A novel mutation in MERTK for rod-cone dystrophy in a North Indian family

Objective: To identify the underlying genetic defect of childhood-onset severe rod-cone dystrophy (RCD) in a consanguineous family from North India with autosomal recessive retinitis pigmentosa. Methods: A detailed family history, clinical data, and blood samples were collected from 11 members of the family, including 4 affected by an autosomal recessive rod-cone dystrophy (arRCD), and DNA was extracted. Whole-exome sequencing (WES) was performed on DNA samples of proband and her unaffected maternal uncle. Ion Reporter software (ver. 4.4) was used for the annotation of variants obtained by WES. The variants detected in proband were tested for validation in all other affected and unaffected family members using Sanger sequencing technique. Results: We have identified a novel nonsense mutation-c.1647T > G (p.Tyr549Ter)-in the exon 11 of MERTK that co-segregated completely with the disease phenotype in all the 4 affected members and was not observed in the 7 unaffected members of the family. This mutation was also not detected in 120 ethnically matched controls (240 chromosomes), hence excluding it as a polymorphism. Conclusions: MERTK has a role in retinal pigment epithelium as a regulator of rod outer segment's phagocytosis. Due to c.1647T > G substitution, the stop codon (p.Tyr549Ter) appears early in the transcript. It seems that either the altered transcript would degenerate through nonsense-mediated decay (NMD) or potentially form truncated protein lacking a functionally important domain (i.e., tyrosine kinase domain). These findings thus further expand the mutation spectrum in MERTK and substantiate its role in the pathogenesis of retinal dystrophy.