PD14 The first documented case of Rothmund–Thomson syndrome with ultraviolet B photosensitivity confirmed by phototesting

Abstract We present a unique case of Rothmund–Thomson syndrome (RTS) with confirmed ultraviolet (UV)B photosensitivity through phototesting in a 16-year-old female patient. The patient described having a consistent reaction to 15 min of photoexposure, resulting in flat, confluent erythema on sun-exposed areas. This would then progress to dry and scaly areas 6–8 h after photoexposure, prior to resolution, without blistering or associated pain. The rash usually took one or more weeks to resolve and occurred throughout the year. However, it was worse during the spring and summer months. Photosensitivity was first noted at 3 months of age, and later at the age of 7 years the diagnosis of RTS was confirmed by geneticists. Clinical assessment revealed significant poikilodermatous changes on the face and neck, severe hyperkeratotic lesions, and lichenification on the dorsal hands, in addition to squamous papillomas on the joints and cutaneous palmar involvement. Her scalp hair texture appeared dense with a few patches of thinning. Her eyebrows and eyelashes were unaffected. Monochromator testing demonstrated severely reduced UVB thresholds at 300 nm, while provocation testing elicited a tanning response to UVA and mild erythema with solar simulator exposure. Negative results were noted from patch and photopatch testing for sunscreens. IgE levels, connective tissue and porphyrin screens were normal, and vitamin D was deficient despite high-dose supplementation. RTS is a rare heterogeneous autosomal recessive genodermatosis. There are two clinical subtypes, type I and type II, with genetic mutations in ANAPC1 and RECQL4, respectively. Both are characterized by facial poikiloderma, short stature, loss of eyelashes and/or eyebrows, juvenile cataracts and skeletal abnormalities. RTS has been associated with photosensitivity, although objective evidence has been limited in the literature to one case report demonstrating UVA sensitivity (Berg EP, Chuang TY, Cripps DJ. Rothmund–Thomson syndrome. J Am Acad Dermatol 1987; 17: 332–8). This case is the first to document UVB photosensitivity in RTS following photoinvestigation. UVB is known to induce DNA damage and hence increase the likelihood of premalignant and malignant cutaneous lesions, which has been observed at a younger age in RTS (Alsabbagh MM. Rothmund–Thomson syndrome: a review of clinical and molecular aspects. J Dermatol Dermatol Surg 2020; 24: 5–12). This highlights the need to consider routine phototesting in this patient demographic to better define their thresholds and tailor a more personalized photoprotective treatment plan accordingly.