DNA linkage analysis of X chromosome-linked chronic granulomatous disease

Inborn errors of immunity: an expanding universe of disease and genetic architecture

Inborn errors of immunity (IEIs) are generally considered to be rare monogenic disorders of the immune system that cause immunodeficiency, autoinflammation, autoimmunity, allergy and/or cancer. Here, we discuss evidence that IEIs need not be rare disorders or exclusively affect the immune system. Namely, an increasing number of patients with IEIs present with severe dysregulations of the central nervous, digestive, renal or pulmonary systems. Current challenges in the diagnosis of IEIs that result from the segregated practice of specialized medicine could thus be mitigated, in part, by immunogenetic approaches. Starting with a brief historical overview of IEIs, we then discuss the technological advances that are facilitating the immunogenetic study of IEIs, progress in understanding disease penetrance in IEIs, the expanding universe of IEIs affecting distal organ systems and the future of genetic, biochemical and medical discoveries in this field.

Contribution of high-throughput DNA sequencing to the study of primary immunodeficiencies

Primary immunodeficiencies (PIDs) are inborn errors of the immune system. PIDs have been characterized immunologically for the last 60 years and genetically, principally by Sanger DNA sequencing, over the last 30 years. The advent of next-generation sequencing (NGS) in 2011, with the development of whole-exome sequencing in particular, has facilitated the identification of previously unknown genetic lesions. NGS is rapidly generating a stream of candidate variants for an increasing number of genetically undefined PIDs. The use of NGS technology is ushering in a new era, by facilitating the discovery and characterization of new PIDs in patients with infections and other phenotypes, thereby helping to improve diagnostic accuracy. This review provides a historical overview of the identification of PIDs before NGS, and the advances and limitations of the use of NGS for the diagnosis and characterization of PIDs.

The human NADPH oxidase: primary and secondary defects impairing the respiratory burst function and the microbicidal ability of phagocytes

Phagocytes, such as granulocytes and monocytes/macrophages, contain a membrane-associated NADPH oxidase that produces superoxide leading to other reactive oxygen species with microbicidal, tumoricidal and inflammatory activities. Primary defects in oxidase activity in chronic granulomatous disease (CGD) lead to severe, life-threatening infections that demonstrate the importance of the oxygen-dependent microbicidal system in host defence. Other immunological disturbances may secondarily affect the NADPH oxidase system, impair the microbicidal activity of phagocytes and predispose the host to recurrent infections. This article reviews the primary defects of the human NADPH oxidase leading to classical CGD, and more recently discovered immunological defects secondarily affecting phagocyte respiratory burst function and resulting in primary immunodeficiencies with varied phenotypes, including susceptibilities to pyogenic or mycobacterial infections.

Gastrointestinal and hepatic manifestations of primary immune deficiency diseases

Primary immune deficiency diseases (PIDs) are a heterogeneous group of inherited diseases characterized by variable genetic immune defects, conferring susceptibility to recurrent infections. They have a vast array of manifestations some of which involve the gastrointestinal and hepatobiliary systems. These complications can be the consequence of five different factors, namely, infection, autoimmune process, unregulated inflammation, malignancies and complications of therapeutic intervention. They may precede the PID diagnosis and, once developed, they pose high risk of morbidity. Untrained clinicians may treat these manifestations only at the level of their presentation, leaving the PIDs dangerously undiagnosed. In fact, early diagnosis of PIDs and accompanied gastrointestinal and hepatic complications clearly require appropriate treatment, and in-turn lead to an improved quality of life for the patient. To improve the awareness of gastroenterologists and related health care providers about these diseases, we have reviewed herein the complications of different PIDs focusing on gastrointestinal and hepatic manifestation.

A novel point mutation in the CYBB gene promoter leading to a rare X minus chronic granulomatous disease variant--impact on the microbicidal activity of neutrophils

This article reports an atypical and extremely rare case of X-linked CGD in an Italian family characterized by a low expression of gp91phox (X91- CGD). A novel point mutation in the CYBB gene's promoter (insertion of a T at position -54T to -56T) appeared to prevent the full expression of this gene in the patient's neutrophils and correlated with a residual oxidase activity in the whole cells population. The expression and functional activity of the oxidase in eosinophils appeared to be almost normal. Gel shift assays indicated that the mutation led to decreased interactions with DNA-binding proteins. The total O2- production in the patient's granulocytes (5-7% of normal) supported no microbicidal power after 45 min and 60 min of contact with S. aureus and C. albicans, respectively. Despite this residual oxidase activity, the patients suffered from severe and life-threatening infections. It was concluded that in these X91- CGD neutrophils, the O2- production per se was not sufficient to protect the patient against severe infections.

Ocular manifestations in chronic granulomatous disease in Saudi Arabia

INTRODUCTION

Chronic granulomatous disease (CGD) is a primary immunodeficiency disease caused by a genetic defect in the NADPH oxidase complex of phagocytic cells. Recent reports indicate that chorioretinal lesions are more common than previously suspected. In this study, ocular findings of CGD patients are described with particular emphasis on chorioretinal lesions as a potentially serious ocular complication of CGD.

METHODS

Medical records of CGD patients attending an immunodeficiency clinic at a tertiary care center from January 2004 to December 2006 were reviewed. Patients underwent full ophthalmologic examination. Patients with chorioretinal lesions were investigated for various causes of chorioretinitis. Molecular studies for common CGD-causing genes were performed in patients with chorioretinal lesions.

