In 1965, a 21-year-old Japanese woman tried to open a sliding door by pushing and pulling it. Her struggle, observed by her parents, continued for 2 h. Although she seemed to answer questions appropriately during the episode, she could not recall it afterwards. During the next 4 years, she had occasional further episodes, lasting 30 min to 3 h, of apparently purposeless, stereotyped behaviour: opening and closing doors, and taking off and putting on her shirt. During these episodes, she had gross fi nger tremors in both hands. Doctors at another hospital prescribed an anticonvulsant, which seemed to exacerbate her illness. In March, 1969, she was admitted to our hospital, for assessment. Neurological fi ndings were normal except for a fl apping tremor, prominent in the fourth and fi fth fi ngers of both hands. Blood tests showed a slightly high ammonia concentration. The electroencephalogram (EEG) showed occasional triphasic waves across much of the brain, on a background of θ waves (4–6 Hz); no epileptic discharges were seen. Review of the patient’s history indicated that the episodes were far longer than is typical for epilepsy. No convincing evidence of psychiatric disorder was elicited. However, doctors noted that the episodes often occurred when the patient was constipated, after eating protein-rich foods. She was diagnosed with hepato cerebral disorder, of a kind described by Inose. After discharge, the frequency and severity of the dis tur bances of consciousness became worse. The patient’s pre ference for beans and tofu, rather than carbohydrate-rich sweets, exacerbated the symptoms. She was readmitted in February, 1972, and given lactulose, which produced a long-term improvement. Over the next 30 years, EEG abnormalities and slightly high blood ammonia concen trations were frequently detected. Nonetheless, the patient was comfortably able to hold down a job as a clerk in a kiosk, and had few (from the mid-1980s, no) disturbances in con sciousness, despite the absence of dietary restrictions. In March, 2005, an EEG revealed a background of θ waves, with an occasional α wave in the occipital area. No triphasic waves were observed. Results of liver function tests were normal, as were serum concentrations of copper and caeruloplasmin. However, the urea concentration was 8·6 mmol/L (normal range 2·6–6·6 mmol/L), and the ammonia concentration 28–79 μmol/L (normal range 9–33 μmol/L). Suspecting a urea-cycle disorder, we tested concentrations of amino acids, and detected citrullinaemia: the blood concen tra tions of citrulline and arginine were 235 μmol/L (normal range 17–43 μmol/L), and 147 μmol/L (normal range 54–130 μmol/L) respectively. The Fischer ratio of branched-chain to aromatic aminoacids, was 1∙80 (normal range 2·4–4·4), indicating liver disease. We took a biopsy sample from the liver, and found evidence of liver damage; however, we saw no prominent fi brosis or lobular changes, of the kind found in cirrhosis. On dideoxy sequencing, we observed a homozygotic (G to A) single nucleotide mutation of the citrin gene, SLC25A13, at the splicing donor site of intron 11 (fi gure). Exon 11 had been spliced out, resulting in a 53-aminoacid deletion. The good prognosis and mild liver damage in this case may refl ect a subtype of the mutation. Type I citrullinaemia is an autosomal recessive disorder caused by a defi ciency of argininosuccinate synthetase, one of the urea cycle enzymes; it aff ects the patient from birth. Type II, or adult-onset citrullinaemia, is caused by muta tions of the gene for citrin, an aspartate-glutamate carrier (AGC) important in the urea cycle (the disorder had pre viously constituted part of Inose’s “hepatocerebral syn drome”). Most people with type II citrullinaemia have a parti cular fondness for foods rich in arginine, such as beans, peas, and peanuts. In many cases, dietary restriction is required to prevent hyperammonaemic encephalo pathy. Episodes can be misdiagnosed as epileptic auto matism. Treat ment with anticonvulsants can cause severe hyper ammonaemia, and deterioration. The carrier frequency, for muta tions of the citrin gene, is 1 in 65 in Chinese people, 1 in 69 in Japanese people, and 1 in 112 in Koreans.