Autosomal recessive chronic granulomatous disease caused by defects in NCF-1, the gene encoding the phagocyte p47-phox: mutations not arising in theNCF-1 pseudogenes

Abstract

Chronic granulomatous disease (CGD) is a primary immunodeficiency caused by defects in any one of 4 genes encoding phagocyte NADPH oxidase subunits. Unlike other CGD subtypes, in which there is great heterogeneity among mutations, 97% of affected alleles in patients previously reported with A470 CGD carry a single mutation, a GT deletion (ΔGT) in exon 2 of the p47-phox gene, NCF-1. This unusually high incidence results from recombination events between NCF-1and its highly homologous pseudogenes, in which ΔGT originates. In 50 consecutive patients with A470 CGD, 4 were identified who were heterozygous for ΔGT in NCF-1, and for the first time, 2 were identified whose DNA appeared normal at this position. To avoid co-amplification of pseudogene sequence and to enable the identification of mutations in these patients, allele-specific polymerase chain reaction was used to amplify alleles not containing ΔGT. In each of the 4 patients who were heterozygous for ΔGT, an additional novel mutation was identified. These were 2 missense mutations, G125 → A in exon 2 (predicting Arg42 → Gln) and G784 → A in exon 8 (Gly262 → Ser), and 2 splice junction mutations at the 5′ end of intron 1, gt → at and gtg → gtt. The first of 2 patients who appeared normal at the GT position was a compound heterozygote with the G125 → A transition on one allele and a deletion of G811 on the other. In the second of these patients, only a single defect was detected, G574 → A, which predicts Gly192 → Ser but is likely to result in defective splicing because it represents the final nucleotide of exon 6.