Autosomal recessive pseudohypoaldosteronism type I is a rare life-threatening disease characterized by severe neonatal salt wasting, hyperkalaemia, metabolic acidosis, and unresponsiveness to mineralocorticoid hormones. Investigation of affected offspring of consanguineous union reveals mutations in either the alpha or beta subunits of the amiloride-sensitive epithelial sodium channel in five kindreds. These mutations are homozygous in affected subjects, co-segregate with the disease, and introduce frameshift, premature termination or missense mutations that result in loss of channel activity. These findings demonstrate the molecular basis and explain the pathophysiology of this disease.

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.

Patients with systemic pseudohypoaldosteronism fail to absorb liquid from airway surfaces; the result is an increased volume of liquid in the airways. These results demonstrate that sodium transport has a role in regulating the volume of liquid on airway surfaces.

Background: In protein engineering, site-directed mutagenesis methods are used to generate DNA sequences with mutated codons, insertions or deletions. In a widely used method, mutations are generated by PCR using a pair of oligonucleotide primers designed with mismatching nucleotides at the center of the primers. In this method, primer-primer annealing may prevent cloning of mutant cDNAs. To circumvent this problem we developed an alternative procedure that does not use forward-reverse primer pair in the same reaction.

Type I pseudohypoaldosteronism (PHA) is a hereditary disease characterized by salt wasting resulting from target organ unresponsiveness to mineralocorticoids. We have studied two kindreds including a total of nine patients with PHA. In kindred I, the propositus presented with renal salt wasting in infancy (vomiting, failure to thrive, short stature, hyponatremia, hyperkalemia) and responded dramatically to a high salt diet (2.5 g/day). Sodium supplementation was discontinued at the age of two. In seven additional family members from three generations, clinical expression of PHA varied from asymptomatic to moderate. In affected members (propositus, mother, and two brothers), hyperaldosteronism persisted over 13 yr; however, the PRA decreased gradually to near normal values. Persistent hyperaldosteronism in the face of a decrease in PRA indicated the development of tertiary hyperaldosteronism due to autonomously functioning zona glomerulosa. The pedigree was consistent with an autosomal dominant mode of transmission with variable expression. In kindred II, the propositus, who was the product of a consanguineous marriage, developed severe renal salt losing at age 9 days. She had also increased salivary and sweat electrolytes consistent with PHA resulting from multiple organ unresponsiveness to mineralocorticoids. Life threatening episodes of salt wasting recurred beyond the age of 2 yr. At 5 yr of age she still requires high amounts of salt supplements (14 g/day). A sister died at 9 days of age with PHA symptoms. Six close relatives (parents, three siblings, maternal uncle) showed no biochemical abnormalities. This pedigree was consistent with an autosomal recessive mode of inheritance. In view of the findings on these two kindreds and the analysis of those in the literature, we conclude that type I PHA includes two clinically and genetically distinct entities with either renal or multiple target organ defects.

Epithelial sodium channels (ENaCs) are located on the apical surface of cells and funnel Na(+) ions from the lumen into the cell. ENaC function also regulates extracellular fluid volume as water flows across membranes accompanying Na(+) ions to maintain osmolarity. To examine the sites of expression and intracellular localization of ENaC, we generated polyclonal antibodies against the extracellular domain of human α-ENaC subunit that we expressed in E. coli. Three-dimensional (3D) confocal microscopy of immunofluorescence using these antibodies for the first time revealed that ENaCs are uniformly distributed on the ciliary surface in all epithelial cells with motile cilia lining the bronchus in human lung and female reproductive tract, all along the fimbrial end of the fallopian tube, the ampulla and rare cells in the uterine glands. Quantitative analysis indicated that cilia increase cell surface area >70-fold and the amount of ENaC on cilia is >1,000-fold higher than on non-ciliated cell surface. These findings indicate that ENaC functions as a regulator of the osmolarity of the periciliary fluid bathing the cilia. In contrast to ENaC, cystic fibrosis transmembrane conductance regulator (CFTR) that channels chloride ions from the cytoplasm to the lumen is located mainly on the apical side, but not on cilia. The cilial localization of ENaC requires reevaluation of the mechanisms of action of CFTR and other modulators of ENaC function. ENaC on motile cilia should be essential for diverse functions of motile cilia, such as germ cell transport, fertilization, implantation, clearance of respiratory airways and cell migration.

Severe PHA cases are associated with mutations leading to absence of normal-length alpha, beta or gammaENaC, while a mild case has been found to be associated with a missense mutation in alphaENaC. The predominance of PHA-causing mutations in the alphaENaC gene may be related to the function of this subunit.

OBJECTIVE -To investigate the prevalence of autoimmune diseases in young patients (probands) with type 1 diabetes and their first-degree relatives, and to determine the spectrum of extrapancreatic manifestations in these subjects. RESEARCH DESIGN AND METHODS-The study population included 109 probands age 13 Ϯ 4.9 years and 412 first-degree relatives age 28.7 Ϯ 16.2 years. The prevalence rates of autoimmune thyroiditis and celiac disease were determined in all probands and in 100 of the 412 first-degree relatives. Control groups included 78 subjects age 14.9 Ϯ 10.4 years for the prevalence of autoimmune thyroiditis and 120,000 youth ages 16 -17 years for the prevalence of celiac disease. Thyroiditis and celiac disease were diagnosed by abnormally high thyroid peroxidase (TPO), thyroglobulin (TG), antigliadin, and antiendomysial antibody titers. Celiac was confirmed by biopsy. A questionnaire was used to interview probands and relatives to determine the spectrum of autoimmune manifestations.RESULTS -The prevalence of autoimmune thyroiditis determined by high TPO and/or TG titers was 27 and 25% for probands and relatives, respectively. These rates were higher than those for control subjects (P Ͻ 000.1). The prevalence of celiac disease among probands and screened relatives was 8.3 and 6%, respectively. These rates were higher than those for control subjects and the 312 family members interviewed only (0.1 and 0.3%, respectively; P Ͻ 0.0001). Interviews of participants revealed a wide range of associated autoimmune diseases. The risk of developing an autoimmune disease was higher (P Ͻ 0.001) in families with a proband who had an additional autoimmune manifestation.CONCLUSIONS -Screening for autoimmune thyroiditis and celiac disease should be performed in patients with type 1 diabetes and their first-degree relatives, especially when the probands have an additional autoimmune manifestation.