Hematologically important mutations: Leukocyte adhesion deficiency (second update).

Leukocyte adhesion deficiency (LAD) is an immunodeficiency caused by defects in the adhesion of leukocytes (especially neutrophils) to the blood vessel wall. As a result, patients with LAD suffer from severe bacterial infections and impaired wound healing, accompanied by neutrophilia. In LAD-I, characterized directly after birth by delayed separation of the umbilical cord, mutations are found in ITGB2, the gene that encodes the ß subunit (CD18) of the ß2 integrins. In the rare LAD-II disease, the fucosylation of selectin ligands is disturbed, caused by mutations in SLC35C1, the gene that encodes a GDP-fucose transporter of the Golgi system. LAD-II patients lack the H and Lewis Lea and Leb blood group antigens. Finally, in LAD-III, the conformational activation of the hematopoietically expressed ß integrins is disturbed, leading to leukocyte and platelet dysfunction. This last syndrome is caused by mutations in FERMT3, encoding the kindlin-3 protein in all blood cells, involved in the regulation of ß integrin conformation. This article contains an update of the mutations that we consider to be relevant for the various forms of LAD.

Science, Anatomy, and Art: Revisiting Leonardo da Vinci, Pioneer of Modern Anatomy.

BACKGROUND: Leonardo da Vinci, the artist and scientist, was an archetype figure of the Renaissance era. He was an autodidactic polymath in natural sciences, engineering, and physical sciences, imbued with universality, prodigious inventive imagination, and curiosity to know and understand the world around him. Among his myriad activities, anatomy, physiology, and biomechanics of the musculoskeletal system and the underlying systems fully engaged him. Leonardo dissected dozens of human and animal corpses to study. His anatomical illustrations were precise, combining art and science with an impeccable integration of both. Multiple drawings, diagrams, sketches, and designs are found in his notes. Leonardo's style was intensely personal, unveiling his thoughts, passions, and emotions. We analyzed significant biographic aspects of Leonardo's life, remarking on his scientific and life conceptions and their manifestation in his anatomical designs. The contribution of preceding anatomists is reported as a source of his inspiration as well as motivation to successors. Leonardo da Vinci left no publications, but rather an extensive collection of personal notebooks. Leonardo's contribution to modern anatomy was enormous and he is considered by the scientific and medical community as the father of the modern anatomy.

Hematologically important mutations: The autosomal forms of chronic granulomatous disease (third update).

Chronic granulomatous disease (CGD) is an immunodeficiency disorder affecting about 1 in 250,000 individuals. CGD patients suffer from severe, recurrent bacterial and fungal infections. The disease is caused by mutations in the genes encoding the components of the leukocyte NADPH oxidase. This enzyme produces superoxide, which is subsequently metabolized to hydrogen peroxide and other reactive oxygen species (ROS). These products are essential for intracellular killing of pathogens by phagocytic leukocytes (neutrophils, eosinophils, monocytes and macrophages). The leukocyte NADPH oxidase is composed of five subunits, four of which are encoded by autosomal genes. These are CYBA, encoding p22phox, NCF1, encoding p47phox, NCF2, encoding p67phox and NCF4, encoding p40phox. This article lists all mutations identified in these genes in CGD patients. In addition, cytochrome b558 chaperone-1 (CYBC1), recently recognized as an essential chaperone protein for the expression of the X-linked NADPH oxidase component gp91phox (also called Nox2), is encoded by the autosomal gene CYBC1. Mutations in this gene also lead to CGD. Finally, RAC2, a small GTPase of the Rho family, is needed for activation of the NADPH oxidase, and mutations in the RAC2 gene therefore also induce CGD-like symptoms. Mutations in these last two genes are also listed in this article.

Hematologically important mutations: X-linked chronic granulomatous disease (fourth update).

