Nonaka distal myopathy - also called GNE myopathy - is a rare genetic disorder widespread especially in Japan. Causes progressive loss of muscle strength and manifests itself around the age of 30. For the moment there are no definitive treatments.
The first symptom consists in weakness in the hands and feet, which spreads to the calves and arms. As the disease progresses, it also affects the rest of the legs and shoulders. The cardiac, pharyngeal and ocular muscles that continue to function are usually spared. Respiratory muscles are involved only in the later stages of the disease.
The disease is caused by an anomaly in the GNE gene, which codes for the enzyme responsible for the production of sialic acid. The mutation causes a decrease in enzyme levels by 30% -60%. The result is a reduction of the sialylation of glycoproteins and glycolipids, with consequent reduction of proteins. The muscles therefore remain without the bricks needed to develop and function properly.
The diagnosis of Nonaka distal myopathy starts from the observation of the "falling foot". Then the doctors check for a possible history in the family, which could give rise to a genetic predisposition. In this case, we proceed with a muscle biopsy, which serves to identify changes in the muscle fibers. In fact, the absence of proteins causes entire empty areas. Genetic testing is usually used to confirm the diagnosis.
The disease forces patients on a wheelchair within 15 to 20 years. To date there are no effective therapies and symptoms can only be treated. Sialic acid supplements can help and some genetic therapies are being studied.