FANCC and Friedreich ataxia: Mosaicism in FA patients was noted prior to initial identification of the first FANC gene (FANCC) in 1992 [11], with initial reports describing FA patients in whom 60–80% of cultured lymphocytes (either PHA-stimulated T cells or EBV-transformed B cells) displayed resistance to concentrations of alkylating agents typically toxic to FA patient cells [12, 13].