Linkage to the FOXC2 region of chromosome 16 for varicose veins in otherwise healthy, unselected sibling pairs.

BACKGROUND The FOXC2 gene on 16q24 is mutated in lymphoedema distichiasis (LD), in which varicose veins (VV) are a common feature. We hypothesised that this gene might be implicated in the development of VV in the normal population, therefore, after performing a classical twin study, we tested for linkage and association in white women. We also tested for linkage with haemorrhoids (H), as a separate venous anomaly at the same locus. METHODS A total of 2060 complete female twin pairs aged 18-80 years from the St Thomas' Adult UK Twin registry replied to questions on VV and H as part of a broader postal survey of 6600 twins (62% response rate). Dizygotic female twin pairs were tested for linkage and association to the candidate marker D16S520 (1903 individuals genotyped), which is located about 80 kb from FOXC2. RESULTS Casewise concordance rates were significantly higher for monozygotic than dizygotic twins for both phenotypes (VV 67% v 45%; p = 2.2x10(-6); H 68% v 59%; p = 0.01; H including during pregnancy 73% v 64%; p = 2.1x10(-4)), corresponding to additive genetic heritabilities in liability of 86% (95% confidence interval (CI) 73% to 99%) for VV and 56-61% for H (95% CI 43% to 73%). The presence of VV and H were significantly correlated. We found significant evidence of linkage to the marker for VV (MLS(ASP) = 1.37, p = 0.01; GLM(ASP/DSP) Z = 3.17 p = 0.002), but no association. Both linkage and association tests were negative for H. The combined phenotype of having VV and H did not show any evidence of linkage or association. CONCLUSION These results demonstrate VV and H to be heritable, related conditions, and the data strongly suggest FOXC2 to be implicated in the development of VV in the general population.