Göran Carlsson

HAX1 deficiency causes autosomal recessive severe congenital neutropenia (Kostmann disease)

Autosomal recessive severe congenital neutropenia (SCN) constitutes a primary immunodeficiency syndrome associated with increased apoptosis in myeloid cells, yet the underlying genetic defect remains unknown. Using a positional cloning approach and candidate gene evaluation, we identified a recurrent homozygous germline mutation in HAX1 in three pedigrees. After further molecular screening of individuals with SCN, we identified 19 additional affected individuals with homozygous HAX1 mutations, including three belonging to the original pedigree described by Kostmann. HAX1 encodes the mitochondrial protein HAX1, which has been assigned functions in signal transduction and cytoskeletal control. Here, we show that HAX1 is critical for maintaining the inner mitochondrial membrane potential and protecting against apoptosis in myeloid cells. Our findings suggest that HAX1 is a major regulator of myeloid homeostasis and underline the significance of genetic control of apoptosis in neutrophil development.

Central nervous system involvement in severe congenital neutropenia: neurological and neuropsychological abnormalities associated with specific HAX1 mutations

Objectives.  Homozygous mutations in the HAX1 gene were recently identified in severe congenital neutropenia patients belonging to the original Kostmann family in northern Sweden. Our observations suggested that these patients also develop neurological and neuropsychological symptoms.

Kostmann syndrome or infantile genetic agranulocytosis, part two: understanding the underlying genetic defects in severe congenital neutropenia

Congenital neutropenia in man was first reported 50 years ago by the Swedish paediatrician Rolf Kostmann. He coined the term ‘infantile genetic agranulocytosis’ for this condition, which is now known as Kostmann syndrome. Recent studies have revealed mutations in ELA‐2, encoding the neutrophil granule protease, neutrophil elastase, in autosomal dominant neutropenia, and mutations in HAX‐1, encoding an anti‐apoptotic protein, in autosomal recessive neutropenia.

Kostmann syndrome or infantile genetic agranulocytosis, part one : celebrating 50 years of clinical and basic research on severe congenital neutropenia

Congenital neutropenia in man was first reported 50 years ago by the Swedish paediatrician Rolf Kostmann. He coined the term “infantile genetic agranulocytosis” for this condition, which is now known as Kostmann syndrome. Recent studies have demonstrated a lack of antibacterial peptides and severe periodontitis in these patients despite recombinant growth factor treatment. Moreover, an increased degree of apoptosis of myeloid progenitor cells in the bone marrow has been shown.

Incidence of severe congenital neutropenia in Sweden and risk of evolution to myelodysplastic syndrome/leukaemia

Severe congenital neutropenia (SCN) is characterized by low blood neutrophil counts, early bacterial infections, and risk of leukaemia development. As yet, no population‐based incidence estimates of SCN have been reported. Children less than 16 years of age with SCN were sought in Sweden during the 20‐year period 1987–2006 by a questionnaire to all Swedish Departments of Paediatrics and by reviewing the Swedish Health and Welfare Statistical Databases. Thirty‐two patients were diagnosed with congenital neutropenia during this period. All received treatment with recombinant granulocyte‐colony stimulating factor (G‐CSF). Twenty‐one patients were diagnosed as SCN or probable SCN, corresponding to 1·0 per 100 000 live births. Nine (43%) had ELANE mutations, four (19%) HAX1 mutations and eight (38%) were children with disease of unknown genetic aetiology. Four out of 21 patients (19%) developed myelodysplastic syndrome/leukaemia and three (14%) died, all with leukaemia. The cumulative incidence of myelodysplastic syndrome/leukaemia was 31%. The observed incidence of SCN in this population‐based study was higher than previously estimated, possibly because genetic testing now can identify SCN cases previously thought to be idiopathic or benign neutropenia. The risk of developing myelodysplastic syndrome/leukaemia is considerable. ELANE mutations are the most commonly identified genetic defects.

Hematopoietic stem cell transplantation in severe congenital neutropenia

Severe congenital neutropenia (SCN) is an immunodeficiency characterized by disturbed myelopoiesis and an absolute neutrophil count (ANC) <0.5 × 109/L. SCN is also a premalignant condition; a significant proportion of patients develop myelodysplastic syndrome or leukemia (MDS/L). Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative treatment for SCN.

