Chronic granulomatous disease

This is the most significant neutrophil defect, although not the most common. It is also the easiest to diagnose. It usually presents initially in childhood; rarely, first presentation may occur in adults, including the elderly.8 There is a defect of intracellular bacterial killing in neutrophils and monocytes, due to a failure of superoxide, oxygen radical, and peroxide production. Other possible reasons for failure of bacterial killing include the failure to acidify phagolysosomes, preventing optimal enzyme activation. X-linked (XL) and autosomal recessive forms are described. The defect is a deficiency of components of cytochrome b558: 91 kDa protein (X-linked; Xp21.1), 22 kDa protein (16q24), NADPH oxidase p47 (7q11.23) or p67 (1q25).9 Very rarely, skewed X-inactivation may give rise to females with XL-CGD.

The presentation is commonly infections with catalase-positive organisms, especially deep-seated abscesses, osteomyelitis and chronic granulomata (including orofacial granuloma). As phagocyte hydrogen peroxide production (due to peroxidase) is normal, organisms that are catalase negative are killed normally, whereas catalase-positive organisms, which rapidly destroy hydrogen peroxide, such as Staphylococcus aureus, Aspergillus, Nocardia and Serratia, cause major problems.10 CGD may mimic inflammatory bowel disease and lead to malabsorption and obstruction of the bowel. Liver abscess is a common first presentation, and any child with a liver abscess has CGD until proven otherwise. A more indolent presentation with widespread atypical non-caseating granulomata, mimicking sarcoidosis or Crohn’s disease may occur.11 Carriers of the gene for XL-CGD are at increased risk of discoid lupus and photosensitivity.12

The diagnostic test of choice is the flow cytometric assay of oxidative metabolism using dihydrorhodamine.13 14 The NBT reduction test can also be used. Both these assays may occasionally miss cases, so, if the history is good, it is always worth repeating the tests. Because the Kell blood group antigens are encoded adjacent to the X-CGD locus, X-L CGD patients should be tested for deficiency of Kell antigens. Kell negative XL-CGD patients are a transfusion hazard, and need to be transfused with Kell negative blood.15

Treatment is usually with long-term prophylactic antibiotics (co-trimoxazole with itraconazole). Itraconazole levels should be monitored for both appropriateness of therapy and as a check on compliance. Interferon-gamma has been used prophylactically in the United States, but in Europe tends to be reserved as adjunctive treatment for severe infections.16 Appropriate antibiotics should be used for acute infections. Cultures are essential as CGD patients often acquire unusual infections. Liaison with microbiology and mycology services is required to ensure that the antibiotics and antifungals are appropriate to the organisms identified. Surgical drainage of large abscesses may be required. Inflammatory bowel disease, which is a common problem, may be significantly helped by high-dose steroids, particularly where there are obstructive lesions due to granulomata, although this probably increases the infection risk. Stem cell transplantation is the definitive treatment and should be carried out as early as possible if the diagnosis is made under the age of 5 years. For older children and adults, bone marrow transplantation now has good results, providing that infective complications and nutritional status are not major factors at the time of transplantation. Outcomes are largely determined by infectious complications and the availability of a suitable donor for transplantation. Gene therapy has also been used. If there is good compliance with prophylaxis, long-term survival can be expected, although CGD still remains a life-shortening illness.17

Glucose-6-phosphate dehydrogenase deficiency

This is a common X-linked (Xq28) condition; the gene is prone to frequent mutation. Absence of functional G6PD (1–5% of normal activity) impairs the NADPH system of oxidative metabolism, with similar effects to CGD. However, most variants have enzyme activity of 20–50% normal and have no phagocytic defect.18

The presentation is similar to that of CGD, when <5% enzyme activity is present.19 Haemolytic anaemia is often present, and can be triggered by certain foods (fava beans) and drugs (sulphones such as dapsone, primaquine, salicylates). Most haematology departments are able to measure G6PD levels, and this should be done in all patients with suspected neutrophil defects. Neutrophil oxidative burst testing may show reduced activity. Treatment, if symptomatic, will be with prophylactic antibiotics, avoiding those that will exacerbate haemolysis.

