PCC patients, compared to controls, had a higher percentage of angulated fibres (median [IQR] 0.43 [0.00–3.20] vs. 0.00 [0.00–0.00]; p < 0.001), small, rounded fibres (0.21 [0.00–1.20] vs. 0.00 [0.00–0.00]; p < 0.001) and fibres expressing fetal myosin (0.26 [0.00–1.15] vs. 0.00 [0.00–0.17]; p = 0.015). The gene discussed is MYH14; the disease is adrenal gland pheochromocytoma.