Congenital erythropoietic porphyria: mutation update and correlations between genotype and phenotype.

High quality genotype/phenotype analysis is a difficult issue in rare genetic diseases such as congenital erythropoietic porphyria (CEP) or Günther's disease, a heme biosynthesis defect due to uroporphyrinogen III synthase deficiency. The historical background and the main phenotypic features of the disease are depicted together with an update of published mutants and genotype/phenotype correlations. General rules concerning the prediction of disease severity are drawn as a guide for patient management and therapeutic choices. The phenotypic heterogeneity of the disease is presented in relation with a likely influence of modifying factors, either genetic or acquired.