Lysine-Restricted Diet as Adjunct Therapy for Pyridoxine-Dependent Epilepsy: The PDE Consortium Consensus Recommendations.

BACKGROUND: Seventy-five percent of patients with pyridoxine-dependent epilepsy (PDE) due to Antiquitin (ATQ) deficiency suffer from developmental delay and/or intellectual disability (IQ < 70) despite seizure control. An observational study showed that adjunct treatment with a lysine-restricted diet is safe, results in partial normalization of lysine intermediates in body fluids, and may have beneficial effects on seizure control and psychomotor development. METHODS: In analogy to the NICE guideline process, the international PDE Consortium, an open platform uniting scientists and clinicians working in the field of this metabolic epilepsy, during four workshops (2010-2013) developed a recommendation for a lysine-restricted diet in PDE, with the aim of standardizing its implementation and monitoring of patients. Additionally, a proposal for a further observational study is suggested. RESULTS: (1) All patients with confirmed ATQ deficiency are eligible for adjunct treatment with lysine-restricted diet, unless treatment with pyridoxine alone has resulted in complete symptom resolution, including normal behavior and development. (2) Lysine restriction should be started as early as possible; the optimal duration remains undetermined. (3) The diet should be implemented and the patient be monitored according to these recommendations in order to assure best possible quality of care and safety. DISCUSSION: The implementation of this recommendation will provide a unique and a much needed opportunity to gather data with which to refine the recommendation as well as improve our understanding of outcomes of individuals affected by this rare disease. We therefore propose an international observational study that would utilize freely accessible, online data sharing technologies to generate more evidence.

A common variant in ERBB4 regulates GABA concentrations in human cerebrospinal fluid.

The neuregulin 1 (NRG1) receptor ErbB4 is involved in the development of cortical inhibitory GABAergic circuits and NRG1-ErbB4 signaling has been implicated in schizophrenia (SCZ). A magnetic resonance spectroscopy ((1)H-MRS) study has demonstrated that a single-nucleotide polymorphism in ERBB4, rs7598440, influences human cortical GABA concentrations. Other work has highlighted the significant impact of this genetic variant on expression of ERBB4 in the hippocampus and dorsolateral prefrontal cortex in human post mortem tissue. Our aim was to examine the association of rs7598440 with cerebrospinal fluid (CSF) GABA levels in healthy volunteers (n=155). We detected a significant dose-dependent association of the rs7598440 genotype with CSF GABA levels (G-allele standardized ß=-0.23; 95% CIs: -0.39 to -0.07; P=0.0066). GABA concentrations were highest in A homozygous, intermediate in heterozygous, and lowest in G homozygous subjects. When excluding subjects on psychotropic medication (three subjects using antidepressants), the results did not change (G-allele standardized ß=-0.23; 95% CIs: -0.40 to -0.07; P=0.0051). The explained variance in CSF GABA by rs7598440 in our model is 5.2% (P=0.004). The directionality of our findings agrees with the aforementioned (1)H-MRS and gene expression studies. Our observation therefore strengthens the evidence that the A-allele of rs7598440 in ERBB4 is associated with increased GABA concentrations in the human central nervous system (CNS). To our knowledge, our finding constitutes the first confirmation that CSF can be used to study genotype-phenotype correlations of GABA levels in the CNS. Such quantitative genetic analyses may be extrapolated to other CSF constituents relevant to SCZ in future studies.

Metabolic profiles in children during fasting.

BACKGROUND: Hypoglycemia is one of the most common metabolic derangements in childhood. To establish the cause of hypoglycemia, fasting tolerance tests can be used. Currently available reference values for fasting tolerance tests have limitations in their use in daily practice. OBJECTIVE: The aim of this study was to determine the reference values of metabolites involved in glucose homeostasis during fasting in healthy children. METHODS: This study included a retrospective analysis of 488 fasting tests. All tests of patients (n = 321) with disorders, including metabolic and endocrine disorders, were excluded, as were tests performed in children who were over- or underweight. RESULTS: In 167 fasting tests performed in the study, hypoglycemia was reached in 52 (31%) tests. On the basis of the time until hypoglycemia was reached, 3 age groups could be defined: (1) children aged 0 to 24 months (median 15 months) (n = 49); (2) children aged 25 to 84 months (median 45 months) (n = 79); (3) and children aged 85 to 216 months (median 106 months) (n = 39). In all groups, a significant increase in ketone body levels and a significant decrease in glucose levels in plasma were observed during fasting. Younger children had a faster increase in ketone body levels and a faster decrease in glucose levels in plasma than older children. CONCLUSIONS: Reference values of the metabolites involved in glucose homeostasis during fasting in children were generated. Those values can be used to determine whether a child has a normal fasting response. For high-risk children, guidelines concerning maximum fasting time and dietary intervention during illness are of the utmost importance.

