Novel trabecular meshwork inducible glucocorticoid response mutation in an eight-generation juvenile-onset primary open-angle glaucoma pedigree

Abstract

Objective: This study aimed to update a large kindred with juvenile-onset primary open-angle glaucoma (POAG) first described in 1940 and to identify the underlying genetic cause of the disease.

Design: Molecular genetic study of a single kindred, including clinical examination, retrospective review of clinical and family history records, linkage analysis, and mutation screening.

Participants: The retrospective review included 957 members of a single large family. The linkage study included 40 members of 1 branch of the family in which juvenile-onset POAG is segregating in an autosomal-dominant pattern. Mutation screening included 15 at-risk family members with juvenile-onset POAG, probands of 40 families with adult-onset POAG, probands of 11 additional unrelated juvenile-onset POAG families, and 43 unrelated normal control subjects.

Intervention: Clinical and family history records were obtained, ophthalmologic examinations were performed, and blood samples were drawn for use in genotyping.

Main outcome measures: Allele sizes of microsatellite repeat genetic markers from the vicinity of the GLC1A glaucoma gene on chromosome 1q were assigned based on size fractionation of DNA fragments generated by polymerase chain reaction (PCR). Linkage was established by the method of lod scores. Mutations were identified by determination of the DNA sequence of PCR products amplified from the trabecular meshwork inducible glucocorticoid response (TIGR) gene. Glaucoma status for purposes of linkage and mutation analysis was based on a combination of ophthalmologic examination, clinical records, family history, and previously published information. For some individuals reported in the pedigree, but not included in the genotyping studies, less information was available as presented in the text and tables.

Results: Autosomal-dominant POAG was confirmed or reported for 78 members of an 8-generation family. Linkage analysis showed significant evidence for linkage of juvenile-onset POAG in one branch of the family to D1S452 (maximum lod score of 6.42 at a recombination fraction of 0.00) and other markers in the vicinity of the GLC1A gene on chromosome 1q. Screening of the TIGR gene identified a mutation that results in substitution of asparagine for isoleucine at codon 477 near the carboxyterminal end of the protein.

Conclusions: The authors' findings strongly suggest that the juvenile-onset POAG locus in this family is the GLC1A locus and that the underlying cause of the disease is the IIe477Asn TIGR mutation that cosegregates with juvenile-onset POAG in one branch of this large family. Lack of samples from deceased individuals prevented the authors from determining whether reported adult-onset cases in this family could also be attributed to the IIe477Asn TIGR mutation. Absence of the IIe477Asn TIGR mutation from other juvenile- and adult-onset POAG families implies that this TIGR mutation is not a common cause of glaucoma.