Key Points
- •
White blood cells (lymphoid or myeloid) can suffer from quantitative or functional congenital disorders.
- •
The type of cells or mechanisms that are mainly affected will define the spectrum of infectious diseases a particular patient will suffer.
- •
The pathophysiology, clinical manifestations and approaches to diagnosis of classic innate immunity defects (e.g. neutropenias, CGD, LAD and mucocutaneous candidiasis among other syndromes) are discussed.
- •
Recently recognized genetic diseases (e.g. IRF8, ISG15 and some forms of mucocutaneous candidiasis are presented.
This chapter focuses on neutrophils and monocytes, and disorders that arise from their quantitative or functional defects. Mature neutrophils develop in the bone marrow from a myeloid stem cell over 14 days, during which time proliferation, differentiation and maturation occur. Mature neutrophils, with their load of primary, secondary and tertiary granules, are released into the bloodstream where they stay 6 to 10 hours before exiting by diapedesis. In tissues, these cells work in ways that are primarily phagocytic, bactericidal, fungicidal or in the removal of damaged tissue. Neutrophil disorders can be divided into quantitative (increase or decrease) and functional (failures in specific metabolic or interactive pathways). Quantitative disorders include neutrophilia (>7,000 neutrophils per microliter in adult patients) and neutropenia (mild: <1,500 neutrophils per microliter, moderate: 500–1,000 neutrophils per microliter, severe: <500 neutrophils per microliter). With very few exceptions (e.g. chronic idiopathic neutrophilia, leukocyte adhesion deficiencies, myeloproliferative diseases) neutrophilia is dependent on causes extrinsic to the neutrophils (e.g. acute or chronic infection, steroids, epinephrine). On the other hand, the causes of neutropenia are multiple and can be intrinsic or extrinsic to neutrophils or their progenitors ( Box 11-1 ). Neutropenia usually falls into categories of decreased production or increased destruction, or a combination of the two.
Neutrophilia
Usually dependent on causes extrinsic to the neutrophils (e.g. acute or chronic infection)
Neutropenia
Caused by defects intrinsic to the neutrophils or their progenitors (severe congenital neutropenia, cyclic neutropenia, neutropenia associated with other well-defined syndromes [e.g. Schwachman syndrome, Fanconi’s syndrome, dyskeratosis congenita, Chédiak-Higashi syndrome, reticular dysgenesis, WHIM syndrome])
Caused by defects extrinsic to the neutrophils or their progenitors (infections, drugs, immune mediated, metabolic diseases, nutritional deficiencies, bone marrow infiltration)
Motility Disorders
Adhesion: Leukocyte adhesion deficiency 1, 2 or 3
Chemotaxis: Leukocyte adhesion deficiency 1, 2 or rac2; localized juvenile periodontitis, neutrophil β-actin deficiency, secondary to extensive burns, secondary to alcohol consumption
Phagocytosis Disorders
Leukocyte adhesion deficiency 1 (complement-mediated only); secondary to antibody deficiencies; complement deficiencies; mannose binding protein deficiency
Disorders of Granule Formation and Content
Chédiak-Higashi syndrome; specific granule deficiency
Microbicidal Disorders
Chronic granulomatous disease; myeloperoxidase deficiency; glucose-6-phosphate dehydrogenase deficiency, glutathione pathway deficiencies
Qualitative myeloid disorders include defects in motility (adhesion, chemotaxis), defects in phagocytosis, defects of granule synthesis and release, and defects in killing (see Box 11-1 ).
