Rare Classroom: Adult Polyglucosan Body Disease

Welcome to the Rare Classroom, a new series from Patient Worthy. Rare Classroom is designed for the curious reader who wants to get informed on some of the rarest, most mysterious diseases and conditions. There are thousands of rare diseases out there, but only a very small number of them have viable treatments and regularly make the news. This series is an opportunity to learn the basics about some of the diseases that almost no one hears much about or that we otherwise haven’t been able to report on very often.

Eyes front and ears open. Class is now in session.

The rare disease that we will be learning about today is:

Adult Polyglucosan Body Disease

What is Adult Polyglucosan Body Disease?

  • Adult polyglucosan body disease (APBD) is a rare genetic disorder that affects glycogen storage
    • The genetic mutation usually results in the production of abnormal glycogen molecules, which are damaging to cells, particularly neurons
  • Symptoms tend to emerge after age 30
  • Diagnosis involves a neurological examination, evaluation of symptoms, and genetic tests
  • In a sense, adult polyglucosan body disease is an adult onset version of glycogen storage disease type IV, which is caused by the same genetic mutation
  • Prevalence of the disease is unknown, but some scientists estimate that there are over 12,000 cases in the US, with the majority being undiagnosed

How Do You Get It?

  • Adult polyglucosan body disease is a genetic disorder that is inherited in an autosomal recessive pattern
  • In most cases, the disorder is linked to loss of function mutations affecting the gene GBE1
    • In a small number of cases, no GBE1 mutation can be identified, suggesting that other mutations can also cause the disorder
    • These mutations typically result in a deficiency of the glycogen branching enzyme
  • This deficiency results in abnormal glycogen molecules, called polyglucosan bodies

What Are The Symptoms?

  • Often the first sign of the disorder is urinary incontinence
  • Other symptoms include:
    • Loss of sensation in the legs (peripheral neuropathy)
      • Consequently, many patients begin losing their ability to walk
    • Progressive muscle weakness
    • Progressive muscle stiffness
    • Cognitive decline leading to dementia occurs in about half of cases

How Is It Treated?

  • There is no cure for adult polyglucosan body disease
  • However, symptoms can be managed
    • Mobility aids and physical therapy can be used to assist with walking
    • Medications, counseling, and occupational therapy can help with dementia
  • Research into disease-modifying treatments is ongoing
  • Prognosis varies from case to case, and rates of progression are varied
  • Adult polyglucosan body disease appears to reduce life expectancy, but many patients can survive for many years and even decades with fairly good quality of life

Where Can I Learn More???

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