Somatic mosaicism in Fanconi anemia: evidence of genotypic reversion in lymphohematopoietic stem cells.
Somatic mosaicism has been observed previously in the lymphocyte population of patients with Fanconi anemia (FA). To identify the cellular origin of the genotypic reversion, we examined each lymphohematopoietic and stromal cell lineage in an FA patient with a 2815-2816ins19 mutation in FANCA and known lymphocyte somatic mosaicism. DNA extracted from individually plucked peripheral blood T cell colonies and marrow colony-forming unit granulocyte-macrophage and burst-forming unit erythroid cells revealed absence of the maternal FANCA exon 29 mutation in 74.0%, 80.3%, and 86.2% of colonies, respectively. These data, together with the absence of the FANCA exon 29 mutation in Epstein-Barr virus-transformed B cells and its presence in fibroblasts, indicate that genotypic reversion, most likely because of back mutation, originated in a lymphohematopoietic stem cell and not solely in a lymphocyte population. Contrary to a predicted increase in marrow cellularity resulting from reversion in a hematopoietic stem cell, pancytopenia was progressive. Additional evaluations revealed a partial deletion of 11q in 3 of 20 bone marrow metaphase cells. By using interphase fluorescence in situ hybridization with an MLL gene probe mapped to band 11q23 to identify colony-forming unit granulocyte-macrophage and burst-forming unit erythroid cells with the 11q deletion, the abnormal clone was exclusive to colonies with the FANCA exon 29 mutation. Thus, we demonstrate the spontaneous genotypic reversion in a lymphohematopoietic stem cell. The subsequent development of a clonal cytogenetic abnormality in nonrevertant cells suggests that ex vivo correction of hematopoietic stem cells by gene transfer may not be sufficient for providing life-long stable hematopoiesis in patients with FA.
Gregory
J J
JJ
Laboratory of Human Genetics and Hematology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
Wagner
J E
JE
Verlander
P C
PC
Levran
O
O
Batish
S D
SD
Eide
C R
CR
Steffenhagen
A
A
Hirsch
B
B
Auerbach
A D
AD
D001483:Base Sequence; D002869:Chromosome Aberrations; D025063:Chromosome Disorders; D017931:DNA Primers; D005199:Fanconi Anemia / Q000235:genetics*; D005838:Genotype; D006412:Hematopoietic Stem Cells / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D009030:Mosaicism; D016133:Polymerase Chain Reaction
D017931:DNA Primers