A neutrophil disorder should be suspected in patients with recurrent, severe, bacterial or fungal infections, especially those caused by unusual organisms (e.g. Chromobacterium violaceum ) or in uncommon locations (e.g. liver abscess; Table 11-1 ). Viral and parasitic infections are not increased in these patients.
| (A) SEVERE INFECTIONS | (B) RECURRENT INFECTIONS | (C) SPECIFIC INFECTIONS | (D) UNUSUALLY LOCATED INFECTIONS | ||||
|---|---|---|---|---|---|---|---|
| Type of Infection | Diagnosis to Consider | Site of Infection | Diagnosis to Consider | Microorganism | Diagnosis to Consider | Site of Infection | Diagnosis to Consider |
| Cellulitis | Neutropenia, LAD, CGD, HIES | Cutaneous | Neutropenia, CGD, LAD, HIES | Staphylococcus epidermidis | Neutropenia, LAD | Umbilical cord stump | LAD |
| Colitis | Neutropenia, CGD | Gums | LAD, neutropenia, neutrophil motility disorders | Serratia marcescens, C. violaceum, Nocardia, Burkholderia cepacia, Granulibacter bethesdensis | CGD | Liver abscess | CGD |
| Osteomyelitis | CGD, MSMD pathway defects | Upper and lower respiratory tract | Neutropenia, HIES, functional neutrophil disorders | Aspergillus | Neutropenia, CGD, HIES | Gums | LAD, neutropenia, neutrophil motility disorders |
| GI tract | CGD, MSMD pathway defects (salmonella) | Nontuberculous mycobacteria, BCG | MSMD pathway defects, SCID, CGD | ||||
| Lymph nodes | CGD, MSMD pathway defects (mycobacteria) | Candida | Neutropenia, CGD, MPO, CMC | ||||
| Osteomyelitis | CGD, MSMD pathway defects | ||||||
Initial laboratory evaluation should take into account the clinical presentation to direct where the defect is likely to be. Some assays, such as repeated white blood cell (WBC) counts with differentials or microscopic evaluation of neutrophils, are relatively simple and can readily exclude neutropenia or some granule defects. Flow cytometry requires a careful consideration of which markers to examine. Functional assays, such as oxidative burst testing, phagocytosis or chemotaxis, are the most challenging because few laboratories perform them routinely ( Table 11-2 ). We will consider some of the clinical, diagnostic and management aspects of a few of the best characterized myeloid disorders.
| Test | If Normal, It Excludes… |
|---|---|
| WBC count and differential (repeated) | All forms of neutropenia |
| Neutrophil morphologic evaluation | Specific granule deficiency, Chédiak-Higashi syndrome |
| Flow cytometry | |
| CD18 | LAD 1 (complete) |
| CD15s (sialyl-Lewis X ) | LAD 2 |
| Dihydrorhodamine (DHR) oxidation | CGD (MPO deficiency, severe G6PD deficiencies and glutathione pathway deficiencies have abnormal DHR oxidation as well) |
| STAT-1 phosphorylation | Complete IFNGR1, IFNGR2 deficiency |
| STAT-4 phosphorylation | Complete IL-12Rβ1 and Tyk2 deficiency |
| Bone marrow aspirate | |
| Neutrophil maturation | Severe congenital neutropenia, cyclic neutropenia |
| Neutrophil retention | WHIM syndrome |
| Nitroblue tetrazolium reduction | CGD (severe G6PD deficiencies and glutathione pathway deficiencies have abnormal NBT reduction as well) |
* Patients should be evaluated considering their familial history, physical examination and associated co-morbid factors.
Severe Congenital Neutropenia
Severe congenital neutropenia (SCN) comprises a heterogeneous group of disorders that share the common characteristics of bone marrow granulocytic maturation arrest at the promyelocyte or myelocyte stage, severe chronic neutropenia (fewer than 200 neutrophils per microliter) and increased susceptibility to acute myeloid leukemia.
In 1956 Kostmann described a Swedish kindred with severe congenital neutropenia inherited in an autosomal recessive pattern. Klein and colleagues identified homozygous mutations in the antiapoptotic molecule HAX1 in patients with autosomal recessive SCN, which was confirmed to be the cause in the original Kostmann pedigree as well. Some patients with HAX1 deficiency also suffer from cognitive problems and/or epilepsy.
