There are several known human diseases that are connected with a faulty DNA repair in the cells. Many of these are somehow related to specific cancers as the defective DNA repair leads to a higher rate of mutation, and thus increases the chance of developing a ‘bad’ mutation.

Xeroderma Pigmentosum

This disease is one of the best studied DNA repair conditions. This rare autosomal recessive disorder is characterized by abnormal skin pigmentation and acute sensitivity to sunlight. People suffering from this condition also have a high probability of developing skin cancer, they are up to 2000 times more likely of developing skin cancer than unaffected people.

The UV light a person is exposed to while in the sun create what are known as ‘pyrimidine dimers’ in the DNA of skin cells. In most people, this harmful event can be corrected through a DNA repair mechanism known as ‘nucleotide excision repair’. People with xeroderma pigmentosum, however, lack this repair mechanism, which leads to an aggregation of such dimmers, which may lead to skin cancer.

So far, at least seven different genes have been identified as causes for this condition. All of these perform one or multiple tasks in the DNA repair mechanisms that are used by the cells.

Cockayne Syndrome and Trichothiodistrophy

Individuals suffering from either of these two conditions, suffer from multiple neurological and developmental problems. Both of them are caused by some of the genes that have also been identified as possible causes for xeroderma pigmentosum. Besides taking part in DNA repair, some of these genes are also relevant for the smooth functioning of recombination and the initiation of transcription. This may account for the various developmental problems encountered by people suffering from either of these conditions.

Hereditary Non-Polyposis Colon Cancer (HNPCC)

This type of colon cancer is also caused by a flawed DNA repair mechanism. It is one of the most common forms of hereditary cancer, in total accounting for around 15% of all colon cancer cases. The condition arises from mutations in genes that code for proteins that are responsible for mismatch repair, which corrects wrongly matched bases (for example when adenine binds with guanine).

Li-Fraumein Syndrome

This syndrome is caused by a mutation in the gene known as p53, which is an important factor in the regulating of the cell cycle. The protein this gene codes for can stimulate DNA repair and stops the cell cycle until the problem is fixed. So, patients with this syndrome will keep dividing cells even if they’re damaged and carry mutations. The result is that this disease is characterized by the development of cancers in several tissues.