The involvement of acid hydrolases in myopathies

In hamsters, the specific activities of acid phosphatase and beta-glucuronidase are much greater in homogenates of dystrophic muscle than in homogenates of normal muscle because, it is argued in this paper, dystrophic muscles concentrate such enzymes within themselves, in contrast to normal muscles which do not, or only very little. Both enzymes are first apparent histochemically (using the appropriate naphthol AS-BI substrates) in the atrophic type I fibres of, for example, 3--4 weeks-old dystrophic hamsters, at which age type II fibres (in the Johnson & Pearse nomenclature) contain neither enzyme and a myopathy is undetectable by standard clinical criteria. We have been unable to find out where the enzymes originate from, or in or on which organelle in dystrophic muscle they are localised; the histochemical, organelle fractionation, isoelectric focussing and electron microscopic evidence on these points is conflicting. On balance it seems that the acid hydrolases are synthesised by the dystrophic muscle fibres themselves, rather than being derived from discharged macrophage granules as is more commonly believed. But whatever their origin, a histochemical test for acid hydrolases should be useful, it is concluded, for diagnosing the preclinical phase of myopathies in children.