectonic pattern formation of different brain areas during development. Reelin gene (RELN) is located on chromosome 7q22; an important autism critical region identified through several genome-wide scans. A number of genetic studies have been carried out to investigate the association of reelin with autism. Recently we reported possible paternal effect in the transmission of CGG repeat alleles of RELN in the susceptibility towards autism. Further analysis on other polymorphisms is warranted to validate the status of RELN as a candidate for autism. Therefore in the present study, we have investigated six more SNPs (rs727531, rs2072403, rs2072402, rs362691, rs362719, rs736707) in 102 patients, 182 parents and 101 healthy controls. We have followed DSM-IV criteria and the screening for autism was carried out using CARS. Genomic DNA isolated from blood was used for PCR and subsequent RFLP analysis. Finally, case-control and family-based association studies were carried out to examine the genetic association of these SNP markers with ASD in the Indian population. But, we failed to detect either preferential parental transmission of any alleles of the markers to affected offspring or any biased allelic or genotypic distribution between the cases and controls. Thus the present study suggests that these SNPs of RELN are unlikely to be associated with ASD in the Indian population. [Copyright &y& Elsevier]

Several studies suggest involvement of serotoninergic system in the pathophysiology of Autism Spectrum Disorder (ASD). The 5-HT receptor binding studies using (3)H-lysergic acid diethylamide ((3)H-LSD) and linkage analysis provided evidences to consider HTR2A as a potential candidate gene for ASD. The three SNPs, -1438A/G (rs6311), 102T/C (rs6313) and 1354C/T (rs6314) of HTR2A have been well studied in the etiology of various neuropsychiatric disorders. But studies on association of this gene with ASD are limited to two reports from American and Korean populations. Additionally there are reports, which demonstrated paternal imprinting of HTR2A with expression from only one allele. So far no reports are available on HTR2A and its association with any neuropsychiatric disorders from Indian population. Therefore, the present study investigates association of the above mentioned three markers of HTR2A with ASD in Indian population using population and family-based approaches. The study also deals with allelic expression pattern of HTR2A in Peripheral Blood Leukocytes (PBLs) to understand the parental imprinting status. The genotyping analyses were carried out for probands, parents and controls. The subsequent association analyses did not show association of these markers with ASD. So, HTR2A is unlikely to be a genetic marker for ASD in Indian population. The expression analyses showed absence of monoallelic expression, suggesting lack of parental imprinting of HTR2A gene. However, we noticed methylation of the CpG sites at -1438A/G and 102T/C loci of HTR2A gene. Further bioinformatics analysis revealed absence of CpG islands in the promoter of the gene supporting biallelic expression pattern of HTR2A in PBLs.

Autism is a neurodevelopmental disorder with early manifestation. It is a multifactorial disorder and several susceptible chromosomal regions for autism are identified through genome scan studies. The gene coding for glutamate receptor 6 (GluR6 or GRIK2) has been suggested as a candidate gene for autism based on its localization in the autism specific region on chromosome 6q21 and the involvement of receptor protein in cognitive functions like learning and memory. Despite its importance, so far no studies have been carried out on possible involvement of GluR6 with autism in the Indian population. Therefore in the present study, we have performed genetic analysis of three markers of GluR6 (SNP1: rs2227281, SNP2: rs2227283, SNP3: rs2235076) for possible association with autism through population, and family-based (TDT and HHRR) approaches. DSM-IV criteria and CARS/ADI-R have been utilized for diagnosis. Genotyping analysis for the SNPs has been carried out in 101 probands with autism spectrum disorder, 180 parents and 152 controls from different regions of India. Since the minor allele frequency of SNP3 was too low, the association studies have been carried out only for SNP1 and SNP2. Even though two earlier studies have shown association of these markers with autism, the present case-control and TDT, as well as HHRR analyses have not demonstrated any biased transmission of alleles or haplotypes to the affected offspring. Thus our results suggest that these markers of GluR6 are unlikely to be associated with autism in the Indian population.

Autism is a neurodevelopmental disorder with high heritability factor and the reelin gene, which codes for an extracellular matrix protein involved with neuronal migration and lamination is being investigated as a positional and functional candidate gene for autism. It is located on chromosome 7q22 within the autism susceptible locus (AUTS1); identified in earlier genome scans and several investigations have been carried out on various ethnic groups to assess possible association and linkage of the gene with autism. However, the findings are still inconclusive. In the present study which represents the first report of such a study on the Indian population, genotyping analyses of CGG repeat polymorphism at 5'UTR, two single nucleotide polymorphisms (SNP) at exon 6 and exon 50 were performed in 73 autistic subjects, 129 parents, and 80 controls. The allelic distributions of the repeat polymorphism and exon 50 T/C SNP were quite different from earlier reports in other populations. Allelic and genotypic distribution of the markers did not show any differences between the cases and controls. While our preliminary data on family-based association studies on 58 trios showed no preferential transmission of any allele from the parents to the affected offspring, TDT and HHRR analyses revealed significant paternal transmission distortions for 10- and > or =11-repeat alleles of CGG repeat polymorphism. Thus, the present study suggests that 5'UTR of reelin gene may have a role in the susceptibility towards autism with the paternal transmission and non-transmission respectively of 10- and > or =11-repeat alleles, to the affected offspring.

Serotonin transporter (5-HTT) is a transmembrane protein belonging to Na+/Cl- dependent membrane transporter family and transports 5-HT across the membranes of presynaptic neurons. 5-HTT-linked polymorphic region (5-HTTLPR) gained much interest because of the differential regulation of expression and activity of 5-HTT by its various genotypes. A population-based study has been conducted on 5-HTTLPR with 358 individuals, which included 79 autistic probands, 136 parents, and 143 controls from two subpopulations of east and northeast regions of India. The genotypic frequencies of all the groups conform to Hardy-Weinberg equilibrium. With the finding of efficacy of serotonin reuptake inhibitors in ameliorating ritualistic behavior in autistic disorder, 5-HTT emerged as a putative candidate gene for autism and association studies have been carried out in different ethnic populations. But these studies were inconclusive due to conflicting results on association. Because such a study has never been performed in the Indian population, we have tested the possible involvement of 5-HTTLPR polymorphism with autism. The present study failed to establish any association or linkage of 5-HTTLPR with autism in the Indian population by case-control studies (chi2 = 1.314, P = 0.63) and family-based approaches (TDT chi2 = 0.22, P = 0.64 and HHRR-chi2 = 0.25, P = 0.61). However, when a meta-analysis of all the available TDT data, inclusive of the present study is carried out, we observed a significant preferential transmission of S-allele from parents to the affected offspring (chi2 = 7.51, P = 0.006) indicating an association of 5-HTTLPR with autism.