G.P.271

Mutations affecting skeletal muscle isoforms of the tropomyosin genes may cause nemaline myopathy (NM), cap myopathy, core-rod myopathy, congenital fibre-type disproportion, core-rod myopathy, distal arthrogryposes and Escobar syndrome. Here we correlate the clinical picture of these diseases with novel (16) and previously reported (31) mutations of the TPM2 and TPM3 genes. Included are altogether 93 families: 53 with TPM2 mutations and 40 with TPM3 mutations. A total of 27 Twenty-seven distinct pathogenic variants of TPM2, and 20 of TPM3, have been published or listed in the Leiden Open Variant Database ( http://www.dmd.nl/ ). Most are heterozygous changes associated with autosomal dominant disease. Patients with TPM2 mutations tended to present with milder symptoms than those with TPM3 mutations, DA being present only in the TPM2 group. Previous studies have shown that five of the mutations in TPM2 and one in TPM3 cause increased Ca2 + sensitivity resulting in a hypercontractile molecular phenotype. Patients with hypercontractile phenotypes more often had contractures of the limb joints (18/19) and jaw (6/19) than those with non-hypercontractile ones (2/22 and 1/22), while patients with the non-hypercontractile molecular phenotypes more often (19/22) had axial contractures than the hypercontractile group (7/19). Our in silico predictions show that most mutations affect tropomyosin–actin association or tropomyosin head-to-tail binding.