Harlequin fetus with abnormal lamellar granules and giant mitochondria.

A case of harlequin ichthyosis was studied with electron microscopy. From the basal cell to granular cell layers, keratinocytes contained giant mitochondria (860 nm) which exhibited vesicular cristae. Typical lamellar granules were absent; instead, numerous dense cored granules (DCG) and particles containing cored granules (PCG) were produced. Some of these were discharged into the intercellular spaces of granular cells, but the majority failed to be released from the cytoplasm. These retained DCG and PCG coalesced to form large vacuoles and cavities in the stratum corneum. In the hair follicle, keratinized cells failed to loosen and desquamate into the hair canal; instead, they formed concentric keratin rings surrounding hair, a diagnostic feature of this disease. It is suggested that the abnormal lamellar granule underlies the pathogenesis of this disease and that giant mitochondria may be related to an abnormal lipid metabolism of keratinocytes which may affect lipid composition of lamellar granules.