Severe Congenital Neutropenia (Kostmann Syndrome)

REVIEW ARTICLE Egypt. J. Med. Hum. Genet. Vol. 11, No. 1, May, 2010 Severe congenital neutropenia (Kostmann Syndrome)

Soad Khalil Al-Jaouni.

Department of Hematology, Faculty of Medicine, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia

ABSTRACT

Severe congenital neutropenia (SCN), Kostmann syndrome is a heterogenous disorder of myelopoiesis characterized by severe chronic neutropenia, absolute neutrophil count (ANC) persistently below 0.50 x 109/L, with maturation arrest of neutrophil precursors in the bone marrow; and associated with serious recurrent bacterial infections from early infancy. Sepsis mortality is reduced by an advent of granulocyte colony stimulating factor (G-CSF) therapy. More than 90% of patients respond to G-CSF therapy. However, hematopoietic stem cell transplantation has shown promise in the treatment of non-responders. About 60-80% of SCN cases are associated with constitutive mutations in one copy of the gene encoding neutrophil elastase ELA2. Myelodysplastic syndrome and acute myeloid leukemia (MDS/AML) have been reported. The hazard of MDS/AML increases significantly overtime. Approximately 10% of patients with severe congenital neutropenia develop AML. This is not thought to be the direct result of G-CSF therapy but related to the underlying disease itself.

Key Words: Corresponding Author: Myeloid leukemia, congenital neutro- Soad Khalil Al-Jaouni, penia, kostmann’s syndrome, myelo- E-mail: [email protected] dysplastic syndrome.

INTRODUCTION

Neutrophils play a vital role in protect- The category of SCN was first clearly ing the body against invasion by bac- described by Kostmann in 1956 in Swed- teria. Severe chronic neutropenia is a ish kindred. An alternative name for general term for conditions with abso- Kostmann syndrome is infantile genetic lute neutrophil count (ANC) of less than agranulocytosis2. Kostmann syndrome 0.50x 109/L, lasting for months or years. represents an autosomal recessive, het- Chronic neutropenia is caused by a va- erogenous hematological disorders, riety of hematological, immunological, characterized by extremely low circu- metabolic and infectious diseases1. lating neutrophils and maturation ar-

Copyright: All rights reserved for The Egyptian Journal of Medical Human Genetics 1 (Kostmann Syndrome) rest at the promyelocyte-myelocyte in matopoietic stem cell transplantation. the bone marrow. Neutrophil counts in these patients are typically <0.2x 109/L, The classic Kostmann syndrome is rec- with the majority presenting with life- ognized in early infancy with an equal threatening infection during the first 6 incidence in males and females. Severe months of life. SCN with similar clini- neutropenia is brought to clinical at- cal features occurs as an autosomal tention after an initial infection which dominant disorder and many sporadic typically occurs shortly after birth. cases also have been reported3. Symptoms of Kostmann include the followings: Temperature instability in Other conditions grouped with se- newborn period, fever, irritability and vere congenital neutropenia (CN) in- localized sites of infection. clude Shwachman-Diamond syndrome (SDS); inborn errors of metabolism Physical and signs of Kostmann syn- (e.g., glycogen-storage disease, type drome include the followings: Oral Ib)4; severe combined immunodefi- ulcers, gingivitis, pharyngitis, sinusitis ciency (SCID) syndromes; hyper-IgM and/or otitis media, bronchitis and/or syndrome and a few other conditions3,32 pneumonia, cellulitis, cutaneous ab- Patients with clinically mild disease, scess and/or boils, perianal abscess, generally tend to have a less abnormal lung or liver abscess, enteritis with bone marrow. The estimated frequency chronic diarrhea and vomiting. Bac- of these conditions is approximately teremia and/or septicemia occur, most 1-2 cases per million population. commonly from streptococci or staphy- lococci; other organisms include Pseu- Pathophysiology: domonas, fungi and in rare cases Clos- tridium species. Neutropenia refers to an ANC that is two or more standard deviations below Pathogenesis of congenital neutrope- the age related mean. Normal neutro- nia: phil levels differ according to age and race. In general, an ANC is calculated The underlying genetic defect of SCN by multiplying the total leukocyte count is still only partially understood. Some per milliliter by the percentage of neu- investigators have proposed that Kost- trophils and immature neutrophil form. mann syndrome represents a defect in In general, an ANC of 1000–1500/mm3 the regulation or production of granu- indicates mild neutropenia; 500-1000/ locyte colony-stimulating factor (G- mm3 indicates moderate neutropenia; CSF). and less than 500/mm3 indicates severe neutropenia. This classification is use- An abnormal G-CSF-induced intracel- ful for predicting risk of infections. lular signal transduction pathway has been suggested as a potential cause of Mortality/Morbidity: the underlying genetic defect. Neutro- phils from patients are shown to have The mortality rate is 70% within the dramatically increased levels of 2 cyto- first year of life in the absence of medi- solic protein tyrosine phosphatases that cal intervention with G-CSF and/or he- contain Src-homology 2 domain (SH2

