Detection and validation of novel mutations in MERTK in a simplex case of retinal degeneration using WGS and hiPSC-RPEs model.

Inherited Retinal degenerations (IRD) are a group of genetically heterogeneous conditions with broad clinical phenotypic heterogeneity. A nuclear family of European ancestry with one individual affected by progressive retinal degeneration was analyzed. Whole genome sequencing of the proband and her unaffected sibling identified a novel intron 8 donor splice site variant (c.1296+1G>A) and a novel 731 base pair deletion encompassing exon 9 (Chr2:112751488-112752218) resulting in c.1297_1451del; p.K433_G484fsTer3 in the Mer tyrosine kinase protooncogene (MERTK) expressed in retinal pigment epithelium (RPE). The proband carried both variants in the heterozygous state which segregated with disease in the pedigree. These MERTK variants are predicted to result in the defective splicing of exon 8 and loss of exon 9 respectively. To evaluate the impact of these novel variants, human induced pluripotent stem cell lines (hiPSC) were reprogrammed from the proband and parental peripheral blood mononuclear cells (PBMCs) and differentiated to hiPSC-RPE. Analysis of the proband's hiPSC-RPE revealed the absence of MERTK transcript and protein as well as abnormal phagocytosis when compared with the parental hiPSC-RPE. In summary, WGS identified novel compound heterozygous variants in MERTK as the underlying cause of IRD in the proband. Further, analysis using an hiPSC-RPE model established a functional impact of novel MERTK mutations and revealed the potential mechanism underlying pathology due to these mutations. This article is protected by copyright. All rights reserved.