Context: Pseudohypoaldosteronism Type I (PHA1) is a rare salt wasting syndrome. Mutations in the NR3C2 gene coding for the mineralocorticoid receptor (MR) cause autosomal dominant PHA1.

Objective: To reveal the cause of renal salt loss in six PHA1 patients and analyze the mutants' functional impact on MR function.

Design: Clinical and hormonal characterization of the patients' phenotype. Analysis of the NR3C2 gene. Determination of receptor affinities to aldosterone and the transcriptional activation abilities of the MR mutants. Investigation of subcellular translocation using fluorescence-labeled MR. Studying changes in mutant receptor conformation with proteolysis experiments and 3-dimensional modeling.

Results: Six heterozygous NR3C2 mutations were detected. One frameshift mutation (c.1131dupT) has been reported previously. The second frameshift mutation (c.2871dupC) which has only recently been reported by our group showed no aldosterone binding and no transactivation because of a major change in receptor conformation. Two novel nonsense mutations generate a truncated receptor protein. Two missense mutations differently affect MR function. S818L was reported recently without complete in vitro data. S818L neither binds aldosterone nor activates transcription nor translocates into the nucleus. A major displacement of several residues involved in aldosterone binding was PHA1 causing. The novel E972G mutation showed a significantly lower ligand binding affinity and only 9% of wild-type transcriptional activity caused by major changes in receptor conformation.

Conclusions: Our data on six mutations extends the spectrum of PHA1-causing NR3C2 gene mutations. Studying naturally occurring mutants helps to clarify their pathogenicity and to identify crucial residues for MR structure and function.