BACKGROUND: Patients with bone marrow failure and undiagnosed underlying Fanconi 
anemia may experience major toxicity if given standard-dose conditioning 
regimens for hematopoietic stem cell transplant. Due to clinical variability 
and/or potential emergence of genetic reversion with hematopoietic somatic 
mosaicism, a straightforward Fanconi anemia diagnosis can be difficult to make, 
and diagnostic strategies combining different assays in addition to classical 
breakage tests in blood may be needed.
DESIGN AND METHODS: We evaluated Fanconi anemia diagnosis on blood lymphocytes 
and skin fibroblasts from a cohort of 87 bone marrow failure patients (55 
children and 32 adults) with no obvious full clinical picture of Fanconi anemia, 
by performing a combination of chromosomal breakage tests, 
FANCD2-monoubiquitination assays, a new flow cytometry-based mitomycin C 
sensitivity test in fibroblasts, and, when Fanconi anemia was diagnosed, 
complementation group and mutation analyses. The mitomycin C sensitivity test in 
fibroblasts was validated on control Fanconi anemia and non-Fanconi anemia 
samples, including other chromosomal instability disorders.
RESULTS: When this diagnosis strategy was applied to the cohort of bone marrow 
failure patients, 7 Fanconi anemia patients were found (3 children and 4 
adults). Classical chromosomal breakage tests in blood detected 4, but analyses 
on fibroblasts were necessary to diagnose 3 more patients with hematopoietic 
somatic mosaicism. Importantly, Fanconi anemia was excluded in all the other 
patients who were fully evaluated.
CONCLUSIONS: In this large cohort of patients with bone marrow failure our 
results confirmed that when any clinical/biological suspicion of Fanconi anemia 
remains after chromosome breakage tests in blood, based on physical examination, 
history or inconclusive results, then further evaluation including fibroblast 
analysis should be made. For that purpose, the flow-based mitomycin C 
sensitivity test here described proved to be a reliable alternative method to 
evaluate Fanconi anemia phenotype in fibroblasts. This global strategy allowed 
early and accurate confirmation or rejection of Fanconi anemia diagnosis with 
immediate clinical impact for those who underwent hematopoietic stem cell 
transplant.