Cockayne syndrome--a primary defect in DNA repair, transcription, both or neither?

Cockayne syndrome is a rare autosomal recessive disease characterized by a complex clinical phenotype. Most Cockayne syndrome cells are hypersensitive to killing by ultraviolet radiation. This observation has prompted a wealth of studies on the DNA repair capacity of Cockayne syndrome cells in vitro. Many studies support the notion that such cells are defective in a DNA repair mode(s) that is transcription-dependent. However, it remains to be established that this is a primary molecular defect in Cockayne syndrome cells and that it explains the complex clinical phenotype associated with the disease. An alternative hypothesis is that Cockayne syndrome cells have a defect in transcription affecting the expression of certain genes, which is compatible with embryogenesis but not with normal post-natal development. Defective transcription may impair the normal processing of DNA damage during transcription-dependent repair.