Varying clinical phenotypes of Danon disease within a large family unit: A case series

Danon disease is a rare, X-linked genetic disorder. We report a case of a 17-year-old male with learning difficulties who presented due to advanced heart failure and the subsequent discovery of this highly penetrant but variable disease among a family unit. Cascade screening was offered to all siblings and parents that demonstrated great phenotypic heterogeneity among family members, most pronounced among female siblings. We highlight the importance of genetic testing to ultimately clinch the diagnosis of Danon disease, but how cost and reimbursement remain a major barrier in ensuring genetic testing is performed more routinely in South-East Asia, and more efforts are needed to improve this. Our case also highlights the utility of echocardiographic strain imaging in detecting subclinical disease as part of the cascade screening process. In view of the myriads of presentations, a high index of suspicion, thorough multi-systemic evaluation at baseline and robust follow-up care following genetic testing and cascade screening are all pivotal in the diagnosis and care of the condition.