Keywords

Introduction

Chronic granulomatous disease (CGD) is a rare inherited primary immunodeficiency due to mutations in any of the critical subunits of the phagocyte NADPH oxidase complex, resulting in impaired oxidase activity of neutrophils, monocytes, and tissue macrophages. It is characterized by increased susceptibility to recurrent and severe infections with a subset of microorganisms, granuloma formation, and inflammatory disease. CGD was first described by Janeway et al. in 1954 [1] and was dubbed “fatal granulomatous disease of childhood” in 1959 [2], with most patients historically succumbing to infection or other complications of disease by 10 years of age. However, with increasing awareness of disease, widespread use of prophylactic antimicrobials, and advancements in hematopoietic stem cell transplantation (HSCT), outcomes have improved dramatically and many patients now live well into adulthood.

Mechanism of Neutrophil Dysfunction

Neutrophils play a key role in the defense against invading pathogens primarily by engulfing and rapidly killing microbes within phagocytic vacuoles via activation of the NADPH oxidase complex and the resultant “respiratory burst” during which reactive oxygen species (ROS) are generated and microbicidal proteases are activated. The NADPH oxidase complex is assembled from both membrane-bound proteins embedded in the walls of secondary granules and distinct cytosolic proteins (Fig. 17.1). The membrane-bound heterodimer cytochrome b558 is composed of the catalytic glycoprotein gp91phox and the non-glycosylated protein p22phox. Upon phagocyte activation, the cytosolic proteins p47phox, p67phox, and p40phox translocate to cytochrome b558 and recruit Rac1/2 to form the activated NADPH oxidase complex. Upon formation of the activated NADPH oxidase complex, gp91phox undergoes a conformational change to expose the protein’s catalytic component, which then shuttles electrons from cytosolic NADPH to molecular oxygen in the phagolysosome, leading to the formation of superoxide ions. Superoxide ions are used to generate reactive oxygen species (ROS) such as hydrogen peroxide, hypochlorous acid, hydroxyl radicals, and secondary amines that participate in the direct killing of phagocytosed microorganisms. The creation of the hydroxyl radical also results in an overall negative charge within the phagolysosome, triggering the rapid influx of potassium, which in turns leads to activation of intraphagosomal proteases that further contribute to microbial clearance [3]. Additionally, the NADPH oxidase complex is required for the activation of neutrophil extracellular traps (NETs) [4], which are webs of chromatin filaments and antimicrobial peptides that are released from apoptotic neutrophils and entrap extracellular pathogens to facilitate clearance by the immune system.

Fig. 17.1
figure 1

The activated NADPH oxidase complex. Upon phagocyte activation, the various components of NADPH oxidase come together to form the activated NADPH oxidase complex. Gp91phox shuttles electrons from cytosolic NADPH to molecular oxygen in the phagolysosome, resulting in the formation of superoxide ion (O2−). Superoxide ion is converted to hydrogen peroxide (H2O2) either spontaneously or by superoxide dismutase (SOD), and hydrogen peroxide is converted to hypochlorous acid (HOCl, bleach) by myeloperoxidase. Bleach is then able to directly kill engulfed pathogens

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Of note, neutrophils are essential for the elimination of a wide spectrum of microorganisms; however, patients with CGD are at increased risk of infection almost exclusively with catalase-positive pathogens. This is thought to be because the distal mechanisms of the bactericidal pathway, including myeloperoxidase, remain intact in patients with CGD. Catalase-positive organisms, however, can degrade host-produced hydrogen peroxide before it is converted to hypochlorous acid by myeloperoxidase, thus escaping this mechanism of killing. That being said, only a subset of catalase-positive microorganisms is responsible for the majority of infections seen in CGD, the reasons for which remain unclear.

Epidemiology

The incidence of CGD varies significantly worldwide. A large retrospective review of a national registry reported an incidence of about 1:200,000–250,000 live births in the United States [5]. Interestingly, the incidence of CGD is quite variable across Europe, ranging from 1:133,000 in the United Kingdom to 1:100,000 in Italy [6, 7]. Published rates of CGD by country are shown in Table 17.1 [5,6,7,8,9,10,11].

Table 17.1 Reported rates of CGD worldwide
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Genetics

Mutations in any of the five structural subunits of the NADPH oxidase complex result in defective ROS production and the clinical presentation of CGD (Table 17.2). Mutations in the CYBB gene, which encodes the transmembrane glycoprotein gp91phox and is the located on the X chromosome, is the most common cause of CGD worldwide and accounts for approximately two-thirds of cases of CGD in North America and Europe [5,6,7, 12,13,14]. Biallelic pathogenic mutation in NCF1 (p47phox) is the most common cause of autosomal recessive CGD and accounts for between 20% and 25% of CGD, and mutations in CYBA (p22phox) and NCF2 (p67phox) each account for about 5% of cases. There have been 26 reported cases of CGD due to NCF4 (p40phox) mutations [15, 16]. Interestingly, these patients suffered from significant autoinflammatory disease but none of the patients had the recurrent infections characteristic of the other genetic forms of CGD. Of note, in countries with high rates of consanguinity, the incidence of autosomal recessive CGD often exceeds that of X-linked CGD.