Among patients with SCN, single allele mutations in the G-CSF receptor (GCSFR, 1p35-p34.3) have been associated with the development of acute myeloid leukemia. However, not all patients with SCN develop mutations in the G-CSF receptor, indicating that these mutations are somatic mutation epiphenomena that occur in the setting of SCN but do not cause it. Autosomal recessive mutations in the glucose-6-phosphatase catalytic subunit 3 (G6PC3) also cause congenital neutropenia along with cardiac and urogenital malformations.
Horwitz and colleagues and Dale and colleagues found that 22 of 25 patients with dominant or spontaneous SCN had heterozygous mutations in the gene encoding neutrophil elastase ( ELA2 ). Interestingly, mutations in this gene are also responsible for cyclic neutropenia. ELA2 mutations are responsible for more than 50% of SCN cases in Caucasian patients.
The clinical manifestations of SCN appear promptly after birth: 50% of affected infants are symptomatic within the first month of life, and 90% within the first 6 months; omphalitis, upper and lower respiratory tract infections, and skin and liver abscesses are common. Subcutaneous recombinant granulocyte-colony stimulating factor (G-CSF; 5 µg/kg/day) has dramatically changed the prognosis of these patients. Since the advent of recombinant G-CSF, reductions in the number of infections and hospitalization days and an increase in life expectancy have been described.
Devriendt and colleagues described a family with an X-linked form of severe congenital neutropenia (XLN) caused by mutations in the Wiskott-Aldrich syndrome protein (WASP). In contrast to the WASP mutations that produce classical Wiskott-Aldrich syndrome or X-linked thrombocytopenia, most of which are caused by mutations resulting in reduced WASP transcription or translation, the mutation causing XLN (Leu270Pro) creates a constitutively active mutant protein.
Two families with heterozygous mutations in GFI1 and congenital neutropenia and monocytosis have been described. GFI1 mutations act in a dominant-negative way, i.e. inheritance is autosomal dominant. Reticular dysgenesis is an autosomal recessive severe combined immunodeficiency characterized by early myeloid arrest, neutropenia, lymphopenia and sensorineural loss (see Chapter 9 ).
Cyclic Neutropenia/Cyclic Hematopoiesis
Cyclic neutropenia/cyclic hematopoiesis is inherited as an autosomal dominant trait and characterized by regular cyclic fluctuations in all hematopoietic lineages. However, clinical manifestations are almost exclusively associated with variations in neutrophils. Neutrophil counts cycle on average every 21 days (range 14 to 36 days), including periods of severe neutropenia (<200/µL) that last from 3 to 10 days. Mutations in ELA2 (neutrophil elastase 2, 19p13.3) have been identified in all pedigrees analyzed. Most patients have manifestations of neutropenia in early childhood. Oral ulcerations, gingivitis, lymphadenopathy, pharyngitis/tonsillitis and skin lesions are the most frequent findings. Early loss of permanent teeth as a consequence of chronic gingivitis and periapical abscesses is common. Bone marrow aspirates obtained during periods of neutropenia show maturation arrest at the myelocyte stage or bone marrow hypoplasia.
Granulocyte-colony stimulating factor (G-CSF) improves peripheral neutrophil counts and decreases morbidity in cyclic neutropenia patients. Infections and hospitalizations appear to lessen naturally with age.
Large granular lymphocytosis is a cause of adult onset cyclic or sustained neutropenia. This disease is caused by clonal expansion of CD8 T cells or NK cells with a tropism for neutrophils and sometimes other marrow elements. This diagnosis is suspected in an adult with new onset neutropenia and is confirmed by identification of clonal CD8 T cells infiltrating bone marrow, often in lymphoid aggregates.
