New deletion in LAMP2 causing familial Danon disease: effect of X-chromosome inactivation

Danon disease (DD), a rare X-linked genetic illness with a poor prognosis, is caused by a mutation in the lysosome-associated membrane protein 2 gene (LAMP2). Three main clinical features of this pathology are cardiomyopathy, skeletal myopathy, and mental retardation. Most Danon disease mutations create premature stop codons resulting in the decrease or absence of LAMP2 protein. The present case reports the frameshift variant c.190_191delАС in the LAMP2 in the family with sudden cardiac death history and three members with cardiomyopathy. The presenting phenotype in a female proband with c.190_191delАС was isolated dilated cardiomyopathy in her thirties whereas in two males, DD presented as hypertrophic cardiomyopathy and mild skeletal myopathy since childhood. To examine the contribution of X-inactivation to cardiomyopathy onset we estimated the X-inactivation status in the heart tissue of the affected female. We observed the random pattern (66:34) with the proportion of cardiomyocytes expressing healthy LAMP2 allele reduced to 34%. Deletion c.190_191delАС has led to a complete loss of function LAMP2 due to a single copy of this gene in males. In a woman, cardiomyopathy developed because of both the LAMP2 mutation and a decrease in the expression of a healthy allele in the heart. Based on the strong association of truncating LAMP2 mutations with DD and phenotypes in affected members, the variant c.190_191delАС was classified as pathogenic.