Mild form of Danon disease: two case reports

Danon disease is typically lethal by the mid-twenties in male patients due to cardiomyopathy. This report aims to describe two unrelated male patients showing mild manifestations of the disease. A 39-year-old man presented with a 10-year history of elevated serum creatine kinase levels with slowly progressive muscle weakness. Muscle pathology showed autophagic vacuoles with sarcolemmal features. Genetic testing revealed a hemizygous mutation in exon 9b, an alternatively spliced exon, of lysosome-associated membrane protein-2 (LAMP-2) (c.1097_1098delAA). Cardiac testing showed asymptomatic mild left ventricular hypertrophy. He had borderline intelligence. Early stage of retinopathy was detected. Another male patient, currently 53-year-old, had asymptomatic supraventricular extrasystole and muscle weakness but no intellectual disability, harboring the same mutation. He also had retinopathy. The present patients commonly carry a mutation in exon 9b of LAMP-2, suggesting that mutations in the exon are associated with a mild form of Danon disease.