Novel Mutations in the SCNN1A Gene Causing Pseudohypoaldosteronism Type 1

Department of Laboratory Medicine, Boston Children's Hospital, Boston, Massachusetts, United States of America.
PLoS ONE (Impact Factor: 3.23). 06/2013; 8(6):e65676. DOI: 10.1371/journal.pone.0065676
Source: PubMed


Pseudohypoaldosteronism type 1 (PHA1) is a rare inherited disease characterized by resistance to the actions of aldosterone. Mutations in the subunit genes (SCNN1A, SCNN1B, SCNN1G) of the epithelial sodium channel (ENaC) and the NR3C2 gene encoding the mineralocorticoid receptor, result in systemic PHA1 and renal PHA1 respectively. Common clinical manifestations of PHA1 include salt wasting, hyperkalaemia, metabolic acidosis and elevated plasma aldosterone levels in the neonatal period. In this study, we describe the clinical and biochemical manifestations in two Chinese patients with systemic PHA1. Sequence analysis of the SCNN1A gene revealed a compound heterozygous mutation (c.1311delG and c.1439+1G>C) in one patient and a homozygous mutation (c.814_815insG) in another patient, all three variants are novel. Further analysis of the splicing pattern in a minigene construct showed that the c.1439+1G>C mutation can lead to the retainment of intron 9 as the 5'-donor splice site disappears during post-transcriptional processing of mRNA. In conclusion, our study identified three novel SCNN1A gene mutations in two Chinese patients with systemic PHA1.

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    ABSTRACT: Pseudohypoaldosteronism type 1 (PHA1) is a monogenic disorder of mineralocorticoid resistance characterized by salt wasting, hyperkalemia, high aldosterone levels, and failure to thrive. An autosomal recessive form (AR-PHA1) is caused by mutations in the epithelial sodium channel ENaC with usually severe and persisting multiorgan symptoms. The autosomal dominant form of PHA1 (AD-PHA1) is due to mutations in the mineralocorticoid receptor causing milder and transient symptoms restricted to the kidney. We identified a homozygous missense mutation in the SCNN1A gene (c.727T>C/p.Ser(243)Pro), encoding α-subunit of ENaC (α-ENaC) in a prematurely born boy with a severe salt-losing syndrome. The patient improved rapidly under treatment, and dietary salt supplementation could be stopped after 6 mo. Interestingly, the patient's sibling born at term and harboring the same homozygous Ser(243)Pro mutation showed no symptom of salt-losing nephropathy. In vitro expression of the αSer(243)Pro ENaC mutant revealed a slight but significant decrease in ENaC activity that is exacerbated in the presence of high Na(+) load. Our study provides the first evidence that ENaC activity is critical for the maintenance of salt balance in the immature kidney of preterm babies. Together with previous studies, it shows that, when the kidney is fully mature, the severity of the symptoms of AR-PHA1 is related to the degree of the ENaC loss of function. Finally, this study identifies a novel functional domain in the extracellular loop of ENaC.
    AJP Endocrinology and Metabolism 06/2011; 301(3):E467-73. DOI:10.1152/ajpendo.00066.2011 · 3.79 Impact Factor
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    ABSTRACT: We report a six-week-old boy with genitourinary structural abnormalities who presented with profound hyponatraemia and hyperkalaemia due to transient type 1 pseudohypoaldosteronism (PHA) precipitated by a urinary tract infection (UTI), which responded rapidly to intravenous saline and antibiotics. In infants with structural abnormalities of the urinary tract, we wish to highlight the importance of recognizing type 1 PHA and its association with a UTI since prompt and appropriate treatment rapidly corrects the associated metabolic abnormalities. Conversely, the identification of type 1 PHA in an infant should precipitate a search for a UTI and structural abnormalities of the urinary tract.
    Annals of Clinical Biochemistry 04/2011; 48(Pt 4):380-2. DOI:10.1258/acb.2011.010264 · 2.34 Impact Factor
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    ABSTRACT: To study patients with autosomal recessive pseudohypoaldosteronism type 1 and to relate pulmonary disease to gene mutations of the epithelial sodium channel (ENaC). Clinical and laboratory data were collected from 4 Swedish patients with pseudohypoaldosteronism type 1. The genes for ENaC and cystic fibrosis transmembrane conductance regulator were analyzed for mutations with methods including DNA sequencing. Three novel mutations were found in the alpha-gene of ENaC, 2 frameshifts (1449delC and 729delA) and 1 missense mutation resulting in the substitution of leucine for serine 562 in the alpha-chain (S562L). The 1449delC mutation was found in all patients in either homozygous or heterozygous form and seems to be the predominant cause of pseudohypoaldosteronism in Sweden. The allele coding for S562L also contained a transition converting tryptophan 493 to arginine (W493R), which seems to be a rare polymorphism. All patients had pulmonary symptoms to various degrees. The bacterial findings resembled, to some extent, those in cystic fibrosis, but development of chronic lung disease and progressive decline in lung function were not observed. Genetic deficiencies of the alpha subunit of the ENaC are associated with prominent lung symptoms, which are, however, clearly different from those in cystic fibrosis.
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