In some of these cases, a mitochondrial defect or others neurodegenerative disorders were suspected, (iii) 10 were cell lines from patients with known mutations in XPB, XPD, TTD-A/p8, XPA (MIM: 278700), XPC (MIM: 78720) or XPF (MIM: 278760); All cells derived from patients who only showed classical dermatological symptoms (either pure TTD phenotype or pure XP phenotype) as well as an XPA silenced cell line (695/6, shXPA34 displayed a normal transcription profile for the three tested genes (CDK5RAP2, NRG1 and NIPBL). Here, ERCC4 is linked to xeroderma pigmentosum.