A 78-year-old Japanese male with late-onset PHKA1-associated distal myopathy: Case report and literature review

Understanding Glycogen Storage Disease Type IX: A Systematic Review with Clinical Focus-Why It Is Not Benign and Requires Vigilance

BACKGROUND/OBJECTIVES

Glycogen storage disease type IX (GSD IX) is a group of inherited metabolic disorders caused by phosphorylase kinase deficiency affecting the liver or muscle. Despite being relatively common among GSDs, GSD IX remains underexplored.

METHODS

A systematic review of GSD IX was conducted per PRISMA guidelines using SCOPUS and PubMed, registered with PROSPERO. Inclusion focused on human clinical studies published up to 31 December 2024.

RESULTS

A total of 400 patients with GSD IX were analyzed: 274 IXa (mean age at diagnosis 5.1 years), 72 IXc (mean age at diagnosis 4.9 years), 39 IXb (mean age at diagnosis 4.2 years), and 15 IXd (mean age at diagnosis 44.9 years). Hepatomegaly was commonly reported in types IXa, IXb, and especially IXc (91.7%), but was rare in IXd. Elevated transaminases were frequently observed in types IXa, IXb, and particularly IXc, while uncommon in IXd. Fasting hypoglycemia was occasionally observed in types IXa and IXb, more frequently in IXc (52.7%), and was not reported in IXd. Growth delay or short stature was observed in a substantial proportion of patients with types IXa (43.8%), IXb, and IXc, but was rare in IXd. Muscle involvement was prominent in IXd, with all patients showing elevated CPK (mean 1011 U/L). Neurological involvement was infrequently reported in types IXa and IXc.

CONCLUSIONS

This systematic review includes the most extensive clinical case history of GSD IX described in the literature. The clinical spectrum of GSD IX varies widely among subtypes, with IXc being the most aggressive. While liver forms are generally present in early childhood, muscle-type IXd shows delayed onset and milder symptoms, often leading to diagnostic delays. For diagnosis, it is essential not to underestimate key clinical features such as hepatic involvement and hypoglycemia in a child under 5 years of age. Other manifestations, including the as-yet unexplored systemic involvement of bone and kidney, remain insufficiently understood and require further investigation. Next-generation sequencing has improved diagnostic precision over traditional biopsy. Dietary management, including uncooked cornstarch, Glycosade®, and high-protein intake, remains the cornerstone of treatment. However, there is a paucity of well-designed, evidence-based studies to determine the most effective therapeutic approach. Despite its historically perceived benign course, the broad phenotypic variability of GSD IX, including progressive liver involvement and potential neurological complications, highlights its substantial clinical relevance and underscores the need for accurate diagnostic classification and long-term multidisciplinary follow-up.

Diagnosis of Inherited Metabolic Disease in Older Patients: A Systematic Literature Review

Inherited metabolic diseases (IMDs) are genetic disorders that disrupt biochemical processes in the human body, due to pathogenic variants in genes encoding enzymes or transporters. While IMDs are mostly diagnosed in infancy or childhood, there is an increasing number of diagnoses in adult patients. Delayed diagnosis, particularly in older patients, may reflect the diagnostic odyssey usually observed in rare diseases' patients and can result in complications and reduced quality of life for patients and their families. The aim of the study was to better characterize the diagnosis of IMDs in older patients (≥ 65 years). We conducted a systematic literature review (SLR) to examine the diagnosis and clinical presentation of IMDs in patients aged 65 and older. We searched databases like PubMed, Embase, and Lilacs for relevant studies from 1965 to 2023. A total of 260 articles were included, representing 293 patients with a median age of 69 years at diagnosis. From this SLR, 67 different diagnoses have been reported. The most frequently reported diseases were Fabry disease, alkaptonuria, Gaucher disease, mitochondrial disorders, and glycogen storage disease type V. Median diagnostic delay was 14.5 years with a wide range of 1-91 years. Musculoskeletal symptoms were the most frequently reported, followed by neurological and cardiovascular symptoms. Our findings underscore the importance of recognizing IMDs in older patients and the need for awareness among healthcare providers to improve diagnosis and patient care. Future guidelines and teaching programs should incorporate metabolic investigations for older patients presenting with symptoms suggestive of IMDs.