Danon disease presenting with atypical non-septal sparing LGE on cardiac MRI: a case report.

Background: Danon disease is a rare genetic disorder that primarily impacts cardiac muscle, skeletal muscle, and the central nervous system. It is frequently undiagnosed in children because the characteristic cardiac symptoms are not yet apparent. Case summary: This case represents the youngest reported patient with a novel lysosome-associated membrane protein-2 variant, presenting with unexplained elevation of cardiac biomarkers, electrical abnormalities, and septal-predominant LGE on CMR, notably without left ventricular hypertrophy or dilation. Ultimately, the diagnosis of Danon disease was confirmed through genetic sequencing. Discussion: This case demonstrates that Danon disease can manifest in young patients with a specific CMR pattern-even in the absence of classic structural changes such as left ventricular hypertrophy. Therefore, clinicians should include Danon disease in the differential diagnosis for paediatric patients presenting with a combination of unexplained elevated biomarkers, electrical abnormalities, and distinctive LGE. Early genetic testing is critical in such scenarios to confirm or exclude the diagnosis.