Functional characterization of naturally occurring NR3C2 gene mutations in Italian patients suffering from pseudohypoaldosteronism type 1.
OBJECTIVE
The renal form of pseudohypoaldosteronism type 1 (PHA1) is a rare disease caused by mutations in the human mineralocorticoid receptor gene (NR3C2).


METHODS
Aim of the study was to analyze the NR3C2 gene in three Italian patients with clinical signs of renal PHA1 and to evaluate the distribution of the -2G > C, c.538A > G, and c.722C > T single nucleotide polymorphism (SNP) pattern in the PHA1 patients and in 90 controls of the same ethnic origin.


METHODS
Analysis of the NR3C2 gene sequence and of the polymorphic SNP markers. Functional characterization of the detected novel NR3C2 mutations utilizing aldosterone-binding assays and reporter gene transactivation assays.


RESULTS
One novel nonsense (Y134X) and one novel frameshift (2125delA) mutation were detected. They exhibited no aldosterone binding and no transactivation abilities. No mutation was detected in the third patient. Haploinsufficiency of NR3C2 was ruled out by microsatellite analysis in this patient. The c.722T SNP was detected in 97% of alleles in the Italian population which is significantly different from the general German or US population.


CONCLUSIONS
Molecular analysis of the NR3C2 gene in PHA1 patients is warranted to detect novel mutations in order to clarify the underlying genetic cause, which may extend the insight into relevant functional regions of the hMR protein. The effect the different distribution of the c.722T SNP is not clear to date. Further studies are necessary to provide evidence as to a possible advantage of a less sensitive hMR in southern countries.
Balsamo
Antonio
A
Division of Pediatric Endocrinology, Department of Pediatrics, Policlinico S. Orsola-Malpighi, University of Bologna, Via Massarenti 11, 40138 Bologna, Italy. antonio.balsamo@unibo.it
Cicognani
Alessandro
A
Gennari
Monia
M
Sippell
Wolfgang G
WG
Menabò
Soara
S
Baronio
Federico
F
Riepe
Felix G
FG
D000328:Adult; D000450:Aldosterone / Q000097:blood; D002675:Child, Preschool; D018389:Codon, Nonsense; D004252:DNA Mutational Analysis; D005260:Female; D016368:Frameshift Mutation; D005787:Gene Frequency; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007558:Italy; D008297:Male; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide; D014176:Protein Biosynthesis; D011546:Pseudohypoaldosteronism / Q000235:genetics*; D018161:Receptors, Mineralocorticoid / Q000235:genetics*
D018389:Codon, Nonsense; D018161:Receptors, Mineralocorticoid; D000450:Aldosterone; D006854:Hydrocortisone