Abstract
Purpose :
Punctiform and Polychromatic Pre-Descemet Corneal Dystrophy (PPPCD) is a rare corneal dystrophy that is characterized by small multi-colored opacities in the posterior stroma of the cornea with an unknown genetic basis. We performed whole-exome sequencing (WES) on two previously unreported Spanish pedigrees affected with PPPCD to identify the genetic basis of PPPCD.
Methods :
Slit lamp examination and diagnostic corneal imaging were performed for members of two families with PPPCD. Genomic DNA was collected from examined individuals of both families and WES was performed on ten members of family 1. Alignment, variant calling and annotation were performed using commercially available software programs. Novel or rare variants that segregated with the affected status were validated by Sanger sequencing and were screened for in the members of family 1 who did not undergo WES and in members of family 2. Identified non-coding variants that segregated with the affected status in both families were characterized using in silico prediction tools and an in vitro splice assay.
Results :
WES analysis of 6 affected and 4 unaffected individuals from family 1 identified one rare heterozygous non-synonymous variant, OR2M5 c.773T>C, that segregated with the affected status. However, screening in family 2 did not reveal a novel or rare coding region variant in OR2M5. A rare non-coding region variant, PDZD8 c.872+10A>T, (minor allele frequency .005 in the ExAC and .006 in the gnomAD databases), was identified by WES to segregate with the affected status in family 1 and was also identified by Sanger sequencing to segregate in family 2. In silico analysis predicted the PDZD8 intronic variant to create an intronic cryptic donor splice site. Corroborating the in silico analysis results, an in vitro splice assay demonstrated that the c.872+10A>T variant altered the production of transcript isoforms.
Conclusions :
The PDZD8 intronic variant c.872+10A>T is predicted to create a cryptic donor splice site and is the likely cause of PPPCD in two previously unreported Spanish pedigrees. Further research is needed to determine the impact of the c.872+10A>T variant on gene splicing and function.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.