An important component of medical genetics is identifying and characterizing the genotypes responsible for particular disease phenotypes. In doing so, it is important not to adhere to an overly simplistic view that each disease phenotype is caused uniquely by one particular mutation in a specific gene or that mutations in a particular gene always cause the same phenotype. In fact, there is often substantial heterogeneity in the complex relationship(s) among disease phenotypes, the genes that are mutated in those diseases, and the nature of the mutations found in those genes. Three main types of heterogeneity are distinguished, as will be illustrated in detail in Chapters 11 and 12. Here, we introduce them and outline their distinguishing features. • Allelic heterogeneity, in which different mutations in a gene may produce the same phenotype • Locus heterogeneity, in which mutations in different genes may cause the same phenotype • Clinical or phenotypic heterogeneity, in which different mutations in a gene may result in different phenotypes.
Correlating Genotype and Phenotype
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