G.P.36

• DOI: 10.1016/j.nmd.2014.06.050
• Publication Date: 2014-09-03T00:06:32Z
• Authors: E. Rivas; R. Phadke; M. Ellis; D. Chambers; L. Feng; C. Sewry
• Keywords: Nemaline myopathy

The neonatal foetal myosin is a skeletal muscle foetal myosin isoform, that is present in muscle during foetal development, just after birth and in regenerating fibres in mature postnatal muscle in several pathological conditions. The aim of this study was to describe the expression pattern of neonatal myosin in normal muscle and muscle from patients with congenital myopathies (CM) in order to identify a potential disease specific marker of CM. We reviewed muscle biopsies from 43 patients with genetically confirmed CM (20 RYR1, 10 SEPN1, 10 ACTA1, 3 NEB) and 10 controls. We used the nMHC antibody as specific marker of neonatal heavy chain myosin isoform and Definiens Tissue Studio Solution for the digital analysis of the muscle to quantify the number, percentage and size of positive-nMHC fibres. We calculated the percentage of small nMHC-positive “pinpricks” fibres with less 5 μm of diameter in each group of patients. We confirmed the presence of a physiological co-expression of neonatal myosin in normal size-fibres during the first 3rd months of postnatal life, disappearing after this period. We found statistical significant differences in the percentage of nMHC-positive “pinpricks” fibres between controls and CM patients, when comparing either using morphological criteria (core or nemaline myopathy vs control) or genetic criteria (each gene vs control). We also identified higher percentage of pinpricks fibres in ACTA1 vs RYR1 patients and in biopsies with core lesions vs biopsies with normal histology or unspecific myopathic changes from RYR1/SEPN1 patients. Our findings strongly suggest that the presence of nMHC-positive “prinpricks” fibres in the biopsy could be a useful marker in the diagnostic pathological approach of CM.