Myeloperoxidase deficiency

This deficiency is also not uncommon (the gene is located at 17q21.3–q23). The prevalence is between 1/2000 and 1/4000 in the USA.20 Cases are usually asymptomatic, although occasional defects in killing Candida have been reported, and infection may occur particularly if the patient is diabetic. Again, haematology departments can usually measure the activity of the enzyme, so it should be undertaken as part of the work-up of suspected neutrophil immune deficiency. If tested for neutrophil oxidative burst, decreased dihydrorhodamine signal can be seen, so it is essential that the MPO levels are tested in parallel to all tests of neutrophil oxidative metabolism.21 Treatment, if symptomatic, will be with prophylactic antibiotics, although concerns have been raised that this might increase the risk of fungal infections.

Secondary (specific) granule deficiency

In this condition, neutrophil structure is abnormal with bilobed nuclei. Secondary (lactoferrin) granules are absent and there is a deficiency of other neutrophil enzymes (alkaline phosphatase, collagenase and defensins). This leads to defective neutrophil oxidative metabolism and bacterial killing, resulting in skin and sinopulmonary infections, similar to CGD. Chemotaxis is also impaired. There are also abnormalities in eosinophils.22 The diagnosis can be made by careful examination of the blood film for the neutrophil nuclear abnormalities and absence of granules, supplemented by cytochemical studies for neutrophil enzymes (NAP score), usually available through haematology laboratories. Some cases have been associated with defects in the C/EBPϵ gene (14q11.2), a CCAAT enhancer protein-binding protein, which acts as a transcription factor in myelopoeisis.23 Bone marrow transplantation has been used successfully.24

Cyclic neutropenia

Cyclic neutropenia (CN) is a rare syndrome characterised by cyclic reductions in neutrophils, but it is perhaps more common than previously thought, with milder variants escaping notice. It is an autosomal dominant disorder due to mutations in ELA2 gene, encoding neutrophil elastase.27 Mutations affect whether elastase localises to granules or to cell surface membrane. Membrane expression is associated with disease. Similar mutations in ELA2 also cause severe congenital neutropenia. The cycle is usually 21 days ± 2–3 days, although other patterns have been described, with cycles of 15–35 days, but the molecular cause of cycling is unknown. The superficially similar disease in dogs (grey collie syndrome) is due to a different gene defect, and has a 14 day cycle; genetic studies have shown that the mutations in CN are different from those in severe congenital neutropenia (SCN).28

The presentation is usually cyclic mouth ulceration, which typically occurs at the neutrophil nadir. More significant invasive infection may also occur. Mood change just before the nadir is often marked. Symptoms may improve with age. The diagnosis is often delayed because by the time a neutrophil count is checked the nadir has passed and the count is already increasing again. If checked at the onset of ulcers the count will be low. There is a compensatory monocytosis at the time of the neutrophil nadir. The diagnosis can only be confirmed by serial full blood counts with full differential, three times weekly over 4–6 weeks. Neutrophils may disappear completely. Symptoms usually occur if the count drops below 1×109/l.

Treatment is with prophylactic co-trimoxazole, continuously or either side of the predicted nadir. More severe infections require prompt cultures and intravenous antibiotics. Granulocyte colony-stimulating factor (G-CSF) prevents a dramatic drop but does not abolish the cycle, which shortens to approximately 14 days. There is, however, a risk of myeloid leukaemia with chronic G-CSF therapy and this should be used with circumspection. Data suggest that ELA2 mutations increase the risk of acute myeloid leukaemia (AML) and myelodysplasia (MDS), and this may be increased further by G-CSF use.

Severe congenital neutropenia

Four different genetic variants of SCN have been reported.26 29 30 The majority of cases have defects in the ELA2 gene, as in cyclic neutropenia, and are at risk of developing MDS and AML. The disorder is autosomal dominant and homozygous defects have not been reported. The neutropenia is however static. Rare cases have been associated with autosomal dominant mutations in the transcriptional repressor Gfi1 gene, causing over-expression of elastase and overflow onto the cell membrane: these cases also have lymphopenia. WASP mutations have been associated with X-linked neutropenia.31 Mutations have also been reported in the gene encoding the receptor for G-CSF: these cases do not develop MDS or AML. Other possible defects in the ELA2 promoter region may also contribute to SCN cases. Treatment is with colony-stimulating factors or with stem cell transplantation.

