Identification and functional characterization of a novel MYOC mutation in two primary open angle glaucoma families from The Netherlands

Abstract

Purpose: Glaucoma is the second most prevalent cause of blindness worldwide, projected to affect more than 60 million people by 2010, 75% of which represents primary open angle glaucoma (POAG). Of the three genes, namely, Myocilin (MYOC), Optineurin (OPTN), and WD repeat-containing protein 36 (WDR36), which have been shown to cause POAG when defective, MYOC is the most frequently mutated gene, accounting for 3%-4% of all POAG cases. The purpose of this study was identification and functional characterization of MYOC mutations in adult-onset, high-pressure POAG patients from The Netherlands.

Methods: The following criteria were required for study participants to be included: have at least two affected family members, an age of diagnosis of more than 35 years, intraocular pressure (IOP) of more than 22 mmHg, glaucomatous optic neuropathy in both eyes, visual field loss consistent with assessed optic neuropathy in at least one eye, and an open anterior chamber angle without morphological abnormalities by gonioscopy. Sequence analysis was performed in genomic DNA of 30 probands for the protein coding region of the MYOC gene. A Chinese hamster ovarian cell line (CHO-K1) was used to express wild type and mutant MYOC protein. Detergent solubility of MYOC was assayed and its secretory property was analyzed by immunoprecipitation.

Results: We recruited 250 individuals from 30 families (120 affected and 130 unaffected family members) with a positive history of POAG. We identified a novel mutation c.1288T>C (p.Phe430Leu) in exon 3 of MYOC in two unrelated families showing the same haplotype around the mutant allele. The novel mutation segregated completely with the disease in these families and was absent in 250 ethnically matched controls. All patients harboring this mutation showed severe glaucomatous damage, pointing to the deleterious effect of this mutation. Compared to the wild type, the mutant protein was less soluble when extracted with Triton X-100 and was secretion-defective.

Conclusions: The novel MYOC mutation, p.Phe430Leu, has the same origin in both POAG families from The Netherlands. The pathogenic nature of this mutation is suggested by the severe phenotype of mutant patients and mistrafficking of mutant protein as observed for other severe disease-causing mutations of MYOC.