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Succinic semialdehyde dehydrogenase (SSADH) deficiency and d -2-hydroxyglutaric aciduria ( d -2-HGA) are rare inborn errors of metabolism primarily revealed by urinary organic acid screening. Three patients with proven SSADH deficiency excreted, in addition to GHB considerable amounts of d -2-HG. We examined whether these patients suffered from two inborn errors of metabolism by measuring d -2-HG concentrations in the culture medium of cells from these patients. In addition, mutation analysis of the d -2-hydroxyglutarate dehydrogenase gene was performed. Normal concentrations of d -2-HG were measured in the culture media of fibroblasts or lymphoblasts derived from the three patients. In one patient, we found a heterozygous likely pathogenic mutation in the d -2-hydroxyglutarate dehydrogenase gene. These combined results argue against the hypothesis that the patients are affected with “primary” d -2-HGA in combination with their SSADH deficiency. Moderately increased levels of d -2-HG were also found in urine, plasma, and cerebrospinal fluid samples derived from 12 other patients with SSADH deficiency, revealing that d -2-HG is a common metabolite in this disease. The increase of d -2-HG in SSADH deficiency can be explained by the action of hydroxyacid-oxoacid transhydrogenase, a reversible enzyme that oxidases GHB in the presence of 2-ketoglutarate yielding SSA and d -2-HG.

A female patient, the first child of healthy non-consanguineous parents, presented at the age of 16 months with delayed motor development and facial dysmorphism. In addition she displayed a palatoschizis and multiple skeletal abnormalities as hypoplastic scapulae, hypoplastic os ilea, and an extreme cervical kyphosis. Biochemical investigation of urine revealed no abnormalities except for the presence of large amounts of reducing sugars. The sugar was identified as L-arabinose, which mainly originated from fruit formula in her diet. In addition highly elevated levels of L-arabitol were found in urine, plasma, and cerebrospinal fluid. Although little is known about human arabinose metabolism, we presume that L-arabitol dehydrogenase is deficient in our patient. As polyols are potentially toxic to the central nervous system there could be deleterious long-term effects of this disorder. Withdrawal of dietary fruit led to normalization of polyol levels. The above-mentioned clinical abnormalities are probably not related to this new inborn error of metabolism and should be considered as a separate entity.

Guanidinoacetate methyltransferase deficiency (MIM 601240) is an autosomal recessive disorder of creatine biosynthesis. Patients present with mental retardation, extrapyramidal symptoms, autistic-like behavior, epilepsy, cerebral creatine deficiency and increased levels of guanidinoacetate. So far 15 mutations have been reported, including six missense variants that are highly likely to be pathogenic mutations. To prove that mutations in the GAMT gene are responsible for GAMT deficiency we overexpressed the GAMT open reading frame in GAMT-deficient fibroblasts by stable transfection. In addition, HeLa cells were transiently transfected with the same expression vector. In contrast to mock transfectants transfection of primary GAMT-deficient fibroblasts with wild-type GAMT results in the restoration of GAMT activity as measured by GC-MS using stable isotope labeled substrates. Moreover, the expression of the GAMT-EGFP fusion protein was analyzed by Western blot, confirming the presence of GAMT fusion protein, both in the stable as well as in the transient transfectants. Here, we prove that mutations in the GAMT gene are responsible for GAMT deficiency, since overexpression of the GAMT open reading frame restores GAMT activity in GAMT-deficient fibroblasts. Furthermore, the transient transfection of HeLa cells will be important for functional analysis of variants of unknown consequence (i.e., missense mutations).

Patients with phenylketonuria (PKU) have a poor LC-PUFA status and require supplementation. The objective of this study was to evaluate the LC-PUFA status of PKU patients supplemented with fish oil or the fatty acid supplement KeyOmega. Plasma and erythrocyte docosahexaenoic acid (DHA) and arachidonic acid (AA) levels were determined in 54 patients (1–18.5 years of age) with confirmed PKU. The influence of supplementation with fish oil versus KeyOmega, a powdered blend of DHA and AA, on LC-PUFA status was investigated and compared to the status in samples obtained from unsupplemented patients. Differential effects on LC-PUFA status were observed upon suppletion with fish oil versus KeyOmega. Whereas supplementation with fish oil increased the level of DHA, the AA concentration did not increase to normal values in these patients. In contrast, both DHA and AA levels increased and reached reference values upon supplementation with KeyOmega. In conclusion: these results indicate that KeyOmega offers additional benefit over fish oil since both AA and DHA status are normalized in PKU patients supplemented with KeyOmega.

Cerebral creatine and guanidinoacetate and blood and urine metabolites were studied in four patients with argininosuccinate synthetase (ASS) or argininosuccinate lyase (ASL) deficiency receiving large doses of arginine. Urine and blood metabolites varied largely. Cerebral guanidinoacetate was increased in all patients, while cerebral creatine was low in ASS and high in ASL deficiency. Because high cerebral guanidinoacetate might be toxic, lowering the arginine supplementation with additional creatine supplementation might be important. (c) 2006 Elsevier Inc. All rights reserved.