Chronic granulomatous disease (CGD) is an immunodeficiency disorder affecting about 1 in 250,000 individuals. CGD patients suffer from severe bacterial and fungal infections. The disease is caused by a lack of superoxide production by the leukocyte enzyme NADPH oxidase. Superoxide and subsequently formed other reactive oxygen species (ROS) are instrumental in killing phagocytosed micro-organisms in neutrophils, eosinophils, monocytes and macrophages. The leukocyte NADPH oxidase is composed of five subunits, of which the enzymatic component is gp91phox, also called Nox2. This protein is encoded by the CYBB gene on the X chromosome. Mutations in this gene are found in about 70% of all CGD patients in Europe and in about 20% in countries with a high ratio of parental consanguinity. This article lists all mutations identified in CYBB and should therefore help in genetic counseling of X-CGD patients' families. Moreover, apparently benign polymorphisms in CYBB are also given, which should facilitate the recognition of disease-causing mutations. In addition, we also include some mutations in G6PD, the gene on the X chromosome that encodes glucose-6-phosphate dehydrogenase, because inactivity of this enzyme may lead to shortage of NADPH and thus to insufficient activity of NADPH oxidase. Severe G6PD deficiency can induce CGD-like symptoms.

Inherited SLP76 deficiency in humans causes severe combined immunodeficiency, neutrophil and platelet defects.

The T cell receptor (TCR) signaling pathway is an ensemble of numerous proteins that are crucial for an adequate immune response. Disruption of any protein involved in this pathway leads to severe immunodeficiency and unfavorable clinical outcomes. Here, we describe an infant with severe immunodeficiency who was found to have novel biallelic mutations in SLP76. SLP76 is a key protein involved in TCR signaling and in other hematopoietic pathways. Previous studies of this protein were performed using Jurkat-derived human leukemic T cell lines and SLP76-deficient mice. Our current study links this gene, for the first time, to a human immunodeficiency characterized by early-onset life-threatening infections, combined T and B cell immunodeficiency, severe neutrophil defects, and impaired platelet aggregation. Hereby, we characterized aspects of the patient's immune phenotype, modeled them with an SLP76-deficient Jurkat-derived T cell line, and rescued some consequences using ectopic expression of wild-type SLP76. Understanding human diseases due to SLP76 deficiency is helpful in explaining the mixed T cell and neutrophil defects, providing a guide for exploring human SLP76 biology.

Malnutrition and inflammation in hemodialysis patients: Comparative evaluation of neutrophil reactive oxygen formation.

BACKGROUND: Impaired phagocytic function has been established in uremic patients. Chemotaxis, particle ingestion, and free radical and metabolic activity were all found to be disturbed in dialysis patients. Malnutrition is common among hemodialysis (HD) patients, with an estimated prevalence of 40% to 70%. Malnutrition-Inflammation Score (MIS) appears to be a useful tool for risk stratification of chronic HD patients. We assessed the correlation between MIS and phagocyte function in HD patients. METHODS: Forty-four chronic HD patients were enrolled from the dialysis unit. The patients were divided into two groups according to the MIS: 1 to 12 (normal-mild) and 13 to 30 (severely malnourished). Hydrogen peroxide release by polymorphonuclear leukocytes was evaluated using the dihydrorhodamine 123 method. Phagocytic activity of neutrophils was evaluated after stimulation with Escherichia coli bacteria and phorbol 12-myristate 13-acetate (PMA) (positive control). RESULTS: Neutrophil oxidative activity in all HD patients versus healthy controls was significantly lower in median fluorescence intensity (MdFI)-E. coli and MdFI-PMA. We found significant correlations among MdFI-PMA and calculated MIS and other nutritional parameters in chronic HD patients. CONCLUSIONS: Impaired phagocytic function was identified in chronic HD patients. The severity of the impairment was associated with nutrition and inflammation parameters, as well as Malnutrition-Inflammation Score.

Leucocyte adhesion deficiency-A multicentre national experience.

Leucocyte adhesion deficiency (LAD) is a rare, innate autosomal recessive immunodeficiency with three subtypes. Twenty-nine patients with LADs were diagnosed and treated in Israeli Medical Centers and in the Palestinian Authority. We discuss the phenotypic, genotypic and biochemical features of LAD-I, LAD-II and LAD-III diagnosed during the neonatal period and early infancy in 18, 6 and 5 patients, respectively. Consanguinity was frequent. Common features were severe infections of variable aetiology, excessive leukocytosis and delayed umbilical cord detachment. In LAD-I, the integrin CD18 expression varied from negligible to normal. However, CD11a expression was negligible in all tested patients, suggesting both CD11a and CD18 should be used to assess this subtype. LAD-II patients showed distinctive facial features, physical malformations, short stature and developmental delay. These patients show defective expression of SLeX (CD15a) on cell surface glycoproteins and lack of H antigen on erythroid cell surfaces resulting in Bombay blood group (hh). LAD-III showed intact but inactive ß2 integrins associated with severe infections and significant bleeding disorders caused by defective platelet aggregation and thrombocytopenia. We report four patients with two new unpublished mutations: two LAD-I patients with c.1099delG in ITGB2 and two LAD-III patients with c.1069C>T in FERMT3. LAD-I patients harbouring the c.119_128 deletion in ITGB2 seemed to have better outcomes as compared to other LAD-I patients. Eight patients with LAD-I and -III underwent successful haematopoietic stem cell transplantation. Cumulative survival was 75%, 50% and 40% for LAD-I, LAD-II and LAD-III, with a median follow-up of 4 (0.08-19), 3.25 (1-32) and 6 (0.08-8) years, respectively. Prenatal diagnosis is recommended in families with LAD syndromes.

