Guest Editorial

Following the rediscovery of Mendel’s work, the onset of the 20 century witnessed an initial con ̄ ict and subsequent resolution of the con ̄ ict, between those who thought of inheritance as comprising discrete traits, as with Mendel’s peas, and those who thought of inheritance as primarily comprising Gaussian traits, or what we would now call genetically complex traits (2). With hindsight it seems dif® cult to understand the dif® culty over the synthesis of these two ideas, put most simply as the familiar observation that as it gets larger the binomial distribution approximates to a normal or Gaussian one. As we enter the 21st century we see an echo of this earlier debate looming large again. On the one hand we have got used to the technical prowess of modern genetics s̀olving’ disorders that show a clear pattern of inheritance, such as epidermolysis bullosa or Darier’s disease, or even quasiMendelian traits such as red hair (3 ± 6). On the other hand the diseases we see most commonly in the clinic, psoriasis, atopic dermatitis and acne show a complex and therefore non-Mendelian pattern of inheritance. Will the technical prowess of modern genetics s̀olve’ these disorders to make once more a seamless transition between Mendelian genetics and complex disorders? Or will the current hyperbole by manyÐ not least the pharmaceutical industryÐ prove unfounded. Several papers published outwith the dermatological literature over the last year are germane to this issue (7 ± 10). In this mini-review we attempt to extrapolate from this work for an audience interested in the common skin diseases. To add perspective to our argument we ® rst start with an outline of the strengths and achievements of the molecular genetics of Mendelian disorders.