SLX4 and Friedreich ataxia: Immunoblotting of MRG15 using extracts of 13 FANCD2-monoubiquitinylation-positive FA cell lines - excluded for genetic defects in the downstream genes FANCD1/BRCA2, FANCJ/BRIP1, FANCN/PALB2, FANCO/RAD51C and FANCP/SLX4, and thus unclassifiable in terms of subtype - failed to show gross reduction of protein expression.