Question

Xeroderma pigmentosum a. is a genetic disorder that results in uncontrolled cell growth. b. is a genetic disorder in which the NER system is not fully functional. c. is a genetic disorder that results in the loss of pigment in certain patches of skin. d. results from the lack of DNA polymerase proofreading. e. both \(b\) and \(d\) are true of this disorder.

Short answer

b. is a genetic disorder in which the NER system is not fully functional.

Step-by-step solution

Understand Xeroderma Pigmentosum

Xeroderma pigmentosum (XP) is a rare genetic disorder in which the body's normal ability to repair damage caused by ultraviolet (UV) light is impaired. The cells can't efficiently repair the damage, which leads to increased chance of skin abnormalities and skin cancers.

Identify NER System Functionality in XP

The main repair system involved in repairing UV-induced damage is the nucleotide excision repair (NER) system. In XP patients, this system is not fully functional, leading to an increased susceptibility to sunlight and a higher probability of developing skin cancer.

Understand XP and Pigmentation

XP can result in the development of freckles and irregular dark spots on the skin, but it does not cause a loss of pigment in the skin.

Evaluate Role of DNA Polymerase Proofreading in XP

DNA polymerase proofreading is a mechanism that corrects errors during DNA replication. XP is not caused by the lack of DNA polymerase proofreading, but rather, by the defects in the NER system.

Evaluate the Option 'Both b and d Are True'

Considering the analysis in Step 2 and Step 4, it is clear that XP is related to issues in the NER system but not with DNA polymerase proofreading. So, this statement is incorrect.

Key concepts

Understanding Genetic Disorders

Genetic disorders occur when mutations or changes happen in an individual's DNA, leading to various health conditions. These mutations can be inherited from parents or occur spontaneously during an individual's lifetime. Xeroderma pigmentosum (XP) is a prime example of a genetic disorder, specifically caused by mutations affecting the nucleotide excision repair system. Unlike conditions that lead to uncontrolled cell growth or pigment loss, XP showcases the devastating effects when the body's capacity to repair DNA damage is compromised.

Genetic testing and family history are critical in diagnosing such disorders. Understanding the specific nature of the genetic alteration can provide insights into the management and care required for those affected.

The Role of Nucleotide Excision Repair System

The nucleotide excision repair (NER) system plays a crucial role in maintaining the integrity of DNA by repairing bulky helix-distorting lesions, primarily those induced by ultraviolet (UV) radiation. This complex system recognizes and excises damaged DNA segments, followed by synthesizing and linking the correct nucleotides to the existing DNA strand.

When functioning correctly, NER helps protect against mutations that could potentially lead to cancer. However, in conditions like XP, the NER system is deficient, leaving the individual highly vulnerable to UV-induced DNA damage. Research into the NER pathway has massively contributed to understanding DNA repair mechanisms and their implications in disease.

UV-induced DNA Damage and Its Implications

Exposure to UV radiation from sunlight or artificial sources can damage the DNA in our cells. This damage usually takes the form of thymine dimers—abnormal chemical bonds between adjacent thymine bases in DNA. Normally, our cells can identify and repair these kinds of damages using the NER system. However, in individuals with XP, these mutations accumulate over time, as the DNA repair process is severely hindered.

This accumulation of damage leads to cellular dysfunctions and increases the risk of skin abnormalities, including cancerous growths. Avoiding UV exposure and wearing protective clothing and sunscreens are crucial preventative measures for those at heightened risk.

Skin Cancer Susceptibility in Xeroderma Pigmentosum

Individuals with xeroderma pigmentosum exhibit a significantly increased susceptibility to skin cancers due to their impaired ability to repair UV-induced DNA damage. The types of skin cancer they are prone to include basal cell carcinoma, squamous cell carcinoma, and melanoma, which are cumulatively more frequent and tend to occur at a younger age compared to the general population.

Understanding the genetic basis of XP provides a framework for potential advancements in treatment, such as gene therapy or enzyme replacement, as well as the development of targeted cancer therapies. Preventative measures and early detection through regular skin examinations are key in managing the elevated risk of skin cancer in XP patients.