GNE myopathy

Overview

GNE myopathy is a rare genetic condition causing progressive muscle weakness and wasting, usually beginning in the late teens to 40s and starting in the lower legs, where it causes foot drop and difficulty walking before spreading to other muscles over time. It belongs to the distal myopathy group and is also known by several older names — Nonaka myopathy, distal myopathy with rimmed vacuoles, quadriceps-sparing myopathy, and hereditary inclusion body myopathy type 2.

Symptoms

Weakness usually starts in the lower legs, and foot drop is often the first noticeable symptom, leading to an unsteady gait and a higher risk of falls; walking on the heels, climbing stairs and getting up from the floor become progressively harder. How quickly this happens varies a great deal, even within the same family.

Over time, weakness can spread to the hands and shoulders, making fine tasks like gripping and using buttons harder, and eventually to the hips and thighs — though, distinctively, the quadriceps (front-of-thigh) muscles are usually spared even as everything around them weakens. Some people develop weakness in the torso and neck, affecting posture and spinal curvature. In advanced stages, a wheelchair (power-assisted, or a riser-recliner chair for support) can help maintain independence. Unlike many muscle conditions, GNE myopathy doesn't typically affect the heart, lungs, or speech and swallowing muscles, though cardiac rhythm changes and some respiratory weakness have occasionally been reported.

Inheritance and cause

GNE myopathy is caused by changes in the GNE gene, which normally provides instructions for an enzyme needed to produce sialic acid — a molecule important for muscle function. When the gene doesn't work properly, too little sialic acid is made, and muscles gradually weaken and waste; the precise mechanism linking the two isn't yet fully understood.

It's inherited in an autosomal recessive pattern — a changed copy is needed from both parents, who are themselves unaffected carriers — and sometimes there's no known family history at all. GNE myopathy can affect anyone but is more common among people of South Asian, Middle Eastern, and Japanese ancestry.

Getting a diagnosis

A GP can refer to a neurologist. An initial diagnosis of distal myopathy rests on the clinical picture, family history, a physical exam, a creatine kinase blood test and EMG, with a leg-muscle MRI helping confirm it, since GNE myopathy tends to affect muscles in a recognisable pattern. Genetic testing then looks specifically at the GNE gene; a muscle biopsy is sometimes needed too, and can show rimmed vacuoles (protein-containing structures) and muscle wasting under the microscope, though it isn't always necessary if genetic testing gives a clear answer.

Management and outlook

A multidisciplinary team is important for managing symptoms and wellbeing, usually led by a neurologist, and care varies with how severe symptoms are. There's currently no treatment that changes the underlying disease course, though research — including gene therapy approaches and sialic acid supplementation — is ongoing; there isn't yet clear evidence that supplements help.

Staying active, with a physiotherapist's guidance, helps maintain strength and flexibility — regular stretching and moderate low-impact exercise (swimming, walking, cycling) are commonly recommended, ideally building up gradually and pacing with rest, particularly early on or when fatigue is an issue. As mobility changes, walking aids help; wheelchair users face a higher risk of osteoporosis-related fractures and joint contractures, so physiotherapists can advise on wheelchair-based exercise and posture to reduce that risk.

Occupational therapy provides practical equipment and home adaptations, and orthotic devices — splints, insoles, ankle or leg braces — help manage foot drop and reduce fall risk. An annual flu vaccine is recommended for everyone, with pneumococcal and COVID-19 vaccines advised for anyone with respiratory weakness.