Compound heterozygosity for the Xeroderma pigmentosum complementation group A gene associated with a mild phenotype

Area of Science:

• Genetics
• Dermatology
• Molecular Biology

Background:

• Xeroderma pigmentosum (XP) is a rare genetic disorder characterized by extreme sensitivity to ultraviolet (UV) radiation.
• Xeroderma pigmentosum complementation group A (XPA) is one of the most common forms, resulting from mutations in the XPA gene responsible for DNA repair.
• Early diagnosis and understanding genotype-phenotype correlations are crucial for managing XP patients.

Observation:

• A 7-year-old boy presented with severe photosensitivity from 5 months of age and multiple facial freckles by age five.
• Fibroblast analysis demonstrated that the XPAC gene could compensate for DNA repair capacity after UV irradiation.
• Clinical examination revealed no significant neurological symptoms or malignant skin tumors at the time of assessment.

Findings:

• Genetic sequencing identified compound heterozygosity for two novel mutations in the XPA gene: a splicing mutation (IV3 -1G => C) and a nonsense mutation (Arg228 => stop).
• The splicing mutation, detectable by Alw NI restriction enzyme, affects intron 3 splicing.
• The nonsense mutation, detectable by Hph I, results in premature protein termination in exon 6.

Implications:

• This specific compound heterozygous genotype (IV3 -1G => C / Arg228 => stop) appears to be associated with a milder clinical phenotype in XPA.
• The observed DNA repair compensation suggests potential therapeutic avenues or a better prognosis.
• Understanding these specific mutations provides valuable insights into XPA pathogenesis and genotype-phenotype correlations, aiding in patient counseling and management.