Coincidental Occurrence of Schnyder Corneal Dystrophy and Posterior Polymorphous Corneal Dystrophy Type 3

To report a simultaneous occurrence of 2 rare corneal dystrophies.

A 30-year-old man with a family history of posterior polymorphous corneal dystrophy type 3 (PPCD3) was invited for ophthalmic examination. Sanger sequencing of the coding regions and intron/exon boundaries of disease-associated genes, ZEB1 and UBIAD1, was performed.

The clinical findings suggested co-occurrence of PPCD3 and Schnyder corneal dystrophy in the proband. This dual diagnosis was supported by genetic findings. He was identified to carry a previously reported heterozygous nonsense mutation in ZEB1: c.2157C>G; p.(Tyr719*), and a novel heterozygous missense mutation in UBIAD1: c.569T>C; p.(Ile190Thr). The mother of the proband only carried c.2157C>G in ZEB1, and slit-lamp examination of her corneas showed endothelial lesions characteristic of PPCD3. The sister of the proband carried c.569T>C in UBIAD1 and had corneal crystal deposition in her anterior stroma consistent with the diagnosis of Schnyder corneal dystrophy.

This case illustrates the coincidental occurrence of 2 rare and genetically distinct corneal dystrophies in a single patient. Furthermore, it highlights the need to perform comprehensive phenotyping in combination with appropriate genetic diagnostic testing to achieve an accurate diagnosis.