ORIGINAL ARTICLE Variation in CASP10 Gene Is Associated With Idiopathic Talipes Equinovarus Amy L. Heck, BS,* Molly S. Bray, PhD,* Allison Scott, MD,† Susan H. Blanton, PhD,‡ and Jacqueline T. Hecht, PhD†§ Abstract: Idiopathic talipes equinovarus (ITEV), more commonly known as clubfoot, is a developmental deformity characterized by rigid ankle equinus, hindfoot varus, and forefoot adduction. This common birth defect is treatable, but the etiology of ITEV is largely unknown. Recently, a deletion in the chromosomal region 2q31-33 was found to be associated with clubfoot. Microsatellite markers span- ning the region were genotyped in 57 multiplex ITEV families and 83 simplex trios. Family-based analysis revealed that two micro- satellite markers, GATA149B10 and D2S1371, were associated with ITEV in the simplex trios. The 6cM region between the two markers contained the candidate genes CASP8, CASP10, and CFLAR. These genes encode proteins that are regulators of apoptosis, which is impor- tant during growth and development. Genotyping of SNPs through- out the genes in this sample of ITEV families has revealed positive linkage with association to the major allele of a variant in CASP10 in simplex ITEV white and Hispanic trios. This study is the first to find evidence for a candidate gene for ITEV and provides a scientific foun- dation to further explore the contributions of other apoptotic genes in the etiology of clubfoot. Key Words: clubfoot, ITEV, CASP10, caspases, linkage and association, birth defect, complex disease (J Pediatr Orthop 2005;25:598–602) I diopathic talipes equinovarus (ITEV) is a birth defect characterized by a rigid foot deformity, with equinus of the ankle, varus of the hindfoot, and adductus of the forefoot. 1 Although it is commonly known as clubfoot, care must be taken to distinguish this group from cases of clubfoot designated congenital talipes equinovarus (CTEV), for which there is a known cause or associated congenital abnormalities. 2 Although ITEVonce resulted in an inability to walk correctly, improvements in treatment can result in a gait that is indistinguishable from normal. Males are affected twice as frequently as females; the basis for this sex difference is unknown. 3 Most cases of ITEV are bilateral, but in unilateral cases the right side is more often affected than the left. ITEV occurs in 1 per 1,000 live births in the United States, but the birth prevalence varies substantially across populations. 4 In Caucasians, clubfoot cases range from 1 to 3 per 1,000 live births, but incidences of 0.39 and 7 per 1,000 are reported in Chinese and Hawaiian populations, respectively. 5 A detailed study of clubfoot in Caucasian, African-American, and Hispanic populations in Texas revealed an overall birth prevalence of 0.74 per 1,000; the prevalence was similar in the Caucasian and Hispanic groups and only slightly lower in the African-American group. 3 The first description of ITEV in the medical literature was from Hippocrates, who theorized that ITEV was the result of external uterine compression holding the foot in a position of equinovarus. 2 Intrauterine pressure has not been substan- tiated as a cause for ITEV, and its etiology remains unknown. Nevertheless, several lines of evidence have implicated genetic factors in the development of ITEV. Multiple cases of ITEV may be seen in a family, with an inheritance pattern more complex than a simple Mendelian disorder. Twin studies have showed that the concordance for ITEV is higher for mono- zygotic twins at 32.5%, compared with 2.9% in dizygotic twins. This finding points to genetic factors being more im- portant than environment, because twins share the same in- trauterine environment. 6 Further evidence for the role of genetic factors in the etiology of ITEV comes from work from Wynne-Davis, who calculated that the risk of ITEV to parents with a first-degree relative affected is 2.9 per 1,000 births, almost three times the general population rate. 7 Attempts to determine the genetics of ITEV have suggested different models of ITEV inheritance, including single major gene and multifactorial models. 8–10 A mutation (R279W) in the sulfate transporter gene, DTDST, has been implicated in two sets of siblings with simplex clubfoot cases of western French ancestry. Bonafe et al 11 examined 207 clubfoot cases and found that the R279W mutation was no more frequent in the ITEV cases than controls. In addition, analysis of markers in DTDST with a transmission disequilibrium test for linkage and association revealed no significant findings for the geno- types when corrected by permutation tests. This current study draws from the identification of chromosomal deletions that are significantly associated with clubfoot. Brewer et al 12 identified six distinct regions of the genome containing deletions in a sample of 176 individuals with talipes equinovarus, including the chromosomal segment From the *University of Texas–Houston School of Public Health, Houston, TX; †Shriners Hospital for Children, Houston, TX; ‡University of Virginia, Charlottesville, VA; and §Universityof Texas–Houston Medical School, Houston, TX. Study conducted at Houston Medical School, University of Texas. This work was supported by Shriners Hospital for Children grant to J.T.H. and by grant DK62148 to support A.L.H. Reprints: Jacqueline T. Hecht, PhD, University of Texas–Houston Medical School, Department of Pediatrics, P.O. Box 20708, Houston, TX 77225 (e-mail: Jacqueline.t.hecht@uth.tmc.edu). Copyright Ó 2005 by Lippincott Williams & Wilkins 598 J Pediatr Orthop  Volume 25, Number 5, September/October 2005