Warts, Hypogammaglobulinemia, Infections and Myelokathexis (WHIM) Syndrome
Myelokathexis (from the Greek, meaning ‘retained in the bone marrow’) is a congenital disorder with severe chronic neutropenia. Unlike other forms of congenital neutropenia, bone marrow aspirates from myelokathexis patients show myeloid hypercellularity with increased numbers of granulocytes at all stages of differentiation. A significant number of patients with myelokathexis also have warts, hypogammaglobulinemia and infections of varying severity. Most WHIM patients have heterozygous deletions affecting the chemokine receptor CXCR4. Enhanced CXCR4 activity delays release of mature neutrophils from the bone marrow, resulting in peripheral neutropenia. Recurrent sinopulmonary infections are frequent. Memory B cells are also depressed in this disease, in part accounting for the humoral defects. During episodes of infection, neutrophil counts typically increase compared to baseline levels. Steroids, subcutaneous epinephrine, intravenous endotoxin, as well as G-CSF and GM-CSF, can mobilize mature neutrophils from WHIM bone marrow. Sustained therapy with G-CSF or GM-CSF increases the number of neutrophils in the peripheral blood and decreases the number of infections. Plerixafor (Mozobil®), a small molecule that binds and blocks CXCR4 and is used for hematopoietic stem cell mobilization for transplantation, has also been shown to have a beneficial effect in WHIM patients.
Immune-Mediated Neutropenias
Alloimmune Neonatal Neutropenia
Alloimmune neonatal neutropenia (ANN) is produced by the transplacental transfer of maternal antibodies against NA1 and NA2, two isotypes of the immunoglobulin receptor FcγRIIIb, causing destruction of neonatal neutrophils. If the mother does not express FcγRIIIb on her own neutrophils, she may elaborate antibodies against paternally encoded FcγRIIIb expressed on fetal neutrophils. These complement-activating antineutrophil antibodies can be detected in 1 in 500 live births, making the potential incidence of ANN high. This disease should be considered in the evaluation of all infants with neutropenia, with or without infection. Antibody-coated neutrophils in ANN are phagocytosed in the reticuloendothelial system and removed from the circulation, leaving the neonate neutropenic and prone to infections. Omphalitis, cellulitis and pneumonia may be the presenting infections within the first 2 weeks of life. The diagnosis can be made by detection of neutrophil-specific alloantibodies in maternal serum. Parenteral antibiotics (even in the absence of other signs of sepsis) and G-CSF should be included in the initial management of ANN. As expected, ANN tends to improve spontaneously with the waning of maternal antibody levels, but this process may take months.
Primary and Secondary Autoimmune Neutropenia
Autoimmune neutropenia (AIN) is a rare disorder, caused by peripheral destruction of neutrophils and/or their precursors by autoantibodies present in patient serum or mediated by large granular lymphocytes (CD3 + /CD8 + /CD57 + T cells) in the bone marrow. Autoimmune neutropenia can be either primary or secondary. When the neutropenia is an isolated clinical entity it is primary AIN, and when associated with another disease, it is secondary AIN.
Primary Autoimmune Neutropenia
Primary AIN is the most common cause of chronic neutropenia (absolute neutrophil count <1500/µL lasting at least 6 months) in infancy and childhood. There is a slight female predominance and it has been reported in about 1:100,000 live births, ten times more frequently than SCN. Antibodies directed against different neutrophil antigens can be detected in almost all patients. Approximately one third of these autoantibodies are anti-NA1 and -NA2 isoforms of FcγRIIIb (the same targets recognized in ANN). Almost 85% of these antibodies are IgG. Other antigens toward which autoantibodies can be found are CD11b/CD18 (Mac-1), CD32 (FcγRII) and CD35 (C3b complement receptor). The average age at diagnosis for primary AIN is 8 months. The majority of patients present with either skin or upper respiratory tract infections. Infrequently, some patients may suffer from severe infections such as pneumonia, meningitis or sepsis. The diagnosis may be incidental, as patients may remain asymptomatic despite low neutrophil counts. Monocytosis is also frequent. Neutrophil counts are usually below 1,500/µL, but the majority of patients have >500 neutrophils/µL at the time of diagnosis. The neutrophil count may increase 2-fold to 3-fold during severe infections and return to neutropenic levels following resolution. The bone marrow may be normal or hypercellular. The cause of this disease remains unknown. Detection of granulocyte-specific antibodies is key to the diagnosis of primary AIN and may require repeated testing.
