POLH gene cause Xeroderma Pigmentosum (XP)...

POLH gene shows 30+ mutations in the variant type of Xeroderma Pigmentosum (XP-V), which is characterized by increased sensitivity to UV rays from sunlight like the other forms of XP. However, XP-V do not associated with neurological abnormalities such as delayed development and hearing loss.

Most of the mutations in POLH gene prevent the production of any detectable DNA polymerase eta. As we know without DNA polymerase eta cells could not effectively replicate damaged DNA. Without DNA replication for damaged DNA, errors resulting from exposure to UV rays accumulate in the genes which control cell growth and division. Due to this damage, cell growth become uncontrollably fast resulting an increased risk of developing skin cancer in the sunlight exposed areas in the XP-V affected individual. 

Source: www.ghr.nlm.nih.gov

Function of the POLH gene...

The POLH gene provides instructions for making DNA polymerase eta. DNA polymerases are a group of enzymes which "read" sequences of DNA and use them as templates to produce new DNA. These enzymes play an important role in replication (copy) for cell division. DNA polymerase also play critical role in DNA repair.

The major function of DNA polymerase eta is to replicate damaged DNA from ultraviolet (UV) rays. Other DNA polymerases are unable to replicate DNA with the damage caused by ultra violet rays. When they reach a segment of damaged DNA, they get stuck and the replication process stalls. However, when DNA polymerase eta encounters damaged DNA, it skips over the abnormal segment and continues copying. This ‘Translesion Synthesis’ activity allows cells to tolerate some abnormalities created by UV exposure. Without this tolerance, unrepaired DNA damage would block DNA replication causing the cell death. Therefore, DNA polymerase eta plays an essential role in protecting cells from some of the effects of DNA damage.

DNA polymerase eta is a relatively "error-prone" polymerase. When it bypasses damaged DNA, it often inserts an incorrect DNA building block (nucleotide). This type of error results in a mutation in the replicated DNA.

Source: www.ghr.nlm.nih.gov

POLH gene … Location

Cytogenetic Location: 6p21.1

Molecular Location : Chromosome 6

base pairs 43,576,140 ~ 43,620,522

The POLH gene is located on the short (p) arm of chromosome 6 at position 21.1, precisely from base pair 43,576,140 to base pair 43,620,522.

POLH gene … Official name

Official Name: polymerase (DNA directed), eta.

Official Symbol: POLH 

Other Names:

Ê DNA polymerase eta

Ê FLJ16395

Ê FLJ21978

Ê POLH_HUMAN

Ê RAD30

Ê RAD30A

Ê RAD30 homolog A

Ê xeroderma pigmentosum variant type protein

Ê XPV

Ê XP-V