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May 1986

Ichthyosis: Genetic Heterogeneity, Genodermatoses, and Genetic Counseling

Author Affiliations

Dermatology Service Veterans Administration Medical Center 4150 Clement St San Francisco, CA 94121

Arch Dermatol. 1986;122(5):529-531. doi:10.1001/archderm.1986.01660170059019

McKusick's1,2 maxim about genetic heterogeneity may be stated as follows: when a genetic disorder is examined closely, what at first was thought to be a single entity will be found, in fact, to be several clinically (ie, phenotypically) similar, but fundamentally (genotypically) distinct, disorders. Dermatologists are well aware of this phenomenon, perhaps best illustrated in the ever-enlarging lists of types of Ehlers-Danlos syndrome and xeroderma pigmentosa. Therefore, it is not surprising that, as the ichthyoses are subjected to closer scrutiny, evidence of genetic heterogeneity should be uncovered here, as well. Such heterogeneity can be demonstrated by a variety of methods (Table). Previously, the various inherited forms of ichthyoses have been categorized largely by differences in disease expression (phenotype) and mode of inheritance. Yet, because of both phenotypic overlap and unclear inheritance patterns in individual cases, the clinician can experience difficulties in assigning a precise diagnosis

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