Mouse mutants as model for human ageing disorders. Defective transcription and premature ageing. DNA damage has been implicated in carcinogenesis and ageing. Our group examines the nucleotide excision DNA repair (NER) process, which can detect and repair various UV- and chemically-induced DNA damages, in addition to some types of oxidative DNA damage. Recently, two mouse models were generated with a defect in one of the NER genes (XPD and CSB), displaying distinctive symptoms of premature ageing. Remarkably, in both cases the NER gene plays an additional role in transcription. Research using these mouse models aims to investigate the link between premature ageing and molecular defects in NER and transcription.