Photosensitivity in children

Ultraviolet radiation signaling through TLR4/MyD88 constrains DNA repair and plays a role in cutaneous immunosuppression

UV radiation (UVR) induces DNA damage, leading to the accumulation of mutations in epidermal keratinocytes and immunosuppression, which contribute to the development of nonmelanoma skin cancer. We reported previously that the TLR4-MyD88 signaling axis is necessary for UV-induced apoptosis. In the dinitrofluorobenzene contact hypersensitivity model, UV-irradiated MyD88-deficient (MyD88(-/-)) C57BL/6 mice had intact ear swelling, exaggerated inflammation, and higher levels of dinitrofluorobenzene-specific IgG2a compared with wild-type (WT) mice. Even with normal UV-induced, dendritic cell migration, DNA damage in the local lymph nodes was less pronounced in MyD88(-/-) mice compared with WT mice. Cultured, UV-irradiated WT APCs showed cleavage (inactivation) of the DNA damage-recognition molecule PARP, whereas PARP persisted in MyD88(-/-) and TLR4(-/-) APCs. Epidermal DNA from in vivo UV-irradiated MyD88(-/-) mice had an increased resolution rate of cyclobutane pyrimidine dimers. Both in vitro treatment of MyD88(-/-) APCs with and intradermal in vivo injections of PARP inhibitor, PJ-34, caused WT-level cyclobutane pyrimidine dimer repair. Lymphoblasts deficient in DNA repair (derived from a xeroderma pigmentosum group A patient) failed to augment DNA repair after MyD88 knockdown after UVR, in contrast to lymphoblasts from a healthy control. These data suggest that interference with the TLR4/MyD88 pathway may be a useful tool in promoting DNA repair and maintaining immune responses following UVR-induced damage.

Erythropoietic protoporphyria in a child

Erythropoietic protoporphyria (EPP), a recently described form of porphyria, often remains unrecognized. We report the case of a 7-year-old girl admitted for investigation of photosensitivity since the age of 18 months without any significant objective cutaneous lesions. Clinical features, quantitative determinations of porphyrins in blood, urine and stools, ferrochelatase activity and cutaneous histopathology helped to confirm the diagnosis of EPP. A familial study was also performed. The clinical, laboratory and genetic characteristics of EPP are reviewed.

Diseases with DNA damage-processing defects

Xeroderma pigmentosum, Cockayne's syndrome, ataxia telangiectasia, Fanconi anemia, and Bloom's syndrome are autosomal recessive diseases with cellular defects in the ability to process DNA damage. Although these diseases are rare, they are seen occasionally in practice and provide insight into the mechanisms of DNA repair and replication in humans. The authors will review the clinical and cytological presentation of each disease, the genetic heterogeneity, as inferred by complementation analysis, and the differentiating characteristics of each. The authors will conclude with a discussion of the state of current research on each disease and possible directions for future research.

Hydroa vacciniforme with inflammatory keratitis and secondary anterior uveitis

A 6-year-old boy had numerous episodes of hydroa vacciniforme. Several of these episodes were accompanied by an anterior uveitis with corneal clouding and stellate keratic precipitates. Wearing sunglasses prevented new eye lesions from developing despite recurrences of skin lesions. Phototesting on facial skin revealed reproduction of skin lesions with ultraviolet B but not ultraviolet A. One should be aware of eye involvement in hydroa vacciniforme, and children who experience this form of photodermatitis should have a careful eye examination and be advised to wear protective sunglasses.