Werner syndrome, RecQ helicase-like
The WRN gene provides instructions for producing the Werner protein, an enzyme called a helicase that plays a critical role in repairing damaged DNA. Helicases generally unwind and separate double-stranded DNA. The Werner protein also functions as an exonuclease, an enzyme that trims the broken ends of damaged DNA by removing DNA building blocks (nucleotides). Research suggests that the Werner protein first unwinds the DNA and then removes abnormal DNA structures that have been accidentally generated. Overall, the Werner protein helps maintain the structure and integrity of a person's DNA. This protein plays an important role in copying (replicating) DNA before cell division and transferring the information in genes to the cell machinery that makes proteins (transcription). Additionally, the Werner protein may be particularly important for maintaining DNA at the ends of chromosomes (telomeres).
More than 60 mutations in the WRN gene are known to cause Werner syndrome. Most of these mutations are rare and result in an abnormally short, nonfunctional Werner protein that is probably not transported into the cell's nucleus. The shortened protein is also broken down more quickly. Without normal Werner protein in the nucleus, DNA replication, repair, and transcription are disrupted. Researchers are still determining how mutations in the WRN gene lead to the signs and symptoms of Werner syndrome. Werner syndrome is an autosomal recessive disorder; carriers of (only) one mutation are generally considered to be unaffected, as only carriers of two mutations exhibit the clinical signs of progeria.
Some changes to a person's genes are acquired during that person's lifetime and are present only in certain cells. These differences, called somatic changes, are not inherited. Somatic changes in the WRN gene are found in nonhereditary tumors and involve a process called methylation. Methylation is a chemical modification that attaches small molecules called methyl groups to certain segments of DNA. When too many methyl groups are attached to the WRN gene (hypermethylation), the gene is turned off and the Werner protein is not produced. Without this protein, cells do not respond normally to DNA damage. The lack of Werner protein allows mutations to accumulate in other genes, which may cause cells to grow and divide in an uncontrolled way. This kind of unregulated cell growth can lead to the formation of cancerous tumors. Hypermethylation of the WRN gene has been found in many different types of tumors, including colon, rectal, lung, stomach, prostate, breast, and thyroid tumors.