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.
Outcomes
The rate of progression varies significantly from person to person.There is not good data on outcomes; it appears that APBD likely leads to earlier death, but people with APBD can live many years after diagnosis with relatively good quality of life. Epidemiology
The prevalence is unknown; about 70 cases had been reported in the medical literature as of 2016. As of 2016 the largest set of case studies included 50 people; about 70% of them were of Ashkenazic Jewish descent. Society and culture
A person with APBD named Gregory Weiss created a foundation, the Adult Polyglucosan Body Disease Research Foundation, to fund research into the disease and its management. Research directions
In 2015 the first transgenic mouse that appeared to be a useful model organism for studying APBD was published. References

 This article incorporates public domain material from Adult polyglucosan body disease. United States Department of Health and Human Services. == External links ==