Exclusion of pathogenic promoter region variants and identification of novel nonsense mutations in the zinc finger E-box binding homeobox 1 gene in posterior polymorphous corneal dystrophy

Abstract

Purpose: To report the identification of five novel nonsense mutations in the zinc finger E-box binding homeobox 1 (ZEB1) gene and exclusion of promoter region mutations in individuals without ZEB1 coding region mutations in posterior polymorphous corneal dystrophy (PPCD).

Methods: Slit-lamp examination and DNA collection were performed for individuals diagnosed with PPCD and, when available, affected and unaffected family members. Genomic DNA prepared from peripheral blood leukocytes and buccal epithelial cells underwent PCR amplification and automated sequencing of the ZEB1 gene and 1 kb 5' of ZEB1, presumably containing the ZEB1 promoter region.

Results: Thirteen unrelated individuals with PPCD were identified, and genomic DNA was collected from each individual. ZEB1 mutations were identified in six of the 13 probands, five of which were novel: p.(Gly150Alafs*36; spontaneous), p.(His230Argfs*7), p.(Ser638Cysfs*5), p.(Glu1039Glyfs*6), and p.(Gln884Argfs*37). Screening of the ZEB1 promoter region in 31 probands with PPCD without a ZEB1 coding region mutation identified only two known single nucleotide polymorphisms (SNPs) whose frequency in the affected probands did not differ significantly from that in the general population.

Conclusions: We report five novel frame-shift mutations, one confirmed as spontaneous, in the ZEB1 gene associated with PPCD, bringing the total number of reported pathogenic mutations to 24, and the percentage of PPCD associated with ZEB1 mutations to 32%. The absence of ZEB1 promoter region mutations in probands without a ZEB1 coding region mutation indicates that other genetic loci, such as the PPCD1 locus, are involved in the pathogenesis of PPCD.

Figure 1

Depiction of the zinc finger E-box binding homeobox 1 (ZEB1) protein, demonstrating the location of the five novel mutations and 19 previously reported mutations. The mutation nomenclature is presented according the Human Genome Variation Society (HGSV) guidelines, and thus may be different from the nomenclature used in original publications. Important functional domains are also depicted.

Figure 2

Pedigrees and zinc finger E-box binding homeobox 1 (ZEB1) sequences for the five families in which novel zinc finger E-box binding homeobox 1 mutations were identified. In each pedigree, the presence of the wild-type allele (designated by the + symbol) or the mutant allele is indicated below the symbol of each individual in whom DNA collection and zinc finger E-box binding homeobox 1 (ZEB1) gene screening were performed. Filled symbols represent affected individuals, open symbols represent unaffected individuals, and question marks indicate individuals of undetermined affected status. Arrowheads indicate probands. Beneath each pedigree, chromatograms demonstrating the identified mutation (MU) and the wild-type DNA sequence (WT) are shown.

Figure 3

Slit-lamp photomicrographs of a patient with posterior polymorphous corneal dystrophy 3 (PPCD3) secondary to p.(Gln884Argfs*37) mutation in the zinc finger E-box binding homeobox 1 gene (ZEB1). Diffusely distributed geographic gray-white Descemet membrane opacities are seen on direct illumination (A) that appear as round and oval-shaped “vesicles” on retroillumination, consistent with posterior polymorphous corneal dystrophy (PPCD).