Cardiac magnetic resonance in glycogen storage disease IIIa: a nationwide study

Background/Introduction Glycogen storage disease type IIIa (GSDIIIa) is a rare autosomal recessive disorder in which myocardial involvement classically presents as left ventricular hypertrophy (LVH). Cardiac magnetic resonance (CMR) permits superior assessment of myocardial morphology and tissue characterization compared to transthoracic echocardiography (TTE), but systematic CMR data in GSDIIIa are limited. Purpose This study aimed to characterize myocardial structure, function and tissue properties in patients with genetically confirmed GSDIIIa using standardized 1.5T multiparametric CMR and to compare CMR detection and grading of LVH with TTE. Methods We performed a multicentre cross-sectional study of 13 of the 15 patients diagnosed with GSDIIIa in Spain (6 adults, 7 children) from 10 tertiary hospitals. All subjects underwent standardized CMR (cine, T2-STIR, native/post-contrast T1, T2, extracellular volume, late gadolinium enhancement) performed at a University Hospital and analysed blinded to prior TTE. Twelve patients had prior TTE for head-to-head concordance analyses. Primary outcome: prevalence and pattern of cardiac involvement on CMR; secondary: adult vs paediatric comparisons and CMR–TTE agreement. Results CMR identified LVH in 8/13 patients (61.5%): 100% of adults vs 28.6% of children (p=0.016). Pattern was predominantly concentric with frequent asymmetry/septal predominance; adults showed greater maximal wall thickness and higher LV mass index (median LV mass index adults 72.5 vs children 42 g/m²; p=0.035). LGE was present in 4/6 adults (66.7%) and in none of the children (p=0.037). Post-contrast T1 mapping was abnormal in 12/13 patients (92.3%), while native T1 elevation was less frequent (23.1%). TTE detected LVH in 5/12 (41.7%); inter-modality agreement for LVH detection was limited (Cohen’s κ=0.676, p=0.013) and agreement for severity and regional distribution was suboptimal. TTE tended to overestimate free-wall thickness and LV mass index while underdetecting asymmetric/segmental hypertrophy. Conclusions In this nationwide cohort, LVH and myocardial tissue abnormalities are common in GSDIIIa. LVH is predominantly concentric and asymmetrical, affecting all adult patients. CMR appears to outperform TTE in detecting and grading LVH, while also enabling unique tissue characterization. Ideally, incorporating CMR into routine follow-ups alongside CRF assessment and individualised surveillance intervals may enhance clinical monitoring and disease management in these patients.