Table 17.2 Genetic etiology of CGD in the United States and Western Europe
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Recently, biallelic loss-of-function mutations in CYBC1 were identified as the genetic cause of CGD in a cohort of eight patients from Iceland and in one patient from Saudi Arabia [17, 18]. Most of the patients suffered from recurrent infections and several had autoinflammatory disease, including colitis and histopathological evidence of granuloma formation. CYBC1 is not directly involved in the respiratory burst but was found to be essential for the expression of the gp91phox/p22phox heterodimer and formation of the NADPH oxidase complex. All patients had an impaired neutrophil oxidative burst on whom testing was performed.

Finally, CYBB is located at Xp21.1, and patients with large deletions in the X chromosome may have other monogenic disorders in addition to CGD. The XK gene, which encodes the Kx blood group, is immediately telomeric to CYBB, and the loss of XK results in McLeod syndrome, the most common syndrome seen with CGD. Patients with McLeod syndrome are severely restricted for receiving transfusions, which may have implications for those patients under consideration for HSCT. Larger deletions may also result in loss of RPGR (retinitis pigmentosa), DMD (Duchenne muscular dystrophy), and OTC (ornithine transcarbamylase deficiency).

Case Presentation 1

A 6-year-old boy with a history of recurrent cutaneous abscesses and one prior episode of Aspergillus fumigatus pneumonia at 4 years of age presents to the ED with 3 days of low-grade fever and vague abdominal pain. The boy appeared tired, and physical exam was notable for slight guarding on palpation of the right upper quadrant and a liver edge palpable 2 cm below the right costal margin. Labs were remarkable for an elevated white blood cell count at 12.6 × 10^3/μL and an elevated C-reactive protein level at 9.8 mg/dL (normal < 1.0). Transaminases, bilirubin, and albumin levels were all normal. A right upper quadrant ultrasound demonstrated a loculated collection of fluid 6.2 cm in diameter in the right hepatic lobe, and the patient was empirically started on piperacillin-tazobactam plus metronidazole. He underwent percutaneous drainage of the abscess, and cultures returned positive for methicillin-sensitive Staphylococcus aureus at 9 h. Antibiotics were transitioned to oxacillin monotherapy at that time. Immunology was consulted given the patient’s infectious history, and the new unusual diagnosis of a Staphylococcal liver abscess. Immune workup demonstrated normal quantitative immunoglobulin levels and lymphocyte subset counts with protective vaccine titers. Dihydrorhodamine assay demonstrated a broad-based histogram peak with a modest shift of the fluorescence signal in stimulated neutrophils characteristic of autosomal recessive CGD. After 9 days on antibiotic therapy, the patient continued to spike intermittent fevers, and his CRP remained elevated despite broadening antibiotics to vancomycin and meropenem. Repeat ultrasound demonstrated that the abscess had increased in size to 8.4 cm in diameter, and so methylprednisolone 1 mg/kg/day was initiated given the patient’s new diagnosis of CGD. The patient defervesced, and repeat ultrasound 3 days later demonstrated shrinking of the abscess. The liver abscess resolved over the next 6 weeks, and glucocorticoids were weaned off over a period of 5 months. Genetic testing ultimately demonstrated a deleterious mutation in the NCF1 gene, and the patient was started on trimethoprim-sulfamethoxazole and itraconazole prophylaxis.

Diagnosis/Assessment

This patient’s clinical presentation is characteristic for CGD with onset of symptoms at an early age and a history of recurrent often unusual infections. In general, patients with X-linked CGD have a more severe disease course with earlier age of onset (9–14 months) and diagnosis (2.1–4.9 years) compared to patients with autosomal recessive disease (mean age of onset 30–41 months and diagnosis 5.8–8.8 years) [5,6,7, 11, 12]. Most patients present with infection, as this patient did, and infection remains the leading cause of death in patients with CGD despite the use of appropriate antimicrobial prophylaxis [5, 19].

