Hypomelanosis of Ito: pigmentary mosaicism with immature melanosome in keratinocytes.

Background: Hypomelanosis of Ito is a rare genetic disorder characterized by whorled areas of hypomelanosis. The purpose of the present study was to revisit some aspects of Ito's hypomelanosis.

Methods: Clinical observations included ultraviolet-light-enhanced visualization (ULEV) method. Histochemistry, immunohistochemistry, and electron microscopy were performed on biopsy samples from the hypopigmented areas and the surrounding skin.

Results: Both the ULEV and microscopic examinations revealed the heterogeneity of the pigmentation. Hypomelanosis was characterized by a reduction in melanosomes, both in melanocytes and keratinocytes. These organelles were immature and atypical, showing a weak tyrosinase immunoreactivity. Melanosome macroautophagy was prominent in keratinocytes. Some clusters of the same cells exhibited strong immunoreactivity for the Mac 387 antibody (Ca(2+) -dependent calprotectin). Ulex europaeus agglutinin-1 (UEA-1) decorated the superficial layers of the epidermis. Such features are typically found in functionally altered keratinocytes. A number of dermal cells exhibited intense phagocytic activity linked to lysozyme immunoreactivity.

Conclusions: Both the melanosome depletion and macroautophagy of immature melanosomes in keratinocytes appeared to represent prominent aspects of hypomelanosis of Ito. In sum, Ito's hypomelanosis combines structural and functional changes affecting both the melanocytes and keratinocytes in the skin.