L-2-hydroxyglutaric aciduria: characterisation of the molecular defect in a spontaneous canine model.

l-2-hydroxyglutaric aciduria (l-2-HGA) is a neurometabolic disorder that produces a variety of clinical neurological deficits, including psychomotor retardation, seizures and ataxia. The biochemical hallmark of l-2-HGA is the accumulation of l-2-hydroxyglutaric acid (l-2-HG) in cerebrospinal fluid, plasma and urine. Mutations within the gene L2HGDH (Entrez Gene ID 79944) on chromosome 14q22 encoding L-2-hydroxyglutaric acid dehydrogenase have recently been shown to cause l-2-HGA in humans. Using a candidate gene approach in an outbred pet dog population segregating l-2-HGA, the causal molecular defect was identified in the canine homologue of L2HGDH and characterised. DNA sequencing and pedigree analysis indicate a common founder effect in the canine model. The canine model shares many of the clinical and MRI features of the disease in humans and represents a valuable resource as a spontaneous model of l-2-HGA.

Global developmental delay in guanidionacetate methyltransferase deficiency: differences in formal testing and clinical observation.

Guanidinoacetate N-methyltransferase (GAMT) deficiency is a defect in the biosynthesis of creatine (Cr). So far, reports have not focused on the description of developmental abilities in this disorder. Here, we present the result of formal testing of developmental abilities in a GAMT-deficient patient. Our patient, a 3-year-old boy with GAMT deficiency, presented clinically with a severe language production delay and nearly normal nonverbal development. Treatment with oral Cr supplementation led to partial restoration of the cerebral Cr concentration and a clinically remarkable acceleration of language production development. In contrast to clinical observation, formal testing showed a rather harmonic developmental delay before therapy and a general improvement, but no specific acceleration of language development after therapy. From our case, we conclude that in GAMT deficiency language delay is not always more prominent than delays in other developmental areas. The discrepancy between the clinical impression and formal testing underscores the importance of applying standardized tests in children with developmental delays. Screening for Cr deficiency by metabolite analysis of body fluids or proton magnetic resonance spectroscopy of the brain deficiency should be considered in any child with global developmental delay/mental retardation lacking clues for an alternative etiology.

Transaldolase deficiency: a new cause of hydrops fetalis and neonatal multi-organ disease.

Transaldolase (TALDO) deficiency is a newly recognized metabolic disease, which has been reported so far in 2 patients presenting with liver failure and cirrhosis. We report a new sibship of 4 infants born to the same consanguineous parents; all presented at birth or in the antenatal period with dysmorphic features, cutis laxa and hypertrichosis, hepatomegaly, splenomegaly, liver failure, hemolytic anemia, thrombocytopenia, and genitourinary malformations. The clinical courses were variable: the first child died of liver failure at 4 months of age; the second pregnancy was medically terminated at 28 weeks gestation because of hydrops fetalis with oligohydramnios. The third child is doing well at age 7 with liver fibrosis and mild kidney failure. The fourth child is now 21 months old and has hepatosplenomegaly, mild anemia, and thrombocytopenia. Urine assessment of polyols showed elevations of erythritol, arabitol, and ribitol consistent with TALDO deficiency. TALDO activity was undetectable in the patients' tissues, and mutation in the TALDO1 gene was found in the 4 patients.

Knockout of Slc25a19 causes mitochondrial thiamine pyrophosphate depletion, embryonic lethality, CNS malformations, and anemia.

SLC25A19 mutations cause Amish lethal microcephaly (MCPHA), which markedly retards brain development and leads to alpha-ketoglutaric aciduria. Previous data suggested that SLC25A19, also called DNC, is a mitochondrial deoxyribonucleotide transporter. We generated a knockout mouse model of Slc25a19. These animals had 100% prenatal lethality by embryonic day 12. Affected embryos at embryonic day 10.5 have a neural-tube closure defect with ruffling of the neural fold ridges, a yolk sac erythropoietic failure, and elevated alpha-ketoglutarate in the amniotic fluid. We found that these animals have normal mitochondrial ribo- and deoxyribonucleoside triphosphate levels, suggesting that transport of these molecules is not the primary role of SLC25A19. We identified thiamine pyrophosphate (ThPP) transport as a candidate function of SLC25A19 through homology searching and confirmed it by using transport assays of the recombinant reconstituted protein. The mitochondria of Slc25a19(-/-) and MCPHA cells have undetectable and markedly reduced ThPP content, respectively. The reduction of ThPP levels causes dysfunction of the alpha-ketoglutarate dehydrogenase complex, which explains the high levels of this organic acid in MCPHA and suggests that mitochondrial ThPP transport is important for CNS development.

