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Genetic studies of cystic fibrosis and atopic asthma: current approaches and future aspects

Since the early 1980s, several major developments in human genetics research have resulted in an explosion of the discovery of genes responsible for inherited diseases, especially those that follow simple Mendelian patterns of inheritance. By using positional cloning, nearly 50 inherited human disease genes have been identified (1). However, these single-gene, “simple” diseases are typically rare (<O. 1 % prevalence) and are frequently fatal. Much less is known about the more common yet complex diseases, such as asthma and atopic allergy. Cystic fibrosis (CF) is a well-characterized monogenic disease and the most common simple disease affecting Caucasians of European descent (2); it affects as many as 1:2500 births among certain Caucasian groups (3). The molecular mechanisms of the CF mutation have been well described and divided into five classes for which a strong genotypephenotype correlation can be observed. There is, however, tremendous aIlelic heterogeneity, resulting in a continuum of disease expression from very mild to very severe. Recently, evidence has emerged which suggests the existence of a modifier gene that potentially impacts CF severity (4). This finding will potentially force the scientific community to redefine monogenic diseases. The study of CF affords us an opportunity to establish a paradigm for the dissection of genetic diseases in general, and highlights the importance of the clinical phenotype in understanding the genetic mechanisms involved in disease expression. Asthma has been described as a complex trait for which genetic predisposition is fundamental in disease etiology, but poorly understood, largely due to the myriad of potential phenotypes. Unraveling the genetic etiology of asthma is further complicated by the multifactorial nature of asthma that is, there is Kathleen C. Barnes, Johns Hopkins Asthma & Allergy Center, 5501 Hopkins Bayview Circle, Baltimore, M D 21224-6801, USA