Family‐based studies indicate association of Engrailed 2 gene with autism in an Indian population

Engrailed 2 (EN2) is a homeobox transcription factor involved in the patterning of cerebellum during brain development. Linkage analysis and studies on knockout mice support EN2, located on chromosome 7q36.3, as a potential risk locus for autism. Candidate gene approach also suggested association of EN2 with autism spectrum disorder (ASD) in various populations. Here, we have investigated the association of five markers [rs3735653 (C/T) in exon 1; rs34808376 (GC/‐) and rs6150410 (CGCATCCCC/‐) in promoter region; rs1861972 (A/G) and rs1861973 (C/T) in the intron] of the gene with autism and ASD in Indian population using family‐based approach. Probands have been recruited using Diagnostic and Statistical Manual of Mental Disorders Fourth Edition (DSM‐IV) diagnostic criteria. Genotypic distributions conform to Hardy–Weinberg equilibrium. Genotyping analysis showed that the intronic single nucleotide polymorphisms (SNPs) are in complete linkage disequilibrium showing A‐C and corresponding G‐T allelic association. We observed significant preferential transmission of C allele of rs1861973 from the parents to affected offspring [transmission disequilibrium test (TDT): narrow diagnosis likelihood ratio statistics (LRS) = 6.63, P = 0.006; broad diagnosis LRS = 4.47, P = 0.05]. Interestingly, gender‐based investigations showed significant transmission of C allele to the affected females [TDT: LRS = 7.36, P = 0.0025; haplotype‐based haplotype relative risk (HHRR): LRS = 7.16, P = 0.02]. A maternal overtransmission for these alleles was also noted (TDT: LRS = 3.65, P = 0.036; HHRR: LRS = 2.81, P = 0.036). Bioinformatic analysis using TFSearch showed generation of Sp1 binding site in the presence of C allele. While Del‐T haplotype formed from rs34808376‐rs1861973 markers showed increased non‐transmission, the Ins‐C showed significant transmission suggesting protective effect and risk, respectively, conferred by these haplotypes in autism etiology. These results suggest positive genetic correlation of EN2 with autism in the Indian population.

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