AIN is usually a self-limited disease. The neutropenia remits spontaneously within 7 to 24 months in 95% of patients, preceded by the disappearance of autoantibodies from the circulation. Symptomatic treatment with antibiotics for infections is usually sufficient. Treatment for severe infections or in the setting of emergency surgery often now includes G-CSF.
Secondary Autoimmune Neutropenia
Secondary AIN can be seen at any age but is more common in adults and has a more variable clinical course. Various systemic and autoimmune diseases such as systemic lupus erythematosus, Hodgkin’s disease, large granular lymphocyte proliferation or leukemia, Epstein-Barr virus infection, cytomegalovirus infection, HIV infection and Parvovirus B19 infection have been associated with secondary AIN. These patients are predisposed to the development of other autoimmune problems as well. Antineutrophil antibodies typically have pan-FcγRIII specificity, rather than specificity to the FcγRIII subunits, making the resulting neutropenia more severe. Anti-CD18/11b antibodies have been detected in a subset of patients. Secondary AIN responds best to therapy directed at the underlying cause.
Defects of Granule Formation and Content
Chédiak-Higashi Syndrome
Chédiak-Higashi syndrome (CHS) is a rare and life-threatening autosomal recessive disease, characterized by oculocutaneous albinism, pyogenic infections, neurologic abnormalities and a late-onset hemophagocytic syndrome-like ‘accelerated phase’. The disease is caused by mutations in the lysosomal trafficking regulator gene, LYST or CHS1 . Patients show hypopigmentation of the skin, iris and hair due to giant and aberrant melanosomes (macromelanosomes). Hair color is usually light brown to blonde, with a characteristic metallic silver-gray sheen. Under light microscopy, CHS hair shafts show pathognomonic small, irregular aggregates of clumped pigment spread throughout the shaft ( Figure 11-1 ).
Giant azurophil granules formed from the fusion of multiple primary granules are seen in neutrophils, eosinophils and basophils. Mild neutropenia due to intramedullary destruction is also common. Progressive neuropathy of the legs, cranial nerve palsies, seizures, mental retardation and autonomic dysfunction are also common.
The accelerated phase, one of the main causes of death in CHS, is clinically indistinguishable from other hemophagocytic syndromes, with fever, hepatosplenomegaly, lymphadenopathy, cytopenias, hypertriglyceridemia, hypofibrinogenemia, hemophagocytosis and tissue lymphohistiocytic infiltration. Etoposide (VP16), steroids and intrathecal methotrexate (when the CNS is involved) have been effective treatments. However, without successful bone marrow transplantation, the accelerated phase usually recurs.
Neutrophil-Specific Granule Deficiency
Neutrophil-specific granule deficiency is a rare, heterogeneous, autosomal recessive disease characterized by the profound reduction or absence of neutrophil-specific granules and their contents. In several cases a homozygous, recessive mutation was found in C/EBPε . However, not all cases have mutations in C/EBPε , suggesting genetic heterogeneity.
Bilobed neutrophils are common (pseudo-Pelger-Huët anomaly), eosinophils may be unapparent in peripheral smears, and there is increased susceptibility to pyogenic infections of the skin, ears, lungs and lymph nodes. Neutrophils have very low specific granule contents (e.g. lactoferrin) and low to absent defensins, a primary granule product. Hemostasis abnormalities, caused by reduced levels of platelet-associated high-molecular-weight von Willebrand factor and platelet fibrinogen and fibronectin, have been reported.
Aggressive diagnosis of infection, prolonged and intensive therapy, and early use of surgical excision and debridement are necessary. Unrelated bone marrow transplantation corrected neutrophil-specific granule deficiency ( C/EBPε mutation negative) in a 13-month-old patient with intractable diarrhea and severe infections.
