A family with Danon disease caused by a splice site mutation in LAMP2 that generates a truncated protein.

The mutation did not result in loss of mRNA exons; rather, a 6-nucleotide (two-codon) insertion, where the latter was a stop codon, leading to early termination of LAMP2 protein translation. The resulting truncated protein lacks an important transmembrane domain, which will impair lysosome/autophagosome fusion, damage autophagy function, and result in the clinical manifestations of Danon disease.