CLONAL HEMATOPOIESIS IN CHILDREN WITH ACQUIRED APLASTIC-ANEMIA

The methylation pattern of three X-linked genes, phosphoglycerate kina se (PGK), hypoxanthine phosphoribosyl transferase (HPRT) and DXS255 de tected by hypervariable M27beta probe, was analysed to determine the p roportion of aplastic anaemia (AA) with clonal haematopoiesis in Japan ese children. Methylation analysis was performed on DNA from separated granulocytes and compared to that of bone marrow derived fibroblasts to exclude selective lyonization in all somatic cells. Of 20 female pa tients examined, the methylation pattern of at least one gene was info rmative in granulocyte DNA from 18 patients (90%). Of these, 8/20 pati ents (40%) were heterozygous for PGK, 8/18 (44%) were heterozygous for HPRT and 17/18 (94%) were heterozygous for DXS255. In 14/18 patients both alleles were equally methylated. Four patients exhibited a unilat eral methylation pattern in their granulocytes. The same unilateral pa ttern was again demonstrated in fibroblasts from two of the four patie nts suggesting that in the latter one X chromosome was selectively ina ctivated in all of the somatic cells. The remaining two patients showe d a unilateral methylation pattern that was restricted to their granul ocytes, suggesting the existence of true clonal haematopoiesis. They r esponded well to antilymphocyte globulin (ALG) and presently have no e vidence of a clonal disorder such as myelodysplastic syndrome (MDS) or paroxysmal nocturnal haemoglobinuria (PNH). Although these results in dicate that some children with AA exhibit clonal haematopoiesis, analy sis of a greater number of subjects will be required to establish the clinical value of clonal haematopoiesis in patients with AA.