UV-sensitive syndrome can result from mutations in the ERCC6 gene (also known as the CSB gene), the ERCC8 gene (also known as the CSA gene), or the UVSSA gene. These genes provide instructions for making proteins that are involved in repairing damaged DNA. DNA can be damaged by UV rays from the sun and by toxic chemicals, radiation, and unstable molecules called free radicals. Cells are usually able to fix DNA damage before it causes problems. If left uncorrected, DNA damage accumulates, which causes cells to malfunction and can lead to cell death.
Cells have several mechanisms to correct DNA damage. The CSB, CSA, and UVSSA proteins are involved in one mechanism that repairs damaged DNA within active genes (those genes undergoing gene transcription, the first step in protein production). When DNA in active genes is damaged, the enzyme that carries out gene transcription (RNA polymerase) gets stuck, and the process stalls. Researchers think that the CSB, CSA, and UVSSA proteins help remove RNA polymerase from the damaged site, so the DNA can be repaired.
Mutations in the ERCC6, ERCC8, or UVSSA genes lead to the production of an abnormal protein or the loss of the protein. If any of these proteins is not functioning normally, skin cells cannot repair DNA damage caused by UV rays, and transcription of damaged genes is blocked. However, it is unclear exactly how abnormalities in these proteins cause the signs and symptoms of UV-sensitive syndrome.