Patients with mitochondrial ornithine transporter deficiency (or HHH syndro
me) present with various neurological symptoms, including mental retardatio
n, spastic paraparesis with pyramidal signs, cerebellar ataxia, and episodi
c disturbance of consciousness or coma due to hyperammonemia. We previously
described three novel mutations in the ORNT1 gene in Japanese patients wit
h HHH syndrome. In this article. we report a new patient with HHH syndrome.
a 52-year-old woman, who had the typical clinical features, except for an
absence of mental retardation. When we screened this patient, as well as a
previously described Japanese patient. for mutations in the ORNT1 gene, we
found that both were homozygous for a nonsense mutation (R179X). Furthermor
e, reverse transcription (RT)-polymerase chain reaction (PCR) of fibroblast
RNA from one patient showed exon 4 skipping, as had been observed in a pre
viously reported patient with R179X. These results, together with the findi
ngs in our previous report, show that, in three of our five reported Japane
se HHH patients (six of ten alleles), R179X is present, suggesting that thi
s is a common mutation in Japanese patients with HHH syndrome.