RESULTS

This cohort included 32 CGD patients: 14 (44%) had abnormal eye findings, 11 (34%) had anterior segment disease, and 4 (12.5%) had chorioretinal lesions. Posterior segment findings consisted of uniformly similar hypopigmented atrophic punched-out chorioretinal scars around the arcades and mid-equator sparing of the macula. One patient had exudative hemorrhagic total retinal detachment in the right eye. Two siblings with chorioretinal lesions had mutation in CYBB, an X-linked gene. Another patient carried a missense mutation in NCF2, causing autosomal-recessive disease.

CONCLUSIONS

While ocular manifestation is common in CGD, chorioretinal lesions seem less frequent. However, they present potential risk of visual loss; it is recommended that patients undergo regular ophthalmologic examinations. This report provides further evidence that chorioretinal lesions occur not only in X-linked, but they can also occur in the autosomal-recessive form of CGD.

Molecular physiology of weight regulation in mice and humans

Evolutionary considerations relating to efficiency in reproduction, and survival in hostile environments, suggest that body energy stores are sensed and actively regulated, with stronger physiological and behavioral responses to loss than gain of stored energy. Many physiological studies support this inference, and suggest that a critical axis runs between body fat and the hypothalamus. The molecular cloning of leptin and its receptor-projects based explicitly on the search for elements in this axis-confirmed the existence of this axis and provided important tools with which to understand its molecular physiology. Demonstration of the importance of this soma-brain reciprocal connection in body weight regulation in humans has been pursued using both classical genetic approaches and studies of physiological responses to experimental weight perturbation. This paper reviews the history of the rationale and methodology of the cloning of leptin (Lep) and the leptin receptor (Lepr), and describes some of the clinical investigation characterizing this axis.

Complex management of a patient with a contiguous Xp11.4 gene deletion involving ornithine transcarbamylase: a role for detailed molecular analysis in complex presentations of classical diseases

A male infant was diagnosed prenatally with a partial ornithine transcarbamylase (OTC) gene deletion and managed from birth. However, he displayed neurological abnormalities and developed pleural effusions, ascites and anasarca not solely explained by OTC deficiency (OTCD). Further evaluation of the gene locus using exon-specific PCR and high-density SNP array copy number analysis revealed a 3.9-Mb deletion from Xp11.4 to Xp21.1 including five additional gene deletions, three causing the known genetic diseases: Retinitis pigmentosa (RP3), X-linked chronic granulomatous disease (CGD) and McLeod syndrome. The case illustrates (1) the complexities of managing a patient with neonatal onset OTCD, CGD, RP3 and McLeod syndrome, (2) the need for detailed evaluation in seemingly "isolated" gene deletions and (3) the clinical utility of high-density copy number analysis for rapidly characterizing chromosomal lesions.

Hyperinflammation in chronic granulomatous disease and anti-inflammatory role of the phagocyte NADPH oxidase

Chronic granulomatous disease (CGD) is an immunodeficiency caused by the lack of the superoxide-producing phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. However, CGD patients not only suffer from recurrent infections, but also present with inflammatory, non-infectious conditions. Among the latter, granulomas figure prominently, which gave the name to the disease, and colitis, which is frequent and leads to a substantial morbidity. In this paper, we systematically review the inflammatory lesions in different organs of CGD patients and compare them to observations in CGD mouse models. In addition to the more classical inflammatory lesions, CGD patients and their relatives have increased frequency of autoimmune diseases, and CGD mice are arthritis-prone. Possible mechanisms involved in CGD hyperinflammation include decreased degradation of phagocytosed material, redox-dependent termination of proinflammatory mediators and/or signaling, as well as redox-dependent cross-talk between phagocytes and lymphocytes (e.g. defective tryptophan catabolism). As a conclusion from this review, we propose the existence of ROS high and ROS low inflammatory responses, which are triggered as a function of the level of reactive oxygen species and have specific characteristics in terms of physiology and pathophysiology.

The respiratory burst oxidase

Sbarra and Karnovsky were the first to present evidence suggesting the presence in phagocytes of a special enzyme designed to generate reactive oxidants for purposes of host defense. In the years since their report appeared, a great deal has been learned about this enzyme, now known as the respiratory burst oxidase. It has been found to be a plasma membrane-bound heme- and flavin-containing enzyme, dormant in resting cells, that catalyzes the one-electron reduction of oxygen to O2- at the expense of NADPH: O2 + NADPH----O2- + NADP+ + H+ Its behavior in whole cells and its response to various activating stimuli have been described in detail, although important insights continue to emerge, as for example a very interesting new series of observations on differences in oxidase activation patterns between suspended and adherent cells. The enzyme has been shown by biochemical and genetic studies to consist of at least six components. In the resting cell, three of these components are in the cytosol and three in the plasma membrane, but when the cell passes from its resting to its activated state the cytosolic components are all transferred to the plasma membrane, presumably assembling the oxidase. Of the components initially bound to the membrane, two constitute cytochrome b558, a heme protein characteristic of the respiratory burst oxidase, and the third may represent an oxidase flavoprotein. With regard to the cytosolic components, one is a phosphoprotein and another is the NADPH-binding component, possibly a second oxidase flavoprotein. The nature of the third (p67phox) is a puzzle. Four of the six oxidase components have now been cloned and sequenced. These findings only scratch the surface, however, and many questions remain. How many oxidase components, for example, remain to be discovered, and how do they fit together to form the active enzyme? How is the route of activation of the oxidase integrated into the general signal transduction systems of the cell? How did the oxidase come to be? Could there be a widespread system that generates small amounts of O2- as an intercellular signaling molecule, as recent work is beginning to suggest, and did the ever-destructive respiratory burst oxidase arise from that innocuous system as the creation of some evolutionary Frankenstein--an oxidase from hell? Finally, will it be possible to develop drugs that specifically block the respiratory burst oxidase, and will such drugs prove to be clinically useful as anti-inflammatory agents?(ABSTRACT TRUNCATED AT 400 WORDS)