Clinical, cytogenetic and molecular characterization of a patient with combined succinic semialdehyde dehydrogenase deficiency and incomplete WAGR syndrome with obesity.

We describe the clinical course, as well as cytogenetic and molecular findings, of a 3-year-old obese boy with psychomotor retardation who exhibited two rare conditions: succinic semialdehyde dehydrogenase deficiency (SSADH deficiency, MIM 271980), a disorder of gamma-aminobutyric acid metabolism with a heterogeneous clinical spectrum, and partial Wilms' tumor, aniridia, genital abnormalities, and mental retardation (WAGR) syndrome, an association between Wilms' tumor, aniridia, genitourinary malformations, and mental retardation due to mutations involving the short arm of chromosome 11, particularly deletions at the chromosomal region 11p13 (MIM 194072). Diagnosis of SSADH deficiency in our patient was established by demonstration of absent enzyme activity in isolated leucocytes, and was associated with a novel missense mutation (c.587G>A; p.Gly196Asp) in the SSADH coding sequence. We further confirmed an incomplete WAGR syndrome in this boy [karyotype 46, XY, del (11) (p13p14.2)] with a normal WT1 (Wilms' tumor) gene and an absence of pathology in the genitourinary tract, but with obesity (WAGR syndrome with obesity, WAGRO syndrome). The patient also exhibited distinctive cerebral anomalies such as increased signals of the globi pallidi, internal hydrocephalus and cerebellar vermian atrophy. However, treatment options for this patient are limited, including supportive treatment, physiotherapy, special educational training, and vigabatrin. In summary, we report the first patient with the exceptional rare findings of both SSADH deficiency and partial WAGR/WAGRO syndrome.

Increased guanidino species in murine and human succinate semialdehyde dehydrogenase (SSADH) deficiency.

Mice with targeted deletion of the GABA-degradative enzyme succinate semialdehyde dehydrogenase (SSADH; Aldh5a1; OMIM 271,980) manifest globally elevated GABA and regionally decreased arginine in brain extracts. We examined the hypothesis that arginine-glycine amidinotransferase catalyzed the formation of guanidinobutyrate (GB) from increased GABA by quantifying guanidinoacetate (GA), guanidinopropionate (GP) and GB in brain extracts employing stable isotope dilution gas chromatographic-mass spectrometry. GA and GB were up to 4- and 22-fold elevated, respectively, in total and regional (cerebellum, hippocampus, cortex) brain extracts derived from SSADH(-/-) mice. Corresponding analyses of urine and cerebrospinal fluid derived from SSADH-deficient patients revealed significant (P<0.05) elevations of GA and GB in urine, as well as GB levels in CSF. These data suggest that GB may be an additional marker of SSADH deficiency, implicate additional pathways of pathophysiology, and identify the second instance of elevated GB in a human inborn error of metabolism.

Metabolism of gamma-hydroxybutyrate to d-2-hydroxyglutarate in mammals: further evidence for d-2-hydroxyglutarate transhydrogenase.

gamma-Hydroxybutyratic acid (GHB), and its prodrugs 4-butyrolactone and 1,4-butanediol, represent expanding drugs of abuse, although GHB is also used therapeutically to treat narcolepsy and alcoholism. Thus, the pathway by which GHB is metabolized is of importance. The goal of the current study was to examine GHB metabolism in mice with targeted ablation of the GABA degradative enzyme succinic semialdehyde dehydrogenase (SSADH(-/-) mice), in whom GHB persistently accumulates, and in baboons intragastrically administered with GHB immediately and persistently. Three hypotheses concerning GHB metabolism were tested: (1) degradation via mitochondrial fatty acid beta-oxidation; (2) conversion to 4,5-dihydroxyhexanoic acid (a putative condensation product of the GHB derivative succinic semialdehyde); and (3) conversion to d-2-hydroxyglutaric acid (d-2-HG) catalyzed by d-2-hydroxyglutarate transhydrogenase (a reaction previously documented only in rat). Both d-2-HG and 4,5-dihydroxyhexanoic acid were significantly increased in neural and nonneural tissue extracts derived from SSADH(-/-) mice. In vitro studies demonstrated the ability of 4,5-dihydroxyhexanoic acid to displace the GHB receptor ligand NCS-382 (IC(50) = 38 micromol/L), although not affecting GABA(B) receptor binding. Blood and urine derived from baboons administered with GHB also accumulated d-2-HG, but not 4,5-dihydroxyhexanoic acid. Our results indicate that d-2-HG is a prominent GHB metabolite and provide further evidence for the existence of d-2-hydroxyglutarate transhydrogenase in different mammalian species.

