Even most full time dermatologists will not see at first hand the majority of skin diseases. Most individual disease entities are rare. Some of these rare disorders, such as epidermolysis bullosa and cancer syndromes such as Gorlin's syndrome or familial melanoma have attracted considerable attention from human geneticists over the last ten years. Many such disorders present with a striking collection of physical signs, rely almost entirely on clinical skills for diagnosis, and are highly penetrant, lending themselves to mapping and subsequent gene identification. Major advances have occurred in our knowledge of the genetics of these rare disorders (van Steensel et al., 1997). For instance, until a decade ago, the biologist of skin was in the ignominious position of not knowing the function of the main class of proteins produced by keratinocytes, namely keratins (van Steensel et al., 1997). A situation akin to a hematologist not knowing the physiological role for hemoglobin in red cells. Subsequently, a large number of rare disorders of the skin have been shown to be due to mutations in keratins, collagens and other structural or signaling proteins in skin. Not withstanding the facility for improved counseling and prenatal diagnosis, the benefit from study of these disorders has been greater in the direction of understanding cell biology rather than in improving current (and usually inadequate) therapy.
This chapter will focus on disorders in which the inheritance appears genetically complex. Given the nature of clinical advance (Rees, 2002a), and the real therapeutic improvements over the last thirty years for many skin diseases, it is not self-evident that studying the genetics of complex skin diseases is the most fruitful research approach to improving dermatological healthcare.
I will take a selective approach dealing with the most common diseases: acne, dermatitis, psoriasis and skin cancer account for over half the dermatology cases seen in primary care and around 80% of the workload of a secondary care dermatologist (Harris et al., 1990). What (little) we know of the genetics of acne, atopic dermatitis and psoriasis will be summarized briefly, and the role of genetic factors in skin cancer dealt with in more detail.
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