SLX4 and Friedreich ataxia: FA is also a genetically heterogeneous disorder with at least 16 genes responsible of the known FA complementation groups (A, B, C, D1 [BRCA2], D2, E, F, G, I, J [BRIP1], L, M, N [PALB2], O [RAD51C], P [SLX4] and XP-F) (Soulier 2011; Alter and Kupfer 2002; Kashiyama et al.