G.P.273: Nemaline myopathy 8 and KLHL40 in diseased and normal skeletal muscle

Abstract

Mutations in the gene ( KLHL40 ), encoding Kelch-like family member 40, were recently identified in patients presenting with severe autosomal recessive nemaline myopathy (NEM8). Using exome sequencing or targeted re-sequencing of 276 known neuromuscular disease genes through a TargetSeq (Life Technologies) capture panel, we have identified two additional cases with KLHL40 mutations. Both were from consanguineous kindreds. Case 1 was diagnosed with severe SMA and congenital fractures. We identified a homozygous nonsense mutation in KLHL40 (c.46C>T, p. Gln16*). Muscle biopsy identified variation in fibre size and miliary nemaline bodies by electron microscopy seen as very fine scattered granules upon Gomori trichrome staining. Case 2 presented with severe nemaline myopathy, the biopsy showing numerous tiny nemaline bodies. We identified a homozygous missense mutation in KLHL40 (c.931C>A, p. Arg311Ser). Neither of the variants was present in 1000genomes or EVS databases. These data further suggest that muscle biopsy may be useful to inform genetic testing and that KLHL40 should be considered in patients presenting with severe miliary nemaline myopathy. Nemaline myopathy should also be considered in the differential diagnosis of severe SMA, especially in patients presenting with congenital fractures and contractures. The normal biological function of KLHL40 is largely unknown and therefore the basis of the severe muscle disease resulting from mutations of KLHL40 is also unknown. In investigations of control and diseased mouse and patient muscle, we show that KLHL40 is more abundant in the mouse soleus and diaphragm (muscles that comprise oxidative type I and IIA myofibres) than in the EDL, gastrocnemius and quadriceps muscles (type II glycolytic predominant). In addition we show that KLHL40 is increased in dystrophic mouse ( mdx ) and regenerating patient muscle (including DMD), suggesting that it may serve as a novel marker of skeletal muscle regeneration.