Danon disease (DD) is a rare glycogen storage disorder with mainly cardiac, neuromuscular, and intellectual involvement, secondary to systemic lysosome-associated membrane protein-2 (Lamp-2) deficiency due to loss-of-function mutations in I LAMP2 i . Successful XCI pattern-disease severity correlations have been observed in DD females,3,4 while discordances are assumed as unrelated or tissue specific.5 In our significantly young patient, inconclusive, nonskewed 57:43 and 49:51 patterns of inactivation were serially obtained in blood and heart samples, respectively. Alu-mediated Xq24 deletion encompassing CUL4B, LAMP2, TMEM255A, and ZBTB33 genes causes Danon disease in a female patient. [Extracted from the article]