The systemic form of pseudohypoaldosteronism type 1 (PHA1) is a rare autosomal recessive disorder with salt-wasting, hyperkalemia, metabolic acidosis, and multiorgan aldosterone unresponsiveness. Recently, this form of PHA1 was found to be caused by the loss-of-function mutations in the gene of each subunit (alpha, beta, and gamma) of the epithelial sodium channel (ENaC). To investigate the molecular basis of one sporadic Japanese patient with a systemic form of PHA1, we determined the nucleotide sequence of the genes of every subunit of ENaC of this patient. The patient was found to be a compound heterozygote for one base deletion in exon 12 (1627delG) in combination with 1570-1-->GA substitution at the 5' splice acceptor site of intron 11 in the gamma subunit gene of ENaC. The 1627delG mutation altered a reading frame, resulting in a premature stop codon in exon 12. Messenger RNA from the allele harboring the splice site mutation was not identified by RT-PCR. In conclusion, two novel mutations in the gamma subunit gene of ENaC caused systemic PHA1 in the sporadic Japanese patient. Identification of the molecular basis of PHA1 is helpful for early diagnosis and understanding the pathophysiology of the disease.