Infections in CGD

Infections are primarily with a subset of catalase-positive microorganisms, and the most common sites of infection are the lungs, skin, lymph nodes, and liver (Table 17.3). Osteomyelitis and bacteremia/fungemia are also common. In North America, the majority of infections are due to Aspergillus spp., Staphylococcus aureus, Burkholderia spp., Serratia marcescens, and Nocardia spp. About 80% of patients have at least one episode of pneumonia, and Aspergillus, Staphylococcus, Burkholderia, and Nocardia are the pathogens most commonly identified in cases of pneumonia [5, 19]. Staphylococcus and Serratia are the most common causes of lymphadenitis and skin abscesses, and Staphylococcus is the most common cause of liver abscesses [5, 19]. Liver abscesses ultimately affect about one-third of patients with CGD and are often recurrent and difficult to treat [5, 19]. Burkholderia is the most common cause of sepsis and is associated with a high fatality rate [19, 20]. Europe and Israel also have high rates of infection with Salmonella spp. and Salmonella spp., which are frequent causes of septicemia in these regions [11, 12, 21]. In addition to the aforementioned pathogens, local or disseminated infections due to bacille Calmette-Guerin (BCG) have been reported at rates of 16.6–59.2% in CGD patients in countries where the BCG vaccine is routinely administered [22,23,24,25]. Mycobacterium tuberculosis infections are also reported at higher rates than what is considered usual for people living in areas endemic for tuberculosis [26, 27].

Table 17.3 Most common infections in CGD
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There are a number of unusual and virtually pathognomonic bacterial infections that have been identified in CGD patients in recent years. Chromobacterium violaceum and Francisella philomiragia are both gram-negative bacteria found in brackish water (i.e., water resulting from the mixing of seawater with freshwater, as in estuaries) and have been reported to cause skin and deep tissue abscesses as well as sepsis in CGD [28,29,30]. Granulibacter bethesdensis is a ubiquitous gram-negative rod found in soil and organic decay that has been isolated from patients with chronic necrotizing lymphadenitis, sepsis, and meningitis [31].

Patients with CGD have one of the highest rates of invasive fungal infection among all primary immunodeficiencies, with Aspergillus spp. being isolated at some point in about 40% of patients [5, 19]. The lungs and chest wall are the most common sites of Aspergillus infection. Aspergillus is also a major cause of osteomyelitis and brain abscesses [5, 32]. A. fumigatus followed by A. nidulans are the most frequently identified Aspergillus species [19, 33,34,35]. Of note, A. fumigatus was previously the leading cause of mortality in CGD, but with the advent of azole antifungal treatment, death from A. fumigatus is now uncommon [35]. However, the incidence of infection with A. nidulans and other Aspergillus species (e.g., A. viridinutans, A. tanneri, A. niger, and A. terreus) has increased with widespread use of azole antifungal prophylaxis. Unfortunately, these Aspergillus species generally cause more severe, refractory, and invasive disease that are difficult to treat and associated with high mortality rates [32,33,34,35,36,37,38,39]. Other fungi frequently seen in CGD include Rhizopus spp., Trichosporon spp., Paecilomyces spp., Phellinus tropicalis, Geosmithia argillacea, and Neosartorya udagawae, among others [40,41,42,43,44,45,46]. Candida infections are also common [5, 19]. Of note, dimorphic mold infections such as histoplasmosis and blastomycosis as well as the yeast infection cryptococcosis are not seen at increased rates in CGD, and mucormycosis is typically seen only in the setting of significant iatrogenic immunosuppression [47].

Diagnostic Testing

CGD should be in the differential diagnosis for all patients with severe or recurrent cutaneous abscesses, lymphadenitis, and pneumonia and any instance of deep tissue abscess, especially in the lungs or liver. Infections with organisms such as Aspergillus spp., B. cepacia, Nocardia spp., and Serratia marcescens should also prompt evaluation for CGD, and infection with any of the other rare or pathognomonic pathogens referenced above should be considered CGD until proven otherwise.

Dihydrorhodamine Assay

There are a number of diagnostic tests available to assess NADPH oxidase function in stimulated neutrophils. The nitroblue tetrazolium (NBT) reduction test was used historically, and the ferricytochrome c oxidase assay has been used on a research basis; however, the dihydrorhodamine (DHR) assay is currently considered the gold standard for diagnosis given the ease, wide availability, and high sensitivity of the assay. In the DHR assay, neutrophils are incubated with DHR-123 and stimulated with phorbol 12-myristate 13-acetate (PMA). Functional neutrophils produce superoxide radicals that oxidize DHR-123 to rhodamine, which fluoresces green and can be detected by flow cytometry. This allows for the enumeration of the proportion of rhodamine-positive (i.e., oxidase-positive) neutrophils (Fig. 17.2). In addition to diagnosing CGD, the DHR assay can also distinguish between those with absent and those with residual NADPH oxidase activity. Mechanistically, the survival of patients with CGD is strongly associated with residual superoxide production independent of the specific gene affected [14]. In general, patients with X-linked CGD have absent and those with AR CGD have residual NADPH oxidase activity. Carriers of X-linked CGD typically have two distinct populations of neutrophils on the DHR assay: a rhodamine-positive and a rhodamine-negative subset. The relative proportions of these populations can be used to evaluate degree of lyonization (i.e., X chromosome inactivation). Of note, there are a number of medical conditions that can result in a false-positive DHR assay, including severe G6PD deficiency, myeloperoxidase deficiency, and the syndrome of synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO). Granulocytic ehrlichiosis, an infection caused the Ehrlichia bacterium primarily transported by the lone star tick, has also been reported to decrease neutrophil oxidase activity and may be associated an abnormal DHR assay [48,49,50,51].

