Variation in WNT7A is unlikely to be a cause of familial congenital talipes equinovarus

Genetics of clubfoot; recent progress and future perspectives

Clubfoot or talipes equinovarus (TEV) is an inborn three-dimensional deformity of leg, ankle and foot. It results from structural defects of several tissues of foot and lower leg leading to abnormal positioning of foot and ankle joints. TEV can lead to long-lasting functional disability, malformation and discomfort if left untreated. Substantial progress has been achieved in the management and diagnosis of limb defects; however, not much is known about the molecular players and signalling pathways underlying TEV disorder. The homeostasis and development of the limb depends on the complex interactions between the lateral plate mesoderm cells and outer ectoderm. These complex interactions include HOX signalling and PITX1-TBX4 pathways. The susceptibility to develop TEV is determined by a number of environmental and genetic factors, although the nature and level of interplay between them remains unclear. Familial occurrence and inter and intra phenotypic variability of TEV is well documented. Variants in genes that code for contractile proteins of skeletal myofibers might play a role in the aetiology of TEV but, to date, no strong candidate genes conferring increased risk have emerged, although variants in TBX4, PITX1, HOXA, HOXC and HOXD clusters genes, NAT2 and others have been shown to be associated with TEV. The mechanisms by which variants in these genes confer risk and the nature of the physical and genetic interaction between them remains to be determined. Elucidation of genetic players and cellular pathways underlying TEV will certainly increase our understanding of the pathophysiology of this deformity.

Evaluation of CAND2 and WNT7a as candidate genes for congenital idiopathic clubfoot

Congenital idiopathic clubfoot is a common pediatric musculoskeletal deformity with no known etiology. The deformity reportedly follows a Mendelian pattern of inheritance. Recent work has demonstrated linkage in chromosome 3 and 13 in a large, multigeneration, highly penetrant family with idiopathic clubfoot. From the linkage region on chromosome 3, we selected the candidate genes CAND2 and WNT7a, which are involved in lower extremity development, and hypothesized mutations in these genes would be associated with the phenotype of congenital idiopathic clubfoot. The CAND2 gene was sequenced in 256 clubfoot patients, and 75 control patients, while WNT7a was screened using 56 clubfoot patients and 50 control patients. We found a polymorphism in each gene, but the single nucleotide change in CAND2 was a silent mutation that did not alter the amino acid product, and the single nucleotide change in WNT7a was in the upstream, non-coding or promoter region before the start codon. Based on these results it is unlikely CAND2 and WNT7a are the major genes that causes clubfoot, however WNT7a might be one of many genes that could increase susceptibility to develop clubfoot but do not directly cause it.

Beta-catenin mediates soft tissue contracture in clubfoot

The contracted tissues from clubfeet resemble tissues from other fibroproliferative disorders such as palmar fibromatosis. Beta-catenin-mediated signaling is a crucial pathway controlling the fibroproliferative response in many fibroproliferative disorders. To determine if beta-catenin signaling plays a role in clubfoot, contracted and less contracted tissues from clubfeet were studied using Western analysis to determine the protein level of beta-catenin. Primary cell cultures were established from these tissues, and they were treated with either lithium to increase beta-catenin or Dickkopf-1 to inhibit beta-catenin. RNA was extracted from the cells and analyzed to determine how beta-catenin regulates expression of Type III collagen, an extracellular matrix protein upregulated in contracted clubfoot tissue. There was a more than twofold increase in beta-catenin protein in the contracted tissues. Treatment with either lithium or Dickkopf-1 showed Type III collagen RNA expression positively correlated with the protein level of beta-catenin. These data support the concept that beta-catenin-mediated signaling plays an important role regulating contracture in clubfeet. Because pharmacologic agents are under development to block this signaling pathway, such drugs could be used in cases of severe stiffness to improve range of motion or to decrease the need for radical surgical approaches.