Glycogen storage disease due to glycogen branching enzyme deficiency, adult neuromuscular form

Glycogen storage disease due to glycogen branching enzyme (GBE) deficiency, adult neuromuscular form, is a rare subtype of glycogen storage disease type IV (GSD IV), also known as Andersen disease or amylopectinosis. It is caused by mutations in the GBE1 gene, which encodes the glycogen branching enzyme responsible for creating branch points in the glycogen molecule. When this enzyme is deficient, an abnormal, poorly soluble glycogen (polyglucosan) accumulates in tissues, particularly in the nervous system and skeletal muscle in this adult-onset form. The adult neuromuscular form typically presents in adulthood and primarily affects the peripheral and central nervous systems as well as skeletal muscles. Key clinical features include progressive upper and lower motor neuron dysfunction, peripheral neuropathy, neurogenic bladder, and progressive skeletal myopathy with proximal and distal muscle weakness. Patients may also develop sensory neuropathy and, in some cases, cognitive decline or pyramidal tract signs. Polyglucosan body accumulation can be found in nerve biopsies. This form overlaps clinically with adult polyglucosan body disease (APBD), which is considered part of the same disease spectrum. There is currently no curative treatment for this condition. Management is supportive and symptomatic, focusing on physical therapy, mobility aids, management of neurogenic bladder, and addressing progressive neurological deficits. Multidisciplinary care involving neurologists, rehabilitation specialists, and urologists is recommended. Research into potential therapies, including gene therapy and substrate reduction strategies, is ongoing but no disease-modifying treatments are yet approved.

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