Les gènes modificateurs dans les maladies héréditaires.

Abstract

Many hereditary diseases are phenotypically variable. The phenotype can be more or less severe between families and within families. Three main factors can cause this phenotypic variability: allelic and non allelic heterogeneity, modifying genes, environmental differences. Modifiying genes which, while not causing the disease may be related to its severity. The modifiying genes can concern a qualitative feature of the disease, i.e. different subsets of organs can be affected, or a quantitative one, a different age of onset can be noted. Three groups of modifier genes can be considered: (1) Allelic or heteroallelic variants of the deleterious gene. (2) Genes very closely linked to the deleterious allele (chromosomal background). (3) non allelic genes. Strategies for the identification of modifiying genes are similar to those used in genetic epidemiology. Two methods are used, association studies and affected sibling pairs analysis. In both cases the candidate gene approache is privileged. Understanding the pathogenesis of a disease and/or animal models may provide clues to likely candidate genes. [References: 28]