Low plasma levels of the protein pro-LL-37 as an early indication of severe disease in patients with chronic neutropenia

Chronic neutropenia comprises several different diseases that vary in degree of severity and management. We analysed the levels of the neutrophil‐derived protein pro‐LL‐37 in plasma of patients with chronic neutropenia to assess whether it could be used to differentiate different categories of chronic neutropenia. All patients with severe congenital neutropenia were pro‐LL‐37 deficient. This was in contrast to patients with autoimmune or idiopathic neutropenia, who exhibited normal pro‐LL‐37 levels while patients with cyclic neutropenia displayed an oscillation of pro‐LL‐37 in plasma. Plasma levels of pro‐LL‐37 may thus prove useful for differential diagnosis of chronic neutropenia.

The natural history of severe anemia in cartilage-hair hypoplasia.

Anemia is seen in over 80% of patients with cartilage‐hair hypoplasia (CHH). While this is usually mild and self‐limited, some patients demonstrate a severe, persistent anemia resembling that seen in Diamond‐Blackfan anemia (DBA). This paper examines the natural history of 12 patients with CHH and severe anemia. Phenotypic features and mutation data (where available) were reviewed, but no significant differences were found that predicted severe anemia. Severe anemia is estimated to occur in approximately 6% of CHH patients and is permanent in more than half of these patients. Thrombocytosis, though not previously reported in CHH, was noted in five patients, similar to that seen in DBA. The role of possible gene–gene and gene–environment interactions is discussed.

Oral bacterial community dynamics in paediatric patients with malignancies in relation to chemotherapy-related oral mucositis: a prospective study.

The role of oral bacteria in the development of chemotherapy-related oral mucositis has not been fully elucidated. This study aimed to investigate oral bacterial community diversity and dynamics in paediatric patients with malignancies in relation to the occurrence of oral mucositis. Patients with malignancies (n = 37) and reference individuals without known systemic disorders (n = 38) were recruited. For patients, oral bacterial samples were taken from mucosal surfaces both at the time of malignancy diagnosis and during chemotherapy. If oral mucositis occurred, samples were taken from the surface of the mucositis lesions. Oral mucosal bacterial samples were also taken from reference individuals. All samples were assessed using a 16S ribosomal RNA gene 454 pyrosequencing method. A lower microbial diversity (p < 0.01) and a higher intersubject variability (p < 0.001) were found in patients as compared with reference individuals. At the time of malignancy diagnosis (i.e. before chemotherapy) patients that later developed mucositis showed a higher microbial diversity (p < 0.05) and a higher intersubject variability (p < 0.001) compared with those without mucositis. The change of bacterial composition during chemotherapy was more pronounced in patients who later developed mucositis than those without mucositis (p < 0.01). In conclusion, we found a higher microbial diversity at the time of malignancy diagnosis in patients who later develop oral mucositis and that these patients had a more significant modification of the bacterial community by chemotherapy before the occurrence of mucositis. These findings may possibly be of clinical importance in developing better strategies for personalized preventive management.

Vitamin D3 induces pro-LL-37 expression in myeloid precursors from patients with severe congenital neutropenia

The innate immune system produces a number of effector molecules that are important for protection against bacterial infections. Neutrophils and antimicrobial peptides are major components of innate defense with the capacity of rapid bacterial killing. Patients with severe congenital neutropenia (SCN) experience recurrent and chronic infections despite recombinant G‐CSF‐mobilized neutrophils. We have shown previously that these neutrophils are deficient in that they lack the antimicrobial peptide LL‐37. Here, we show that pro‐LL‐37 mRNA is not expressed in neutrophil precursors from patients with SCN, although the gene and promoter region for pro‐LL‐37, CAMP, does not display any mutations. The hormonal form of vitamin D3 [1,25(OH)2D3] induced the expression of pro‐LL‐37 in isolated neutrophil progenitors and in EBV‐transformed B cells from patients with SCN, whereas all‐trans retinoic acid only induced expression in transformed B cells. These results demonstrate that myeloid cells of patients with SCN can produce pro‐LL‐37, suggesting that other pathways are impaired.