Substitution at IL1RN and deletion at SLC4A11 segregating with phenotype in familial keratoconus.

PURPOSE: Keratoconus (KTCN) is a thinning and anterior protrusion of the cornea that results in altered refractive powers and loss of visual acuity. Despite numerous studies, the reasons for development and progression of KTCN remain unknown. Genetic studies have led to identification of several loci linked with KTCN, including a locus in one multigenerational Ecuadorian family. The purpose of this study was to identify sequence variants in candidate genes segregating with the KTCN phenotype in another Ecuadorian family.

METHODS

Nonparametric linkage analysis was performed in Ecuadorian family KTCN-019. Candidate genes IL1A, IL1B, IL1RN, and SLC4A11 were selected and examined in this family by direct sequencing of all exons, promoters, and intron-exon junctions.

RESULTS

Two novel suggestive loci were identified in 2q13-q14.3 and 20p13-p12.2. Screening of the candidate genes revealed 66 sequence variants, including five novel variants, in both coding and noncoding regions. The substitution c.214+242C > T in the IL1RN gene was observed in all affected individuals and three apparently unaffected family members. The novel deletion of 54 nucleotides in position c.2558+149_2558+203 in SLC4A11 was observed in all patients but one, as well as two healthy individuals and one person with an unknown phenotype.

CONCLUSIONS

The analyses of selected genes have led to identification of numerous sequence variants in the examined Ecuadorian family. Both substitution c.214+242C > T in IL1RN and novel deletion c.2558+149_2558+203del54 in SLC4A11 were observed significantly more frequently in family members with KTCN (P = 0.004525 and P = 0.00761, respectively), suggesting involvement of these two genes in KTCN etiology in the studied family.