Transmission disequilibrium was observed in 84 nuclear pedigrees for SNPs (rs592121, rs1135056) within the collagen type IX alpha 1 chain (COL9A1) gene, with elevated expression of COL9A1 detected in clubfoot patients compared with unaffected individuals (t = 4.7500; p < 0.05), indicating its potential significance as a susceptibility gene for clubfoot development.58 Here, COL9A1 is linked to clubfoot.