Defects of Oxidative Metabolism
Chronic Granulomatous Disease
Chronic granulomatous disease (CGD) predisposes to recurrent life-threatening infections caused by catalase-positive bacteria and fungi, and exuberant granuloma formation due to defects in the NADPH oxidase. The NADPH oxidase exists as a heterodimeric membrane-bound complex embedded in the walls of secondary granules, and four distinct cytosolic proteins. These structural components are referred to as phox proteins ( ph agocyte ox idase). The secondary granule membrane complex is also called cytochrome b 558 , composed of a 91-kDa glycosylated β chain (gp91 phox ) and a 22-kDa non-glycosylated α chain (p22 phox ), which together bind heme and flavin. The cytosol contains the structural components p47 phox and p67 phox , and the regulatory components p40 phox and rac. On cellular activation the cytosolic components p47 phox and p67 phox associate with p40 phox and rac, and these proteins combine with the cytochrome complex (gp91 phox and p22 phox ) to form the intact NADPH oxidase. Superoxide is formed and, in the presence of superoxide dismutase, is converted to hydrogen peroxide, which, in the presence of myeloperoxidase and chlorine, is converted to bleach. It has been postulated that production of reactive oxygen species is most critical for microbial killing through the activation of certain primary granule proteins inside the phagosome. This hypothesis for NADPH oxidase-mediated microbial killing suggests that the reactive oxidants are most critical as intracellular signaling molecules, leading to activation of other pathways rather than exerting a microbicidal effect per se.
Mutations in five genes of the NADPH oxidase have been found to cause CGD. Mutations in the X-linked gp91 phox account for about two thirds of cases. The remainder are autosomal recessive; there are no autosomal dominant cases of CGD. A single case of p40 phox deficiency has been reported. The frequency of CGD in the USA is higher than 1:200,000. Clinically, CGD is quite variable but the majority of patients are diagnosed as toddlers and young children. Infections and granulomatous lesions are the usual first manifestations. The lung, skin, lymph nodes and liver are the most frequent sites of infection ( Table 11-3 ). The majority of infections in CGD in North America are caused by only five organisms: Staphylococcus. aureus, Burkholderia cepacia complex , Serratia marcescens, Nocardia and Aspergillus . Trimethoprim-sulfamethoxazole prophylaxis has reduced the frequency of bacterial infections, especially with staphylococcus. On prophylaxis, staphylococcal infections are essentially confined to the liver and cervical lymph nodes. Staphylococcal liver abscesses encountered in CGD are dense, caseous and difficult to drain, and previously required surgery in almost all cases. More recently, however, focusing on the dysregulated inflammatory response in CGD, a combination of steroid and antibiotic therapy has obviated the need for surgery in almost all cases.
| Type of Infection (Most Frequent Microorganisms Isolated) | Total ( N = 368) No. (%) |
|---|---|
| Pneumonia ( Aspergillus spp; Staphylococcus spp; Burkholderia cepacia ; Nocardia spp; Mycobacteria spp) | 290 (79%) |
| Abscess ( Staphylococcus spp; Serratia spp; Aspergillus spp) | 250 (68%) |
| Suppurative adenitis ( Staphylococcus spp; Serratia spp; Candida spp) | 194 (53%) |
| Osteomyelitis ( Serratia spp; Aspergillus spp; Paecilomyces spp; Staphylococcus spp) | 90 (25%) |
| Bacteremia/fungemia ( Salmonella spp; Burkholderia cepacia ; Candida spp; Staphylococcus spp; Pseudomonas spp) | 65 (18%) |
| Cellulitis ( Chromobacterium violaceum and Serratia marcescens were identified in one case each) | 18 (5%) |
| Meningitis ( Candida spp was identified in three cases) | 15 (4%) |
| Other † | 112 (30%) |
* These data include patients on variable prophylactic regimens, if any, and are meant to portray the natural history of disease over the last 20 years.
† Includes impetigo, sinusitis, otitis media, septic arthritis, urinary tract infection/pyelonephritis, gingivitis/periodontitis, chorioretinitis, gastroenteritis, paronychia, conjunctivitis, hepatitis, epididymitis, empyema, epiglottitis, cardiac empyema, mastoiditis and suppurative phlebitis.