Chronic Granulomatous Disease; fundamental stages in our understanding of CGD

It has been 50 years since chronic granulomatous disease was first reported as a disease which fatally affected the ability of children to survive infections. Various milestone discoveries from the insufficient ability of patients' leucocytes to destroy microbial particles to the underlying genetic predispositions through which the disease is inherited have had important consequences. Longterm antibiotic prophylaxis has helped to fight infections associated with chronic granulomatous disease while the steady progress in bone marrow transplantation and the prospect of gene therapy are hailed as long awaited permanent treatment options. This review unearths the important findings by scientists that have led to our current understanding of the disease.

Characterization of six novel mutations in the CYBB gene leading to different sub-types of X-linked chronic granulomatous disease

Chronic granulomatous disease is an inherited disorder in which phagocytes lack a functional NADPH oxidase and so cannot generate superoxide anions (O(2) (-)). The most common form is caused by mutations in CYBB encoding gp91 phox, the heavy chain of flavocytochrome b(558) (XCGD). We investigated 11 male patients and their families suspected of suffering from X-linked CGD. These XCGD patients were classified as having different variants (X91(0), X91(-) or X91(+)) according to their cytochrome b(558) expression and NADPH oxidase activity. Nine patients had X91(0) CGD, one had X91(-) CGD and one had X91(+) CGD. Six mutations in CYBB were novel. Of the four new X91(0) CGD cases, three were point mutations: G65A in exon 2, G387T in exon 5 and G970T in exon 9, leading to premature stop codons at positions Try18, Try125 and Glu320, respectively, in gp91 phox. One case of X91(0) CGD originated from a new 1005G deletion detected in exon 9. Surprisingly, four nonsense mutations in exon 5 led to the generation of two mRNAs, one with a normal size containing the mutation and the other in which exon 5 had been spliced. A novel X91(-) CGD case with low gp91 phox expression was diagnosed. It was caused by an 11-bp deletion in the linking region between exon 12 and intron 12, activating a new cryptic site. Finally, a new X91(+) CGD case was detected, characterized by a missense mutation Leu505Arg in the potential NADPH-binding site of gp91 phox. No clear correlation between the severity of the clinical symptoms and the sub-type of XCGD could be established.

Functional analysis of two-amino acid substitutions in gp91 phox in a patient with X-linked flavocytochrome b558-positive chronic granulomatous disease by means of transgenic PLB-985 cells

Chronic granulomatous disease (CGD) is a rare inherited disorder in which phagocytes lack NADPH oxidase activity. The most common form is caused by mutations in the CYBB gene encoding gp91 phox protein, the heavy chain of cytochrome b(558), which is the redox element of NADPH oxidase. In some rare cases, the mutated gp91 phox is normally expressed but no NADPH oxidase can be detected. This type of CGD is called X91(+) CGD. We have previously reported an X(+) CGD case with a double-missense mutation in gp91 phox. Transgenic PLB-985 cells have now been made to study the impact of each single mutation on oxidase activity and assembly to rule out a possible new polymorphism in the CYBB gene. The His303Asn/Pro304Arg gp91 phox transgenic PLB-985 cells exactly mimic the phenotype of the neutrophils of the X(+) CGD patient. The His303Asn mutation is sufficient to inhibit oxidase activity in intact cells and in a broken cell system, whereas in the Pro304Arg mutant, residual activity suggests that the Pro304Arg substitution is less devastating to oxidase activity than the His303Asn mutation. The study of NADPH oxidase assembly following the in vitro and in vivo translocation of cytosolic factors p47 phox and p67 phox has demonstrated that, in the double mutant and in the His303Asn mutant, NADPH oxidase assembly is abolished, although the translocation is only attenuated in Pro304Arg mutant cells. Thus, even though the His303Asn mutation has a more severe inhibitory effect on NADPH oxidase activity and assembly than the Pro304Arg mutation, neither mutation can be considered as a polymorphism.

Genetic, biochemical, and clinical features of chronic granulomatous disease

The reduced nicotinamide dinucleotide phosphate (NADPH) oxidase complex allows phagocytes to rapidly convert O2 to superoxide anion which then generates other antimicrobial reactive oxygen intermediates, such as H2O2, hydroxyl anion, and peroxynitrite anion. Chronic granulomatous disease (CGD) results from a defect in any of the 4 subunits of the NADPH oxidase and is characterized by recurrent life-threatening bacterial and fungal infections and abnormal tissue granuloma formation. Activation of the NADPH oxidase requires translocation of the cytosolic subunits p47phox (phagocyte oxidase), p67phox, and the low molecular weight GT-Pase Rac, to the membrane-bound flavocytochrome, a heterodimer composed of the heavy chain gp91phox and the light chain p22phox. This complex transfers electrons from NADPH on the cytoplasmic side to O2 on the vacuolar or extracellular side, thereby generating superoxide anion. Activation of the NADPH oxidase requires complex rearrangements between the protein subunits, which are in part mediated by noncovalent binding between src-homology 3 domains (SH3 domains) and proline-rich motifs. Outpatient management of CGD patients relies on the use of prophylactic antibiotics and interferon-gamma. When infection is suspected, aggressive effort to obtain culture material is required. Treatment of infections involves prolonged use of systemic antibiotics, surgical debridement when feasible, and, in severe infections, use of granulocyte transfusions. Mouse knockout models of CGD have been created in which to examine aspects of pathophysiology and therapy. Gene therapy and bone marrow transplantation trials in CGD patients are ongoing and show great promise.

