Evidence that FIBL-6 is the ARMD1 Gene

Abstract

Abstract: : Purpose: The ARMD1 gene was previously mapped to lq25-31 in a large family with age-related macular degeneration (AMD). We searched within this region to identify genes that contained sequence changes that segregate with the disease locus in this family. Methods:We performed mutational screening of 30 candidate genes within the critical region including FIBL-6, which was chosen because of its similarities with EFEMP1. Using monoallelic strains derived from an affected individual in this family, we analyzed 107 exons of FIBL-6. When a potential disease-causing sequence variation was identified, we used both sequencing and allele specific oligonucleotide (ASO) hybridization to screen all family members for this variation. We also screened 188 sporadic cases of AMD, 174 control subjects, and 991 members of 100 AMD families by ASO hybridization and denaturing high performance liquid chromatography. Expression and alternative splicing were evaluated in several tissues by RT-PCR and sequencing. Protein conservation was evaluated in several species by RT-PCR or genomic sequencing. Results: We identified a sequence variation in exon 104 of the FIBL-6 gene that produces a Gln5345Arg change. This variation segregated with the disease haplotype in our family that had been linked to 1q25-31. We also detected this change in some affected members of 3 other AMD families, 2 unaffected members, 1 sporadic AMD case, and 2 control subjects. Unaffected individuals with the variation may appear normal due to their relatively young age or other phenotypic determinants. The amino acid found at the position corresponding to codon 5345 of human FIBL-6 is conserved as glutamine among 8 species analyzed. RT-PCR analysis demonstrated FIBL-6 mRNA in human skin fibroblasts and retinal pigment epithelium (RPE) cells, and porcine trabecular meshwork cells, sclera and retina. Two transcripts were identified, one with exon 104 and one without. Conclusions: The evidence of segregation, similarity to EFEMP1, and protein conservation supports the conclusion that the Gln5345Arg variation in FIBL-6 is the mutation responsible for AMD in this large family, which maps to 1q25-31.

Keywords: age-related macular degeneration • macula/fovea • extracellular matrix