Fig. 17.2
figure 2

The DHR-123 assay. Typical DHR histograms from a (a) healthy donor, patients with (b) autosomal recessive and (c) X-linked CGD, and a (d) carrier of X-linked CGD. Patients with autosomal recessive CGD classically have residual oxidase activity while patients with X-linked CGD are typically oxidase null. Carriers of X-linked CGD have two distinct populations of neutrophils – a rhodamine-negative and a rhodamine-positive population

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Genetic Testing

Patients with an abnormal neutrophil function test should undergo confirmatory genetic testing. In general, patients with nonsense, frameshift, and splice site variants or deletions are more likely to be associated with absent or severely decreased residual NADPH oxidase activity and worse clinical outcomes than patients with missense mutations. Of note, the NCF1 gene is flanked by highly homologous (>98%) pseudogenes, which may complicate genetic testing in patients with suspected p47phox deficiency. Western blot assays and flow cytometry have both been used on a research basis to evaluate for p47phox protein expression in patients with inconclusive genetic testing as a confirmatory diagnostic measure [52, 53].

Management/Outcome

Prophylaxis

All patients diagnosed with CGD should be promptly started on trimethoprim-sulfamethoxazole (5 mg/kg/d div BID up to 320 mg trimethoprim a day) and itraconazole (5 mg/kg/d up to 200 mg daily) prophylaxis, and prophylaxis should be continued lifelong or until the patient has successfully undergone definitive curative therapy. Trimethoprim-sulfamethoxazole has been shown to markedly reduce the incidence of bacterial infections in patients with CGD [54,55,56,57,58]; in one large retrospective study, trimethoprim-sulfamethoxazole prophylaxis decreased the rate of bacterial infection from 15.8 to 6.9 per 100 patient-months in patients with X-linked disease and from 7.1 to 2.4 per 100 patient-months in those with autosomal recessive disease [58]. Trimethoprim alone, dicloxacillin, ciprofloxacin, and quinolones are alternative options for patients with sulfamethoxazole allergy or G6PD deficiency.

The advent of azole antifungals and the widespread adoption of itraconazole prophylaxis have led to improved overall survival rates for patients with CGD around the world. In a seminal trial of 39 patients with CGD randomized to receive either placebo or itraconazole, only one patient receiving itraconazole had a serious fungal infection compared to seven in the placebo group over a follow-up period of approximately 113 patient-years [59]. For those unable to tolerate itraconazole, posaconazole has been shown to be safe and effective [60]. Of note, azole antifungal therapy may be complicated by transaminitis, and as such, liver function tests should be periodically monitored. Azole absorption is also quite variable, so many clinicians choose to monitor drug levels, especially in patients with gastrointestinal disease.

IFN-gamma has been shown to stimulate superoxide production and bactericidal activity of neutrophils in vitro, and in one large randomized, double-blind, placebo-controlled trial of 128 patients with CGD from the National Institutes of Health (NIH), IFN-gamma prophylaxis was associated with a decrease in both the number and severity of infections compared to controls [61]. Furthermore, long-term follow-up of 9 years demonstrated sustained benefit [62]. However, a large prospective Italian study found that long-term IFN-gamma prophylaxis did not significantly decrease the rate of infection [7], and there was no significant difference in the number of fungal infections between patients receiving IFN-gamma and those not receiving it in the itraconazole study discussed above [59]. Additionally, side effects are common, including fever, malaise, chills, fatigue, and injection site swelling and/or tenderness, and as such, many patients do not tolerate IFN-gamma injections. For these reasons, the use of IFN-gamma prophylaxis remains variable. However, when used, IFN-gamma is started at a dose of 50 μg/m2 (or 1.5 μg/kg if BSA is <0.5 m2) administered subcutaneously three times weekly.

In addition to antimicrobial prophylaxis, patients with CGD should receive all routine childhood immunizations except for the BCG vaccine. They should also be counseled to avoid decaying organic matter (e.g., mulch, hay, dead leaves), where fungal spores are often found, and brackish water as described above. CGD patients may otherwise participate in all normal activities without restriction.