X-Linked chronic granulomatous disease: mutations in the CYBB gene encoding the gp91-phox component of respiratory-burst oxidase

Chronic granulomatous disease (CGD) is a hereditary disorder of host defense due to absent or decreased activity of phagocyte NADPH oxidase. The X-linked form of the disease derives from defects in the CYBB gene, which encodes the 91-kD glycoprotein component (termed "gp91-phox") of the oxidase. We have identified the mutations in the CYBB gene responsible for X-linked CGD in 131 consecutive independent kindreds. Screening by SSCP analysis identified mutations in 124 of the kindreds, and sequencing of all exons and intron boundary regions revealed the other seven mutations. We detected 103 different specific mutations; no single mutation appeared in more than seven independent kindreds. The types of mutations included large and small deletions (11%), frameshifts (24%), nonsense mutations (23%), missense mutations (23%), splice-region mutations (17%), and regulatory-region mutations (2%). The distribution of mutations within the CYBB gene exhibited great heterogeneity, with no apparent mutational hot spots. Evaluation of 87 available mothers revealed X-linked carrier status in all but 10. The heterogeneity of mutations and the lack of any predominant genotype indicate that the disease represents many different mutational events, without a founder effect, as is expected for a disorder with a previously lethal phenotype.

PU.1 as an essential activator for the expression of gp91(phox) gene in human peripheral neutrophils, monocytes, and B lymphocytes

We have reported a deficiency of a 91-kDa glycoprotein component of the phagocyte NADPH oxidase (gp91(phox)) in neutrophils, monocytes, and B lymphocytes of a patient with X chromosome-linked chronic granulomatous disease. Sequence analysis of his gp91(phox) gene revealed a single-base mutation (C --> T) at position -53. Electrophoresis mobility-shift assays showed that both PU.1 and hematopoietic-associated factor 1 (HAF-1) bound to the inverted PU.1 consensus sequence centered at position -53 of the gp91(phox) promoter, and the mutation at position -53 strongly inhibited the binding of both factors. It was also indicated that a mutation at position -50 strongly inhibited PU.1 binding but hardly inhibited HAF-1 binding, and a mutation at position -56 had an opposite binding specificity for these factors. In transient expression assay using HEL cells, which express PU.1 and HAF-1, the mutations at positions -53 and -50 significantly reduced the gp91(phox) promoter activity; however, the mutation at position -56 did not affect the promoter activity. In transient cotransfection study, PU.1 dramatically activated the gp91(phox) promoter in Jurkat T cells, which originally contained HAF-1 but not PU.1. In addition, the single-base mutation (C --> T) at position -52 that was identified in a patient with chronic granulomatous disease inhibited the binding of PU.1 to the promoter. We therefore conclude that PU.1 is an essential activator for the expression of gp91(phox) gene in human neutrophils, monocytes, and B lymphocytes.

Practice parameters for the diagnosis and management of immunodeficiency. The Clinical and Laboratory Immunology Committee of the American Academy of Allergy, Asthma, and Immunology (CLIC-AAAAI)

In this brief review, only the most useful immunologic tests available for defining host defects that lead to susceptibility to infection have been emphasized. It should be pointed out that those evaluations and tests ordered by the physician will rule out the vast majority of the currently recognized defects. Finally, it is important that any patients identified as abnormal by these screening tests be characterized as fully as possible in centers specializing in these diseases before therapy is initiated, since what may appear to be a simple diagnosis on the surface may be an indicator of more complex underlying problems.

Mutations in the promoter region of the gene for gp91-phox in X-linked chronic granulomatous disease with decreased expression of cytochrome b558

We examined the molecular defect in two kindreds with "variant" X-linked chronic granulomatous disease (CGD). Western blots of neutrophil extracts showed decreased immunoreactive cytochrome b558 components gp91-phox and p22-phox. Analysis of mRNA demonstrated reduced gp91-phox transcripts, with relative preservation of an alternative mRNA species created by transcription initiation in the third exon of the gene. Single strand conformation polymorphism analysis of the 5' flanking region of the patients' gp91-phox genes revealed an electrophoretic abnormality not detected in 40 other gp91-phox genes. Genomic sequencing demonstrated a single base change associated with CGD in each kindred: in one, adenine to cytosine at base pair-57 and in the other, thymidine to cytosine at -55. These mutations are located between the "CCAAT" and "TATA" box consensus sequences involved in eukaryotic gene transcription. Gel shift assays revealed two specific DNA-protein complexes formed between phagocyte nuclear extracts and an oligonucleotide probe representing bases -31 to -68 of the gp91-phox promoter region; the faster-migrating complex could not be formed with oligonucleotides containing either of the promoter mutations. Thus, these promoter region mutations appear to be causally related to the loss of association of a DNA-binding protein and lead to diminished gp91-phox expression, abnormal transcription initiation, and the development of CGD.