Analysis of Chronic Granulomatous Disease in the Kavkazi Population in Israel Reveals Phenotypic Heterogeneity in Patients with the Same NCF1 mutation (c.579G>A).

PURPOSE: Chronic granulomatous disease (CGD) is an innate immune deficiency disorder of phagocytes, resulting from mutations in the components of the NADPH oxidase complex that impair the synthesis of oxygen radicals, thus rendering patients susceptible to recurrent infections and excessive hyperinflammatory responses. The most common autosomal recessive form of CGD is p47phox deficiency, which is often clinically milder than the more common X-linked recessive form. Here, we report data on genetics, clinical and biochemical findings in 17 CGD patients of Kavkazi origin with the nonsense mutation c.579G>A in the NCF1 gene, leading to p47phox deficiency. METHODS: Diagnosis was based on detailed clinical evaluation, respiratory burst activity by cytochrome c reduction and dihydrorhodamine-1,2,3 (DHR) assay by flow cytometry, expression of p47phox by immunoblotting and molecular confirmation by DNA sequence analysis. RESULTS: Twelve male and five female patients with median age at onset of 2.5 years (range 1 day to 9 years) were included in the study. The present cohort displays an encouraging 88% overall long-term survival, with median follow-up of 17 years. Clinical manifestations varied from mild to severe expression of the disease. Correlation between genotype and phenotype is unpredictable, although the Kavkazi patients were more severely affected than other patients with p47phox deficiency. CONCLUSIONS: Kavkazi CGD patients harbor a common genetic mutation that is associated with a heterogeneous clinical phenotype. Early diagnosis and proper clinical management in an experienced phagocytic leukocyte center is imperative to ensure favorable patient outcome. New treatment strategies are ongoing, but results are not yet conclusive.

A false-carrier state for the c.579G>A mutation in the NCF1 gene in Ashkenazi Jews.

BACKGROUND: Mutations in the NCF1 gene that encodes p47phox, a subunit of the NADPH oxidase complex, cause chronic granulomatous disease (CGD). In Kavkazi Jews, a c.579G>A (p.Trp193Ter) mutation in NCF1 is frequently found, leading to CGD. The same mutation is found in about 1% of Ashkenazi Jews, although Ashkenazi CGD patients with this mutation have never been described. METHODS: We used Sanger sequencing, multiplex ligation-dependent probe amplification (MLPA), gene scan analysis and Ion Torrent Next Generation Sequencing for genetic analysis, and measured NADPH oxidase activity and p47phox expression. RESULTS: In an Ashkenazi couple expecting a baby, both parents were found to be heterozygotes for this mutation, as was the fetus. However, segregation analysis in the extended family was consistent with the fetus inheriting both carrier alleles from the parents. MLPA indicated four complete NCF1 genes in the fetus and three in each parent. Gene sequencing confirmed these results. Analysis of fetal leucocytes obtained by cordocentesis revealed substantial oxidase activity with three different assays, which was confirmed after birth. In six additional Ashkenazi carriers of the NCF1 c.579G>A mutation, we found five individuals with three complete NCF1 genes of which one was mutated (like the parents), and one individual with in addition a fusion gene of NCF1 with a pseudogene. CONCLUSION: These results point to the existence of a 'false-carrier' state in Ashkenazi Jews and have wide implications regarding pre-pregnancy screening in this and other population groups.

Chronic granulomatous disease: Clinical, functional, molecular, and genetic studies. The Israeli experience with 84 patients.

