Genetic association of COL5A1 variants in keratoconus patients suggests a complex connection between corneal thinning and keratoconus

Abstract

Purpose: Single nucleotide polymorphisms (SNPs) located near or within the COL5A1 gene, at 9q34.2-q34.3 chromosomal region have been reported in association with central corneal thickness (CCT). Using family linkage analysis, we identified a keratoconus susceptibility locus at 9q34. These findings led us to perform an association study between COL5A1 variation and keratoconus susceptibility.

Methods: A Caucasian case-control cohort of 222 keratoconus patients and 3324 controls was selected as the discovery panel. An independent case-control panel of 304 cases and 518 controls and a family panel of 186 subjects were replicated for genotyping and association. Forty-four SNPs (21 for discovery and 23 for fine-mapping) spanning 300 kilobases in and around COL5A1 were genotyped and tested for genetic association. Logistic regression models implemented in PLINK were used to test for association in case controls. Generalized estimating equation models accounting for familial correlations implemented in genome-wide interaction analyses with family data were used for association testing in families.

Results: Two CCT associated SNPs (rs1536482 and rs7044529 near and within COL5A1) were identified in the keratoconus discovery cohort (P values of 6.5 × 10(-3) and 7.4 × 10(-3)). SNP rs1536482 was replicated in the second case-control sample (P = 0.02), and SNP rs7044529 was replicated in a keratoconus family panel (P = 0.03). Meta P values of rs1536482 and rs7044529 in the keratoconus cohorts were 1.5 × 10(-4) (odds ratio [OR] = 1.30) and 2.9 × 10(-3) (OR = 1.39). After Bonferroni correction, the association of SNP rs1536482 remained significant (P = 6.5 × 10(-3)).

Conclusions: SNPs in the COL5A1 region, which regulate normal variation in CCT, may play a role in the thinning associated with keratoconus.

Figure 1.

Forest plots for top SNPs. (A) rs1536482-A: OR and 95% CI; (B) rs7044529-T: OR and 95% CI.

Figure 2.

Regional plot of COL5A1 region.

Figure 3.

(A) Videokeratography right of an 18-year-old male with a family history of keratoconus (two cousins on maternal side). Topography illustrates with the rule astigmatism and no evidence of “forme frusta” keratoconus. (B) OCT pachymetry of the same eye demonstrating low CCT measurements with diffuse corneal thinning and no evidences of focal ectasia.

Figure 4

(A) Videokeratography of the right eye of the mother of the 18-year-old male described in Figure 3A. Topography demonstrates mild contact lens warpage with no evidence of “forme frusta” keratoconus. (B) OCT pachymetry of this eye demonstrating low CCT measurements with diffuse corneal thinning and no evidence of focal ectasia.