Xeroderma pigmentosum (XP), trichothiodystrophy (TTD) and Cockayne syndrome (CS) 
are rare genetic diseases characterized by a large range of clinical symptoms. 
However, they are all associated with defects in nucleotide excision repair 
(NER), the system responsible for removing bulky DNA lesions such as those 
generated by UV light: cyclobutane pyrimidine dimers (CPDs) and 
pyrimidine-pyrimidone photoproducts (6-4 PPs). Over the past years, detailed 
structural and biochemical information on NER-associated proteins has emerged. 
In the first part of the article we briefly present the main steps of the NER 
pathway with an emphasis on the precise role of certain proteins. Further, we 
focus on clinical manifestations of the disorders and describe the diagnostic 
procedures. Then we consider how current therapy and advanced technology could 
improve patients' quality of life. Although to date the discussed diseases 
remain incurable, effective sun protection, a well thought out diet, and 
holistic medical care provide longer life and better health. This review 
summarizes the current state of knowledge regarding the epidemiology of 
NER-associated diseases, their genetic background, clinical features, and 
treatment options.