Danon disease: rare or unrecognized entity in the Czech Republic?

Danon disease is an X-linked lysosomal genetic disorder caused by mutation of one of the lysosomal associated membrane proteins Lamp2. Its main manifestation is hypertrophic cardiomyopathy, which dominates the clinical picture, less expressed myopathy, hepatopathy and neurologicsymptoms. It belongs to the group lysosomal disorders caused by mutation of noncatalytic proteins, the function of which is still not well understood. Consequences of these disorders are variable and differ from the classical lysosomal enzymopathies featured by intralysosomal accumulation of uncleaved enzyme substrates. Cell pathology of Lamp2 mutation is featured by altered macroautophagy which is increased but ineffective and by deficient chaperon mediate autophagy.

We applied diagnostic procedures relevant to recognize Lamp2 deficiency in endomyocardial biopsies together with a reliable screening procedure.

Endomyocardial biopsies and blood smears were used for detection of LAMP2 protein with a specific polyclonal antibody working in both unfixed and paraffin embedded samples.

The diagnosis was reached in one family by endomyocardial and skeletal muscle biopsies in a proband which displayed autophagic process and absence of LAMP2 protein either in situ or in cell lysates. Pathogenic mutation (new type) was defined by sequencing the responsible gene. Several affected members of the family were recognized additionally. Two of them are after successful heart transplantation. The findings in biopsies were correlated with findings in the blood smears, which showed absence of detectable Lamp2 in lysosomal, and lysosome related organelles in white blood cells.

Absence of Lamp2 protein should become part of differential diagnosis of cardiomyopathies, especially those types displaying signs of lysosomal affection. Screening procedure based on detection of Lamp2 protein in peripheral blood smears is highly recommended and is going to be applied in the future.