BackgroundRYR1 mutations are typically associated with core myopathies and are the most common overall cause of congenital myopathy. Dominant mutations are most often associated with central core disease and malignant hyperthermia, and genotype-phenotype patterns have emerged from the study of these mutations that have contributed to the understanding of disease pathogenesis. The recent availability of genetic testing for the entire RYR1 coding sequence has led to a dramatic expansion in the identification of recessive mutations in core myopathies and other congenital myopathies. To date, no clear patterns have been identified in these recessive mutations, though no systematic examination has yet been performed.MethodsIn this study, we investigated genotype-phenotype correlations in a large combined cohort of unpublished (n = 14) and previously reported (n = 92) recessive RYR1 cases.ResultsOverall examination of this cohort revealed nearly 50% of cases to be non-core myopathy related. Our most significant finding was that hypomorphic mutations (mutations expected to diminish RyR1 expression) were enriched in patients with severe clinical phenotypes. We also determined that hypomorphic mutations were more likely to be encountered in non-central core myopathies. With analysis of the location of non-hypomorphic mutations, we found that missense mutations were generally enriched in the MH/CCD hotspots and specifically enriched in the selectivity filter of the channel pore.ConclusionsThese results support a hypothesis that loss of protein function is a key predictive disease parameter. In addition, they suggest that decreased RyR1 expression may dictate non-core related pathology though, data on protein expression was limited and should be confirmed in a larger cohort. Lastly, the results implicate abnormal ion conductance through the channel pore in the pathogenesis in recessive core myopathies. Overall, our findings represent a comprehensive analysis of genotype-phenotype associations in recessive RYR1-myopathies.

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The reactions of Cr(VI/V/IV) with a model thiolato complex [Zn(SR)2] (RSH = O-ethyl-l-cysteine), resembling a tetrahedral (2S,2N) Zn(II) binding site in zinc-finger proteins, have been studied in comparison with those of the free ligand. The stability of [Zn(SR)2] in aqueous solutions with pH 6−11 (25 °C, Ar-saturated) has been established by CD spectroscopy. Stoichiometries and products of the reactions of [Zn(SR)2] or RSH with [CrVIO4]2- or [CrVO(ehba)2]- (ehba = 2-ethyl-2-hydroxybutanoato(2−)) at pH 6.5−8.5 (25 °C, Ar) were studied by UV−vis and CD spectroscopies and by electrospray mass spectrometry. Disulfide (RSSR) is the only detectable oxidation product of both [Zn(SR)2] and RSH. In the case of RSH, relatively stable Cr(III) complexes, [CrIII(SR)3]0 and [CrIII(SR)2]+, are also formed and subsequently hydrolyzed to [CrIII(Cys)2]-. This is the first observation of a Cr(III)-facilitated hydrolysis of a cysteine ester. Ascorbate promotes the oxidation of [Zn(SR)2] by [CrVIO4]2-; this reaction leads to formation of RSSR and of the Cr(III)−thiolato complexes. Kinetics of the reactions of [Zn(SR)2] or RSH with [CrVIO4]2-, [CrVO(ehba)2]-, or [CrIVO(qa)(qaH)]- (qa = quinato(2−) = (1R,3R,4R,5R)-1,3,4,5-tetrahydroxycyclohexanecarboxylato(2−)) at pH 7.40 (25 °C, Ar) were studied by conventional and stopped-flow UV−vis spectrophotometry and by global kinetic analysis. Complexes of Cr(V) and Cr(IV) rapidly react with both the reductants, and reactions of Cr(V) pass through the Cr(IV) intermediates. By contrast with the reaction with RSH, the reaction of [CrVO(ehba)2]- with [Zn(SR)2] is not accompanied by a significant O2 consumption (measured by an oxygen electrode), suggesting the ability of [Zn(SR)2] to inhibit free radical reactions, similar to that of zinc metallothioneins. The mechanism of [Zn(SR)2] oxidation by Cr(VI/V/IV), including intramolecular formation of a disulfide bond, has been proposed. Implications of the results to the Cr(VI)-induced carcinogenesis and to the biological activity of Cr(III) are discussed.