Among patients with bone marrow failure (BMF) syndrome, some are happened to 
have underlying Fanconi anemia (FA), a genetically heterogeneous disease, which 
is characterized by progressive pancytopenia and cancer susceptibility. Due to 
heterogeneous nature of the disease, a single genetic test, as in vitro response 
to DNA cross-linking agents, usually is not enough to make correct diagnosis. 
The aim of this study was to evaluate whether measuring repair kinetics of 
radiation-induced DNA double-strand breaks (DSBs) can distinguish Fanconi anemia 
from other BMF patients. An early step in repair of DSBs is phosphorylation of 
the histone H2AX, generating gamma-H2AX histone, which extends over mega 
base-pair regions of DNA from the break site and is visualised as foci 
(gamma-H2AX foci) with specific antibodies. The primary fibroblasts, established 
from FA patients, were exposed to gamma-rays, a dose of 2 Gy ((60)Co), incubated 
for up to 24 hours under repair-permissive conditions, and assayed for the level 
of gamma-H2AX foci and apoptosis at different recovery times after the 
treatment. Cell lines originating from FA patients displayed a significant delay 
in the repair of radiation-induced DNA DSBs relative to non-FA bone marrow 
failure (non-FA BMF) and control cell lines. The delay is especially evident at 
recovery time of 24 hours, and is seen as about 8-fold increase of residual 
gamma-H2AX foci compared to self-state before irradiation. The delay in repair 
kinetics of FA cells represents the unique feature of FA cellular phenotype, 
which should be exploited to distinguish FA cellular phenotype.