Subsequently, further clinical evaluations showing muscle weakness and mild intellectual disability confirmed the diagnosis of Danon disease.<h4>Conclusions</h4>This report highlights the role of genetic testing in the rapid diagnosis of Danon disease, underscoring the need to routinely consider the inclusion of LAMP2 gene in the genetic screening for HCM, since an early diagnosis of Danon disease in patients with a phenotype mimicking HCM is essential to plan appropriate treatment, ie cardiac transplantation. The gene discussed is LAMP2; the disease is Intellectual disability.