CYP21A1P and chronic granulomatous disease: In addition to CGD, several other diseases are caused by the chimeric products of the crossover between a gene and its pseudogenes, such as congenital adrenal hyperplasia, caused by the chimeric genes CYP21A1P/CYP21A2 [28], and Gaucher disease, caused by a fusion gene formed from GBA (glucosylceramidase beta) and its pseudogene GBAP1 (glucosylceramidase beta pseudogene 1) [29].