Rare Duplication or Deletion of Exons 6, 7 and 8 in CYBB Leading to X-Linked Chronic Granulomatous Disease in Two Patients from Different Families

Abstract

Chronic granulomatous disease (CGD) is a rare congenital disorder in which phagocytes cannot generate superoxide (O(2)(-)) and other microbicidal oxidants due to mutations in one of the five components of the O(2)(-)-generating NADPH oxidase complex. The most common form is caused by mutations in CYBB on the X chromosome, encoding gp91phox, the enzymatic subunit of the phagocyte NADPH oxidase. Here, we report two rare cases of male X-linked CGD patients, one caused by a 5.7-kb duplication of a region containing CYBB exons 6 to 8 and the other caused by a deletion of this same region. We found both the duplication in patient 1 and the deletion in patient 2 to be bordered by a GT repeat. Indeed, in control DNA, the 3' part of CYBB intron 5 contains a GT repeat and the 5' part of intron 8 also contains such a repeat. Duplication of exons 6, 7 and 8 in patient 1 was probably caused by a non-homologous crossing over between the two GT repeats. The deletion found in patient 2 probably arose from a similar misalignment. The results found in these patients were confirmed by multiplex ligation-dependent probe amplification. The clinical profile of XCGD is severe in both patients.

Chronic granulomatous disease: Clinical, molecular, and therapeutic aspects

“…Stasia et al. reported two interesting cases of male XR‐CGD patients, one with a 5.7‐kb duplication spanning exons 6 and 8 of CYBB gene and the other with a deletion of the same region. Both mutations are probably caused by a single event of non‐homologous meiotic or mitotic crossing‐over between two high‐similarity short‐tandem‐gene therapy (GT) repeats of introns 5 and 8.…”

“…So far, large deletions and duplications are considered uncommon genetic mutation events in CGD patients, probably due to the difficulty to detect multiple exon deletions/insertions with conventional methods (sequencing, PCR-SSCP, Southern blot). Recently, array comparative genomic hybridization (array CGH) and multiplex ligationdependent probe amplification were proposed for the detection of copy number variations (26,27) in CGD patients also. Stasia et al (27) reported two interesting cases of male XR-CGD patients, one with a 5.7-kb duplication spanning exons 6 and 8 of CYBB gene and the other with a deletion of the same region.…”

“…Recently, array comparative genomic hybridization (array CGH) and multiplex ligationdependent probe amplification were proposed for the detection of copy number variations (26,27) in CGD patients also. Stasia et al (27) reported two interesting cases of male XR-CGD patients, one with a 5.7-kb duplication spanning exons 6 and 8 of CYBB gene and the other with a deletion of the same region. Both mutations are probably caused by a single event of nonhomologous meiotic or mitotic crossing-over between two high-similarity short-tandem-gene therapy (GT) repeats of introns 5 and 8.…”

Molecular diagnosis of chronic granulomatous disease

“…However, in case the indicator patient has a complete deletion of CYBB (on the X chromosome), the mother cannot be defined as a carrier of this deletion by simple gene sequencing. MLPA or array CGH analysis can then be applied .…”