Tremendous advances in human genetics have been made in recent years, as the fruits of the Human Genome Project are facilitating the identification of genes associated with myriad genetic diseases. Among the many triumphs in positional (and positional candidate) cloning are a number of cases where apparently unrelated diseases have been found to share common genetic origins. A vivid example of this has unfolded in the past few years with the identification of the genes causing diastrophic dysplasia, congenital chloride diarrhoea and Pendred syndrome. While these three disorders are clinically distinct, the associated genes ( DTDST, CLD and PDS, respectively) emanate from a well conserved family of genes that all encode anion transporters. Our current knowledge of these diseases coupled with new insights about the implicated genes and proteins illustrates the complex nature of mammalian genomes, especially with respect to the evolutionary subtleties of protein families and tissue-specific gene expression.