Myopathy, Myofibrillar, Zasp-Related

A rare genetic non-dystrophic myofibrillar myopathy disorder with characteristics of late-adult onset of distal and/or proximal limb muscle weakness with initial involvement of posterior lower leg muscles, medial gastrocnemius and soleus. Patients present with ankle weakness followed by weakness of finger and wrist extensors and later of the proximal muscles. Ambulation is usually preserved. Late-onset associated cardiomyopathy and/or neuropathy has been reported in a minority of cases. Caused by heterozygous mutation in the ZASP gene on chromosome 10.