Increased frequency of somatic mutations at glycophorin A loci in patients with aplastic anaemia, myelodysplastic syndrome and paroxysmal nocturnal haemoglobinuria

Abstract

Summary. Paroxysmal nocturnal haemoglobinuria (PNH), aplastic anaemia (AA) and myelodysplastic syndrome (MDS) are haemopoietic stem cell disorders. These disorders have some features in common, and a percentage of cases progress to acute leukaemia. We speculated that changes in gene stability are involved in the pathogenesis of these haemopoietic stem cell disorders. Therefore we investigated in vivo mutation frequencies in these disorders by erythrocyte glycophorin A (GPA) mutation assay. The assay enumerates NO or NN variant cells in 10 6 erythrocytes of the MN type using a flowcytometric technique. Patients undergoing chemotherapy known to be at risk of hypermutageneity were also studied. Events exceeding the 95th percentile of healthy donors (у 32 and 34 events, respectively for NO and NN variants) were defined as abnormal. Abnormal events in the NO variants were found in three out of seven patients undergoing chemotherapy, two out of nine patients with AA, two out of seven patients with MDS, and four out of nine patients with PNH. Abnormal events in the NN variants were found in three out of seven patients undergoing chemotherapy, two out of nine patients with AA, one out of seven patients with MDS, and two out of nine patients with PNH. These results suggest that not only PIG-A, but also other genes including the GPA gene, are hypermutable in haemopoietic stem cell disorders, and that mutagenic pressure and/or gene instability can contribute to the pathogenesis of these disorders.

HLA class II haplotype and quantitation of WT1 RNA in Japanese patients with paroxysmal nocturnal hemoglobinuria

“…The possibility indicates that expansion of a PNH clone requires a gene abnormality in addition to a PIG-A gene mutation due to gene instability. 64,65 Also, a relationship between levels of WT1 RNA and the proportion of CD166 Ϫ granulocytes may suggest that the expression is related to eliciting cytotoxic T lymphocytes for WT1-expressing hematopoietic stem cells and then to physiologic mechanisms of bone marrow recovery that are not specific to PNH if WT1 protein acts as an autoimmune target for cytotoxic T lymphocytes during selection. 4,11,17,18,[40][41][42][43] However, because of the functional diversity of the WT1 gene, as described above, there is no convincing evidence that WT1 expression immediately causes or contributes to the expansion or selection of the PNH clone.…”

“…Also, it is possible that the characteristic haplotype or other genes linked to this haplotype tend to cause the circumstances of gene instability in bone marrow hematopoietic precursor cells by some immune mechanisms. 64,65 Our views with respect to the HLA class II haplotypes in PNH suggest some important and relevant problems, including the possibility that CD4 ϩ clone(s) elicited in an HLArestricted manner are related to negative selection of hematopoietic precursor cells in PNH patients, 30 and this should be resolved in the future.…”

The spectrum of PIG-A gene mutations in aplastic anemia/paroxysmal nocturnal hemoglobinuria (AA/PNH): a high incidence of multiple mutations and evidence of a mutational hot spot

“…It is possible that we may be observing a different mutational process in AA/PNH with a possibly increased mutation rate. 43,44 In order to examine these hypotheses, it is necessary to reinvestigate the mutational spectrum in de novo PNH to determine whether the preponderance of multiple mutations we have observed is indeed unique to AA/PNH.…”

The mutation rate in PIG-A is normal in patients with paroxysmal nocturnal hemoglobinuria (PNH)

“…[15][16][17][18] Indeed, it is not uncommon for patients to harbor distinct red cell populations with a partial and complete lack of CD59 (termed PNH II and PNH III cells 4 ), which likely reflects the presence of distinct clones with partial and complete loss of GPI-anchor synthesis, respectively. 17 While the PIG-A mutant clones in patients are at least 4 orders of magnitude larger than in healthy individuals (eg, 1:5 versus 1:100 000), 5 smaller relative increases in the frequency (f) of lymphocytes with mutations in HPRT (Xq26-q27.2) [19][20][21] and red cells with variants in glycophorin A (4q28.2-q31.1) 22 have also been found in some patients with PNH. These findings have been regarded as suggestive of an increased mutation rate in PIG-A itself.…”

“…These findings have been regarded as suggestive of an increased mutation rate in PIG-A itself. 15,19,20,22,23 To investigate this hypothesis, we analyzed in PNH using the PIG-A gene itself as a sentinel gene. 24 The 5 patients whom we studied are representative of patients in whom the hypermutability hypothesis would be most applicable: those with large PNH granulocyte populations and evidence of oligoclonality based on the presence of both PNH II and PNH III red cells.…”