Skeletal Muscle Contractile Gene (TNNT3, MYH3, TPM2) Mutations Not Found in Vertical Talus or Clubfoot

Arthrogryposis presents with lower limb contractures that resemble clubfoot and/or vertical talus. Recently, mutations in skeletal muscle contractile genes MYH3 (myosin heavy chain 3), TNNT3 (troponin T3), and TPM2 (tropomyosin 2) were identified in patients with distal arthrogryposis DA2A (Freeman-Sheldon syndrome) or DA2B (Sheldon-Hall syndrome). We asked whether the contractile genes responsible for distal arthrogryposis are also responsible for cases of familial clubfoot or vertical talus. We determined the frequency of MYH3, TNNT3, and TPM2 mutations in patients with idiopathic clubfoot, vertical talus, and distal arthrogryposis type 1 (DA1). We resequenced the coding exons of the MYH3, TNNT3, and TPM2 genes in 31 patients (five with familial vertical talus, 20 with familial clubfoot, and six with DA1). Variants were evaluated for segregation with disease in additional family members, and the frequency of identified variants was determined in a control population. In one individual with DA1, we identified a de novo TNNT3 mutation (R63H) previously identified in an individual with DA2B. No other causative mutations were identified, though we found several previously undescribed single-nucleotide polymorphisms of unknown importance. Although mutations in MYH3, TNNT3, and TPM2 are frequently associated with distal arthrogryposis syndromes, they were not present in patients with familial vertical talus or clubfoot. The TNNT3 R63H recurrent mutation identified in two unrelated individuals may be associated with either DA1 or DA2B.