A 40-base-pair duplication in the gp91-phox gene leading to X-linked chronic granulomatous disease

Chronic granulomatous disease (CGD) is characterized by the inability of the patients' phagocytic leukocytes to generate superoxide. Therefore, these cells fail to kill certain bacteria and fungi. As a result, patients with CGD suffer from recurrent, life-threatening infections with these micro-organisms. Superoxide is produced by NADPH oxidase, a multicomponent enzyme exclusively present in phagocytic leukocytes. The most common form of CGD is X-linked, originating from a deficiency of the high-molecular-weight subunit of cytochrome b558 (gp91-phox). Here we describe a patient suffering from X-linked CGD due to a 40-base-pair duplication in exon 7 of the CYBB gene coding for gp91-phox, predicting a frameshift, substitution of 22 amino acids and a premature stop codon at amino-acid position 253. The mother as well as the grandmother of this patient were proven to be heterozygous for this mutation; the father and sister were normal. However, the great-grandmother proved to have normal oxidative functions, suggesting that the mutation occurred three generations ago. This is the first description of a nucleotide duplication leading to CGD.

The respiratory burst oxidase and the molecular genetics of chronic granulomatous disease

The phagocyte respiratory burst oxidase plays a central role in the inflammatory response. This membrane-bound enzyme complex is comprised of both integral membrane and cytosolic proteins and catalyzes the formation of large quantities of superoxide in response to inflammatory stimuli. While superoxide and its oxidant derivatives normally serve a microbicidal function, excessive or inappropriate release of these products contribute to inflammatory tissue injury. Chronic granulomatous disease (CGD) is a group of inherited disorders characterized by an absent neutrophil respiratory burst, which leads to recurrent and often life-threatening infections in affected patients. The analysis of the specific cellular defects in CGD has been instrumental in the identification and characterization of individual oxidase components. Four distinct genetic subgroups are presently recognized, each involving a different protein essential for respiratory burst oxidase function. This article summarizes recent advances in the characterization of the protein components and cellular biochemistry of the respiratory burst oxidase and reviews the classification and molecular genetics of CGD. The application of these findings to new approaches to the diagnosis and treatment of CGD are also reviewed.

Genetic control of streptococcus-induced hepatic granulomatous lesions in mice

Hepatic granulomatous lesions were induced in mice by a single intraperitoneal injection of 3 mg of disrupted Streptococcus pyogenes cell-wall material. Mice carrying the H-2b or H-2k haplotypes were highly susceptible to the induction and three weeks after the injection produced numerous granulomas. In contrast, mice of the H-2d haplotype were resistant and produced only a few hepatic granulomas. Resistance was inherited as a dominant trait and in the backcross generation segregated together with the H-2d phenotype. Testing of the H-2-recombinant mice indicated that the putative gene(s) determining resistance/susceptibility is located to the right of the S and to the left of the D region. This location corresponds to the recently described gene cluster consisting of tumor necrosis factor (TNF) and lymphotoxin genes and several BAT sequences. The known effect of TNF on granuloma formation in mice is consistent with a possible effect of TNF genes, and their variants, on S. pyogenes-inducibility of hepatic granulomas in mice.

Sex chromosome evolution: platypus gene mapping suggests that part of the human X chromosome was originally autosomal

To investigate the evolution of the mammalian sex chromosomes, we have compared the gene content of the X chromosomes in the mammalian groups most distantly related to man (marsupials and monotremes). Previous work established that genes on the long arm of the human X chromosome are conserved on the X chromosomes in all mammals, revealing that this region was part of an ancient mammalian X chromosome. However, we now report that several genes located on the short arm of the human X chromosome are absent from the platypus X chromosome, as well as from the marsupial X chromosome. Because monotremes and marsupials diverged independently from eutherian mammals, this finding implies that the whole human X short arm region is a relatively recent addition to the X chromosome in eutherian mammals.

The superoxide-generating oxidase of phagocytic cells. Physiological, molecular and pathological aspects

Professional phagocytes (neutrophils, eosinophils, monocytes and macrophages) possess an enzymatic complex, the NADPH oxidase, which is able to catalyze the one-electron reduction of molecular oxygen to superoxide, O2-. The NADPH oxidase is dormant in non-activated phagocytes. It is suddenly activated upon exposure of phagocytes to the appropriate stimuli and thereby contributes to the microbicidal activity of these cells. Oxidase activation in phagocytes involves the assembly, in the plasma membrane, of membrane-bound and cytosolic components of the oxidase complex, which were diassembled in the resting state. One of the membrane-bound components in resting phagocytes has been identified as a low-potential b-type cytochrome, a heterodimer composed of two subunits of 22-kDa and 91-kDa. The link between NADPH and cytochrome b is probably a flavoprotein whose subcellular localization in resting phagocytes remains to be determined. Genetic defects in the cytochrome b subunits and in the cytosolic factors have been shown to be the molecular basis of chronic granulomatous disease, a group of inherited disorders in the host defense, characterized by severe, recurrent bacterial and fungal infections in which phagocytic cells fail to generate O2- upon stimulation. The present review is focused on recent data concerning the signaling pathway which leads to oxidase activation, including specific receptors, the production of second messengers, the organization of the oxidase complex and the molecular defects responsible for granulomatous disease.