2 Al-Jaouni domain): Anti-Src Homology Phos- national Registry (SCNIR) is an impor- phatase-1 (SHP-1) and Src Homology tant resource for studies on genetic and Phosphatase 2 (SHP2). One hypothesis molecular bases for disorders causing is that over expression of these proteins, severe chronic neutropenia. which are involved in cytokine receptor signaling, plays a role in altering intra- Approximately 60-80% of SCN cases cellular signal transduction processes. are associated with inherited or spon- taneous point mutation in one copy A selective decrease of B-Cell Lym- of the gene encoding neutrophil elas- phoma-2 (BCL-2) expression in my- tase ELA2. This mutation is found in eloid cells and an increase in apoptosis the analysis of congenital neutropenia in bone marrow progenitor cells have (CN) families with autosomal dominant been observed. The primary function inheritance. of BCL-2, a mitochondria-targeted protein, is the prevention of Cytochrome Although neutrophil elastase mutations release. Cytochrome has the capability have been found in a subgroup of pa- of activating a cytosolic caspases cas- tients with Kostmann syndrome, as in cade. Caspases are integral proteolytic cyclic neutropenia. Adverse events in- enzymes involved in cellular apoptosis. clude the development of acute myeloid They are activated through one of two leukemia in approximately 7% of the pathways: patients within the cohort of patients with Kostmann’s syndrome suggesting 1. An extrinsic, death receptor-depen- that congenital neutropenia is a preleu- dent pathway or. kemia syndrome. None of the patients 2. An intrinsic, mitochondria-depen- with cyclic of idiopathic neutropenia dent pathway. Mitochondrial re- developed leukemia.1, 6 lease of Cytochrome c serves to initiate the cytosolic caspases cas- A subset of SCN patients harbor ac- cade through the second pathway. quired somatic mutations in the CSF3R The decreased BCL-2 results in an gene; encoding the granulocyte colony- enhanced release of Cytochrome stimulating factor receptor (G-CSF-R), c, which then perpetuates the cas- which has shown a strong predisposi- pases cascade leading to more pro- tion to acute myeloid leukemia7, 8.These nounced apoptosis. mutations truncate the intracellular domain, producing strong hyper-prolif- In Kostmann syndrome, the G-CSF re- eration, but with defective maturation ceptors are expressed on myeloid cells due to defective internalization and loss in slightly increased numbers and the binding sites for several negative regu- binding affinity for G-CSF to its recep- lators, thus lead to extended signaling tors is normal. This is in contrary to especially of STAT5 (Signal transduc- the original theory that the underlying er and activator of transcription 5)9-12. Kostmann defect was related to either Other studies reported a further subset decreased G-CSF production or dimin- of SCN patients, with constitutive mu- ished binding of G-CSF to its receptor.5 tations in the extracellular domain of the G-CSF-R that collectively act in a The Severe Chronic Neutropenia Inter- dominant-negative manner leading to

