Identification a novel MYOC gene mutation in a Chinese family with juvenile-onset open angle glaucoma

Abstract

Purpose: To describe the clinical and genetic findings in one Chinese family with juvenile-onset open angle glaucoma (JOAG).

Methods: One family was examined clinically and a follow-up took place 5 years later. After informed consent was obtained, genomic DNA was extracted from the venous blood of all participants. Linkage analysis was performed with three microsatellite markers around the MYOC gene (D1S196, D1S2815, and D1S218) in the family. Mutation screening of all coding exons of MYOC was performed by direct sequencing of PCR-amplified DNA fragments and restriction fragment length polymorphism (RFLP) analysis. Bioinformatics analysis by the Garnier-Osguthorpe-Robson (GOR) method predicted the effects of variants detected on secondary structures of the MYOC protein.

Results: Clinical examination and pedigree analysis revealed a three- generation family with seven members diagnosed with JOAG, three with ocular hypertension, and five normal individuals. Through genotyping, the pedigree showed a linkage to the MYOC on chromosome 1q24-25. Mutation screening of MYOC in this family revealed an A-->T transition at position 1348 (p. N450Y) of the cDNA sequence. This missense mutation co-segregated with the disease phenotype of the family, but was not found in 100 normal controls. Secondary structure prediction of the p.N450Y by the GOR method revealed the replacement of a coil with a beta sheet at the amino acid 447.

Conclusions: Early onset JOAG, with incomplete penetrance, is consistent with a novel mutation in MYOC. The finding provides pre-symptomatic molecular diagnosis for the members of this family and is useful for further genetic consultation.

Figure 1

Family structure and haplotype analysis of a Chinese family with JOAG. Pedigree and haplotype analysis of the family with JOAG showed segregation with three microsatellite markers on chromosome 1, listed in descending order from the centromeric end. Squares indicate males; circles indicate females; slashed symbols indicate deceased; solid symbols indicate affected; open symbols indicate unaffected; symbols with upper left filled-in quadrant indicate members with ocular hypertension; symbols with dot in the center indicate carriers.

Figure 2

Fundus appearances of patients with JOAG. A: Fundus images of II:7 showed late-stage glaucomatous cupping of the optic disc. B: Fundus images of III:7, who was confirmed to have glaucoma in 2009, presented early glaucomatous appearances of the optic disc.

Figure 3

DNA sequence chromatograms and co-segregation analysis of the p.N450Y mutation with disease phenotype. A: Heterozygote sequence (sense strand) shows an A/T transition in codon 450 that changed asparagine (AAC) to tyrosine (TAC). B: Restriction fragment length analysis shows the p.N450Y mutation abolishing a HindII site co-segregated with JOAG patients, ocular hypertensions, and the carriers (342 and 279 bp), but not with unaffected individuals (279 bp).

Figure 4

The effect of p. N450Y on the secondary structure of MYOC using the GOR method. A: The secondary structure of wild type MYOC around the site N450. B: The secondary structure of mutant Y450 of MYOC of the corresponding region.

Figure 5

Sequence alignment portion of the olfactomedin-like domain spanning the novel missense mutation p.N450Y of human MYOC and a comparison with other species.