Chronic granulomatous disease (CGD) is an innate immunodeficiency with a genetic defect of the nicotinamide adenosine dinucleotide phosphate, reduced, oxidase components. This leads to decreased reactive oxygen species (ROS) production, which renders patients susceptible to life-threatening infections. Over the course of 30 years, we diagnosed CGD in 84 patients from 61 families using functional, molecular, and genetic studies. The incidence of CGD in Israel is 1.05 per 100,000 live-births in the Jewish population and 1.49 in the Israeli Arab population. We diagnosed 52 patients (62%) with autosomal recessive inheritance (AR-CGD) and 32 (38%) with X-linked recessive inheritance (XLR-CGD). Consanguinity was detected in 64% of AR-CGD families (14% in Jews and 50% in Israeli Arabs). We found 36 different mutations (23 in XLR-CGD and 13 in AR-CGD patients), 15 of which were new. The clinical spectrum of CGD varied from mild to severe disease in both XLR and AR forms, although the AR subtype is generally milder. Further, residual ROS production correlated with milder clinical expression, better prognosis and improved overall survival. Patients with recurrent pyogenic infections developed fibrosis and hyperinflammatory states with granuloma formation. The management of CGD has progressed substantially in recent years, evolving from a fatal disease of early childhood to one of long-term survival. Our present cohort displays an encouraging 81% overall long term survival. Early hematopoietic stem cell transplantation is advisable before tissue damage is irreversible. Successful transplantation was performed in 18/21 patients. Therapeutic gene modification could become an alternative cure for CGD. Am. J. Hematol. 92:28-36, 2017. © 2016 Wiley Periodicals, Inc.

A founder effect for p47(phox)Trp193Ter chronic granulomatous disease in Kavkazi Jews.

Chronic granulomatous disease (CGD) is a rare congenital immune deficiency caused by mutations in any of the five genes encoding NADPH oxidase subunits. One of these genes is NCF1, encoding the p47(phox) protein. A group of 39 patients, 14 of whom are of Kavkazi Jewish descent, was investigated for a founder effect for the mutation c.579G>A (p.Trp193Ter) in NCF1. We analyzed various genetic markers in the NCF1 region, including two single nucleotide polymorphisms (SNPs) in NCF1 and two short tandem repeats (STRs) located near NCF1. Most patients were homozygous for the c.579G>A mutation, but three patients were hemizygotes, with a deletion of NCF1 on the other allele, and three patients were compound heterozygotes with another mutation in NCF1. All Kavkazi Jewish patients had a c.295G_c.345T SNP combination in NCF1 and shared a common number of repeats in STR3. In addition, 90% of the Kavkazi Jewish patients shared a common number of repeats in STR1. This uniformity indicates that the c.579G>A mutation in NCF1 was introduced some 1200-2300 years ago in the Kavkazi Jewish population. Variation amongst the other investigated populations from the Middle East indicates that this mutation exists in these non-Kavkazi populations already for more than 5000 years.

Leukocyte adhesion deficiency type III: clinical features and treatment with stem cell transplantation.

Leukocyte adhesion deficiency type III (LADIII) is an autosomal recessive disorder that presents with a severe leukocyte adhesion defect and a Glanzmann-type thrombocytopathy. Hematopoietic stem cell transplantation (HSCT)--the only definitive treatment for LADIII--appears to have a high rate of complications. In this study, we describe a new group of patients with LADIII, highlighting further clinical and immunologic aspects of this disease, and reevaluating the effectiveness of HSCT for its treatment. The patients had clinical and laboratory findings consistent with LADIII. Molecular analysis confirmed the presence of a mutation in the kindlin-3 gene. HSCT was carried out in 3 patients and was successful in 2. The diagnosis of LADIII should be considered in all patients who present with recurrent infections and a bleeding diathesis, regardless of the leukocyte count. LADIII is a primary immune deficiency, which can be successfully corrected by bone marrow transplantation if applied early in the course of the disease using appropriate conditioning.

Variable clinical expressivity of STAT3 mutation in hyperimmunoglobulin E syndrome: genetic and clinical studies of six patients.

