Further Genetic and Clinical Insights of Posterior Polymorphous Corneal Dystrophy 3

Abstract

Posterior polymorphous corneal dystrophy (PPCD) is a very rare disorder characterized by primary changes of the posterior corneal layers. Sequence variants in 3 genes are associated with the development of PPCD, including ZEB1 that is responsible for PPCD3. Evidence suggests at least 1 more gene remains to be identified. To determine the molecular genetic cause of PPCD3. We performed extensive ophthalmological examination, including rotating Scheimpflug imaging technology and specular microscopy, and direct sequencing of the ZEB1 coding region. Comprehensive review of published PPCD3-causing variants was undertaken. Ophthalmology department of a university hospital. Four Czech probands. Results of ophthalmological examination and direct sequencing of the ZEB1 coding region. The following 2 novel frameshift mutations within ZEB1 were identified: c.2617dup in exon 8 in a 22-year-old woman, considered to be most likely de novo in origin, and c.698dup in exon 6 in a 20-year-old man. The first patient had mild changes consistent with PPCD and bilateral best-corrected visual acuity of 1.00. The corneal phenotype of the patient in the second case was more severe, with best-corrected visual acuity of 0.40 OD and 0.05 OS. Corneas of both probands were abnormally steep (keratometry readings, flat ≥ 47.4 diopters [D] and steep ≥ 49.2 D) with increased pachymetry values but no pattern indicative of keratoconus. Specular microscopy in both patients revealed reduced endothelial cell density (range, 1055/mm² to 1655/mm²). Both probands had a history of surgery for inguinal hernia; the male patient also reported hydrocele. Nucleotide changes within the coding region of ZEB1 underlie the pathogenesis of PPCD in 4 of 23 Czech probands (17%). The cumulative de novo ZEB1 mutation rate is at least 14%. Possible involvement of ZEB1 sequence variants not readily identified by direct sequencing of coding regions needs to be further investigated. Our findings also have implications for patient counseling.