A novel X-linked combined immunodeficiency disease

A novel X-linked combined immunodeficiency disease was found in five living males in an extended family in the United States. The age of the affected males ranged from 2.5 to 34 yr. The most prominent clinical abnormalities were a paucity of lymphoid tissue; recurrent sinusitis, otitis media, bronchitis, and pneumonia; severe varicella; and chronic papillomavirus infections. The principal immunologic features of the disorder were normal concentrations of serum immunoglobulins but restricted formation of IgG antibodies to immunogens; normal numbers of B cells and NK cells but decreased numbers of CD4+ and CD8+ T lymphocytes, particularly the CD45RA+ subpopulations; diminished proliferative responses of blood T cells to allogeneic cells, mitogens and antigens; and decreased production of IL-2 by mitogen stimulated blood lymphocytes. Thus, affected males in this family carry an abnormal gene on their X chromosome that results in a combined immunodeficiency that is distinct from previously reported disorders.

Human neutrophil cytochrome b light chain (p22-phox). Gene structure, chromosomal location, and mutations in cytochrome-negative autosomal recessive chronic granulomatous disease

A membrane-bound cytochrome b, a heterodimer formed by a 91-kD glycoprotein (heavy chain) and a 22-kD polypeptide (light chain), is an essential component of the phagocyte NADPH-oxidase responsible for superoxide generation. Cytochrome b is absent in two subgroups of chronic granulomatous disease (CGD), an inherited disorder characterized by the lack of oxidase activity. Mutations in the cytochrome heavy chain gene, encoded by the CYBB locus in Xp21.1, result in the X-linked form of CGD. A rare subgroup of autosomal recessive CGD also lacks cytochrome b (A- CGD), but the genetic defect has not previously been identified. In order to search for possible mutations in the cytochrome light chain locus, CYBA, the structure of this gene was characterized. The CYBA locus was localized to 16q24, and the approximately 600-bp open reading frame determined to be encoded by six exons that span approximately 8.5 kb. Three unrelated patients with A- CGD were studied for evidence of mutations in the light chain gene. One patient, whose parents were first cousins, was homozygous for a large deletion that removed all but the extreme 5' coding sequence of the gene. The other two patients had a grossly normal light chain transcript on Northern blot of mononuclear cell RNA. The light chain transcript was amplified by the polymerase chain reaction and sequenced. One patient was a compound heterozygote for two alleles containing point mutations in the open reading frame that predict a frame shift and a nonconservative amino acid replacement, respectively. The second patient, whose parents were second cousins, was homozygous for a different single-base substitution resulting in another nonconservative amino acid change. These results indicate that A- CGD can results from defects in the gene encoding the 22-kD light chain of the phagocyte cytochrome b.

Retinitis pigmentosa: genetic mapping in X-linked and autosomal forms of the disease

Retinitis pigmentosa (RP) is an hereditary degenerative disease of the retina and a major cause of visual impairment, prevalence estimates ranging from 1 in 3000 to 1 in 7000. The condition may segregate as an autosomal dominant, autosomal recessive or an X-linked recessive trait and it may also occur on a sporadic basis in up to 50% of cases. In the autosomal dominant form, close linkage to the DNA marker C17 (D3S47) was recently established in a large family of Irish origin displaying early-onset disease (McWilliam et al. 1989), multipoint analysis indicating the gene for rhodopsin as a likely candidate (Farrar et al. 1990). In that gene, a C----A transversion in codon 23, resulting in a proline----histidine substitution has now been identified in 17 of 148 unrelated ADRP patients in the United States (Dryja et al. 1990). This mutation is absent however in the original Irish pedigree (it is also absent in 21 other dominant Irish pedigrees, representing approximately 70% of the estimated ADRP population) indicating that another mutation, either in rhodopsin itself, or in a gene very closely linked to rhodopsin is responsible for the disease in that family. Analysis of other dominant pedigrees using the C17 and/or rhodopsin probes has indicated either tight linkage (Bhattacharya, Personal Communication), looser linkage, possibly indicative of a second locus on 3q (Olsson et al. 1990) or no linkage (Farrar et al. 1990, Blanton et al. 1990, Inglehearn et al. 1990). Extensive genetic heterogeneity thus exists in the autosomal dominant form of this disease, and in the light of these new observations, earlier tentative evidence for linkage of ADRP to the Rhesus locus on chromosome 1 will be re-evaluated. A locus for type II Usher syndrome (classical RP combined with congenital pedial deafness, and normal vestibular function) has now been established on the long arm of chromosome 1 (Kimberling et al. 1990). Type I Usher families, in which hearing loss is more profound and vestibular function absent, do not segregate with the same chromosome 1q markers, indicating the existence of another, as yet unlocated gene. In the X-linked form of the disease, two genes, XLRP2 and XLRP3, have been located on the proximal short arm of the X chromosome using a combination of physical and linkage mapping techniques, and there is some evidence to suggest a possible third locus more distally located.(ABSTRACT TRUNCATED AT 400 WORDS)

Mapping of the X-linked recessive retinitis pigmentosa gene. A review

X-linked retinitis pigmentosa is caused by (a) mutation(s) on the X chromosome. One of the problems encountered in the genetic counselling of this disease is the identification of carrier females who appear ophthalmologically and electrodiagnostically normal. Despite normal testing these women are at risk of transmitting the XLRP gene to their children. Since the biochemical basis of XLRP is unknown, prenatal diagnosis and definitive carrier detection remain elusive. Existing methods of diagnosis and carrier detection are subject to limitations and are dependent on X-inactivation. The application of recombinant DNA probes to families with XLRP has provided a large number of genetic marker loci at the level of DNA. These markers are called restriction fragment length polymorphisms (RFLPs). By analysis of linkage relationships in affected kindreds, the XLRP gene(s) has (have) been localized to two subregions of the short arm of the X chromosome, Xp11 and Xp21. These findings suggest that there may be more than one retinitis pigmentosa gene on the X chromosome. Until further families are studied to clarify the localization(s) of XLRP, neither locus can be excluded if prenatal diagnosis and accurate carrier detection is to be established.