Management of Acute Infections

Patients with CGD have reported rates of significant infection of around 0.3 per year despite appropriate antimicrobial prophylaxis [7, 19]. As such, all CGD patients with fever or any other signs or symptoms concerning for infection should be promptly evaluated with a thorough physical and laboratory evaluation. It should be noted that some patients with CGD, particularly young children, may not present with classic signs and symptoms of infection, and laboratory values may be falsely reassuring. Therefore, there should be a low threshold for imaging, particularly of the chest and/or abdomen, and when in doubt, one should err on the side of treating empirically with antimicrobials. Initial antibiotic therapy should provide good coverage for both S. aureus and gram-negative bacteria, including B. cepacia (e.g., combination of vancomycin/clindamycin/oxacillin and ceftazidime/carbapenem depending on local resistance patterns). The addition of treatment strength dosing of trimethoprim-sulfamethoxazole to cover ceftazidime-resistant B. cepacia and Nocardia spp. and voriconazole to cover Aspergillus spp. may also be considered as part of initial empiric therapy. If patients do not improve within 24–48 h, and an infectious agent has not been identified, voriconazole should be started if not already done so, and more aggressive diagnostic procedures should be considered. Of note, Aspergillus serological tests (e.g., Aspergillus galactomannan), the (1-3)-beta-D-glucan assay, and bronchoalveolar lavage all have low sensitivity in patients with CGD, and therefore, invasive sampling of involved tissues is often needed [35]. However, even with invasive sampling, a causative pathogen is only identified about 50% of the time [19, 20]. Surgical intervention is often necessary, and patients frequently require prolonged treatment courses extending for several months.

Granulocyte transfusions have also been used successfully for patients with severe and/or refractory infections unresponsive to antimicrobials [63]. The number of infused granulocytes is typically about 10^9–10^10 per transfusion with variable dosing schedules, ranging from daily to a few times per week which are sometimes limited by granulocyte availability. Adverse events are common, most frequently manifested as chills and fever but hypotension, respiratory distress, and transfusion-related acute lung injury have also been reported. Many patients develop alloimmunization [64,65,66], and as such, granulocyte transfusions should be used cautiously for those patients being considered for HSCT. Some centers have used sirolimus with granulocyte transfusions to decrease the risk of alloimmunization, and rituximab has been used to treat alloimmunization, although the effectiveness of these measures has not been well described.

In general, glucocorticoids are typically avoided in patients with active infection; however, one of the hallmarks of CGD is an exuberant and aberrant inflammatory response to infection. As such, glucocorticoids are sometimes used for CGD patients with severe and/or refractory infections [67, 68]. In particular, glucocorticoids in addition to appropriate antimicrobial agents are recommended for the treatment of liver abscesses [69, 70], as was done for the patient described in the case above. Liver abscesses are dense, caseous, and often difficult to drain, and traditionally, CGD patients often required surgical resection. However, in a case series from the NIH, nine patients who received glucocorticoids for the treatment of Staphylococcal liver abscesses refractory to conventional therapy all experienced resolution of the liver abscesses without the need for surgical intervention [69]. Glucocorticoids are typically dosed at 1 mg/kg/day for 2–3 weeks, followed by a taper over several months (on average 5 months).

Case Presentation 2

An otherwise healthy boy developed abdominal pain; bloody, mucousy stools; and failure to thrive at 18 months of age and was diagnosed at age 24 months with very early-onset inflammatory bowel disease based on results from an endoscopy and flexible sigmoidoscopy. Inflammatory bowel disease was complicated by recurrent perirectal abscesses and multiple enterocutaneous fistulae requiring surgical intervention. Colitis was poorly responsive to multiple therapies, including azathioprine, methotrexate, infliximab (anti-TNF-alpha), anakinra (anti-IL-1), and vedolizumab (anti-alpha 4 beta 7 integrin), and the patient ultimately underwent partial colectomy with diverting ileostomy at 8 years of age. The patient was referred to immunology for evaluation at 12 years of age given the early onset and severe nature of his inflammatory bowel disease. At time of evaluation, he was on methotrexate, ustekinumab (anti-IL-12/IL-23), and prednisone 10 mg daily with moderate control of disease. His height and weight were both at the third percentile. Infectious history was not significant. The patient’s mother had systemic lupus erythematous, but family history was otherwise unremarkable. A DHR assay demonstrated absent neutrophil oxidative burst consistent with X-linked CGD, and genetic testing identified a pathogenic mutation in CYBB. The decision was made at that time to pursue curative HSCT. Fortunately, the patient’s younger brother was found to be a full 10/10 HLA-identical match, and the patient underwent HSCT at 13 years of age with reduced-toxicity myeloablative conditioning. His posttransplant course was overall unremarkable, and the patient had full resolution of CGD colitis by 3 months posttransplant. Growth also improved, and the patient is now at the tenth percentile for height and weight 2 years posttransplant.

