The Term ichthyosis describes a group of heritable disorders which are characterized by cutaneous scaling. The visible scale differentiates these disorders from xeroderma in which the skin is dry but does not visibly desquamate. Many classifications of the ichthyoses have been proposed, but most are descriptive and contribute little to an understanding of etiology and pathogenesis. Often clinical variants or patients with minor associated anomalies have been categorized separately on an empirical basis and, in some cases, several names have been used for one entity to indicate severity of involvement.
The most useful classification appears to be that of Wells and Kerr,1 who segregated the various types by their pattern of inheritance and retained the nomenclature in common usage. Differences in clinical features and histologic patterns also correlate with these genetically distinguishable types. Thus, with careful attention to the distribution and type of scale, family history, and skin histology, the physician will be able to classify patients in a meaningful way. Such an approach is helpful for several reasons. The prognosis, troublesome features, and degree of handicapping differ for the various ichthyoses. Sensible genetic counseling, an important part of the management of such patients, is possible only with the correct diagnosis. Moreover, clinical investigation of affected individuals will be further confused unless the entity under study is well defined. The need for an understanding of the physiologic and biochemical defects of ichthvotic skin is underscored by the limitations of currently available therapy.
The four major types of ichthyosis include: (1) ichthyosis vulgaris, transmitted as an autosomal dominant trait; (2) sexlinked ichthyosis, transmitted as an Xlinked trait; (3) bullous congenital ichthyosiform erythroderma (CIE), inherited as an autosomal dominant trait; and (4) nonbulbus congenital ichthyosiform erythroderma, autosomal recessive mode of inheritance (Table I).
Huntington’s disease: Pathophysiology and therapeutic intervention