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 β subunit (CD18) of the β₂ 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 Le^a and Le^b blood group antigens. Finally, in LAD-III, the conformational activation of the hematopoietically expressed β 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 β integrin conformation. This article contains an update of the mutations that we consider to be relevant for the various forms of LAD.

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 p22^phox, NCF1, encoding p47^phox, NCF2, encoding p67^phox and NCF4, encoding p40^phox. 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 gp91^phox (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.

Two CGD Families with a Hypomorphic Mutation in the Activation Domain of p67phox

STUDY BACKGROUND

Chronic granulomatous Disease (CGD) is a rare immunodeficiency caused by a defect in the leukocyte NADPH oxidase. This enzyme generates superoxide, which is needed for the killing of bacteria and fungi by phagocytic leukocytes. Most CGD patients have mutations in CYBB, the X-linked gene that encodes gp91^phox, the catalytic subunit of the leukocyte NADPH oxidase. We report here three autosomal recessive CGD patients from two families with a homozygous mutation in NCF2, the gene that encodes p67^phox, the activator subunit of the NADPH oxidase.

METHODS

Leukocyte NADPH oxidase activity, expression of oxidase components and gene sequences were measured with standard methods. The mutation found in the patients' NCF2 gene was expressed as Ala202Val-p67^phox in K562 cells to measure its effect on NADPH oxidase activity. Translocation of the mutated p67^phox from the cytosol of the patients' neutrophils to the plasma membrane was measured by confocal microscopy and by Western blotting after membrane purification.

RESULTS

The exceptional feature of the A67 CGD patients reported here is that the p.Ala202Val mutation in the activation domain of p67^phox was clearly hypomorphic: substantial expression of p67^phox protein was noted and the NADPH oxidase activity in the neutrophils of the patients was 20-70% of normal, dependent on the stimulus used to activate the cells. The extent of Ala202Val-p67^phox translocation to the plasma membrane during cell activation was also stimulus dependent. Ala202Val-p67^phox in K562 cells mediated only about 3% of normal oxidase activity compared to cells transfected with the wild-type p67^phox.

CONCLUSION

The mutation found in NCF2 is the cause of the decreased NADPH oxidase activity and the (mild) clinical problems of the patients. We propose that the p.Ala202Val mutation has changed the conformation of the activation domain of p67^phox, resulting in reduced activation of gp91^phox.

Hematologically important mutations: leukocyte adhesion deficiency (first 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, mutations are found in ITGB2, the gene that encodes the β subunit of the β(2) integrins. This syndrome is characterized directly after birth by delayed separation of the umbilical cord. 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 Le(a) and Le(b) blood group antigens. Finally, in LAD-III (also called LAD-I/variant) the conformational activation of the hematopoietically expressed β 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 that is involved in the regulation of β integrin conformation.

Predictive values of neutrophil CD64 expression compared with interleukin-6 and C-reactive protein in early diagnosis of neonatal sepsis

BACKGROUND

Despite major advances in the management of newborn infants, neonatal sepsis (NS) remain important causes of neonatal morbidity and mortality in the newborn, mainly among preterm and low birth weight infants.

OBJECTIVE

The aim of this study was to investigate the usefulness of neutrophil CD64 expression alone and together with other infection markers in NS.

METHODS

Peripheral blood samples were taken from 109 neonates, who were categorized into three groups: proven or clinical sepsis (n=35); disease without infection (n=42); and healthy controls (n=32). Complete blood count with differential, interleukin-6 (IL-6), C-reactive protein (CRP), and cell surface expression of CD64 on neutrophils have been evaluated in a prospective manner as a diagnostic aid for NS.

RESULTS

Expression of CD64 was significantly enhanced in neonates with sepsis compared with newborns with disease without infection and healthy controls (P=0.001 and P=0.001, respectively). Cutoff values of IL-6, CRP, CD64(MFI), and CD64(i) were 24.9  pg/ml, 4.05  mg/l, 87.7, and 4.39, respectively. Sensitivity-negative predictive values of IL-6, CRP, and CD64(MFI)/CD64(i) were 80.0-90.6%, 80.0-88.8%, and 88.6-94.0%, respectively. Combining all three tests increased the sensitivity to 100%; however, specificity and positive predictive value decreased to 62.1 and 55.5%, respectively.

