This paper reports clinical and metabolic studies of two Italian siblings with a novel form of persistent isolated hypermethioninaemia, i.e. abnormally elevated plasma methionine that lasted beyond the first months of life and is not due to cystathionine beta-synthase deficiency, tyrosinaemia I or liver disease. Abnormal elevations of their plasma S-adenosylmethionine (AdoMet) concentrations proved they do not have deficient activity of methionine adenosyltransferase I/III. A variety of studies provided evidence that the elevations of methionine and AdoMet are not caused by defects in the methionine transamination pathway, deficient activity of methionine adenosyltransferase II, a mutation in methylenetetrahydrofolate reductase rendering this activity resistant to inhibition by AdoMet, or deficient activity of guanidinoacetate methyltransferase. Plasma sarcosine (N-methylglycine) is elevated, together with elevated plasma AdoMet in normal subjects following oral methionine loads and in association with increased plasma levels of both methionine and AdoMet in cystathionine beta-synthase-deficient individuals. However, plasma sarcosine is not elevated in these siblings. The latter result provides evidence they are deficient in activity of glycine N-methyltransferase (GNMT). The only clinical abnormalities in these siblings are mild hepatomegaly and chronic elevation of serum transaminases not attributable to conventional causes of liver disease. A possible causative connection between GNMT deficiency and these hepatitis-like manifestations is discussed. Further studies are required to evaluate whether dietary methionine restriction will be useful in this situation.
The early onset type of cobalamin (Cbl) C/D deficiency is characterised by feeding difficulties, failure to thrive, hypotonia, seizures, microcephaly and developmental delay. It has an unfavourable outcome, often with early death and significant neurological impairment in survivors. While clinical and biochemical features of Cbl C/D deficiency are well known, only a few isolated case reports are available concerning neurophysiological and neuroimaging findings. We carried out clinical, biochemical, neurophysiological and neuroradiologic investigations in 14 cases with early-onset of the Cbl CID defect. Mental retardation was identified in most of the cases. A variable degree of supratentorial white matter atrophy was detected in 11 cases by MR imaging and tetraventricular hydrocephalus was present in the remaining 3 patients. Waking EEG showed a clear prevalence of epileptiform abnormalities, possibly related to the high incidence of seizures in these cases. Increased latency of evoked responses and/or prolongation of central conduction time were the most significant neurophysiological abnormalities. The selective white matter involvement, shown both by neuroradiologic and neurophysiological studies, seems to be the most consistent finding of Cbl C/D deficiency and may be related to a reduced supply of methyl groups, possibly caused by the dysfunction in the methyl-transfer pathway.
Tyrosinemia type III, caused by deficiency of 4-hydroxyphenylpyruvate dioxygenase, is a rare disorder of tyrosine catabolism. Primary 4-hydroxyphenylpyruvate dioxygenase deficiency has been described in only three patients. The biochemical phenotype shows hypertyrosinemia and elevated urinary excretion of 4-hydroxyphenyl derivatives. We report the clinical and biochemical findings and the results of long-term follow-up in a new patient with this disorder presenting with severe mental retardation and neurological abnormalities. The clinical phenotype is compared with those reported in the three previously described patients.
Cerone R, Schiaffino MC, Di Stefano S, Veneselli E. Phenylketonuria: diet for life or not? Acta Pædiatr 1999; 88: 664‐6. Stockholm. ISSN 0803‐5253 In order to evaluate the argument whether or not a restricted phenylalanine diet should be maintained for life in patients with phenylketonuria (PKU), 16 patients with early treated PKU but off diet since their 11th birthday were investigated. The evaluation included a detailed neurological examination, IQ, neurophysiological testing and MRI of the brain. Even if IQ and electrophysiological studies were normal or unchanged if compared to results before diet discontinuation, all patients revealed abnormal neurological signs. We conclude that the diet should be continued during adult life, but somewhat higher phenylalanine levels (<10mg/dl;< 600 μmol/l) than at younger ages should be allowed. □Adolescence, dietary treatment, phenylketonuria
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