Introduction

Equally powerful for generalists or specialists, with simple principles available for every field of medicine, genetics is fundamental to diagnosis and prevention. Neurocutaneous syndromes illustrate the value of the genetic approach, since they often exhibit Mendelian inheritance. They also illustrate the value of pattern recognition, since the association of congenital brain and skin anomalies often predicts a broad spectrum of disease. This chapter presents basic principles of genetics and dysmorphology, illustrating the use of these principles in approaching the spectrum of neurocutaneous diseases.

Key to the genetic approach are resources that provide information on rare diseases. Paramount among these is the catalogue of genetic diseases originally assembled by Victor McKusick (Online Mendelian Inheritance in Man, 2002). Each disease thought to exhibit Mendelian inheritance and, more recently, each characterized human gene or protein has been assigned a 6-digit number. McKusick numbers will be provided for the genetic and neurocutaneous diseases mentioned in this chapter, allowing easy reference at the on-line website. Management of the more common disorders is discussed by Wilson & Cooley (2000).

The genetic approach in medicine

While individual genetic disorders may be rare, the effect of genetic factors on disease is widespread. Coronary artery disease is an example where a focus on extreme disease (young people with heart attacks) identified a gene involved in cholesterol uptake. Once autosomal dominant hypercholesterolemia was characterized by mutations in the low density lipoprotein receptor, cholesterol testing became an indicator of genetic risk that led to diet or drug therapy.