Chemical Pathology

Polyglucosan bodies are composed principally of glucose polymers, with a small but variable component of phosphate and sulfate groups and less than 5% protein.

Glycogen branching enzyme activity can be either deficient or normal in patients with APBD. Most patients of Ashkenazi Jewish ethnic background have a deficiency of this enzyme, but so do some patients of other ethnic background. It is likely that APBD is genetically heterogeneous and that the disease may have more than one biochemical etiology resulting in similar phenotypes.

Polyglucosan bodies are composed principally of glucose polymers and occur in various conditions. The polyglucosan bodies of APBD greatly resemble and may be identical to corpora amylacea, which accumulate in the CNS with normal aging, Lafora bodies present in Lafora body disease, and Bielschowsky bodies. Corpora amylacea are seen in a characteristic topography in the healthy nervous system with aging. They develop in astrocytic processes and are mainly distributed subpially, subependymally, and perivas-cularly, although intra-axonal corpora amylacea may also occur. Lafora bodies are found in association with Lafora body disease, a progressive myoclonus epilepsy. Lafora bodies appear in neuronal perikarya and processes, especially in the cerebral cortex, thalamus, globus pallidus, substantia nigra, and dentate nucleus. Bielschowsky bodies are found in the peri-karya and processes of neurons. They differ from Lafora bodies in their much more limited distribution and pleiomorphic appearance. They are usually only found in the external segment of the globus pal-lidus. They may represent a variant of Lafora body disease. Besides these specific conditions, polyglu-cosan bodies may be seen as a nonspecific phenomenon within the CNS in olivopontocerebellar atrophy and amyotrophic lateral sclerosis, and in peripheral nerves in exceptional cases of diabetes mellitus, motor neuropathy, familial spastic paraparesis, and spin-ocerebellar syndromes, as well as in normal aging.

It is unclear how the polyglucosan bodies arise in APBD. They may represent systemic glycogen storage due to deficiency of glycogen branching enzyme or another enzyme related to glycogen metabolism. The relationship with the CNS structural damage and dysfunction is unclear. It is conceivable that there is an underlying metabolic defect, which damages neurons by itself and as an independent side effect leads to the production of polyglucosan bodies. The growth of polyglucosan bodies within axons could also become deleterious for those axons, at the very least impeding or blocking axonal flow.

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