Genotype-Phenotype Correlations of Malignant Hyperthermia and Central Core Disease Mutations in the Central Region of the RYR1 Channel

ABSTRACT Type 1 ryanodine receptor (RYR1) is a Ca2+ release channel in the sarcoplasmic reticulum of skeletal muscle and is mutated in some muscle diseases, including malignant hyperthermia (MH) and central core disease (CCD). Over 200 mutations associated with these diseases have been identified, and most mutations accelerate Ca2+‐induced Ca2+ release (CICR), resulting in abnormal Ca2+ homeostasis in skeletal muscle. However, it remains largely unknown how specific mutations cause different phenotypes. In this study, we investigated the CICR activity of 14 mutations at 10 different positions in the central region of RYR1 (10 MH and four MH/CCD mutations) using a heterologous expression system in HEK293 cells. In live‐cell Ca2+ imaging, the mutant channels exhibited an enhanced sensitivity to caffeine, a reduced endoplasmic reticulum Ca2+ content, and an increased resting cytoplasmic Ca2+ level. The three parameters for CICR (Ca2+ sensitivity for activation, Ca2+ sensitivity for inactivation, and attainable maximum activity, i.e., gain) were obtained by [3H]ryanodine binding and fitting analysis. The mutant channels showed increased gain and Ca2+ sensitivity for activation in a site‐specific manner. Genotype–phenotype correlations were explained well by the near‐atomic structure of RYR1. Our data suggest that divergent CICR activity may cause various disease phenotypes by specific mutations. Mutations in type 1 ryanodine receptor (RYR1)/Ca2+ release channel cause muscle diseases, e.g., malignant hyperthermia and central core disease. Using live‐cell Ca2+ imaging and [3H]ryanodine binding assay, we evaluated Ca2+‐induced Ca2+ release (CICR) activity of 14 disease‐associated mutations in the central region of RYR1. Our results reveal divergent alterations of CICR activity by individual mutations. This novel evaluation system provides useful information about rank order of the disease severity and structure‐function relationship of the mutations in the RYR1 channel.