Recombination events between the p47-phoxgene and its highly homologous pseudogenes are the main cause of autosomal recessive chronic granulomatous disease

Abstract

AbstractChronic granulomatous disease (CGD) is an inherited disease caused by defects in the superoxide-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidase of phagocytes. Genetic lesions in any of 4 components of this antimicrobial enzyme have been detected. Family-specific mutations are found in 3 of 4 forms of CGD due to deficiencies of the gp91-phox, p22-phox, andp67-phox genes. In p47-phox–deficient CGD (autosomal recessive form A47°) patients, a GT deletion (▵GT) at the beginning of exon 2 of the p47-phox gene has been reported in 19 of 20 alleles. This GT deletion is also characteristic for the recently identified p47-phox pseudogenes. To explore a possible link between these findings, a sequence analysis of 28 unrelated, racially diverse A47° CGD patients and 37 healthy individuals was performed. The GT deletion in exon 2 was present on all alleles in 25 patients. Only 3 patients but all healthy individuals contained the GTGT and ▵GT sequences. A total of 22 patients carried additional pseudogene-specific intronic sequences on all alleles, either only in intron 1 or in intron 1 and intron 2, which lead to different types of chimeric DNA strands. It is concluded that recombination events between the p47-phox gene and its highly homologous pseudogenes result in the incorporation of ▵GT into the p47-phox gene, thereby leading to the high frequency of GT deletion in A47° CGD patients.