Myofibrillar myopathies may be diagnosed in childhood but most often appear after 40 years of age.
A diagnosis is made based on clinical findings, electromyography, nerve conduction studies and muscle biopsy. Molecular genetic testing for the DES, CRYAB, MYOT, ZASP, BAG3, DNAJB6, TTN and FLNC genes is available to confirm the diagnosis.