Electronmicroscopic observation of the basement membrane zone in focal dermal hypoplasia.

A 3-month-old boy had reticulated achromic and atrophic skin lesions on the right buttock and thigh, as well as partial syndactyly of the third and fourth toes of the right foot. With hematoxylin and eosin stain, an epidermal defect, abnormally located fat cell lobules, and absence of the upper and midportions of the dermis were observed, conforming to a typical histopathologic picture of focal dermal hypoplasia. Electron microscopic examination of the atrophic site showed loose collagen bundles, collagen fibers with loss of regular bands, abnormal fibroblasts, and disruption of the basement membrane zone. These defects in the basement membrane zone strongly suggest that abnormal formation of type IV collagen is associated with focal dermal hypoplasia, and that this abnormal formation of collagen is correlated with the clinical sign of skin atrophy.