Polyglucosan is an
amylopectin-like
polysaccharide associated with defective
glycogen metabolism and, unlike normal
glycogen, it is to some extent resistant to α-
amylase digestion. It also has a characteristic fibrillar appearance under the electron microscope.
Polyglucosan may aggregate into dense inclusions known as
polyglucosan bodies. Its accumulation can be found in various tissues to some degree in normal ageing, but it is also the hallmark of some diseases associated with defects in
glycogen metabolism. These diseases frequently involve both skeletal and cardiac muscle tissue, causing
myopathy with
muscle weakness and wasting, and
cardiomyopathy with
arrhythmia, conduction block, and
cardiac failure. Mutations in eight human genes are known to be associated with
polyglucosan storage involving muscle, namely GYG1, GBE1, RBCK1 (HOIL-1), PFKM, EPM2A, EPM2B (NHLRC1), PRDM8, and PRKAG2. There is also a common equine
polysaccharide storage
myopathy belonging to this group of diseases involving the GYS1 gene. The pathogenic mechanisms that cause the abnormal
glycogen accumulation appearing as
polyglucosan have been studied in some of these diseases. In most cases the pathogenesis is largely unknown. In this review, we summarize the
polyglucosan storage diseases from a clinical, morphological, and genetic standpoint. We also identify some important similarities and differences regarding the morphological appearance of
polyglucosan accumulation and discuss pathogenic pathways.