The use of sodium resonium in pseudohypoaldosteronism

A Novel SCNN1A Variation in a Patient with Autosomal-recessive Pseudohypoaldosteronism Type 1

Pseudohypoaldosteronism type 1 (PHA1) is an autosomal-recessive disorder characterized by defective regulation of body sodium (Na) levels. The abnormality results from mutations in the genes encoding subunits of the epithelial Na channel. Patients with PHA1 present in infancy as being in adrenal crisis. A 41-day-old female who presented with recurrent adrenal crisis did not adequately respond to hydrocortisone and required mineralocorticoid therapy. The patient’s demographic data and clinical features were recorded. Blood samples were collected and tested for endocrine and metabolic characteristics and for use in genetic studies. Bidirectional Sanger sequencing of SCNN1A was conducted. The entire coding region of 12 exons and 20 bp of flanking intron were sequenced. Genetic analyses revealed a new mutation - c.729_730delAG (p.Val245Glyfs*65) - in SCNN1A exon four. Adrenal crisis during the neonatal period highlights the importance of early screening for PHA1. Genetic testing could help to anticipate the prognosis, severity, onset of the disease, and the mode of inheritance, especially given its extensive phenotype.

Systemic Pseudohypoaldosteronism Type 1 due to 3 Novel Mutations in SCNN1Aand SCNN1BGenes

OBJECTIVE

The systemic form of pseudohypoaldosteronism type 1 (PHA1) is an autosomal recessive disorder characterized by defective sodium transport in multi-organ systems. Mutations in the genes encoding the amiloride-sensitive epithelial sodium channel, ENaC, account for genetic causes of systemic PHA1. We describe systemic PHA1 due to 4 novel variants detected in SCNN1A and SCNN1B in 3 cases from 3 unrelated consanguineous families.

PATIENTS AND METHODS

We evaluated the clinical presentations, biochemical and hormonal characteristics, and molecular genetic analysis results of 3 patients from 3 unrelated consanguineous families and parents from whom samples were available.

RESULTS

The ages at presentation were postnatal days 9, 10, and 5. The main presentation symptoms were vomiting, poor feeding, weakness, weight loss, and skin rash. All patients exhibited laboratory characteristics including severe hyponatremia, hyperkalemia, metabolic acidosis, elevated plasma renin, elevated aldosterone, and positive sweat tests, suggesting a diagnosis of systemic PHA1. Molecular genetic analysis revealed 2 novel pathogenic variants [c.87C>A(p.Tyr29*)/IVS9 + 1G>A (c.1346 + 1G>A)] in SCNN1Bin case 1, a novel homozygous pathogenic variant [p.His69Arg(c.206A>G] in SCNN1Ain case 2, and a homozygous one-base duplication, p.A200Gfs*6 (c.598dupG), in SCNN1A in case 3.

CONCLUSION

PHA1 should be considered at differential diagnosis in patients presenting with hyponatremia, hyperkalemia, and metabolic acidosis. The cases in this report involving 4 novel variants will add valuable insights into the phenotype-genotype relationship and will expand the mutation database.

Rare Cause of Hyperkalemia in the Newborn Period: Report of Two Cases of Pseudohypoaldosteronism Type 1

Pseudohypoaldosteronism (PHA) Type 1 is characterized by mineralocorticoid resistance, manifesting as neonatal salt wasting, hypotension, hyperkalemia, hyponatremia, and metabolic acidosis in spite of elevated aldosterone levels and plasma renin activity. It is important to differentiate children with systemic PHA from renal PHA, as these children are likely to decompensate even with mild symptoms. Here, we report two neonates with PHA that presented to us with multiorgan involvement.

Epithelial sodium channel (ENaC) family: Phylogeny, structure-function, tissue distribution, and associated inherited diseases

The epithelial sodium channel (ENaC) is composed of three homologous subunits and allows the flow of Na(+) ions across high resistance epithelia, maintaining body salt and water homeostasis. ENaC dependent reabsorption of Na(+) in the kidney tubules regulates extracellular fluid (ECF) volume and blood pressure by modulating osmolarity. In multi-ciliated cells, ENaC is located in cilia and plays an essential role in the regulation of epithelial surface liquid volume necessary for cilial transport of mucus and gametes in the respiratory and reproductive tracts respectively. The subunits that form ENaC (named as alpha, beta, gamma and delta, encoded by genes SCNN1A, SCNN1B, SCNN1G, and SCNN1D) are members of the ENaC/Degenerin superfamily. The earliest appearance of ENaC orthologs is in the genomes of the most ancient vertebrate taxon, Cyclostomata (jawless vertebrates) including lampreys, followed by earliest representatives of Gnathostomata (jawed vertebrates) including cartilaginous sharks. Among Euteleostomi (bony vertebrates), Actinopterygii (ray finned-fishes) branch has lost ENaC genes. Yet, most animals in the Sarcopterygii (lobe-finned fish) branch including Tetrapoda, amphibians and amniotes (lizards, crocodiles, birds, and mammals), have four ENaC paralogs. We compared the sequences of ENaC orthologs from 20 species and established criteria for the identification of ENaC orthologs and paralogs, and their distinction from other members of the ENaC/Degenerin superfamily, especially ASIC family. Differences between ENaCs and ASICs are summarized in view of their physiological functions and tissue distributions. Structural motifs that are conserved throughout vertebrate ENaCs are highlighted. We also present a comparative overview of the genotype-phenotype relationships in inherited diseases associated with ENaC mutations, including multisystem pseudohypoaldosteronism (PHA1B), Liddle syndrome, cystic fibrosis-like disease and essential hypertension.

Pseudohypoaldosteronism type 1: clinical features and management in infancy

Type 1 pseudohypoaldosteronism (PHA) is a rare heterogeneous group of disorders characterised by resistance to aldosterone action. There is resultant salt wasting in the neonatal period, with hyperkalaemia and metabolic acidosis. Only after results confirm isolated resistance to aldosterone can the diagnosis of type 1 PHA be confidently made. Type 1 PHA can be further classified into i) renal type 1 (autosomal dominant (AD)) and ii) multiple target organ defect/systemic type 1 (autosomal recessive (AR)). The aim of this case series was to characterise the mode of presentation, management and short-term clinical outcomes of patients with PHA type 1. Case notes of newly diagnosed infants presenting with PHA type 1 were reviewed over a 5-year time period. Seven patients were diagnosed with PHA type 1. Initial presentation ranged from 4 to 28 days of age. Six had weight loss as a presenting feature. All subjects had hyperkalaemia, hyponatraemia, with elevated renin and aldosterone levels. Five patients have renal PHA type 1 and two patients have systemic PHA type, of whom one has had genetic testing to confirm the AR gene mutation on the SCNN1A gene. Renal PHA type 1 responds well to salt supplementation, whereas management of patients with systemic PHA type 1 proves more difficult as they are likely to get frequent episodes of electrolyte imbalance requiring urgent correction.

Salt wasting disorder in the newborn

The clinical presentation of pseudohypoaldosteronism (PHA) mimics congenital adrenal hyperplasia (CAH). Poor response of the dehydration and electrolyte abnormalities to steroid therapy should make one suspect PHA. The treatment is supportive in the form of salt replacement and sodium resonium. We report a case of PHA that presented as salt wasting on the second day of life, initially appearing like CAH. The baby responded well to sodium resonium and salt replacement.