Germline homozygous mutations in the FA genes led to deficiencies of FA DNA repair pathway, which was thought to be the main mechanism responsible for bone marrow failure in FA [32]: (a) HSC defect starts before birth, and mutant HSCs are unambiguously reduced during development resulting in stem cell apoptosis [32, 33]; (b) attrition of HSC pools caused by unresolved DNA damage-dependent cell cycle arrest and apoptosis [32]. This evidence concerns the gene FANCA and Friedreich ataxia.