Diagnosis/Assessment

Inflammatory Complications of CGD

In addition to recurrent and severe infections, CGD is characterized by immune dysregulation with high rates of autoinflammation, particularly of the GI tract, lungs, and liver. Importantly, patients may present with inflammatory disease as their only disease manifestation in the absence of a significant infectious history, as was the case for the patient described above. Autoinflammation is seen with all genotypes, but in general, severe inflammatory disease occurs more commonly in patients with X-linked CGD than in those with autosomal recessive disease [71]. Furthermore, up to 18% of CGD patients reaching adulthood develop autoimmune disease, including lupus-like symptoms, sarcoidosis, IgA nephropathy, and rheumatoid arthritis, among others [5, 12, 72].

Inflammatory bowel disease or colitis is the most common inflammatory disease seen in patients with CGD. In a series of 140 pediatric patients with CGD at the NIH, 32.8% had colitis [73], and rates as high as 60% have been reported in other series [71]. The median age of onset of GI disease was 5 years in the NIH cohort, although symptoms may develop at any point. Furthermore, the GI symptoms may be nonspecific, including abdominal pain, noninfectious diarrhea, nausea and vomiting, and failure to thrive. Any portion of the GI tract may be involved, but the colon is the most common site affected, and colitis is often fistulizing [73, 74]. Perirectal disease, frequently with recurrent and/or severe perirectal abscesses, is also particularly common. Many patients develop failure to thrive due to poorly controlled disease; in the aforementioned NIH study, 32% of patients had delayed growth [73]. In addition to colitis, about 50% of patients also develop gastrointestinal granulomas, which may be obstructive [71, 73, 75].

Other common sites of inflammatory disease include the lungs, liver, genitourinary tract, eyes and skin. About 20–30% of patients surviving into adulthood develop inflammatory lung disease [71, 76], and granulomatous disease, with or without lymphocyte infiltration, interstitial lung disease, pulmonary nodules, pleural thickening and/or effusions, and chronic obstructive pulmonary disease have all been reported [71, 76, 77]. Of note, inflammatory lung disease may occur independently from or simultaneously with infection, and infection may be the trigger for onset of inflammatory disease. Inflammatory liver disease is also common in CGD patients. In one review from the NIH, granulomas, venopathy of the portal vein, and nodular regenerative hyperplasia were all reported [78]. Poorly controlled liver disease may progress to non-cirrhotic pulmonary hypertension; the development of thrombocytopenia in this setting is associated with especially poor outcomes [79]. Inflammatory genitourinary symptoms are not uncommon, and granuloma formation in the genitourinary tract may result in ureteral or bladder outlet obstruction [71, 80]. Eosinophilic cystitis is also a rare complication that has also been reported [81, 82]. Ocular manifestations of CGD include chorioretinitis, uveitis, and ocular granulomas [71]. Common dermatologic manifestations include severe and/or granulomatous acne, inflammatory nodular lesions, and cutaneous lymphocytic infiltration [71, 72]. Poor wound healing with increased risk of wound dehiscence has also been described [83, 84]. Furthermore, macrophage activation syndrome or hemophagocytic lymphohistiocytosis has been reported in CGD patients and may be life-threatening [85,86,87,88].

Finally, patients with CGD may develop an entity known as mulch pneumonitis, which is due to an exuberant inflammatory response to inhalation of fungal elements in decaying organic matter (e.g., mulch, hay, and dead leaves) [89,90,91]. Symptoms typically occur 1–10 days after exposure to fungal elements, and symptoms tend to progress rapidly. Chest x-ray characteristically demonstrates diffuse interstitial infiltrates. Mulch pneumonitis is associated with a high mortality rate if not identified early and should be considered for all CGD patients who present with acute onset of fever, dyspnea, and hypoxia.

X-Linked Carriers

The patient’s mother in the case above reported a history of systemic lupus erythematosus, which may be related to her presumed status as a carrier of X-linked CGD. Female carriers of X-linked CGD have a dual phagocyte population due to lyonization, and in some cases, severe skewing of X chromosome inactivation may lead to the clinical syndrome of CGD. Furthermore, female carriers may have progressive skewing with age and may develop manifestations of CGD later in life. However, recent studies from the United Kingdom and the NIH also indicate that female carriers are at increased risk of medical complications, particularly autoimmune disease, regardless of degree of lyonization.

