BACKGROUND

Mutations in the skeletal muscle ryanodine receptor gene may result in altered calcium release from sarcoplasmic reticulum stores, giving rise to malignant hyperthermia (MH). MH is a pharmacogenetic skeletal muscle disorder triggered by volatile anesthetics and depolarizing muscle relaxants. Diagnosis of MH is by in vitro contracture testing of quadriceps muscle. DNA analysis of causative mutations is limited by the large number of mutations that cosegregate with MH and the relatively few that have been biochemically characterized.

METHODS

DNA sequence analysis was used to screen the skeletal muscle ryanodine receptor gene in MH-susceptible individuals. A diagnostic test using real-time polymerase chain reaction was developed to detect the mutation in individuals diagnosed as MH susceptible by in vitro contracture testing. The functional relevance of this mutation was examined in Epstein-Barr virus-immortalized B-lymphoblastoid cells.

RESULTS

A novel ryanodine receptor mutation (cytosine 14997 thymine resulting in a histidine 4833 tyrosine substitution) was identified in pathology specimens from two patients with fatal MH reactions. B lymphocytes from patients with this mutation were approximately twofold more sensitive than MH-negative cells to activation with 4-chloro-m-cresol. The amount of Ca released from B lymphocytes of MH-susceptible patients was significantly greater than that released from cells of family members without this mutation. Haplotype analysis suggests that both families had a common ancestor.

CONCLUSIONS

DNA analysis to detect mutations which cosegregate with MH as well as biochemical assays on cultured lymphocytes obtained from blood can serve as useful diagnostic tools for MH susceptibility and genotype-phenotype correlations.