The sole genetic basis for RBS resides in loss of function mutations in ESCO2, which encodes a highly conserved (Eco1/Ctf7 in budding yeast) N-acetyltransferase (Skibbens et al. 1999; Tóth et al. 1999; Bellows et al. 2003; Hou and Zou 2005; Schüle et al. 2005; Gordillo et al. 2008). Here, ESCO1 is linked to Roberts-SC phocomelia syndrome.