CONCLUSIONS

CD64 might be used either alone or combined with IL-6 and CRP for early diagnosis of NS. The advantages of CD64 when compared with IL-6 and CRP are rapid quantitation, very small blood volume required, and easy handling.

Chronic granulomatous disease presenting with hypogammaglobulinemia

Chronic granulomatous disease (CGD) is a primary immunodeficiency disorder caused by inherited defects in the nicotinamide adenine dinucleotide phosphate oxidase complex. The neutrophils of patient with CGD can ingest bacteria normally, but the oxidative processes that lead to superoxide anion formation, hydrogen peroxide production, nonoxidative pathway activation, and bacterial killing are impaired. Serious infections result from microorganisms that produce catalase. Immunoglobulin levels of patients with CGD are usually normal or elevated. We describe a patient with CGD associated with hypogammaglobulinemia, an unusual co-occurrence.

Clinical features of chronic granulomatous disease: a series of 26 patients from a single center

Chronic granulomatous disease is a genetically determined immunodeficiency disorder affecting phagocytic cells rendering them unable to kill certain bacteria and fungi. The present study is a single-center retrospective study that aimed to document the clinical course of 26 children, with a median age of 2.5 years, from 21 families diagnosed as chronic granulomatous disease from 1989-2008. A median delay of 39 months was observed between the onset of infections and age at diagnosis. Pneumonia was the most common initial manifestation of the disease followed by lymphadenitis, skin abscess and diarrhea. An AR inheritance was predominant in the study group. All patients received antibacterial and antifungal prophylaxis, resulting in a marked decrease in the incidence of infections. Overall mortality was 19.2%. These results showed that all features in our group (clinical, progression and outcome) were similar to the literature except for the predominance of autosomal recessive form.

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

Chronic granulomatous disease (CGD) is an immunodeficiency disorder affecting about 1 in 250,000 individuals. The disease is caused by a lack of superoxide production by the leukocyte enzyme NADPH oxidase. Superoxide is used to kill phagocytosed micro-organisms in neutrophils, eosinophils, monocytes and macrophages. The leukocyte NADPH oxidase is composed of five subunits, of which the enzymatic component is gp91-phox, 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. This article lists all mutations identified in CYBB in the X-linked form of CGD. Moreover, apparently benign polymorphisms in CYBB are also given, which should facilitate the recognition of future disease-causing mutations.

Four different NCF2 mutations in six families from Turkey and an overview of NCF2 gene mutations

BACKGROUND

One of the rarest forms of autosomal recessive chronic granulomatous disease (AR-CGD) is attributable to mutations in the NCF2 gene, which encodes the polypeptide p67(phox), a key cytoplasmic protein in the phagocyte NADPH oxidase system. NCF2 is localized on chromosome 1q25, encompasses 40 kb and contains 16 exons.

MATERIALS AND METHODS

We report here the clinical and molecular characterization of six patients with CGD from six consanguineous Turkish families. The ages of the five female patients were between 3 and 22 years and a male patient was 2 years old; all patients showed clear clinical symptoms of CGD.

RESULTS

The mothers of the patients did not show a bimodal histogram pattern specific for X-CGD in the dihydrorhodamine-1,2,3 (DHR) assay. Moreover, p67(phox) protein expression was not detectable using flow cytometric analysis of the patients' neutrophils except in those from patient 6, which had a diminished expression. Mutation analysis of NCF2 revealed four different homozygous mutations: a novel nonsense mutation in exon 3 c.229C>T, p.Arg77X; a novel missense mutation in exon 4 c.279C>G, p.Asp93Glu; a nonsense mutation in exon 4 c.304C>T, p.Arg102X; and a novel missense mutation in exon 6 c.605C>T, p.Ala202Val. The parents were found to be heterozygotes for these mutations.

