Contribution of common and rare variants of the PTCHD1 gene to autism spectrum disorders and intellectual disability

Recent findings revealed rare copy number variants and missense changes in the X-linked gene PTCHD1 in autism spectrum disorder (ASD) and intellectual disability (ID). Here, we aim to explore the contribution of common PTCHD1 variants in ASD and gain additional evidence for the role of rare variants of this gene in ASD and ID. A two-stage case-control association study investigated 28 tag single nucleotide polymorphisms (SNPs) in 994 ASD cases and 1035 controls from four European populations. Mutation screening was performed in 673 individuals who included 240 ASD cases, 183 ID patients and 250 controls. The case-control association study showed a significant association with rs7052177 (P=6.13E-4) in the ASD discovery sample that was replicated in an independent sample (P=0.03). A Mantel-Haenszel meta-analysis for rs7052177T considering the four European populations showed an odds ratio of 0.58 (P=7E-05). This SNP is predicted to be located in a transcription factor binding site. No rare missense PTCHD1 variants were found in our ASD cohort and only one was identified in the ID sample. A duplication (27 bp) in the promoter region, absent from 590 controls, was found in three ASD patients (Fisher exact test, P=0.024). A gene reporter assay showed a significant decrease in the transcriptional activity (26%) driven by this variant. Moreover, we found that the longest allele of a trinucleotide repeat located upstream from PTCHD1 was associated with ASD (P=0.003, permP=0.0186). Our results further support the involvement of PTCHD1 in ASD, suggesting that both common and rare variants contribute to the disorder.