Characterization of photosensitivity in the Smith-Lemli-Opitz syndrome: a new congenital photosensitivity syndrome

Photosensitivity has recently been reported as a feature of the Smith-Lemli -Opitz syndrome (SLO), The aim of this study was to establish the photobiol ogical features of this disorder and to examine the hypothesis that the pho tosensitivity is caused by the high levels of 7-dehydrocholesterol found in SLO. All known cases of SLO in the U.K. were reviewed and clinical details of photosensitivity were recorded in detail. The action spectrum of the ph otosensitive eruption was defined by monochromator light testing, Thirteen of the 23 subjects (57%) had severe photosensitivity, and in 10 there was n o photosensitivity. No correlation was identified between levels of 7-dehyd rocholesterol and severity of photosensitivity, suggesting that the photose nsitivity in SLO is not caused by a direct phototoxic effect mediated by 7- dehydrocholesterol A novel pattern of photosensitivity was observed, with o nset of a sunburn-like erythema on sun-exposed skin within minutes of sun e xposure, which persisted in most cases for up to 24-48 h before fading, Mon ochromator light testing in three subjects showed an ultraviolet (UV) A-med iated photosensitivity eruption with greatest photosensitivity at 350 nm, P hotosensitivity is a common and prominent feature of SLO and appears to be UVA-mediated. Elucidation of its biochemical basis may provide insight into normal cutaneous protective mechanisms against UVA-induced photodamage, an d also sun sensitivity in general.