3 (Kostmann Syndrome) hypo-responsiveness to G-CSF.13, 14 age dependent range for electrolytes, kidney and liver functions. Testing for Studies of the G CSF gene have shown anti-neutrophil antibodies is helpful to that mutation occur mainly within a exclude autoimmune neutropenia of in- critical region of the intracellular part fancy. of the receptor.16, 18 The bone marrow usually shows matu- Using a positional cloning approach and ration arrest of neutrophil precursors at candidate gene evaluation in autosomal an early stage (Promyelocyte/myelo- recessive severe congenital neutropenic cyte level) with few cells of the neu- patients (Kostmann disease) were iden- trophilic series. Promyelocytes often tified a recurrent homozygous germ line have morphologically atypical nuclei mutation in HAX1. HAX1 encodes the and vacuolization of cytoplasm. The mitochondrial protein HAX1, which absolute number of promyelocytes is has been assigned functions in signal slightly increased. Megakaryocytes transduction and cytoskeletal control. are normal in number and morphology. HAX1 is a critical for maintaining the In vitro growth of granulocyte macro- inner mitochondrial membrane poten- phage progenitor cell is defective, with tial and protecting against apoptosis few colonies formed and evidence for in neutrophil development, HAXI de- “Maturation arrest”. Cytogenetic at the ficiency causes autosomal recessive time of diagnosis of CN are almost al- Kostmann disease.15, 33 ways normal. Bone marrow cytogenetics may change during the course of the Diagnosis: disease, with monosomy 7 being the most frequent aberration in about 50% Severe Congenital Neutropenia is usu- of abnormal cytogenetic results. The in- ally detected in infancy after fever or terval from the original finding of nor- signs of severe infection develop. Pa- mal cytogenetics to the appearance of tients have ANCs continuously below an abnormality is often several years. 0.2 x 109/L; in many cases, periph- Abnormal cytogenetics is often associ- eral blood neutrophils are completely ated with morphologic changes of the absent. With infection, there may be a bone marrow indicating the develop- transient increase in neutrophils, but ment of MDS or Leukemia. counts rarely increase to normal levels. Repeated differential blood counts in- Differential Diagnosis: dicate persistent ANCs within a range of 0 to 0.2 x 109/L is required for di- The differential diagnosis of CN in- agnosis. Blood counts often indicate cludes a number of congenital and ac- mild anemia and thrombocytosis. There quired diseases17. The most common is usually a two to four fold increase in difficulty is determining whether the blood monocytes and an increase in the patient has cyclic neutropenia, autoim- blood eosinophils count is common. mune neutropenia of infancy, or idio- IgG levels are elevated in the majority pathic neutropenia. Cyclic neutropenia of patients. The specific immunologic is diagnosed by serial measurement of competence after vaccination is normal. blood neutrophils on at least 3 days per Blood chemistry is within the normal, week for at least 6 weeks, graphing the

4 Al-Jaouni count. Cyclic neutropenia is also a he- ment of dosages on the basis of both the reditable disease. Family and genetic patient’s clinical course and the ANC. studies show that it is an autosomal The efficiency of rHuG-CSF has been dominant disorder19. An important dif- demonstrated by increasing the number ferential diagnostic evaluation is testing of neutrophils with reduction of infec- for neutrophilic antibodies20. Although tion23, 24. In contrast, GM-CSF treatment these infants lack peripheral blood neu- did not led to an increase in blood neutrophils, the marrow function is nor- trophils, but only in blood eosinophils25. mal; maturation of myeloid precursors In 1994, the SCNIR collected data from to mature neutrophil stage is usually more than 600 patients with CN, results observed. Neutrophil or granulocyte demonstrated that more than 95% re- specific antibodies in serum are detect- sponded to rHuG-CSF treatment with able using immunologic test. Idiopathic an increase in ANCs to 1.0 x ≥109/L.3 neutropenia is a form of acquired neu- Most CN patients responded to a dose tropenia, it includes patients without between 3 and 10 mg/kg/d.16,17 evidence of congenital, neoplastic, or immunological causes of neutropenia, Generally, rHuG-CSF should be initi- the clinical phenotype is similar to au- ated at 5 mg/kg/day, the dose should toimmune neutropenia. Patients are cat- be escalated to 10 mg/kg/day and then egorized as having idiopathic neutro- by increments of 10 mg/kg/day at 14- penia unless they are positive for anti days intervals if the ANC remains be- neutrophil antibodies.21, 22 low 1.0 x 109/L. As soon as the ANC can be maintained at 1.0 to 1.5 x 109/L Therapy: or above, further increase in rHuG-CSF dose can be stopped since the occur- Severe CN is often recognized when rence of bacterial infection is reduced patients present with life-threatening dramatically at this level. The dose of infection during the few months of rHuG-CSF can be reduced if the ANC life and are found to have extremely increases to ≥5.0 x 109/L to keep the low circulating neutrophils. Antibiotic patient at the lowest dose necessary for therapy for these infections follows the maintaining sufficient neutrophil count same principles as for other patients: to overcome infections.23, 29 broad-spectrum antibiotics for severe infections until the pathogen is identi- Non responders to rHuG-CSF are de- fied; targeted therapy for specific patho- fined by failure to benefit at dose lev- gens; administration of antibiotics until els exceeding 120 mg/kg/day. Partial the signs and symptoms of infection responders have ANCs increased to 0.5 have cleared. Prophylactic antibiotics to 1.0 x 109/L but still have bacterial in- may be considered, but are required infections. In some patients, the dose of frequently since the advent of G-CSF in rHuG-CSF cannot be increased to these 198723. Recombinant human granulo- levels because of the large volume and cyte colony-stimulating factor (rHuG- frequency of injections required. Pa- CSF) requires long-term daily adminis- tient was refractory to standard and tration to maintain clinical benefit. The high dose G-CSF therapy, but respond- ANC should not be the sole indicator ed to a combined corticosteroid/G-CSF of clinical efficacy. Individual adjust- treatment, apparently through synergis-

