C.P.2 In silico analysis of recessive RYR1 mutations identifies novel potential disease mechanisms

Mutations in RYR1 are responsible for malignant hyperthermia (MH) and several forms of congenital myopathy. Dominant mutations that give rise to central core disease (CCD) and MH cluster in three hotspot regions and the disease mechanisms associated with these diseases are well studied. In comparison, little is known about how recessive mutations, which occur throughout the gene, lead to disease. To address this issue, we reviewed the literature to map potentially functional domains within the ryanodine receptor type 1 (RyR1) and then analysed the nature and position of RYR1 mutations in 74 individuals with recessive disease, together with their clinical and histological phenotypes. Hypomorphic mutations, which abolish or markedly reduce RyR1 protein expression, were associated with more severe clinical phenotypes and with histological phenotypes other than CCD, such as multi-minicore disease, centronuclear myopathy and congenital fibre type disproportion. For non-hypomorphic mutations, CCD mutations were enriched in MH/CCD hotspot 3 and non-CCD core mutations in hotspot 2. Clustering of non-hypomorphic mutations in the triadin-binding domain (which lies within hotspot region 3) highlights abnormal triadin-binding as a potentially important disease mechanism. Non-hypomorphic mutations associated with ophthalmoplegia clustered in regions involved in ‘interdomain interactions’ which play roles in stabilising the closed conformation of the RyR1 channel. These results suggest that the variability seen in recessive RYR1 histological phenotypes may stem from differences in disease mechanism, determined in part by the location of non-hypomorphic mutations. Reduced overall RyR1 function, reduced stability of the closed channel conformation and abnormal triadin-RyR1 interactions are highlighted as potentially important disease mechanisms in various recessive RYR1-myopathies.