A novel nonstop MYOC mutation in a Large Filipino Family with Juvenile-Onset Open-Angle Glaucoma

Abstract

Purpose : Juvenile-onset primary open-angle glaucoma (JOAG) is an important cause of blindness world-wide. Mutations in the myocilin (MYOC) gene are known to result in JOAG by causing myocilin protein misfolding and sequestration in the endoplasmic reticulum (ER) in trabecular meshwork (TM) cells eventually leading to ER stress-induced TM cell death. In this study we describe the clinical features of a large Filipiino family with JOAG and identify the first known MYOC nonstop mutation as the cause of disease.

Methods : Fifty-six members of a 4-generation family were enrolled in this study. All study subjects underwent a clinical exam and a blood sample was obtained for DNA sequencing for MYOC. A COS-7 cell line was used to test MYOC mutations for pathogenicity. The wild type MYOC cDNA sequence was cloned into a Gateway® entry vector and moved into an expression vector by LR recombination. Mutagenesis was created in the entry vector. A COS-7 cell line was used to test MYOC mutations for pathogenicity. The COS-7 cells were transfected with expression vectors encoding wild-type or mutated MYOC cDNA.

Results : MYOC mutation screening in this Filipino family identified a novel nonstop mutation, c.1515A>G (p.*505Wext*42). This mutation segregated in all affected individuals in the family and was also found in 7 currently unaffected subjects who were between 1 and 15 years of age. The average age of disease onset in mutation carriers was 28 years and the range of disease onset was 14 to 49 years of age. Antibody staining of cultured COS-7 cells transfected with MYOC c.1515A>G showed sequestration of the MYOC protein in the ER similar to cells transfected with a known MYOC mutation c.734G>A (p.C245Y).

Conclusions : This study suggests that the c.1515A>G MYOC mutation is the disease causing mutation in this Filipino family with JOAG. This is the first nonstop MYOC mutation identified to date. The mutant protein becomes restricted to the ER causing ER stress-induced TM cell death similar to other glaucoma causing MYOC mutations. Clinical features of affected individuals suggest that the nonstop mutation exhibits variable expressivity with respect to age of disease onset. Identifying this mutation makes it possible to initiate genetic screening for other family members allowing for close monitoring and timely treatment for mutation carriers.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.