Chronic granulomatous disease of childhood: clinical, pathological, biochemical, molecular, and genetic aspects of the disease

The pathobiology of chronic granulomatous disease (CGD) of childhood, a heterogeneous phenotypic disorder characterized by chronic and recurrent infection, has become more completely understood over the past three decades. Blood neutrophils, monocytes, and eosinophils lack a respiratory burst required for effective killing of catalase positive bacteria by reduced by-products of oxygen. The disease is transmitted in at least two genetic forms: X-linked and autosomal recessive. In the X-linked form, a gene coding for a beta subunit protein required for cytochrome b presence on the plasma membrane of phagocytic cells is not expressed. The protein appears to be a constituent of the cytochrome b complex that requires an additional alpha subunit for complete expression. Cytochrome b is likely a component of leukocyte oxidase, which catalyzes the respiratory burst. The autosomal recessive form of the disorder appears to be controlled by a set of genes coding for soluble cofactors essential for oxidase expression. One or more of these cofactors have recently been shown to be deficient in several patients with autosomal recessive CGD. Optional therapy for CGD patients is presently not available. Long-term use of antibiotics may be helpful. The cloned product interferon gamma has been reported to improve superoxide generation, bactericidal activity, and immunoreactive cytochrome b in some CGD neutrophils and monocytes, both in vitro and in vivo. Currently a prospective clinical evaluation of the efficacy of interferon gamma is in progress. Molecular studies of expression and function of the X-CGD gene in phagocytic cells are in progress as well.

A missense mutation in the neutrophil cytochrome b heavy chain in cytochrome-positive X-linked chronic granulomatous disease

A membrane-bound cytochrome b, a heterodimer formed by a 91-kD glycoprotein and a 22-kD polypeptide, is a critical component of the phagocyte NADPH-oxidase responsible for the generation of superoxide anion. Mutations in the gene for the 91-kD chain of this cytochrome result in the X-linked form of chronic granulomatous disease (CGD), in which phagocytes are unable to produce superoxide. Typically, there is a marked deficiency of the 91-kD subunit and the cytochrome spectrum is absent (X- CGD). In a variant form of CGD with X-linked inheritance, affected males have a normal visible absorbance spectrum of cytochrome b, yet fail to generate superoxide (X+ CGD). The size and abundance of the mRNA for the 91-kD subunit and its encoded protein were examined and appeared normal. To search for a putative mutation in the coding sequence of the 91-kD subunit gene, the corresponding RNA from an affected X+ male was amplified by the polymerase chain reaction and sequenced. A single nucleotide change, a C----A transversion, was identified that predicts a nonconservative Pro----His substitution at residue 415 of the encoded protein. Hybridization of amplified genomic DNA with allele-specific oligonucleotide probes demonstrated the mutation to be specific to affected X+ males and the carrier state. These results strengthen the concept that all X-linked CGD relates to mutations affecting the expression or structure of the 91-kD cytochrome b subunit. The mechanism by which the Pro 415----His mutation renders the oxidase nonfunctional is unknown, but may involve an impaired interaction with other components of the oxidase.

Urinary tract disorders in patients with chronic granulomatous disease

Twelve of the 25 patients with chronic granulomatous disease treated at our institution between 1957 and 1987 were found to have urinary tract disorders. All 12 patients were male and 22 years of age or younger when chronic granulomatous disease was diagnosed. Six patients had hydroureteronephrosis in association with recurrent episodes of pyelonephritis, retroperitoneal lymphadenitis, and granuloma formation. The other six patients had genital lesions or dysuria. Among the six patients with hydroureteronephrosis, a nephrectomy was performed in two, ureterolysis was used to relieve obstruction in one, and hydroureteronephrosis resolved after antibiotic therapy alone in three. We conclude that complications involving the genitourinary system occur frequently in patients with chronic granulomatous disease. Periodic imaging of the urinary tract may detect asymptomatic hydroureteronephrosis or other treatable genitourinary abnormalities in these patients.

Tumor necrosis factor and immune interferon synergistically induce cytochrome b-245 heavy-chain gene expression and nicotinamide-adenine dinucleotide phosphate hydrogenase oxidase in human leukemic myeloid cells

Recombinant tumor necrosis factor (rTNF) and rIFN-gamma induce in the human leukemia cell lines HL-60, ML3, and U937 the accumulation of transcripts of the X chromosome-linked chronic granulomatous disease (X-CGD) gene, encoding the 91-kD heavy chain of cytochrome b-245, a component of the NADPH oxidase of phagocytic cells. The gene is induced within 6 h by either cytokine, and its accumulation is observed upon induction with rIFN-gamma up to 5 d. The combined effect of the two cytokines is more than additive. rIFN-gamma also induces accumulation of X-CGD mRNA in immature myeloid cells from peripheral blood of chronic myeloid leukemia (CML) patients, whereas rTNF has almost no effect. The cells from CML patients constitutively express TNF mRNA, suggesting that endogenously produced TNF may play a role in the effect of rIFN-gamma on these cells. rTNF induces X-CGD gene expression in the myeloid cell lines acting, at least in part, at the transcriptional level, as shown in nuclear run-on experiments. The gene encoding the 22-kD light chain of cytochrome b-245 is constitutively expressed in the human myeloid cell lines and the accumulation of its transcripts is affected by neither rTNF nor rIFN-gamma, rTNF and rIFN-gamma synergistically to induce the cell lines to express the cytochrome b-245 heterodimer (as evaluated by its visible spectrum), and to produce NADPH oxidase activity and H2O2 upon stimulation with phorbol diesters.

