Abstract
Purpose:
Posterior amorphous corneal dystrophy (PACD) is a rare, autosomal dominant disorder linked to a 3.5 Mb region on chromosome 12q21.33. We sought to identify the genetic basis of PACD in the family linked to this region (family 1) as well as in two other affected families.
Methods:
Whole exome sequencing (WES) was performed using DNA from 5 affected and 1 unaffected members of family 1. Copy number variant (CNV) analysis was performed by cytogenetic array using DNA from 9 members of family 1, 3 members of a second (unreported) family and one member of a third (previously reported) family with PACD. Copy number analysis by qPCR was performed for 43 (12 affected and 31 unaffected) individuals from family 1, 7 (6 affected and 1 unaffected) individuals from family 2 and in 3 (2 affected and 1 unaffected) individuals from family 3. qPCR was used to determine keratocyte transcript levels for the small leucine-rich proteoglycans (SLRP) encoded by genes in the PACD locus.
Results:
WES failed to identify a novel, heterozyzous, non-synonymous coding region mutation in the PACD locus that segregated with the affected phenotype. CNV analysis by cytogenetic array detected a 701kb heterozygous deletion in PACD locus containing the four SLRP genes (EPYC, KERA, LUM, and DCN) and a fifth protein-coding gene, CCER1, in family 1. The deletion was confirmed to segregate in the other family members using copy number analysis by qPCR. In family 2, a 1.318Mb heterozygous deletion that involved only the SLRP genes and CCER1 was detected in the PACD locus in affected individuals only. In family 3, the same 701kb deletion present in family 1 segregated with the affected phenotype, although haplotype analysis demonstrated that the families were not related. Evaluation of corneal expression of the SLRP genes demonstrated that LUM and KERA exhibited significantly higher expression than DCN, which showed a higher level of expression than EPYC and CCER1.
Conclusions:
PACD is caused by a heterozygous deletion of a region on chromosome 12q21.33 that contains the 4 SLRPs, KERA, LUM, DCN and EPYC, as evidenced by the segregation of the deletion with the affected phenotype in an unreported and 2 previously reported families. The only other protein-coding gene contained within the deleted region, CCER1, is unlikely to play a role in the pathogenesis of PACD given its negligible expression in the cornea.
Keywords: 480 cornea: basic science •
539 genetics •
494 degenerations/dystrophies