Most of the initial testing that came out negative was performed by an external commercial laboratory using Sanger sequencing and a panel with the following 11 genes: MYH7, MYBPC3, MYL2, MYL3, TNNT2, TPM1, ACTC, TNNI3, CSRP3, TCAP, and PLN. The test did not include genes for metabolic HCM in children, such as LAMP2 for Danon’s disease, PRKAG2 etc., and produced some unreliable results for which we have received no explanation. The gene discussed is CSRP3; the disease is Danon disease.