In a UK survey of 94 female carriers of X-linked CGD [92], cutaneous symptoms, most frequently photosensitivity but also malar-like lupus rash and eczema, were reported by 63 (79%) women. Skin abscesses were reported by 14 (17%), and gastrointestinal symptoms were reported by 40 (42%) women. Twenty-four (26%) women also met criteria for systemic lupus erythematosus. The NIH study [93], which included 162 female carriers of X-linked CGD, also found high rates of cutaneous symptoms and autoimmune disease, at 25% and 19%, respectively. Fifteen percent of women also had a history of severe CGD-related infections. There was a clear correlation between history of infection and neutrophil oxidative capacity in the NIH study; women with less than 10–20% oxidase-positive neutrophils were at increased risk of infection. Interestingly, in both studies, there was no relationship between autoimmune disease and neutrophil respiratory oxidative burst.

In addition to an increased rate of the medical complications described above, a recent publication, also from the United Kingdom, reported impaired emotional health with high rates of anxiety and significantly reduced quality of life scores in female carriers of X-liked CGD [94]. Taken together, these studies suggest that female carriers should be monitored long term, and in general, experts recommend antimicrobial prophylaxis for those with less than 10% oxidase-positive neutrophils. Furthermore, based on the increased risk of autoimmune disease and potential skewing of X inactivation with time, many centers prefer not to use female carriers as donors for HSCT in their affected family members, although HSCT outcomes using female carrier donors have not been published.

Diagnostic Testing

Patients with granulomatous inflammation, early-onset inflammatory bowel disease, or any of the unusual inflammatory complications described above should be screened for CGD regardless of infectious history. In particular, all patients with early-onset inflammatory bowel disease should receive a DHR assay at presentation, as a diagnosis of CGD may influence treatment decisions.

Management/Outcome

Treatment of Autoinflammation

Glucocorticoids are the mainstay of treatment of inflammatory disease in patients with CGD, and they are often effective for the treatment of granulomatous lesions. However, CGD colitis, interstitial lung disease, and other inflammatory manifestations of CGD are often difficult to treat, and additional immunomodulators are often necessary. This raises a dilemma for CGD patients, as iatrogenic immunosuppression increases their already high risk of infection and may be associated with significant morbidity and mortality.

Patients with CGD colitis typically respond to glucocorticoids, but relapse is common, and many patients become glucocorticoid dependent [71, 73]. Infliximab may be effective at treating colitis, but has been associated with increased risk of infection and death in patients with CGD, and as such, infliximab and other TNF-alpha inhibitors are generally strictly avoided [94]. Patients have variable response to the typical glucocorticoid-sparing agents used for the treatment of inflammatory bowel disease, including salicylic acid derivatives, antimetabolites such as azathioprine, and 6-mercaptopurine. Anakinra, ustekinumab, and vedolizumab have all been used in small numbers of patients with CGD colitis with varying degrees of success [95,96,97,98]. Ultimately, many patients remain refractory to treatment and fail multiple therapies as described in the case above, and their only curative option is hematopoietic stem cell transplantation and possibly gene therapy.

Hematopoietic Cell Transplantation

Allogeneic HSCT is the only widely available definitive treatment for CGD with the potential for resolution of both infectious and inflammatory complications. Initial studies showed that HSCT for CGD was possible, but rates of graft failure were high and overall survival outcomes were poor [99,100,102]. However, with optimization of clinical status pre-HSCT, fine-tuning of conditioning regimens, and improved supportive care peri- and post-HSCT, outcomes have improved significantly over the last two decades (Table 17.4). Overall survival rates are now consistently near or >90% for pediatric patients less than 14 years regardless of donor source [102,103,104,105,106,107,109], and pediatric patients who undergo HSCT have fewer infections, improved growth parameters and performance scores, and higher quality of life measures compared to those treated conventionally [109,110,112]. Adolescents and adults have traditionally been difficult to transplant; however, there have been several studies in recent years reporting high disease-free survival rates in adolescents and adult patients, including those with severe infection and/or uncontrolled inflammatory disease at time of transplantation [66, 112,113,117].

Table 17.4 Published HSCT outcomes in patients with CGD
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There remains debate as to the optimal conditioning regimen for CGD, and practice varies significantly from center to center. Many centers throughout the world have adopted a highly successful reduced-toxicity myeloablative conditioning regimen reported by Güngör and others in 2014 [113] that includes customized busulfan dosing with pharmacokinetic analysis, fludarabine, and antithymocyte globulin. However, some centers have subsequently reported an increased incidence of graft rejection, late graft failure, and mixed myeloid chimerism [119]. This is notable, as data on female carriers of X-linked CGD suggests the level of neutrophil oxidase activity that protects a CGD patient from infection may be different than that which protects against autoinflammation [92, 93], and the degree of myeloid chimerism needed to protect against new-onset inflammatory and autoimmune disease posttransplant is unknown.

