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In gyrate atrophy of the choroid and retina with hyperornithinaemia (GA), a genetically determined deficiency of ornithine delta-aminotransferase activity leads to high ornithine concentrations in body fluids. GA is characterized by centripetally progressing retinal and choroidal destruction and selective atrophy with tubular aggregates in type II skeletal muscle fibres. These findings have been suggested to be mediated by hyperornithinaemia-induced deficiency of high-energy creatine phosphate. As abnormal brain magnetic resonance images and electroencephalograms are found in another disorder of creatine metabolism, guanidinoacetate methyltransferase deficiency, we investigated the central nervous system involvement in GA, which seems to be associated with a milder degree of phosphocreatine deficiency. We compared 23 untreated GA patients with age-matched healthy controls, and with 9 patients who had received creatine or creatine precursor supplementation daily for several years. The mean age of the patients (32 +/- 18 years) was similar to that of the controls (36 +/- 22 years). The MRI or EEG findings of the patients on creatine supplementation did not differ from those of the untreated group. Brain MRI revealed degenerative lesions in the white matter in 50% of the GA patients, and 70% of the patients had premature atrophic changes, with a striking increase in the number of Virchow's spaces. Of the patients whose EEG was recorded, 58% had abnormal slow background activity, focal lesions or high-amplitude beta rhythm (50 microV). The EEG findings were not associated with the MRI changes or with the age or the sex of the patients. Early degenerative and atrophic brain changes and abnormal EEG are thus features of GA, in addition to the well-characterized eye and muscle manifestations.

Creatine (Cr) and phosphocreatine play an essential role in energy storage and transmission. Maintenance of creatine pool is provided by the diet and by de novo synthesis, which utilizes arginine, glycine and s-adenosylmethionine as substrates. Three primary Cr deficiencies exists: arginine:glycine amidinotransferase deficiency, guanidinoacetate methyltransferase deficiency and the defect of Cr transporter SLC6A8. Secondary Cr deficiency is characteristic of ornithine-aminotransferase deficiency, whereas non-uniform Cr abnormalities have anecdotally been reported in patients with urea cycle defects (UCDs), a disease category related to arginine metabolism in which Cr must be acquired by de novo synthesis because of low dietary intake. To evaluate the relationships between ureagenesis and Cr synthesis, we systematically measured plasma Cr in a large series of UCD patients (i.e., OTC, ASS, ASL deficiencies, HHH syndrome and lysinuric protein intolerance). Plasma Cr concentrations in UCDs followed two different trends: patients with OTC and ASS deficiencies and HHH syndrome presented a significant Cr decrease, whereas in ASL deficiency and lysinuric protein intolerance Cr levels were significantly increased (23.5 vs. 82.6 μmol/L; p < 0.0001). This trend distribution appears to be regulated upon cellular arginine availability, highlighting its crucial role for both ureagenesis and Cr synthesis. Although decreased Cr contributes to the neurological symptoms in primary Cr deficiencies, still remains to be explored if an altered Cr metabolism may participate to CNS dysfunction also in patients with UCDs. Since arginine in most UCDs becomes a semi-essential aminoacid, measuring plasma Cr concentrations might be of help to optimize the dose of arginine substitution.

A novel disease of the metabolism of creatine and guanidinoacetate (GUAC) in a 22-month-old child has been reported recently from our department (Stockler et al 1994). Following an uneventful development in the first 3 months, the boy developed muscular hypotonia, weakness and a distinct extrapyramidal disorder with hemiballistic-dystonic movements. In magnetic resonance spectroscopy of the brain the absence of a creatine signal and a massively increased GUAC signal eventually led to the diagnosis of guanidinoacetate methyltransferase deficiency. The boy was successfully treated with oral creatine monohydrate. Standard laboratory results were not very specific, so that the need has arisen for a readily available method to screen for the elevated levels of guanidinoacetate seen in this disease. Presently HPLC is the established method (Marescau et al 1985). We have developed a simple mass fragmentographic method for the determination of GUAC in urine and plasma. The reaction of the guanidino group of GUAC with hexafluoroacetylacetone (Malcolm and Marten 1976) results in the formation of a bis(trifluoromethyl)pyrimidine derivative and the carboxyl group is then converted to the trimethylsilyl ester. 2-Phenylbutyrate is used as the internal standard since this has a suitable retention time and is widely available.

