Figure 3

Histopathological features of Multi-minicore disease. NADH-TR (a–c) and cytochrome oxidase (COX) (d) stains, horizontal (a,c) and transverse (b,d) sections from a 3-year-old (a–b) and a 9-year-old girl (c–d) from different families. Predominance of darker staining type 1 fibres is prominent in both patients, whilst appearance of core lesions is widely variable, ranging from numerous small lesions of limited extent ("minicores") (a-b) to few multiple large lesions often extending throughout the entire fibre diameter ("multicores") (c, →) and occasionally affecting the same area in adjacent fibres (d, →). Whilst "minicores" are more frequently found in SEPN1-related MmD, the latter appearance is more typical of the RYR1-related form and indicates a possible histopathologic continuum with central core disease (CCD) due to mutations in the same gene.