Fine mapping of new glaucoma locus GLC1M and exclusion of neuregulin 2 as the causative gene

PURPOSE: We recently identified a novel glaucoma locus on 5q22.1-q32, designated as GLC1M, in a family from the Philippines with autosomal dominant juvenile-onset primary open angle glaucoma (JOAG). No mutations in myocilin (MYOC), optineurin (OPTN), and WD-repeat protein 36 (WDR36) were found. Neuregulin 2 (NRG2) is an excellent potential functional as well as positional candidate at GLC1M. The goal of the present study was to evaluate the role of the NRG2 gene in this JOAG family and unrelated JOAG patients and to refine the critical interval for GLC1M. METHODS: Genomic DNA was obtained from 27 family members. All coding exons and splicing sites of NRG2 were screened for sequence alterations by polymerase chain reaction (PCR) and DNA sequencing. A cohort of 92 unrelated JOAG patients and 92 control subjects were genotyped for the three single nucleotide polymorphisms (SNPs) of NRG2 by PCR and DNA sequencing. Haplotype and segregation analyses were performed in the family. Fisher's exact test was used to compare the frequencies of the NRG2 polymorphisms between affected and unaffected subjects in the family and between unrelated JOAG patients and control subjects. RESULTS: Three SNPs were identified: c.98G>A (S33N), IVS3+13A>G (rs889022), and c.1976A>G (G659G). None of them segregated with the JOAG phenotype in this family. No association was found between NRG2 and JOAG in the case-control study (p>0.12). However, further inspection of the haplotypes in the family localized the NRG2 gene telomeric to the disease locus. The critical interval of GLC1M was therefore refined to a region of 28 Mb between D5S2051 and NRG2. CONCLUSIONS: The linkage interval for GLC1M was refined to a smaller region. The NRG2 gene was excluded as the causative gene for JOAG.