Natural history study of hepatic glycogen storage disease type IV and comparison to Gbe1ys/ys model

BACKGROUND. Glycogen storage disease type IV (GSD IV) is an ultrarare autosomal recessive disorder that causes deficiency of functional glycogen branching enzyme and formation of abnormally structured glycogen termed polyglucosan. GSD IV has traditionally been categorized based on primary hepatic or neuromuscular involvement, with hepatic GSD IV subclassified as discrete subtypes: classic (progressive) and nonprogressive. METHODS. To better understand the progression of liver disease in GSD IV, we present clinical and histopathology data from 23 patients from around the world and characterized the liver involvement in the Gbe1 ys/ys knockin mouse model. RESULTS. We propose an alternative to the established subtype -based terminology for characterizing liver disease in GSD IV and recognize 3 tiers of disease severity: (i) "severe progressive" liver disease, (ii) "intermediate progressive" liver disease, and (iii) "attenuated" liver disease. Analysis of liver pathology revealed that risk for liver failure cannot be predicted from liver biopsy findings alone in individuals affected by GSD IV. Moreover, analysis of postmortem liver pathology from an individual who died over 40 years after being diagnosed with nonprogressive hepatic GSD IV in childhood verified that liver fibrosis did not regress. Last, characterization of the liver involvement in a mouse model known to recapitulate the adult -onset neurodegenerative form of GSD IV ( Gbe1 ys/ys mouse model) demonstrated hepatic disease. CONCLUSION. Our findings challenge the established subtype -based view of GSD IV and suggest that liver disease severity among patients with GSD IV represents a disease continuum.