Argininemia is caused by a deficiency of arginase 1, which catalyzes the final 
step in the urea cycle, i.e., the cytosolic hydrolysis of arginine to ornithine 
and urea. In contrast to other urea cycle disorders, hyperammonemic 
encephalopathy is rarely observed in patients with argininemia. Rather, most 
exhibit an insidious onset and progression of neurologic manifestations, 
including spastic diplegia. We describe the first Korean patient with 
argininemia, manifesting as slowly progressive spastic diplegia. Our patient 
carries c.[32T>C]+[913G>A] (p.[Ile11Thr]+[Gly305Arg]) mutations in the ARG1 
gene. The latter mutation was not previously reported. Although argininemia is a 
very rare disease, it is recognized as a pan-ethnic disorder. We conclude that 
argininemia should be considered more frequently in the differential diagnosis 
of a patient with slowly progressive neurologic manifestations, especially 
progressive spastic diplegia, even in a population where argininemia was 
previously unknown.