The gastrointestinal ( Figure 11-2A ) and genitourinary ( Figure 11-2B ) tracts are frequently affected by inflammatory and granulomatous manifestations in CGD patients. Gastrointestinal inflammatory manifestations occur in up to 43% of X-linked and 11% of autosomal recessive cases. Recent analysis of older p47 phox deficient patients suggests that even in that group the rate of inflammatory bowel disease is almost 40% by later adulthood (SMH, personal observation). Abdominal pain is the most common gastrointestinal symptom; diarrhea, nausea and vomiting also occur. Colonic granulomatous lesions mimicking Crohn’s-like inflammatory bowel disease (IBD), oral ulcers, esophagitis, gastric outlet obstruction, villous atrophy, intestinal strictures, fistulae and perirectal abscesses also occur. The extraintestinal manifestations of Crohn’s (pyoderma, arthritis) are typically absent.
Most CGD-associated IBD manifestations are responsive to steroids. Prednisone (1 mg/kg/day for several weeks followed by progressive tapering) usually resolves the symptoms. Unfortunately, relapses occur in nearly 70% of patients. Low-dose maintenance prednisone may control symptoms without an apparent increase in serious infections. Sulfasalazine, mesalazine, 6-mercaptopurine, azathioprine and cyclosporine are effective second-line treatment options. The use of TNF-α blocking antibodies in severe cases of IBD in CGD patients have been associated with symptom control in anecdotal reports but there were also severe infections with typical CGD pathogens. Therefore, intensified prophylaxis and vigilance for intercurrent infections are needed in the setting of these potent immunosuppressives.
Genitourinary strictures and granulomas occur in up to 18% of CGD patients, mostly in the cytochrome b558-mutated patients. Steroid therapy similar to that used for gastrointestinal manifestations usually controls these complications.
Inflammatory retinal involvement is found in up to 24% of X-linked CGD patients. Interestingly, this has also been detected in three X-linked CGD female carriers. These lesions are typically nonprogressive and asymptomatic and need no specific treatment. However, two CGD patients needed enucleation for painful retinal detachments. These retinal lesions have been found to have bacterial DNA within them, but the importance of this finding is unclear since they rarely change after discovery.
Autoimmune disorders such as idiopathic thrombocytopenic purpura and juvenile rheumatoid arthritis are more common in CGD than in the general population. Discoid and systemic lupus erythematosus occur in CGD patients and in X-linked CGD female carriers.
The X-linked carriers of gp91 phox have one population of phagocytes that produces superoxide and one that does not, giving carriers a characteristic mosaic pattern on oxidative testing. Infections are not usually seen in these female carriers unless the normal neutrophils are below 10%, in which case these carriers are at risk for CGD type infections.
The diagnosis of CGD is usually made by direct measurement of superoxide production, ferricytochrome c reduction, chemiluminescence, nitroblue tetrazolium (NBT) reduction or dihydrorhodamine oxidation (DHR). The DHR assay is preferred because of its relative ease of use, its ability to distinguish X-linked from autosomal patterns of CGD on flow cytometry, and its sensitivity to even very low numbers of functional neutrophils. Of note, several other conditions, such as glucose-6-phosphate dehydrogenase deficiency, myeloperoxidase deficiency, and synovitis, acne, pustulosis, hyperostosis and osteitis (SAPHO) can also affect the respiratory burst.
Male sex, earlier age at presentation and increased severity of disease suggest X-linked disease, but the precise gene defect should be determined in all cases for the purposes of genetic counseling and prognosis. Autosomal recessive forms of CGD (mostly p47 phox deficient) have a significantly better prognosis than X-linked disease.