5 (Kostmann Syndrome) tic activation of STAT5 and stimulate R mutation), which may be useful for G-CSF-induced cell proliferation.26, 27 identifying subgroups of patients at high risk. Marrow cells from approximately All responding patients require signifi- 75% of the severe CN cases that trans- cantly fewer antibiotics and fewer days formed to MDS/AML also show point of hospitalization. Hematopoietic stem mutations in the gene for the G-CSF- cell transplantation (HSCT) remains the R; resulting in a truncated C-terminal only currently available treatment for cytoplasmic region of the receptor that patients who are refractory to rHuG- is crucial for maturation signaling30. G- CSF treatment or in those with leuke- CSF therapy can cause cataract and this mic transformation.28 adverse event is dose related.31

Adverse events to rHuG-CSF therapy CONCLUSION include mild splenomegaly, osteoporo- sis and malignant transformation into The use of rHuG-CSF remains first-line MDS/Leukemia. If and how G-CSF treatment for most CN patients, which treatment impacts on these adverse greatly improved patient’s quality of events is not fully understood. The haz- life. ard of MDS/Leukemia increases significantly overtime. All CN patients, regardless of their treatment or response, are at risk to In the study of Rosenberg, et al.29, the develop MDS/ or leukemia at an ac- hazard of MDS/AML increased sig- tual evidence of 11.5% and accumula- nificantly during the period of - obser tive incidence of 21% after 10 years. vation of SCN on G-CSF, from 2.9% Careful monitoring for cytogenetic per year after 6 years to 8.0% per year abnormalities and G-CSF-R mutation after 12 years. The cumulative inci- is necessary to initiate. Hematopoietic dence of MDS/AML was 21% after 10 Stem Cell Transplant (HSCT) should years. The risk of MDS/AML increased be restricted to G-CSF non-respond and with the dose of G-CSF. Less respon- leukemic transformation. sive patients, defined as those requiring greater than 8 mg/kg/d of G-CSF, had ACKNOWLEDGEMENTS a cumulative incidence of MDS/AML of 40% after 10 years and compared to The author would like to extend sincere 11% of more responsive patients. The thanks for Mrs. Susana de Guzman for data were interpreted as indicating that her assistance in writing this article. a poor response to G-CSF defines an “at-risk” population and predicts an ad- REFERENCES verse outcome.29 1. Welte K and Dale D. Pathophysiology Conversion to MDS/AML in CN pa- and treatment of severe chronic neutro- tients was associated with one or more penia. Ann.Hematol. 1996 72(4):158- cellular genetic abnormalities (Such as 65. monosomy7 and as mutation or G-CSF-

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