Kostmann syndrome

This is a congenital severe neutropenia due to a neutrophil maturation defect with arrest at the pro-myelocyte stage. This is genetically distinct from severe congenital neutropenia and has been associated with mutations in the HAX-1 gene.32 It presents with recurrent severe infections. Immunoglobulins are raised; there is a compensatory monocytosis, eosinophilia, and a thrombocytosis. Stem cell transplantation may be used as treatment. Co-trimoxazole prophylaxis is necessary.

Shwachman–Bodian–Diamond syndrome

This is an autosomal recessive syndrome of hereditary exocrine pancreatic insufficiency, accompanied by neutropenia, abnormal neutrophil chemotaxis, thrombocytopenia, anaemia and metaphyseal chrondrodysplasia.33 NK cell lymphopenia is common. A gene has been identified (SBDSP),34 but the function is only just being explored. Studies suggest that it controls gene expression in multiple organs (brain, bone, blood and cell adhesions) and is involved in rRNA synthesis.35 Short stature is usual. Hypogammaglobulinaemia with recurrent sinopulmonary infections may also occur. Responses to polysaccharide antigens may be absent.36 Treatment with intravenous immunoglobulin may be helpful, and G-CSF has been used although there is concern over potential risk of myeloid leukaemias. Haematopoeitic stem cell transplantation has also been tried.37

WHIM syndrome

Warts, hypogammaglobulinaemia, infection, myelokathexis (WHIM) syndrome is a rare autosomal recessive immunodeficiency and is the first to be associated with deficiency of a chemokines receptor (CXCR4; gene located at 2p21).38 39 CXCR4 is the receptor for stromal derived factor 1 (SDF-1). SDF-1 is essential for normal myeloid maturation and differentiation; absence of SDF-1 increases granulocyte apoptosis and causes myelokathexis (white blood cell retention). CXCR4 has also been identified as the co-receptor for HIV.

WHIM syndrome presents early in childhood with recurrent bacterial infections, developing into bronchiectasis.40 Severe granulocytopenia and lymphopenia are present and the bone marrow shows granulocyte hyperplasia. Neutrophil function is normal. Hypogammaglobulinaemia is present with reduced B cell numbers, especially memory B cells. Warts (papillomavirus infection) develop later and are extensive and confluent; genital warts will predispose to cervical carcinoma. Rare patients have cardiac defects.

Treatment will involve the use of prophylactic antibiotics, immunoglobulin replacement therapy where humoral immune function is impaired, and G-CSF to increase neutrophil emigration (even though levels in vivo may be raised).

Leucocyte adhesion molecule deficiency (LAD-1, LAD-2, LAD-3 and Rac2 deficiency

LAD-1 is due to a deficiency of the β-chain (CD18) for LFA-1 (CD11a), Mac-1 (CD11b) and CR4 (CD11c).47 The gene is located at 21q22.3. There may be variable expression: the severe phenotype has <1% expression, while in the moderate (incomplete) phenotype there may be as much as 10% of control expression. Rare cases may be due to defects in other chains (CD11c?) and the Lewis X ligand (LAD-2),48 caused by an inability to synthesise fucose. These defects lead to an inability of the phagocytic cells to migrate to sites of inflammation.49 There is usually a peripheral blood neutrophilia.

LAD-3 has been described recently in two patients due to defects in which lymphocytes, neutrophils and platelets share severe defects in β-integrin activation due to homozygous splice junction mutation in their CalDAG-GEFI gene, a Rap-1/2 guanine exchange factor (GEF).50

An autosomal dominant mutation in the rho-GTPase Rac2, (22q12.13) has been associated with a presentation similar to LAD-1, with delayed umbilical cord separation, absence of pus and perirectal ulceration.51

The presentation is variable, depending on the phenotype, but a key feature in the newborn is delayed (>10 days) umbilical cord separation. Skin infections, intestinal and perianal ulcers and fistulae are typical, but typically there is an absence of pus and inflammation, due the failure of neutrophils to migrate to sites of infection. Periodontitis occurs in older children and may lead to loss of teeth. Immunisations may leave scarred nodules.

The diagnosis is highly dependent on the clinical presentation and can be confirmed by flow cytometric analysis of the expression of the relevant surface markers in LAD-1 and LAD-2. Stimulation with phorbol esters to look for up-regulation may be necessary in mild–moderate phenotypes. The treatment is early bone marrow transplantation, although moderate phenotypes may be difficult to transplant.