Danon disease: Two case reports and literature review.

RATIONALE: Danon disease (DD) is an X-linked lysosomal storage disorder caused by LAMP2 variants, with males presenting more severe phenotypes. However, evidence for genotype-phenotype correlation remains limited. This study reports 2 male DD patients with distinct LAMP2 mutations to clarify mutation-specific prognostic differences.

PATIENT CONCERNS: A 15-year-old male: chest tightness and palpitations, creatine kinase (CK) 3867 U/L, and hypertrophic cardiomyopathy. A 12-year-old male: exertional dyspnea and syncope, left ventricular ejection fraction 36%, left ventricular thrombus, and CK 5210 U/L.

DIAGNOSES: Both were diagnosed with DD via genetic testing: the 15-year-old had a LAMP2 IVS6 + 1G > T splice mutation, and the 12-year-old carried a LAMP2 exon 1 deletion.

INTERVENTIONS: The 15-year-old underwent heart transplantation followed by immunosuppressive therapy. The 12-year-old received only symptomatic treatment without transplantation.

OUTCOMES: The 15-year-old had normal cardiac function and normalized CK levels during 24-month posttransplant follow-up. The 12-year-old died of heart failure 8 months after diagnosis.

LESSONS: LAMP2 mutation types correlate with DD severity. Heart transplantation improves prognosis in severe cases, emphasizing the importance of early diagnosis and intervention.