XPD

XPD, also known as xeroderma pigmentosum group D, is a genetic disorder characterized by extreme sensitivity to ultraviolet (UV) rays from sunlight. This condition is part of a group of disorders known as xeroderma pigmentosum (XP), which affects the body's ability to repair damage caused by UV light. Individuals with XPD have a defect in the DNA repair mechanism, specifically in the nucleotide excision repair (NER) pathway.

Genetics

XPD is caused by mutations in the ERCC2 gene, which provides instructions for making a protein involved in the NER pathway. This pathway is crucial for repairing DNA damage caused by UV light and other environmental factors. The ERCC2 gene is located on chromosome 19q13.2-q13.3.

Inheritance

XPD is inherited in an autosomal recessive pattern, which means that both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Clinical Features

Individuals with XPD may present with a range of symptoms, including:

• Severe sunburn after minimal sun exposure
• Freckling of the skin at an early age
• Dry skin (xerosis)
• Changes in skin pigmentation
• Increased risk of skin cancers, such as basal cell carcinoma, squamous cell carcinoma, and melanoma

Some individuals with XPD may also experience neurological abnormalities, such as:

• Progressive neurological degeneration
• Hearing loss
• Poor coordination
• Intellectual disability

Diagnosis

The diagnosis of XPD is based on clinical evaluation, family history, and genetic testing. Genetic testing can confirm the presence of mutations in the ERCC2 gene. Skin biopsy and cellular studies may also be conducted to assess the DNA repair capacity of skin cells.

Management

There is no cure for XPD, and management focuses on protecting the skin from UV exposure and monitoring for skin cancer. Strategies include:

• Avoiding sun exposure and using protective clothing
• Applying broad-spectrum sunscreen with a high SPF
• Regular dermatological examinations to detect and treat skin cancers early

Prognosis

The prognosis for individuals with XPD varies depending on the severity of the condition and the presence of neurological symptoms. Early diagnosis and strict UV protection can improve the quality of life and reduce the risk of skin cancer.

Research

Ongoing research aims to better understand the molecular mechanisms of XPD and develop potential therapies to improve DNA repair in affected individuals.

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  XPD (Len Deighton novel - front cover)