The collagen, type IX, alpha 1 (COL9A1) gene was previously identified as a candidate gene for idiopathic congenital talipes equinovarus (ICTEV), a congenital lower limb deformity in humans. In the present study, increased expression levels of COL9A1 were identified in the abductor hallucis muscle of ICTEV patients compared with those in control samples. The COL9A1 gene is regulated by SRY (sex‑determining region Y)‑box 9 (SOX9). Immunofluorescence analysis of SOX9 and COL9A1 proteins identified colocalization to the sarcolemma, endomysium and muscle membrane in muscle samples of ICTEV. No mutations in the exons and promoters of SOX9 were detected in blood samples of 84 ICTEV patients by denaturing gradient gel electrophoresis. mRNA and protein expression levels of SOX9 were detected by real‑time polymerase chain reaction and western blot analysis, respectively and were found to be significantly higher in ICTEV muscle samples compared with those in control samples. Based on present observations, we hypothesize that overexpression of the SOX9 gene may play a role in the genetic etiology of ICTEV.