Steroid 21-hydroxylase deficiency is the most common enzymatic defect causing congenita ladrenal hyperplasia. A large number of new mutations has been detected in the laboratory, which centralizes the biggest cohort of families in the world, and evaluation of their severity wasessential to optimize the care of the patients (treatment, genetic counselling). Thanks to detailed analysis of the patients phenotype and to the development of functional studies (in vitro, in silico), we were able to evaluate the severity of most of the 85 novel mutations; we decided touse as controls frequent known mutations and to compare our results with those of literature. Themore detailed analysis of about fifteen rare mutations confirmed the existence of goodcorrelations phenotype-genotype as this is described in this pathology. Moreover, the structural studies we developed led to improve the knowledge on structure-function relationship of theP450 cytochromes family.
