Patients that fall in this category (termed XP/CS)manifest, in addition to CS features, the classical XP characteristics (skinpigmentation and extremely high skin cancer predisposition) and harbor mutations inthe genes XPB, XPD, XPG, or (morerecently identified) XPF or ERCC1 (Weeda et al., 1990; Kashiyama et al., 2013; Lehmann et al., 2014; Moriel-Carretero et al.,2015). Here, ERCC3 is linked to Cowden syndrome 1.