Xeroderma pigmentosum that results from mutations in the XPB gene is extremely rare. The few cases that have been described present with either XP, TTD or combined features of XP and Cockayne Syndrome. XP is associated with hypersensitivity of the skin to ultraviolet light-induced freckle-like pigmentation changes and carcinogenesis. Patients present with extreme sunburn sensitivity and neurological degeneration. Prevalence of XP in the West is approx. 1 in 500,000 but is much higher in Japan (1 in 20,000) and North Africa. Only a handful of patients with mutations in this gene have been reported.
Trichothiodystrophy (TTD) is associated with involvement of multiple body systems. The defining feature is short, brittle, sulphur-deficient hair with a “tiger tail” pattern under polarizing microscopy. Other common features include dry skin (scaly patches called ichthyosis), failure to thrive, developmental delay, microcephaly, eye abnormalities (such as congenital cataracts), bony abnormalities and a propensity to recurrent infections in some patients. Maternal pregnancy complications are common. Some babies can be born with a shiny parchment-like covering (collodion membrane) which will resolve with time but may require specialist support. Approximately 50% of TTD patients are photosensitive and a few of these are mutated in the XPB gene. Prevalence is about 1/1,000,000.
There are also a few cases of patients having the clinical features of both XP and Cockayne Syndrome.
Inheritance of both XP and TTD is autosomal recessive.
XPB