The Journal of investigative dermatology
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J. Invest. Dermatol. · Dec 1992
Membrane structural abnormalities in the stratum corneum of the autosomal recessive ichthyoses.
Congenital ichthyosiform erythroderma (CIE) and classic lamellar ichthyosis (LI) are autosomal recessive disorders of cornification (DOC), distinguished previously by clinical, histologic, ultrastructural, and cell kinetic criteria. Whether there is further heterogeneity within the CIE group is uncertain. To address the issue of genetic heterogeneity, and to study the pathogenesis of these DOC, skin biopsies from eight CIE, three LI, and six normal subjects were assessed by electron microscopy, including ruthenium tetroxide postfixation with optical diffraction, to visualize and quantitate intercellular membrane domains. ⋯ Our ultrastructural observations support the previously reported phenotypic distinction between CIE and LI, and the further likelihood of genetic heterogeneity within CIE. However, these studies do not support the division of the autosomal recessive ichthyoses into three subgroups based upon cytosolic structural abnormalities. Finally, these studies provide new insights into the pathogenesis of the autosomal recessive DOC.
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Lamellar granules are specialized lipid-rich organelles present in epidermal granular cells. They fuse with the apical cell surface and discharge their contents into the intercellular space forming lamellar sheets. It was previously shown by electron microscopy that lamellar granules in biopsies of infants affected with harlequin ichthyosis are either absent or abnormal and no intercellular lamellae could be detected. ⋯ The immunohistochemical staining pattern correlated with the electron microscopic localization of abnormal vesicles and the absence of intercellular lamellae in the affected samples. We conclude that the vesicles represent lamellar granules that contain the AE17 antigen but are structurally abnormal and defective in their ability to discharge both their lipid and protein contents into the intercellular space. We suggest that this defect in the lamellar granules represents the underlying basis for stratum corneum cell retention and subsequent accumulation of scale in harlequin ichthyosis.