RYR1 and congenital myopathy: This observation is consistent with (a) our previous observation for RAPSN that homozygosity for a null mutation can cause FADS/LMPS other mutation combinations with only a single null mutation can cause a milder phenotype, (b) that mice homozygous for a Ryr1 mutation die in the perinatal period with gross abnormalities of skeletal muscle [31] and (c) a history of foetal akinesia may be found with early onset autosomal recessive RYR1-related congenital myopathies [25].