BACKGROUND AND PURPOSE: Autosomal dominant Hyper IgE syndrome (AD-HIES) is a rare and complex primary immunodeficiency that affects multiple systems. Mutations in signal transducer and activator of transcription 3 (STAT3) gene cause AD-HIES. These mutations have a dominant-negative effect and the presence of such mutations is associated with a clinical phenotype. We aim to describe genetic and clinical characteristics of patients with AD-HIES in our clinic and to highlight the variability of clinical patterns in the same family. METHODS: We describe six patients, four individuals of the same family and two unrelated patients. All patients were given a clinical score based on disease phenotype according to the National Institute of Health (NIH) score. Mutation analysis of STAT3 was done by PCR amplification of all coding exons followed by bidirectional sequencing using the BigDye kit v1.1 and an ABI3700 genetic analyzer (Applied Biosystems). RESULTS: All six patients had DNA binding region point mutations: a proband and his three children with p.Phe384Leu mutation, a patient with p.Arg382Trp substitution and a patient with p.Arg382Gln mutation. All of these mutations were previously reported. Patients differed in infectious, immunologic and somatic features. We observed an extreme variability in disease phenotype within the reported family with one genetically affected patient displaying an 'unaffected' phenotype. CONCLUSIONS: Although the genetic cause of AD-HIES is known, more studies are required to better understand the possible additional factors that may affect disease expressivity within families and the clinical diversity of the disease.

A congenital neutrophil defect syndrome associated with mutations in VPS45.

BACKGROUND: Neutrophils are the predominant phagocytes that provide protection against bacterial and fungal infections. Genetically determined neutrophil disorders confer a predisposition to severe infections and reveal novel mechanisms that control vesicular trafficking, hematopoiesis, and innate immunity. METHODS: We clinically evaluated seven children from five families who had neutropenia, neutrophil dysfunction, bone marrow fibrosis, and nephromegaly. To identify the causative gene, we performed homozygosity mapping using single-nucleotide polymorphism arrays, whole-exome sequencing, immunoblotting, immunofluorescence, electron microscopy, a real-time quantitative polymerase-chain-reaction assay, immunohistochemistry, flow cytometry, fibroblast motility assays, measurements of apoptosis, and zebrafish models. Correction experiments were performed by transfecting mutant fibroblasts with the nonmutated gene. RESULTS: All seven affected children had homozygous mutations (Thr224Asn or Glu238Lys, depending on the child's ethnic origin) in VPS45, which encodes a protein that regulates membrane trafficking through the endosomal system. The level of VPS45 protein was reduced, as were the VPS45 binding partners rabenosyn-5 and syntaxin-16. The level of ß1 integrin was reduced on the surface of VPS45-deficient neutrophils and fibroblasts. VPS45-deficient fibroblasts were characterized by impaired motility and increased apoptosis. A zebrafish model of vps45 deficiency showed a marked paucity of myeloperoxidase-positive cells (i.e., neutrophils). Transfection of patient cells with nonmutated VPS45 corrected the migration defect and decreased apoptosis. CONCLUSIONS: Defective endosomal intracellular protein trafficking due to biallelic mutations in VPS45 underlies a new immunodeficiency syndrome involving impaired neutrophil function. (Funded by the National Human Genome Research Institute and others.).

Infections associated with chronic granulomatous disease: linking genetics to phenotypic expression.

Chronic granulomatous disease (CGD) is an inherited primary immunodeficiency characterized by the absence or malfunction of the NADPH oxidase in phagocytic cells. As a result, there is an impaired ability to generate superoxide anions and the subsequent reactive oxygen intermediates. Consequently, CGD patients suffer from two clinical manifestations: recurrent, life-threatening bacterial and fungal infections and excessive inflammatory reactions leading to granulomatous lesions. Although the genotype of CGD was linked to the phenotypic expression of the disease, this connection is still controversial and poorly understood. Certain correlations were reported, but the clinical expression of the disease is usually unpredictable, regardless of the pattern of inheritance. CGD mainly affects the lungs, lymph nodes, skin, GI tract and liver. Patients are particularly susceptible to catalase-positive microorganisms, including Staphyloccocus aureus, Nocardia spp. and Gram-negative bacteria, such as Serratia marcescens, Burkholderia cepacea and Salmonella spp. Unusually, catalase-negative microorganisms were reported as well. New antibacterial and antimycotic agents considerably improved the prognosis of CGD. Therapy with IFN-γ is still controversial. Bone marrow stem cell transplantation is currently the only curative treatment and gene therapy needs further development. In this article, the authors discuss the genetic, functional and molecular aspects of CGD and their impact on the clinical expression, infectious complications and the hyperinflammatory state.

Evidence for bistable bacteria-neutrophil interaction and its clinical implications.

