Principles of genetics as related to the chromosome disorders and congenital malformations with reference to prenatal diagnosis and genetic counseling.

A basic discussion of the chromosome disorders and congenital malformations with specific reference to syndromes of interest to the dermatologist is presented. Although the chromosome disorders are uncommon, an introduction to the most prevalent clinical findings should enable the clinician to increase his/her index of suspicion as to the presence of one of these disorders. The latest chromosome banding technics and their application to clinical diagnosis are discussed. Congenital malformations are also uncommonly seen in the practice of dermatology. However, approximately 7% of all newborns have a cutaneous lesion at birth; some of these are of serious medical significance or the manifestation of a systemic disease. These include café au lait marks, congenital nevocellular nevi, and sebaceous nevi. A basic understanding of the mechanics and theory of prenatal diagnosis is becoming increasingly necessary for the dermatologist. Recently, epidermolytic hyperkeratosis has ben diagnosed antenatally, with the promise of other primary dermatologic disorders also being amenable to detection before birth. As the ability to detect and diagnose genetic disease becomes more refined, patients who are at risk themselves or whose offspring are at risk for these disorders will require more detailed information than ever before. Appropriate advice regarding recurrence risk, full spectrum of disease, availability of prenatal diagnosis, and any potential therapy will have to be proffered via genetic counseling.