To investigate the characteristic of pathology in Chinese patients with Nonaka myopathy.

Thirteen patients (7 males and 6 females) diagnosed with Nonaka myopathy in our laboratory from January 2002 to March 2011 were included in this study. Their mean age was 39.5 years old and the mean duration of illness was 4.15 years. The most common symptoms were weakness of raising feet with sparing of quadriceps femoris muscles in the early stage of disease. One patient presented the initial symptoms of upper limb weakness. Muscles biopsies were obtained from all these 13 patients. Histology study including immunohistochemical (IHC) staining with antibody against amyloid β, phosphorylated tau protein, ubiquitin, glucose-regulated protein of molecular weight 78 000（GRP78）, calnexin, caspase-12 and Bax were performed. Skeletal muscle samples from 3 chronic fatigue syndrome patients, 2 myofibrillar myopathy patients were used for control in the IHC staining. All coding exons of uridinediphospho-N-acetylglucosamine 2-epimerase gene were directly sequenced in genomic DNA from these patients.

The main pathological changes of tibialis anterior muscle in 12 cases were muscle dystrophy with rimmed vacuoles. The rimmed vacuoles were positive for anti-β-amyloid, tau protein and ubiquitin in IHC studies. In the atrophy fibers, IHC showed the increased expression of endoplasmic reticulum stress related proteins GRP78 and calnexin, and apoptosis proteins of caspase-12 and Bax.

There is accumulation of abnormal proteins in muscle fibers in Chinese patients with Nonaka myopahty. These proteins may stimulate endoplasmic reticulum stress and apoptosis, which may be a mechanism responsible for muscle damage.

Distal myopathies; Muscle;  skeletal; Amyloid beta-protein; Endoplasmic reticulum; Apoptosis