GNE Myopathy

Clinical characteristics: GNE myopathy is a slowly progressive muscle disease that typically presents between age 20 and 40 years with bilateral foot drop caused by anterior tibialis weakness. Lower-extremity muscle involvement progresses from the anterior to the posterior compartment of the lower leg, followed by hamstrings, then hip girdle muscles, with relative sparing of the quadriceps. A wheelchair may be needed about ten to 20 years after the onset of manifestations. The upper extremities, which may be affected within five to ten years of disease onset, do not necessarily follow a distal-to-proximal progression. In advanced stages, neck and core muscles can become affected.

Diagnosis/testing: The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing.

Management: Treatment of manifestations: Evaluation and management are often by a multidisciplinary team that includes neuromuscular specialists, physiatrists, and physical and occupational therapists to address issues secondary to muscle weakness, including the use of assistive ambulatory devices (e.g., ankle-foot orthoses, cane, walker, wheelchair, or powerchair). Adaptive devices to support fine motor function and activities of daily living are needed in advanced stages of the disease. Recommended evaluations also include baseline echocardiogram and pulmonary function tests in nonambulatory individuals, with management by pulmonologists as clinically indicated.

Surveillance: Follow up at least annually by neuromuscular specialists, physiatrists, and physical and occupational therapists to evaluate disease progression and address muscle strength, mobility, function, and activities of daily living; by pulmonologists to monitor respiratory muscle function in patients with advanced disease.

Agents/circumstances to avoid: Cautious use of medications/drugs with potential myotoxicity (e.g., colchicine and statins); avoidance of weight-lifting and repetitive activities that cause muscle pain.

Genetic counseling: GNE myopathy is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for a GNE pathogenic variant, each sib of an affected individual has at conception a 25% chance of inheriting both pathogenic variants and being affected, a 50% chance of inheriting one pathogenic variant and being an unaffected carrier, and a 25% chance of inheriting both normal alleles. When the GNE pathogenic variants have been identified in an affected family member, molecular genetic carrier testing of at-risk relatives, prenatal testing for pregnancies at increased risk, and preimplantation genetic testing are possible.