Three novel mutations in the liver-type arginase gene in three unrelated Japanese patients with argininemia

Argininemia is caused by a hereditary deficiency of liver-type arginase (E.C.3.5.3.1) and is characterized by psychomotor retardation and spastic tetraplegia. We examined findings in three Japanese patients with argininemia, by using the PCR, cloning, and sequencing procedures. We found three different mutations--G-to-A-365 in exon 4, G-to-C-703 in exon 7, and C-del-842 in exon 8--thereby leading to mutant arginase proteins of W122X, G235R, and L282FS, respectively. Patient 1 was a compound heterozygote, inheriting the allele with G-to-A-365 from his mother and the allele with G-to-C-703 from his father. Patients 2 and 3 were homozygotes of the allele with G-to-C-703 and of the allele with C-del-842, respectively. Expression tests of these mutant arginases in Escherichia coli indicated that the mutant arginase of W122X did not remain a stable product. The other two mutant arginases--G235R and L282FS--were detected by immunoblot analyses. There was no evidence of activity of the three mutant arginases expressed in E. coli. We tentatively conclude that argininemia is heterogeneous, at the molecular level.