Prophylactic trimethoprim-sulfamethoxazole (5 mg/kg/day based on trimethoprim in two doses) reduces the frequency of major infections from about once every year to once every 3.5 years. It reduces staphylococcal and skin infections without increasing the frequency of serious fungal infections in CGD. Itraconazole prophylaxis prevents fungal infection in CGD (100 mg daily for patients <13 years or <50 kg; 200 mg daily for those ≥13 years or ≥50 kg). IFN-γ also reduces the number and severity of infections in CGD by 70% compared to placebo, regardless of the inheritance pattern of CGD, sex or use of prophylactic antibiotics. Therefore, our current recommendation is to use prophylaxis with trimethoprim-sulfamethoxazole, itraconazole and IFN-γ (50 µg/m 2 ) in CGD. Because the differential diagnosis for a given process in these patients includes bacteria, fungi and granulomatous processes, a microbiologic diagnosis is critical. Leukocyte transfusions are often used for severe infections, but their efficacy is anecdotal.
Winkelstein and colleagues reported that mortality in the USA from the 1970s through 1990s was around 5% per year for the X-linked form of the disease and 2% per year for the autosomal recessive varieties. The accumulated European experience from 1954 to 2003 found that autosomal recessive CGD patients had an average life expectancy of 50 years, while X-linked CGD patients had an average life expectancy of close to 38 years. Mortality in CGD correlates with noncirrhotic portal hypertension and progressive damage of the hepatic microvasculature. Local or systemic infections, in addition to drug-induced liver injury, may be underlying conditions. A history of liver abscess, alkaline phosphatase elevations and platelet decrease over time were individually associated with mortality in CGD patients.
Successful hematopoietic stem cell transplantation (HSCT) provides a cure for CGD. Gungor and colleagues reported on 56 pediatric and adult European CGD patients transplanted with stem cells from matched siblings or matched unrelated donors, even in the setting of active inflammatory and infectious complications. They had an overall success rate of 93% with modest toxicity.
Vectors providing normal phox genes can reconstitute NADPH oxidase activity in deficient cells, establishing the proof-of-principle for gene therapy in CGD. Several gene therapy protocols have been attempted, but they have been hampered by either retroviral-mediated myeloproliferative disease or poor persistence of transduced cells. However, there are examples of at least transient benefit from gene therapy. Newer protocols are using lentiviral vectors to avoid leukemogenesis and mild bone marrow ablation to permit more definitive engraftment.
Myeloperoxidase Deficiency
Myeloperoxidase (MPO) deficiency is the most common primary phagocyte disorder. It is an autosomal recessive disease with variable expressivity: 1:4,000 individuals have complete MPO deficiency, and 1:2,000 have a partial defect. Myeloperoxidase catalyzes the conversion of H 2 O 2 to hypohalous acid. In those MPO-deficient patients who have had clinical findings, infections caused by different Candida strains were the most common: mucocutaneous, meningeal and bone infections, as well as sepsis, have been described. Diabetes mellitus appears to be a critical co-factor for Candida infections in the context of MPO deficiency. A definitive diagnosis is established by sequencing of the MPO gene, neutrophil/monocyte peroxidase histochemical staining or specific protein detection. There is no specific treatment for MPO deficiency; diabetes should be sought and controlled, and infections should be treated.
Leukocyte Adhesion Deficiency Type 1 (LAD1)
LAD1 is an autosomal recessive disorder produced by mutations in the common β2 chain (CD18) of the β2 integrin family ( ITGB2 , 21q22.3; Table 11-4 ). Each of the β2 integrins is a heterodimer composed of an α chain (CD11a, CD11b or CD11c), noncovalently linked to the common β2 subunit (CD18). The α-β heterodimers of the β2 integrin family include CD11a/CD18 (lymphocyte-function-associated antigen-1, LFA-1), CD11b/CD18 (macrophage antigen-1, Mac-1 or complement receptor-3, CR3) and CD11c/CD18 (p150,95 or complement receptor-4, CR4). CD18 is required for normal expression of the α-β heterodimers. Therefore, mutations resulting in failure to produce a functional β2 subunit lead to either very low or no expression of CD11a, CD11b and/or CD11c, causing LAD1.
