The proband (III-1) and three of the four cousins (III-2, III-4, III-5) had Danon disease caused by a missense mutation, c.1150 G > C, leading to an amino acid change (p.Gly384Arg) in splice variant B (exon 9B) of the LAMP2 gene (reference sequence NM_013995.1; nomenclature according to http://www.hgvs.org/Mutnomen/). The gene discussed is LAMP2; the disease is Danon disease.