Cornified cell envelope proteins and keratins are normally distributed in harlequin ichthyosis

Long-term survivors of harlequin ichthyosis (HI) have raised a controversy over the differences between HI and lamellar ichthyosis (LI). Abnormal lamellar granules and the failure of conversion from profilaggrin to filaggrin have been reported in HI. On the other hand, malformation of the cornified cell envelope as a result of mutation of keratinocyte transglutaminase has been found in LI. In the present study, we analyzed the distribution of keratins, filaggrin/profilaggrin and cornified cell envelope proteins in the epidermis in HI. We studied a newborn Japanese male with typical clinical features of HI. Electron microscopic observation of a skin biopsy specimen taken from the trunk revealed the presence of lipid inclusions within the cornified cells, the absence of lamellar granules in the granular layer keratinocytes, and a lack of extracellular lamellar structures between the first cornified cell and the granular cell. Immunohistochemical labeling showed a normal distribution of keratins (keratins 1, 5, 10, and 14), filaggrin/profilaggrin and cornified cell envelope proteins (involucrin, small proline-rich proteins, and loricrin) in the epidermis of lesional skin. The present observations of the patient's skin verified that keratins and cornified cell envelope proteins are normally expressed in HI, thus demonstrating a different pathogenesis between HI and LI.