Tropomyosin (TM), a sarcomeric thin-filament protein, plays an essential part in muscle contraction by regulating actin-myosin interaction. We describe two patients, a woman and her daughter, with muscle weakness and distal arthrogryposis (DA) type 2B, caused by a heterozygous missense mutation, R133W, in TPM2, the gene encoding beta-TM. Our results demonstrate the involvement of muscle dysfunction in the pathogenesis of DA and the fact that DA2B may be caused by mutations in TPM2.