Estimating prevalence in single-gene kidney diseases progressing to renal failure

Incidence and prevalence, the measures of "frequency," are often confused. While in a nonhereditary situation, the useful parameter is the incidence r ate, evaluating the impact of an etiologic factor, it is prevalence that is considered useful in a hereditary disease. Prevalence may concern either t he whole population or a fraction of this population, that is, males or fem ales or individuals at a given age, for example, at birth. Pathologic pheno type and morbid genotype prevalences have to be clearly differentiated. In this article, we review the epidemiologic surveys allowing an estimation of the distribution of major single-gene kidney diseases progressing to renal failure in different populations. In order to compare their results, the g eographic/ethnic composition of the population, the determination of its si ze, the choice and mode of calculation of the epidemiologic measure, the de finition of the disease and modes of diagnosis, the inclusion of cases, the sources of ascertainment and the possible causes of underascertainment, an d the period of time during which events were counted should be analyzed ac curately. Although their impact in terms of morbidity, hospitalizations, mo rtality, and cost to society is high, this review shows that information on the prevalence of single-gene kidney diseases is far from complete. To dat e, the data essentially apply to large populations of European origin. A pa rt of the variation among prevalence data may be due to methodological diff erences. Not representative are the small populations in which some rare di seases, especially recessive, are found with a high prevalence.