Examination of tissue biopsied from the sural nerve under a microscope can reveal the presence of polyglucosan bodies. There will also be white matter changes visible in a magnetic resonance imaging scans. Classification
Adult polyglucosan body disease is an orphan disease and a glycogen storage disorder that is caused by an inborn error of metabolism, that affects the central and peripheral nervous systems.The condition in newborns caused by the same mutations is called glycogen storage disease type IV. Prevention
APBD can only be prevented if parents undergo genetic screening to understand their risk of producing a child with the condition; if in vitro fertilization is used, then preimplantation genetic diagnosis can be done to identify fertilized eggs that do not carry two copies of mutated GBE1. Management
As of 2015 there was no cure for APDB, instead symptoms are managed. There are various approaches to managing neurogenic bladder dysfunction, physical therapy and mobility aids to help with walking, and dementia can be managed with occupational therapy, counseling and drugs. Presently a number of promising research initiatives are underway in universities and hospitals in the United States, Canada, and Israel. These studies are in need of funding but due to the small number of known cases both research funding and participation is small. It is estimated that there are upwards of 12,000 cases in the United States, most of which are undiagnosed.
Causes
APBD is an autosomal recessive disorder that is caused when a person inherits genes from both parents containing one or more loss-of-function mutations in the gene GBE1 which encodes for glycogen branching enzyme, also called 1,4-alpha-glucan-branching enzyme. Mechanism
The GBE1 gene provides instructions for making the glycogen branching enzyme. This enzyme is involved in the production of a complex sugar called glycogen, which is a major source of stored energy in the body. Most GBE1 gene mutations result in a shortage (deficiency) of the glycogen branching enzyme, which leads to the production of abnormal glycogen molecules. These abnormal glycogen molecules, called polyglucosan bodies, accumulate within cells and cause damage. Neurons appear to be particularly vulnerable to the accumulation of polyglucosan bodies in people with this disorder, leading to impaired neuronal function.Some mutations in the GBE1 gene that cause adult polyglucosan body disease do not result in a shortage of glycogen branching enzyme. In people with these mutations, the activity of this enzyme is normal. How mutations cause the disease in these individuals is unclear. Other people with adult polyglucosan body disease do not have identified mutations in the GBE1 gene. In these individuals, the cause of the disease is unknown. Diagnosis
Along with evaluation of the symptoms and a neurological examination, a diagnosis can be made based on genetic testing. Whether or not a person is making sufficient amounts of functional glycogen branching enzyme can be determined by taking a skin biopsy and testing for activity of the enzyme.