Neutropenia, which may develop as a consequence of chemotherapy, increases the risk of bacterial infection. Similarly, increased risk of bacterial infection appears in disorders of phagocytic functions, such as the genetic disorder chronic granulomatous disease. To elucidate the organizing principles behind these distinct immunodeficiency conditions, we investigated the interaction between in vitro bacteria and human neutrophils by experiments and mathematical modeling. The model and the experiments showed that the in vitro bacterial dynamics exhibit bistability for a certain range of neutrophil concentration and function. Thus, there is a critical bacterial concentration above which infection develops, and below which neutrophils defeat the bacteria. Whereas with normal neutrophil concentration and function, an infection may develop when the initial bacterial concentration is very high, under neutropenic conditions or when there is neutrophil dysfunction, the critical bacterial concentration can be lower, within the clinically relevant range. We conclude that critical bacterial concentration has clinically relevant implications. The individual maximum bearable bacterial concentration depended on neutrophil concentration, phagocytic activity, and patient barrier integrity; thus, the resulting maximal bearable bacterial concentration may vary by orders of magnitude between patients. Understanding the interplay between neutrophils and bacteria may enhance the development of new therapeutic approaches to bacterial infections.

Lessons learned from phagocytic function studies in a large cohort of patients with recurrent infections.

BACKGROUND: There is a paucity of data on the relationship between demographic characteristics, specific clinical manifestations, and neutrophil dysfunction, guiding physicians to decide which clinical signs and symptoms are a code for an underlying phagocytic disorder. METHODS: The data over a 21-year period of all adult and pediatric patients referred to our Laboratory for Leukocyte Functions with recurrent pyogenic infections were analyzed. Neutrophil function studies included chemotaxis, superoxide production (SOP), bactericidal activity (BA), and specific studies in case of suspected primary phagocytic disorder (PPD). RESULTS: Neutrophil dysfunction was found in 33.6% of 998 patients; chemotaxis in 16.6%, SOP in 6%, and BA in 24.5%. The younger the patient and the more organ systems involved, the greater the probability of finding phagocytic impairment. Impaired chemotaxis correlated with recurrent aphthous stomatitis, infections associated with elevated IgE, and purulent upper respiratory tract infections. Impaired SOP and BA correlated with deep-seated abscesses, recurrent lymphadenitis, sepsis, and bone and joint and central nervous system infections. PPDs were identified in 5.7%, chronic granulomatous disease in 4.8%, neutrophil glucose-6-phosphate dehydrogenase deficiency in 0.3%, leukocyte adhesion deficiency type 1 in 0.4%, and myeloperoxidase deficiency in 0.2%. Phagocytic evaluation contributed to the diagnosis of hyperimmunoglobulin-E syndrome (n = 21) and Chediak-Higashi syndrome (n = 3). CONCLUSIONS: PPDs are identified in 5.7% of patients with recurrent pyogenic infections; in the remainder, phagocytic dysfunction may be related to deleterious effects of persistent infection, drug consumption, or disorders not yet established.

Two X-linked chronic granulomatous disease patients with unusual NADPH oxidase properties.

BACKGROUND: Chronic granulomatous disease (CGD) is an immune deficiency syndrome caused by defects in the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, the enzyme that generates reactive oxygen species (ROS) in phagocytizing leukocytes. This study evaluates the NADPH oxidase capacity in two X-linked CGD patients with mutations in gp91(phox) that alter the regions in this membrane-bound NADPH oxidase component involved in docking of the cytosolic component p47(phox). MATERIALS AND METHODS: Hydrogen peroxide and superoxide generation, bactericidal activity, and NADPH oxidase protein expression by the patients' neutrophils were measured, and genetic analysis was performed. RESULTS: We report two patients, each with a novel missense mutation in CYBB, the gene that encodes gp91(phox). Surprisingly, neutrophils from these patients showed total absence of superoxide production, although they retained 13-30% of the hydrogen peroxide production capability. We speculate that this is due to direct electron transfer from flavin adenine dinucleotide (FAD) in gp91(phox) to oxygen, leading to inefficient hydrogen peroxide formation instead of efficient superoxide production. CONCLUSIONS: X-linked CGD patients with mutations that alter the gp91(phox) protein in regions involved in docking of the cytosolic NADPH oxidase component p47(phox) may have higher than expected hydrogen peroxide generation capability.