Is It Time to Take the Heat Out of the Problem?

Fig. 47.1

(a) Muscle MRI showed no abnormalities. (b) Cytochrome c oxidase (COX) staining showed a preserved two-fibre pattern. (c) Electron microscopy showed several fibres with one or more small mini-cores (arrows). (d) Larger core-like areas (arrows) of myofibrillar disruption with Z-line streaming

Muscle biopsy

Staining for glycogen, lipid, acid phosphatase, phosphorylase and adenylate deaminase was normal. Cytochrome c oxidase (COX) staining showed a preserved two-fibre pattern (Fig. 47.1b). Poorly-defined areas of central pallor were seen in both dark (type I) and light (type II) staining fibres. Electron microscopy showed several fibres with one or more small mini-cores (Fig. 47.1c, arrows) and larger core-like areas (Fig. 47.1d, arrows) of myofibrillar disruption with Z-line streaming.

Mitochondrial respiratory chain enzyme activities in muscle were within normal limits.

Genetic testing

Genetic testing for common mitochondrial DNA point mutations and large scale rearrangements was negative. Sequence analysis of the RYR1 gene showed a heterozygous missense mutation (p.Lys1393Arg) in exon 28, previously reported as pathogenic in a patient with malignant hyperthermia (MH). A sequence variant of uncertain significance was also detected. His father carried both variants.

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