CONCLUSIONS

The prevalence of NCF2 mutant families is approximately 15% in our series of 40 CGD families. This high incidence of A67 CGD in Turkey is undoubtedly caused by the high incidence of consanguineous marriages. We found three new mutations in NCF2 and one previously described. These are presented together with an overview of all NCF2 mutations now known.

Prenatal diagnosis of chronic granulomatous disease in a male fetus

Mutations in any of four known NADPH-oxidase components lead to CGD. X-linked CGD (X-CGD) is caused by defects in CYBB, the gene that encodes gp91-phox. Autosomal recessive (AR) CGD is caused by defects in the genes for p47 phox, p22-phox or p67-phox. The aim of this study was to screen the molecular defect in the fetus of an X-CGD carrier mother and postnatal confirmation of the results. In a family whose first-born child died from X-CGD, fetal DNA was obtained from an ongoing pregnancy by chorionic villus sampling (CVS). Direct sequencing was used to detect the previously identified CYBB gene mutation. The NADPH oxidase activity in the neutrophils from the carrier mother and from the newborn was analyzed by the DHR assay. Our studies predicted that the fetus in question was not affected by chronic granulomatous disease, which was demonstrated to be correct at birth. For prenatal screening in a pregnant X-CGD carrier, direct sequencing is a good method for detecting the mutation in the fetal DNA. Postnatal confirmation of results with the DHR assay is more practical than mutation screening to show whether the newborn have normal NADPH oxidase activity or does not.

Six different CYBA mutations including three novel mutations in ten families from Turkey, resulting in autosomal recessive chronic granulomatous disease

BACKGROUND

One of the rarest forms of autosomal recessive chronic granulomatous disease (AR-CGD) is attributable to mutations in the CYBA gene, which encodes the alpha polypeptide of cytochrome b(558), (also known as p22-phox), a key transmembrane protein in the phagocyte NADPH oxidase system. This gene is localized on chromosome 16q24, encompasses 8.5 kb and contains six exons.

MATERIALS AND METHODS

We report here the clinical and molecular characterization of 12 AR-CGD patients from 10 consanguineous, unrelated Turkish families with clinical CGD and positive family history. The ages of the six male and six female patients were between 1and 18 years. Before mutation analysis, subgroup analysis of patients was made by flow cytometry with antibodies against NADPH-oxidase components and with the DHR assay (flow cytometric assay of NADPH oxidase activity in leucocytes).

RESULTS

Mutation analysis of CYBA showed six different mutations: a frameshift insertion in exon 3 (C after C166); a missense mutation in exon 2 (p.Gly24Arg), a splice-site deletion in intron 1 (4-bp deletion +4_+7 AGTG), a novel nonsense mutation in exon 6 (p.Cys113X), a novel large deletion of exons 3-6 and a novel 1-bp deletion in exon 6 (c.408delC). All mutations were present in homozygous form and all parents investigated were found to be heterozygotes for these mutations.

CONCLUSIONS

In our series of 40 CGD families, approximately 25% of the families have p22-phox defects, with six different mutations, including three novel mutations. The high rate of consanguineous marriages seems to be the underlying aetiology.

Mutations of chronic granulomatous disease in Turkish families

BACKGROUND

Chronic granulomatous disease (CGD) is an inherited disorder of the innate immune system characterized by impairment of intracellular microbicidal activity of phagocytes. Mutations in one of four known NADPH-oxidase components preclude generation of superoxide and related antimicrobial oxidants, leading to the phenotype of CGD. Defects in gp91-phox, encoded by CYBB, lead to X-linked CGD and have been reported to be responsible for approximately 70% of all CGD cases. The aim of this study was to identify the CGD mutations in a group of Turkish CGD patients and to evaluate the predominance of CGD mutations as X-linked or autosomal recessive (AR) within the Turkish CGD families with known mutations.

MATERIALS AND METHODS

Two Turkish CGD families were included in the study, and mutations were identified by sequence analysis of DNA and RNA from peripheral blood in the patients. Before mutation analysis, subgroup analysis of patients was made by flow cytometry with antibodies against NADPH oxidase components and with DHR-123 oxidase activity assay. For comparison, we included previously reported results from four other Turkish CGD families.

