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Chapter 14: Problem 17

What genetic defects result in the disorder xeroderma pigmento\(\operatorname{sum}(\mathrm{XP})\) in humans? How do these defects create the phenotypes associated with the disorder?

Short Answer

Expert verified
Answer: The genetic defects in xeroderma pigmentosum (XP) are mutations in one of the following genes: XPA, ERCC3 (XPB), XPC, ERCC2 (XPD), DDB2 (XPE), ERCC4 (XPF), ERCC5 (XPG), and POLH (XPV). These genes are essential for the nucleotide excision repair (NER) pathway, responsible for repairing DNA damage caused by UV radiation. These mutations result in reduced or impaired NER pathway function, leading to an insufficient ability to repair DNA damage. Consequently, the accumulation of unrepaired DNA damage in skin cells increases the risk of skin cancer, skin abnormalities, and potentially neurological issues.

Step by step solution

01

Introduce Xeroderma Pigmentosum (XP)

Xeroderma pigmentosum (XP) is a rare inherited genetic disorder that affects the body's ability to repair DNA damage, particularly damage caused by ultraviolet (UV) radiation from the sun. This results in an increased susceptibility to skin cancer and other skin abnormalities, as well as possible neurological problems.
02

Explain the cause of XP

XP is caused by mutations in several genes that are essential for the nucleotide excision repair (NER) pathway. The NER pathway is responsible for repairing DNA damage, including damage caused by UV radiation. There are at least eight different complementation groups (XP-A to XP-G and XP-V) of XP, which correspond to mutations in different genes involved in the NER pathway or DNA polymerase.
03

Detail specific genetic defects

The genetic defects that lead to XP include mutations in one of the following genes: XPA, ERCC3 (XPB), XPC, ERCC2 (XPD), DDB2 (XPE), ERCC4 (XPF), ERCC5 (XPG), and POLH (XPV). These genes are involved in various aspects of the NER pathway, from recognizing DNA damage to repairing the damaged DNA. Mutations in these genes result in reduced or impaired NER pathway function, leading to an insufficient ability to repair DNA damage.
04

Describe how defects create the phenotypes associated with XP

When the NER pathway is not functioning efficiently due to mutations in one of the genes mentioned above, DNA damage from UV radiation accumulates in the skin cells without being repaired. This accumulation of DNA damage leads to an increased risk of skin cancer, as well as other skin abnormalities such as freckling, pigmentation changes, and premature aging. In some cases, the impaired DNA repair may also affect the nervous system, leading to neurological problems like progressive hearing loss, difficulty walking, and cognitive decline.
05

Summarize the findings

In conclusion, xeroderma pigmentosum (XP) is a rare genetic disorder caused by mutations in genes involved in the nucleotide excision repair (NER) pathway. These mutations result in an impaired ability to repair DNA damage, specifically damage caused by UV radiation, leading to an increased risk of skin cancer, skin abnormalities, and potentially neurological issues.

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Most popular questions from this chapter

It has been noted that most transposons in humans and other organisms are lacated in noncoding regions of the genome regions such as introns, pseudogenes, and stretches of particular types of repetitive DNA. There are several ways to interpret this observation. Describe two possible interpretations. Which interpretation do you favor? Why?

Mammography is an accurate screening technique for the early detection of breast cancer in humans. Because this technique uses X rays diagnostically, it has been highly controversial. Can you explain why? What reasons justify the use of X rays for such a medical screening technique?

A significant number of mutations in the \(H B B\) gene that cause human \(\beta\) -thalassemia occur within introns or in upstream noncoding sequences. Explain why mutations in these regions often lead to severe disease, although they may not directly alter the coding regions of the gene.

In this chapter, we focused on how gene mutations arise and how cells repair DNA damage. At the same time, we found opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, (a) How do we know that many cancer-causing agents (carcinogens) are also mutagenic? (b) How do we know that certain chemicals and wavelengths of radiation induce mutations in DNA? (c) How do we know that DNA repair mechanisms detect and correct the majority of spontaneous and induced mutations?

Describe a tautomeric shift and how it may lead to a mutation.
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