Functional Characterization of a Central Core Disease RyR1 Mutation (p.Y4864H) Associated with Quantitative Defect in RyR1 Protein.

BACKGROUND

Central Core Disease (CCD) is a congenital myopathy often resulting from a mutation in RYR1 gene. Mutations in RyR1 can increase or decrease channel activity, or induce a reduction in the amount of protein. The consequences of a single mutation are sometimes multiple and the analysis of the functional effects is complex.

OBJECTIVE

The consequences of the p.Y4864H mutation identified in a CCD patient have been studied regarding both RyR1 function and amount.

METHODS

The amount of RyR1 in human and mouse muscles was evaluated using qRT-PCR and quantitative Western blot, and calcium release was studied using calcium imaging on primary cultures. The results were compared between human and mouse.

RESULTS

The p.Y4864H mutation induced an alteration of calcium release, and in addition was associated to a reduction in the amount of RyR1 in the patient's muscle. This suggests two possible pathophysiological mechanisms: the alteration of calcium release could result from a modification of the channel properties of RyR1 or from a RyR1 reduction. In order to discriminate between the two hypotheses, we used the heterozygous RyR1 knockout (RyR1+/-) mouse model showing a comparable RyR1 protein reduction. No reduction in calcium release was observed in primary muscle culture from these mice, and no muscle weakness was measured.

CONCLUSIONS

Because the reduction in the amount of RyR1 protein has no functional consequences in the murine model, the muscle weakness observed in the patient is most likely the result of a modification of the calcium channel function of RyR1 due to the p.Y4864H mutation.