Novel frameshift mutation in Indian autistic population causes neuroligin and neurexin binding defect

Highlights

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In recent days, Neuroligin is the most targeted gene for genetic studies on autism and other neurological disorders.

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Present study is the first preliminary study in Indian autistic population explaining role of neuroligin 4X gene.

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Novel frameshift mutation, p.Gly214GlyfsTer2 causes abnormal synapses by preventing the binding of NLGN4x to NRXN.

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Neuroligin is probably a candidate gene for future molecular and functional study in Indian autistic population.

Abstract

Autism is a complex neurodevelopmental condition which is clinically, etiologically and genetically heterogeneous. The predisposition of genes and genetic loci has been under study over the last few decades. Autism is increasing dramatically over the last few years in India. Mutations in two x-linked neuroligin genes viz. NLGN3 and NLGN4X have been recently implicated in autism pathogenesis. In the current study, for the first time in India, we screened the genetic variations in transmembrane neuroligin 4× gene in the Indian autistic population using sequencing technology. 1828 mentally ill children were screened around the North Karnataka region of India and 136 autistic children were identified, out of which 108 autistic children who were fulfilling the inclusion criteria were taken for the study. DNA was isolated from the clinical samples and exonic regions were amplified. Sanger sequencing was carried to screen the genetic variations and expression profiling was performed using Real time PCR. Sequencing results revealed 25 different variants (eight 5′UTR variants, four missense variants, four synonymous variants, one frameshift variant and eight 3′ UTR variants). One novel frameshift variation (p.Gly214GlyfsTer2) was recorded in 19 (17.5%) autistic individuals. This novel frameshift mutation leads to a premature stop codon. Relative expression of the NLGN4X gene in autistic children with novel frameshift mutation was largely reduced compared to the control group [0.052 and 1.217 respectively, p-value 0.00001]. The present study shows novel frameshift mutation causes abnormal NLGN4× protein that leads to loss of binding to presynaptic neurexin during synapses. Therefore neuroligin 4× is the potential target gene in the Indian autistic population for future functional analysis.