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.