RESULTS

Two different mutations were identified, one of them a novel mutation g.700G>T located in exon 7 of CYBB, and the other a hot-spot mutation located in exon 2 of the NCF1 gene. These mutations were detected in three patients from two Turkish families.

CONCLUSIONS

Until now, we have altogether identified mutations in six Turkish CGD families. In this limited number of families our results show AR-CGD in two-thirds of the Turkish families investigated, in contrast to previous reports in the literature. This is probably due to the high rate of consanguineous marriages in Turkey. Consanguineous parents were found in 75% of the families with AR-CGD patients, which favours homozygous deficiencies.

Chronic granulomatous disease caused by mutations other than the common GT deletion in NCF1, the gene encoding the p47phox component of the phagocyte NADPH oxidase

Chronic granulomatous disease (CGD) is an inherited immunodeficiency caused by defects in any of four genes encoding components of the leukocyte nicotinamide dinucleotide phosphate, reduced (NADPH) oxidase. One of these is the autosomal neutrophil cytosolic factor 1 (NCF1) gene encoding the p47phox protein. Most (>97%) CGD patients without p47phox (A47 degrees CGD) are homozygotes for one particular mutation in NCF1, a GT deletion in exon 2. This is due to recombination events between NCF1 and its two pseudogenes (psiNCF1) that contain this GT deletion. We have previously set up a gene-scan method to establish the ratio of NCF1 genes and pseudogenes. With this method we now found, in three CGD families patients with the normal number of two intact NCF1 genes (and four psiNCF1 genes) and in six CGD families, patients with one intact NCF1 gene (and five psiNCF1 genes). All patients lacked p47phox protein expression. These results indicate that other mutations were present in their NCF1 gene than the GT deletion. To identify these mutations, we designed PCR primers to specifically amplify the cDNA or parts of the genomic DNA from NCF1 but not from the psiNCF1 genes. We found point mutations in NCF1 in eight families. In another family, we found a 2,860-bp deletion starting in intron 2 and ending in intron 5. In six families the patients were compound heterozygotes for the GT deletion and one of these other mutations; in two families the patients had a homozygous missense mutation; and in one family the patient was a compound heterozygote for a splice defect and a nonsense mutation. Family members with either the GT deletion or one of these other mutations were identified as carriers. This knowledge was used in one of the families for prenatal diagnosis.

Skewing of X-chromosome inactivation in three generations of carriers with X-linked chronic granulomatous disease within one family

BACKGROUND

Chronic granulomatous disease (CGD) is an inherited disorder of the innate immune system characterized by impairment of intracellular microbicidal activity of phagocytes. Mutations in one of the four known NADPH-oxidase components preclude generation of superoxide and related antimicrobial oxidants, leading to the phenotype of CGD. Defects in gp91-phox, encoded by CYBB, lead to X-linked CGD, responsible for approximately 70% of all CGD cases. The aim of the study was to evaluate the hypothesis that age-related skewing of X-chromosome inactivation, as described in several CGD families, is caused by preferential survival of bone marrow clones with an inactive NADPH oxidase.

MATERIALS AND METHODS

We studied the neutrophils from three patients and four carriers in three generations of a Turkish family with X-linked CGD. Carrier detection was carried out by the dihydrorhodamine (DHR)-1,2,3 assay, which measures on a per-cell basis the NADPH oxidase-dependent oxidation of DHR by phagocytes. The X-chromosome inactivation pattern was determined with the HUMARA assay in DNA from leucocytes as well as in DNA from a buccal smear of the four carriers.

RESULTS

The three patients were identified by a negative DHR test, and the mutation in their CYBB gene was characterized by DNA sequencing. Moreover, we found an age-related degree of skewing of X-chromosome inactivation in the leucocytes of the four X-CGD carriers, both at the protein level (NADPH oxidase activity) and at the DNA level (HUMARA assay). However, similar skewing of X-chromosome inactivation was found in the buccal DNA from these women.

CONCLUSIONS

These novel findings indicate that the age-related degree of skewing was probably a chance finding, not related to preferential survival of NADPH oxidase-deficient precursor cells, because this enzyme is not expressed in (buccal) epithelial cells.