The aetiology of congenital club foot is unclear. Although studies on populations, families and twins suggest a genetic component, the mode of inheritance does not comply with distinctive patterns.

The Odense-based Danish Twin Registry contains data on all 73 000 twin pairs born in Denmark over the last 130 years. In 2002 all 46 418 twins born between 1931 and 1982 received a 17-page questionnaire, one question of which was ‘Were you born with club foot?’ A total of 94 twins answered ‘Yes’, giving an overall self-reported prevalence of congenital club foot of 0.0027 (95% confidence interval (CI) 0.0022 to 0.0034). We identified 55 complete twin pairs, representing 12 monozygotic, 22 dizygotic same sex (DZ_ss), 18 dizygotic other sex (DZ_os) and three unclassified. Two monozygotic and 2 DZ_ss pairs were concordant. The pairwise concordance was 0.17 (95% CI 0.02 to 0.48) for monozygotic, 0.09 (95% CI 0.01 to 0.32) for DZ_ss and 0.05 (95% CI 0.006 to 0.18) for all dizygotic (DZ_tot) twins.

We have found evidence of a genetic component in congenital club foot, although non-genetic factors must play a predominant role.