Scientists have pinpointed a rare, genetic flaw that makes people unusually sensitive to sunlight and predisposes them to skin cancer, it was reported this week.

A Japanese team headed by Kiyoji Tanaka at Osaka University said it has discovered and made copies of a gene that when defective causes the most common type of a disease called xeroderma pigmentosum.About one in 250,000 people suffer from xeroderma pigmentosum, an inherited disease in which skin cells lack the normal ability to repair the damage the sun's ultraviolet light inflicts on genetic material.

People with xeroderma pigmentosum must avoid exposure to sunlight. If they fail to do so, they run a high risk of developing skin cancer and potentially blinding growths on the eyelids and cornea.

At least eight genes are believed to be linked to the disease.

But the genetic defect singled out by the Japanese team on chromosome 9 is believed to be the most common, accounting for about one-quarter of cases.

The latest discovery, published in the British journal Nature, comes on the heels of a Dutch team's findings that a gene on chromosome 2 appears to cause a rare type of xeroderma pigmentosum.