Investigation of sarcomeric protein diseases

[Truncated abstract] The sarcomeric protein diseases are heterogeneous, both genetically and phenotypically. For example, mutations in a number of different thin filament genes (skeletal muscle -actin, ACTA1; -fast tropomyosin, TPM2, -slow tropomyosin, TPM3; troponin T1, TNNT1; nebulin, NEB) can all cause nemaline myopathy (NM), while mutations in ACTA1 alone can cause three distinct disease phenotypes (NM, cap disease and congenital fibre type disproportion). The work presented in this Thesis identifies a novel NM disease gene, and novel mutations in the -MyHC gene (MYH7). Furthermore it expands our knowledge of the mechanisms underlying the pathology and clinical heterogeneity of MYH7- and TPM2-diseases. Cofilin (CFL2) mutations had not previously been identified as a cause of NM. However, due to CFL2 interacting with other NM-associated proteins of the thin filament and its role in the regulation of actin assembly and disassembly, it was a strong candidate NM gene. Screening DNA from 23 NM probands for mutations in the candidate gene CFL2 did not identify any mutations. However, it formed part of a collaborative effort, which identified a single homozygous CFL2 mutation (p.Ala35Thr, c.103G>A) from a total of 113 probands {Agrawal, 2007 #611}. This published study indicated mutations in CFL2 are a rare cause of NM, suggesting that it would be logical to screen only patients that show abnormalities upon cofilin immunohistochemistry and are negative for mutations in the other known NM disease genes. Mutations in MYH7 had previously been demonstrated to cause two skeletal myopathies: Laing early-onset distal myopathy (MPD1) and myosin storage myopathy (MSM). In this Thesis, three novel mutations in MYH7 were identified (p.Arg1588Pro, p.Leu1793del and p.Glu1856Lys) and recurrent mutations in a further five probands were demonstrated. The discovery of novel MYH7 mutations broadens the region of the gene in which skeletal myopathy mutations are found.