ABSTRACT
Systemic pseudohypoaldosteronism type I (PHAI) is an autosomal recessive disorder that arises from loss of function mutations of the alpha, beta, or gamma subunit of Epithelial Na(+) Channel (ENaC). In addition to a severe renal phenotype in the neonatal period, patients with PHAI develop a childhood pulmonary syndrome characterized by cough and frequent respiratory infections. We tested a patient, born to consanguineous parents, who presented with dehydration, metabolic acidosis, hyperkalemia, elevated renin and aldosterone levels at birth, and recurrent respiratory symptoms in his first year. He demonstrated defective epithelial Na(+) transport in multiple organs (raised sweat Cl(-), 120 mM; raised salivary Na(+) and Cl(-), 118 and 111 mM, respectively; and little nasal amiloride-sensitive potential difference). No deleterious mutation was identified in the coding region of the three ENaC subunits. Reverse transcriptase-polymerase chain reaction of nasal epithelial RNA showed reduced betaENaC expression, and inability to amplify promoter elements indicated the possibility of a deletion in the 5' region. Using a probe that corresponded to exon 1A of betaENaC, we confirmed a large deletion (> 1,300 bp). In summary, a homozygous mutation in the promoter region of betaENaC leads to PHAI, the first description of a mutation in the regulatory regions of an ENaC subunit leading to a clinical phenotype.
Subject(s)
Promoter Regions, Genetic , Pseudohypoaldosteronism/genetics , Sequence Deletion , Sodium Channels/genetics , 5' Flanking Region , Biological Transport , Child , Epithelial Sodium Channels , Exons , Homozygote , Humans , Infant, Newborn , Male , Pseudohypoaldosteronism/drug therapy , Reverse Transcriptase Polymerase Chain Reaction , Sodium/metabolism , Sodium Channels/metabolismABSTRACT
BACKGROUND: Mutations in the erythroid-specific 5-aminolevulinate-synthase gene (ALAS2) have been identified in many cases of X-linked sideroblastic anemia (XLSA). METHODS: A polymerase chain reaction-mediated restriction fragment length polymorphism (RFLP) assay was used. RESULTS: A G527T point mutation was identified. This resulted in a substitution of tyrosine for asparagine at residue 159 (D159Y). This mutation was also identified in the mother of the two probands. Mutations in all three individuals were confirmed by DNA sequencing analysis. CONCLUSIONS: We identified a missense mutation in exon 5 of the ALAS2 gene in two brothers of a consanguineous marriage, who were clinically pyridoxine-responsive.
