Histological findings of patient 1 (A–G), patient 2 (H–J), patient 3 (L) and patient 5 (K). Muscle biopsies of all patients show moderate to severe vacuolar myopathy (H&E stain: A, E, K; semithin section, toluidin blue: H); the vacuolar change was most prominent in type 1 fibers (ATPase pH 9.4: B). There are few COX negative fibres (asterixis in C, F). Sudan black (D, G) or Oil-Red-O (J, L) stain shows lipid accumulation in type 1 fibres of all patients. Ragged red fibres were seen rarely (Gomori trichrome stain: I). There is no significant difference between the first and second biopsy specimens of patient 1 (A–D; E–G) Bars in A–L adjusted to 30μm.