Strategies for linkage studies in schizophrenia

Significant advances in linkage studies have occurred the past decade based on the use of polymorphic DNA markers known as restriction fragment length polymorphisms (RFLPs). This approach has led to the chromosomal localization of a number of important genetic diseases, and is being increasingly applied to schizophrenia. We discuss two strategies for performing linkage studies in schizophrenia, one based on methodical testing of the human genome, and the other based on selective use of markers. The selective approach uses data from the mode of transmission, previous linkage studies, cytogenetic studies, association studies, case reports, and candidate genes to identify markers that may have an increased likelihood for linkage.

Diagnosis of genetic disorders at the DNA level

In the past 10 years considerable progress has been made in the diagnosis of hereditary disorders at the DNA level. Many monogenic disorders can now be examined at the gene level; such examination has led to a better understanding of the molecular basis of these disorders and made carrier detection and prenatal diagnosis possible. Each year, more and more monogenic disorders can be added to the list of diseases that can be diagnosed by DNA analysis. Future research will be devoted to the identification of genes responsible for other known monogenic hereditary disorders, the elucidation of the molecular lesion associated with chromosomal abnormalities, and the characterization of the genes and gene defects involved in the common multifactorial diseases. The goal of diagnosis is the identification of the genetic defect in affected patients, persons destined to be affected, and carriers.

Genetic prediction in X-linked agammaglobulinaemia

S21 (DXS17) and pXG12 (DXS94), two probes linked to the locus of X-linked agammaglobulinaemia (XLA), were used for genetic prediction in 13 such families. A method of allowing for nonallelic genetic heterogeneity was demonstrated in the calculation of the genetic risks, specifying a certain proportion of unlinked families. We further estimated the impact due to the uncertainty of the proportion of unlinked families on the final genetic risks in each family and this can be taken into account during genetic counselling.

Localization of the gene for X-linked recessive type of retinitis pigmentosa (XLRP) to Xp21 by linkage analysis

The X-linked recessive type of retinitis pigmentosa (XLRP) causes progressive night blindness, visual field constriction, and eventual blindness in affected males by the third or fourth decade of life. The biochemical basis of the disease is unknown, and prenatal diagnosis and definitive carrier diagnosis remain elusive. Heterogeneity in XLRP has been suggested by linkage studies of families affected with XLRP and by phenotypic differences observed in female carriers. Localization of XLRP near Xp11.3 has been suggested by close linkage to an RFLP at the locus DXS7 (Xp11.3) detected by probe L1.28. In other studies a locus for XLRP with metallic sheen has been linked to the ornithine transcarbamylase (OTC) locus mapping to the Xp21 region. In this study, by linkage analysis using seven RFLP markers between Xp21 and Xcen, we examined four families with multiple affected individuals. Close linkage was found between XLRP and polymorphic sites OTC (theta = .06 with lod 5.69), DXS84 (theta = .05 with lod 4.08), and DXS206 (theta = .06 with lod 2.56), defined by probes OTC, 754, and XJ, respectively. The close linkage of OTC, 754, and XJ to XLRP localizes the XLRP locus to the Xp21 region. Data from recombinations in three of four families place the locus above L1.28 and below the Duchenne muscular dystrophy (DMD) gene, consistent with an Xp21 localization. In one family, however, one affected male revealed a crossover between XLRP and all DNA markers, except for the more distal DXS28 (C7), while his brother is recombined for this marker (C7) and not other, more proximal markers. This suggests that in this family the XLRP mutation maps near DXS28 and above the DMD locus.

Xp21 DNA microdeletion in a patient with chronic granulomatous disease, retinitis pigmentosa, and McLeod phenotype

The clinical, biochemical, and molecular analysis of a patient with chronic granulomatous disease (CGD), retinitis pigmentosa (RP), and McLeod phenotype and of his parents demonstrated the X-linked transmission of these three traits in this family and a deletion of the entire X-CGD gene of the patient DNA. All but one other DNA markers tested, including those in Xp21, were present. These findings strongly suggest that the McLeod locus and at least one XL RP gene are closely linked to the X-CGD locus in the Xp21 region of the human X chromosome.

Inherited deletion of subband Xp21.13 in a male with Duchenne muscular dystrophy

The chromosomes of a male patient who suffers from Duchenne muscular dystrophy (DMD) with a molecular deletion were examined with an improved high resolution R type replication banding technique. High resolution cytogenetic analysis of the proband revealed a deletion of the Xp21.13 subband. His healthy mother was heterozygous for the deletion, which is subject to random X inactivation in lymphocytes. The X chromosomes of the proband's grandmother were normal, suggesting that the deletion of the Xp21.13 subband in the mother was a new mutation. The finding of a very small, cytologically visible Xp21.1 deletion in a male DMD patient with a molecular deletion emphasises the importance of resolving the fine structure in the Xp21 region.