YF Hui, SY Chan, YL Lau

Chronic Granulomatous Disease (CGD) is an uncommon primary immunodeficiency due to the defective NADPH oxidase for superoxide production. X-linked CGD caused by the mutated gp91phox gene is responsible for >50% of the cases. Since its cloning in 1986, mutations have been reported in Caucasian and Japanese patients. Here we report mutations in seven Chinese X-linked CGD patients from six unrelated families. Southern hybridization did not show any gross abnormalities in the patients' genomic DNA. Single-stranded conformation polymorphism and sequence analysis of their genomic DNA and/or cDNA identified their disease-causing mutations. Two patients were found affected by amino acid substitutions. One was a T → A transversion at nucleotide 1037 (Leu342 → Gln) and the another was a T → A at nucleotide 625 (Phe205 → I1e). A trinucleotide deletion from nucleotide 655 to 657 was found in a patient causing the deletion of the Phe215. The Leu342 and Phe215 were predicted to bind the isoalloxazine ring and the ADP moiety of the FAD molecular respectively. A nonsense mutation (Glu519 → Stop) was found due to a G → T mutation at nucleotide 1567. An insertion of A at nucleotide 754 in two brothers caused a frameshift and led to a premature stop. Lastly, a G → A mutation at nucleotide 264 was found, which is the last nucleotide of exon 3. This mutation caused the skipping of exon 3 in the patient's mRNA which may affect the stability and function of the protein. In addition, this rare splice site mutation provided information on the understanding of splicing mechanism. These results showed extreme heterogeneity of mutations in the gp91phox gene in X-linked CGD patients, and their wide distribution along the gene. The absence of hot spot in the gene is further confirmed.