Dietary and Therapeutic Management of Glycogen Storage Disease Type IX: Analysis of a Systematic Review

Background/objectives: Glycogen storage disease type IX (GSD IX) is an inherited metabolic disorder characterized by marked clinical heterogeneity and variable severity. Dietary therapy is considered the cornerstone of management, but evidence on treatment strategies, efficacy, and safety remains limited. This study aimed to systematically synthesize available data on therapeutic approaches and clinical outcomes in GSD IX. Methods: A focused analysis of treatment-related data was conducted from a previously performed PRISMA-based systematic review. Clinical studies reporting treatment and follow-up data in genetically confirmed GSD IX patients were included. Results: Among 400 patients identified in the original review, 129 from 26 studies had treatment and follow-up data available. Dietary management combined with uncooked cornstarch (UCCS) was the most common approach (96.1%), with highly heterogeneous protocols. Hepatic manifestations improved in 59/129 (45.7%) of patients, and hypoglycemia in 45/129 (34.9%). Growth outcomes were variable, with catch-up growth in 14.0% and persistent impairment in 19.4%, although data were often missing. Muscle involvement was rarely assessed. No treatment-related adverse events were reported. However, disease-related complications were described, including liver cirrhosis, neurological involvement, osteopenia/osteoporosis, and two deaths in GSD IXa patients. Conclusions: Dietary therapy combined with UCCS remains the mainstay of treatment in GSD IX and is associated with improvement in key clinical domains. However, evidence is limited, heterogeneous, and largely based on small studies. Data on modified cornstarch formulations, such as Glycosade®, are scarce. Prospective studies and standardized treatment protocols are needed to support evidence-based management.