Congenital neutropenia: a case study

Structural abnormalities in the G-CSF receptor in severe congenital neutropenia

Structural abnormalities in the cytoplasmic region of the G-CSF receptor (G-CSF-R) or defects in signal transduction pathways triggered by the G-CSF-R or both have been implicated in the development of neutropenia and increased prediposition to leukemia in patients with severe congenital neutropenia (SCN). To assess the structural integrity of the G-CSF-R in SCN patients, the transmembrane and cytoplasmic regions of the G-CSF-R from 5 SCN patients were cloned and sequenced. DNA mutations (point, deletion, frame-shift, and silent) were observed in 3 patients. In 2 of these, the DNA mutations resulted in altered G-CSF-R protein sequences, including additions of novel C-terminal sequences. Three of the 5 mutant receptor clones lacked 115-121 amino acids in the cytoplasmic region, and 2 showed complete loss of the transmembrane and cytoplasmic regions. Neutrophils from 1 patient expressing these mutant receptors showed normal binding of radiolabeled G-CSF. G-CSF-R in 2 other patients with SCN showed no mutations. Our results indicate that structural abnormalities in the G-CSF-R may be present in some SCN patients. They may not affect the binding of G-CSF to the receptor but may contribute to the pathogenesis of SCN through impaired signal transduction pathways of the mutant G-CSF-R.

An abnormal clone with monosomy 7 and trisomy 21 in the bone marrow of a child with congenital agranulocytosis (Kostmann disease) treated with granulocyte colony-stimulating factor. Evolution towards myelodysplastic syndrome and acute basophilic leukemia

Cytogenetic analysis of bone marrow cells revealed an abnormal clone with monosomy 7 and trisomy 21 in a 12-year-old child with Kostmann disease (KD). The patient presented with anemia, thrombocytopenia, and splenomegaly after 5 years of treatment with granulocyte colony-stimulating factor (G-CSF). The bone marrow morphology was consistent with the diagnosis of myelodysplastic syndrome (MDS). Administration of G-CSF was discontinued at this point. Bone marrow studies 2 and 5 months later showed persistence of both myelodysplasia and the abnormal clone with monosomy 7 and trisomy 21. Monosomy 7 was also confirmed by fluorescence in situ hybridization (FISH). After 2 months of follow-up, the patient presented with acute basophilic leukemia, a very rare variant of acute myeloid leukemia (AML), expressing the same bone marrow chromosome abnormalities as observed earlier. This is a rare case of KD with prolonged survival and a cytogenetically abnormal clone evolving to MDS and acute basophilic leukemia. The significance of monosomy 7 and trisomy 21 in KD treated with G-CSF is discussed.

Identification of a nonsense mutation in the granulocyte-colony-stimulating factor receptor in severe congenital neutropenia

Severe congenital neutropenia (Kostmann syndrome) is characterized by profound absolute neutropenia and a maturation arrest of marrow progenitor cells at the promyelocyte-myelocyte stage. Marrow cells from such patients frequently display a reduced responsiveness to granulocyte-colony-stimulating factor (G-CSF). G-CSF binds to and activates a specific receptor which transduces signals critical for the proliferation and maturation of granulocytic progenitor cells. Here we report the identification of a somatic point mutation in one allele of the G-CSF receptor gene in a patient with severe congenital neutropenia. The mutation results in a cytoplasmic truncation of the receptor. When expressed in murine myeloid cells, the mutant receptor transduced a strong growth signal but, in contrast to the wild-type G-CSF receptor, was defective in maturation induction. The mutant receptor chain may act in a dominant negative manner to block granulocytic maturation.

Hematopoietic growth factors in clinical hematology

Five primary hematopoietic growth factors have been extensively evaluated in trials in patients with inadequate blood cell formation. Results have convincingly demonstrated that various chronic anemias can be corrected with erythropoietin. Similarly, there is no doubt that granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony stimulating factor (G-CSF) increase the number of leukocytes and improve the function of cells in patients with congenital and acquired leukopenias. Recent studies indicate that interleukin-3 (IL-3) and macrophage colony-stimulating factor (M-CSF) can also stimulate blood cell production in patients. As a result, morbidity and perhaps mortality associated with severe cytopenias can be reduced substantially.