Furthermore, the role of autoinflammation on HSCT outcomes also remains incompletely understood. Encouragingly, one recent study report from the Primary Immunodeficiency Treatment Consortium that included 49 CGD patients with IBD and 96 patients without IBD who underwent allogeneic HSCT reported a 5-year overall survival was equivalent for patients with and without colitis at 80% and 83%, respectively [120]. Furthermore, colitis was not associated with an increased risk of graft-versus-host disease and all surviving patients with a history of colitis had resolution of disease posttransplant. However, further studies are needed to fully elucidate how the presence of autoinflammation and accompanying organ dysfunction at time of HSCT impacts overall survival, engraftment, immune reconstitution, and risk of post-HSCT complications.

Gene Therapy

As with all monogenic diseases, gene therapy is an appealing alternative to HSCT, providing an option for patients without an HLA-identical donor and eliminating the risk of graft-versus-host disease. The first gene therapy trials for CGD took place at the NIH in the 1990s [121], and several small trials have subsequently been conducted to treat gp91phox deficiency using gamma-retroviral vectors and reduced-intensity conditioning [118,119,120,121,126]. Notably, many of the patients had active and refractory severe infection at time of gene therapy. All trials demonstrated initial engraftment of transduced neutrophils at 10–30% of circulating neutrophils, and most patients experienced full or partial resolution of infection. However, cell engraftment progressively decreased with time, and several patients developed myelodysplastic syndrome (MDS) due to insertional activation of proto-oncogenes [123, 125].

In response to the high incidence of MDS seen with γ-retroviral vectors, gene therapy trials are currently underway using self-inactivating (SIN) lentiviral vectors. Encouragingly, a recent report from a multicenter trial using a SIN lentiviral vector and near-myeloablative conditioning demonstrated sustained persistence of 12–46% oxidase positive neutrophils and no new infections in six of seven patients (aged at 7–27 years) at 1–2.5-year follow-up [127]. Furthermore, one of these patients had a history of colitis that resolved completely following gene therapy.

Ultimately, long-term outcomes with gene therapy are unknown, and as with HSCT, it is unclear what level of oxidase-positive neutrophils is necessary for resolution of preexisting autoinflammation and to prevent new-onset inflammatory and autoimmune disease.

Conclusion

Overall, CGD outcomes have improved markedly over the past few decades. In 2000, Winkelstein et al. reported a mortality rate for 5% per year for X-linked CGD and 2% per year for autosomal recessive CGD5. However, several large registries have subsequently reported survival rates approaching 90% by age 10 years, largely attributed to the widespread adoption of itraconazole prophylaxis [6, 7, 14]. Current long-term survival rates are unknown, however, as recognition and management of disease and transplant outcomes continue to improve with time. Furthermore, there remain no standard long-term treatment guidelines for patients with CGD. Indications for HSCT remain controversial, particularly for patients with residual oxidase activity, and transplant procedures for CGD patients vary markedly from center to center. Thus, additional large, multicenter studies are needed to further optimize HSCT procedures, and long-term follow-up is needed to clarify the role of gene therapy for CGD.

Clinical Pearls and Pitfalls

  • All patients with severe or recurrent cutaneous abscesses, lymphadenitis, and/or pneumonia, any instance of deep tissue abscess, and infection with Aspergillus spp., B. cepacia, Nocardia spp., and Serratia marcescens should be evaluated for CGD.

  • All patients with early-onset inflammatory bowel disease (<10 years of age), particularly those with perirectal and/or difficult to control disease, should be screened for CGD, particularly before starting infliximab or other anti-TNF-alpha agents.

  • CGD patients should be counseled to avoid decaying organic matter (e.g., hay, mulch, dead leaves) and brackish water (i.e., water resulting from the mixing of seawater with freshwater, as in estuaries).

  • CGD patients with fever or any signs or symptoms of infection should be evaluated promptly with a thorough physical and laboratory evaluation even if symptoms are mild and guardians/patients report that they are overall well appearing.

  • Aspergillus galactomannan, (1-3)-beta-D-glucan, and bronchoalveolar lavage all have poor sensitivity in CGD, and negative results do not exclude fungal infection.

  • CGD patients often require prolonged antimicrobial courses with courses 4–6 months or longer in duration common.

  • Glucocorticoids may be necessary in addition to antimicrobial therapy for the treatment of the hyperactive inflammatory response frequently seen in CGD patients with infection.

  • Female relatives of patients with X-linked CGD should be screened for carrier status and, if positive, followed long term. Those with <10% oxidase-positive neutrophils on DHR assay should be started on antimicrobial prophylaxis.

  • Definitive therapy with allogeneic hematopoietic cell transplantation should be considered for all patients with CGD. Transplant should not be delayed, as outcomes are better for younger patients before they develop severe infection or autoinflammation with resultant organ dysfunction.