North Carolina Macular Dystrophy (NCMD / MCDR1) mutations found; PRDM13

Abstract

Purpose : To identify mutations causing North Carolina macular dystrophy (NCMD, MCDR1).

Methods : We targeted whole-genome sequencing, whole exome sequencing. In addition to our original 11 MCDR1 families recently published (141 total subjects), we now have an additional cohort of 23 families with the NCMD phenotype available for study (total of 367 subjects, 32 families). Linkage analysis of 14 families was performed which narrowed the minimal candidate region to 870kb. A physical map was constructed using YACs, BACs and PACs. NexGen targeted whole genomic sequencing was performed on 8 affected individuals from 3 families representing 3 different haplotypes affected with chromosome 6 linked NCMD (MCDR1). Variants observed in the MCDR1 locus with frequencies <1% in published databases were confirmed using Sanger sequencing. Confirmed variants absent from all published databases were sought in the additional MCDR1 families and 261 unrelated controls. The RT-PCR analysis of selected genes was performed in stem cell derived human retinal cells. IRB approval was obtained.

Results : Five sequenced individuals with MCDR1 linked NCMD shared a haplotype of 14 rare variants spanning 1 Mb of the disease-causing allele. One of these variants (V1, ch6:1000400906) was absent from all published databases and all 261 controls, but was found in a total of 13 NCMD kindreds. This variant lies in a DNase 1 hypersensitivity site (DHS) upstream of both the PRDM13 and CCNC genes. Sanger sequencing of 1 kb centered on V1 was performed in the remaining NCMD probands, and 2 additional novel single nucleotide variants (V2, ch6:10000987, in 6 families and V3, ch6:100041040 in 1 family) were identified in the DHS within 134 bp of the location of V1. A complete duplication of the PRDM13 gene was also discovered in a single family (V4). The RT-PCR analysis of PRDM13 expression in developing retinal cells revealed marked developmental regulation. The 4 mutations V1 to V4 segregated perfectly in the 118 affected and 33 unaffected members of 22 NCMD families. We have yet to find the mutations in the remaining 11 families.

Conclusions : We identified 4 rare mutations in a non-coding region, each capable of arresting human macular development by causing over expression of PRDM13. Additional families with the NCMD phenotype continue to support that these mutations are causative of MCDR1 / NCMD.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.