Frequency of point mutations in the gene for the G-CSF receptor in patients with chronic neutropenia undergoing G-CSF therapy.

Point mutations in the gene for the G-CSF receptor have been reported previously in a subgroup of patients with severe congenital neutropenia. Here, we investigated the frequency of these specific G-CSF receptor mutations in patients with neutropenic disorders undergoing treatment with recombinant human (r-metHu)G-CSF (Filgrastim). Nucleotides 2306 to 2561, including the critical region (nucleotides 2384-2429) from the intracellular domain of the G-CSF receptor gene, were amplified by reverse transcriptase-polymerase chain reaction, and DNA was sequenced directly and after transformation in E. coli. Four of 30 patients with severe congenital neutropenia displayed a point mutation in the tested cytoplasmic region of the G-CSF receptor gene. Two of the four patients with a mutated G-CSF receptor developed acute myeloid leukemia secondary to congenital neutropenia. G-CSF receptor analyses were performed in myeloid cells taken at different time points in the four patients with the mutated receptor, and no correlation between occurrence of the mutation and time or dose of r-metHuG-CSF treatment was found. No point mutations in the G-CSF receptor critical domain could be detected in cells from the other 26 congenital neutropenia patients. Additionally, no G-CSF receptor point mutations could be seen in neutrophils, blood and bone marrow mononuclear cells from patients with cyclic or idiopathic neutropenia, and bone marrow mononuclear cells from patients suffering from severe aplastic anemia. Similar results were obtained by Touw et al., demonstrating that five out of 25 patients with congenital neutropenia reveal G-CSF receptor mutations. These data show that the point mutations in the critical region of the intracellular part of the G-CSF receptor occur only in a subgroup of severe congenital neutropenia patients. Furthermore, our data suggest that the described G-CSF receptor point mutations are not correlated with the start, duration or doses of r-metHuG-CSF treatment, but might result from genetic instability in the G-CSF receptor gene in severe congenital neutropenia.