Jj. Gregory et al., Somatic mosaicism in Fanconi anemia: Evidence of genotypic reversion in lymphohematopoietic stem cells, P NAS US, 98(5), 2001, pp. 2532-2537
Citations number
34
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Somatic mosaicism has been observed previously in the lymphocyte population
of patients with Fanconi anemia (FA). To identify the cellular origin of t
he genotypic reversion, we examined each lymphohematopoietic and stromal ce
ll lineage in an FA patient with a 2815-2816ins19 mutation in FANCA and kno
wn lymphocyte somatic mosaicism. DNA extracted from individually plucked pe
ripheral blood T cell colonies and marrow colony-forming unit granulocyte-m
acrophage and burst-forming unit erythroid cells revealed absence of the ma
ternal FANCA exon 29 mutation in 74.0%, 80.3%, and 86.2% of colonies, respe
ctively. These data, together with the absence of the FANCA exon 29 mutatio
n 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 lymphocyt
e population. Contrary to a predicted increase in marrow cellularity result
ing from reversion in a hematopoietic stem cell, pancytopenia was progressi
ve. Additional evaluations revealed a partial deletion of 11q in 3 of 20 bo
ne marrow metaphase cells. By using interphase fluorescence in situ hybridi
zation with an MLL gene probe mapped to band 11q23 to identify colony-formi
ng unit granulocyte-macrophage and burst-forming unit erythroid cells with
the 11q deletion, the abnormal clone was exclusive to colonies with the FAN
CA exon 29 mutation. Thus, we demonstrate the spontaneous genotypic reversi
on in a lymphohematopoietic stem cell. The subsequent development of a clon
al cytogenetic abnormality in nonrevertant cells suggests that ex vivo corr
ection of hematopoietic stem cells by gene transfer may not be sufficient f
or providing life-long stable hematopoiesis in patients with FA.