Danon disease is a rare X-linked dominant disease, caused by mutations in the LAMP2 gene located at Xq24-q25.[10] At least 110 different mutations in the LAMP2 gene have been detected, with the c.926gG>A mutation (causing exon 7 skipping) being the most common.[7] The p.Gly221Ilefs∗19 mutation in the present patient had not been previously reported, suggesting it is a rare phenotype. The gene discussed is LAMP2; the disease is X-linked dominant disease.