Creatine deficiency syndromes are a newly described group of inborn errors of creatine synthesis (arginine:glycine amidinotransferase (AGAT) deficiency and guanidinoaceteate methyltransferase (GAMT) deficiency) and creatine transport (creatine transporter (CRTR) deficiency). The common clinical denominator of creatine deficiency syndromes is mental retardation and epilepsy, suggesting the main involvement of cerebral grey matter (grey matter disease). Patients with GAMT deficiency exhibit a more complex clinical phenotype with dystonic hyperkinetic movement disorder and epilepsy that in some cases is unresponsive to pharmacological treatment. The common biochemical denominator of creatine deficiency syndromes is cerebral creatine deficiency which is demonstrated by in vivo proton magnetic resonance spectroscopy. Measurement of guanidinoacetate in body fluids may discriminate GAMT (high concentration), AGAT (low concentration) and CRTR (normal concentration). Further biochemical characteristics include changes in creatine and creatinine concentrations in body fluids. GAMT and AGAT deficiency are treatable by oral creatine supplementation, while patients with CRTR deficiency do not respond to this type of treatment. Further recognition of patients will be of major importance for the estimation of the frequency, for the understanding of phenotypic variations and for treatment strategies.

1Department of Paediatrics and 2Centre for Molecular Neurobiology University ofHamburg, Martinistr. 52, D-20246 Hamburg, Germany* Correspondence: E-mail: das=uke.uni-hamburg.deIn guanidinoacetate N-methyltransferase (GAMT) de—ciency (McKusick 601240)synthesis of creatine is compromised. This leads to intracellular depletion of creatinephosphate, which serves as a short-term fienergy buƒerˇ, especially in organs withhigh, Nuctuating energy demand like the brain. Therefore, cells from GAMT-de—cient patients have to rely almost exclusively on ATP produced directly by themitochondrial respiratory chain. This increased metabolic strain on the respiratorychain may lead to compensatory upregulation of respiratory chain enzymes. Wetherefore examined activities of respiratory chain enzymes in —broblasts from apatient with GAMT de—ciency.MATERIALS AND METHODSSkin —broblasts were taken from the —rst patient diagnosed with GAMT-de—ciency(Sto” ckler et al 1996). Cells were cultured in MEM medium with 10% fetal calf serumFCS) or, for creatine-free incubations, in Waymouth medium (Life Technologies)without FCS for 21 days. Fibroblasts were incubated in Waymouth medium supple-mented with 1mmol/L creatine, which is the approximate concentration reached invivo in patients supplemented with creatine for 14 days in an attempt to reverse theeƒect of creatine depletion.Respiratory chain enzyme activities, including active regulation of the mitochon-drial ATP synthase (complex V) in response to metabolic conditions of the cells,were determined spectrophotometrically after sonication as described in detail in aprevious study (Das and Kohlschu” tter 1999).Creatine phosphate, ATP and ADP were measured in the cell homogenatequenched in DMSO (]3mmol/L EDTA) by bioluminescence using a luciferin/luciferase test kit (Bioorbit Turku, Finland) according to published methods (Harrisand Slater 1975; Holm-Hansen and Karl 1978; Lundin 1978).375

Guanidinoacetate methyltransferase (GAMT) deficiency is a rare disorder of creatine synthesis. We report a patient who presented at 10 months of age with hypotonia and global developmental delay. Subsequently, she developed seizures and choreoathetosis. Magnetic resonance imaging showed high signal bilaterally in the globus pallidus on T2-weighted images. Mitochondrial respiratory chain studies revealed low complex I activity (in muscle 0.052 nmol NADH oxidized per min per unit citrate synthase, controls 0.166 +/- 0.047; in fibroblasts 0.080 nmol NADH oxidized per min per unit citrate synthase, controls 0.197 +/- 0.034). The true diagnosis was suspected at 21 months of age because of persistent low plasma and urine creatinine concentrations. GAMT activity was undetectable in fibroblasts and compound heterozygous mutations were found in the GAMT gene (c.327GA and c.522GA). The patient was treated with creatine, dietary arginine restriction and ornithine supplements. Her movement disorder and seizures resolved but she still has severe cognitive impairment and no expressive language. The occurrence of secondary respiratory chain abnormalities in GAMT deficiency may lead to misdiagnosis, particularly as the clinical and radiological features resemble those seen in mitochondrial encephalopathies. It is important to establish the correct diagnosis because specific treatment is available.