"The fact that CS proteins have additional functions is noteworthy. This discovery could help to explain the pathological differences between xeroderma pigmentosum and Cockayne syndrome," says Stingele.

Figure 1 | Evidence of defective DNA repair in cells from people with xeroderma pigmentosum.

For instance, some people are born with xeroderma pigmentosum, a rare, incurable genetic disorder in which the skin cannot repair the damage caused by ultraviolet light, leaving them vulnerable to cancer when they are children.

The couple, who are Navajo, had two children with a severe form of xeroderma pigmentosum, or X.P., a genetic disorder, and then met other Navajo parents whose children had it as well.

People with a rare inherited disorder called xeroderma pigmentosum have extreme sensitivity to the sun and must avoid exposure at all times.