A novel, quantitative assay for homocarnosine in cerebrospinal fluid using stable-isotope dilution liquid chromatography-tandem mass spectrometry.

We describe a rapid and sensitive method for the quantification of homocarnosine in physiological fluids, with particular emphasis on cerebrospinal fluid (CSF). Homocarnosine was quantified as the butyl derivative, with (2)H(2)-l-homocarnosine as internal standard. Following deproteinization of CSF samples, supernatants were evaporated to dryness and derivatized with 10% 6M HCl in butanol. Samples were chromatographed on a C(18) column and detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS) operating in the multiple reaction monitoring mode. The intra- and inter-assay variations were 4.6 and 10.9%, respectively. Mean recovery of homocarnosine at two concentrations was 105%. The limit of detection in CSF approximated 20 nmol/L. CSF homocarnosine is age dependent and ranges from <0.02 to 10 micromol/L. Our method is applicable to the analysis of CSF derived from patients with heritable defects in the GABA pathway, patients with homocarnosinosis or serum carnosinase deficiency, and should be applicable to other model systems in order to further explore the biological role and significance of homocarnosine in mammalian systems.

Laboratory diagnosis of defects of creatine biosynthesis and transport.

In recent years, three inherited defects in the biosynthesis and transport of creatine have been described. The biosynthetic defects include deficiencies of L-arginine:glycine amidinotransferase and guanidinoacetate methyltransferase. The third defect is a functional defect in the creatine transporter (SLC6A8). Clinical symptoms of the three defects vary in severity, are aspecific and include mental retardation with severe speech delay, autistiform behaviour, and epilepsy. Some patients with GAMT deficiency exhibit a more complex clinical phenotype with extrapyramidal movement disorder. All three defects can be diagnosed by in vivo proton magnetic resonance spectroscopy of the brain, which shows a severe reduction or absence of creatine. Laboratory investigations for the diagnosis start with the analysis of guanidinoacetate, creatine and creatinine in body fluids (plasma and urine). Based on these findings, enzyme assays for AGAT or GAMT, or a creatine uptake assay for the transporter defect can be performed. DNA mutation analysis of the genes involved can prove the defects at the molecular level. To diagnose female patients with SLC6A8 deficiency, mutation analysis may be the only choice.

Quantification of sugar phosphate intermediates of the pentose phosphate pathway by LC-MS/MS: application to two new inherited defects of metabolism.

We describe a liquid chromatography tandem mass spectrometry (LC-MS/MS) method to quantify pentose phosphate pathway intermediates (triose-3-phosphates, tetrose-4-phosphate, pentose-5-phosphate, pentulose-5-phosphates, hexose-6-phosphates and sedoheptulose-7-phosphate (sed-7P)) in bloodspots, fibroblasts and lymphoblasts. Liquid chromatography was performed using an ion pair loaded C(18) HPLC column and detection of the sugar phosphates was carried out by tandem mass spectrometry using an electron ion spray source operating in the negative mode and multiple reaction monitoring. Reference values for the pentose phosphate pathway intermediates in blood spots, fibroblasts and lymphoblasts were established. The method was applied to cells from patients affected with a deficiency of transaldolase. The transaldolase-deficient cells showed an increased concentration of sedoheptulose-7-phosphate. (Bloodspots: 5.19 and 5.43 micromol/L [0.49-3.33 micromol/L]; fibroblasts 7.43 and 26.46 micromol/mg protein [0.31-1.14 micromol/mg protein]; lymphoblasts 16.03 micromol/mg protein [0.61-2.09 micromol/mg protein].) The method was also applied to study enzymes of the pentose phosphate pathway by incubating fibroblasts or lymphoblasts homogenates with ribose-5-phosphate or 6-phosphogluconate and the subsequent analysis of the formed sugar phosphates.

The transmethylation cycle in the brain of Alzheimer patients.

Homocysteine accumulation, frequently observed in plasma of AD patients, may be a sign of a reduced activity of the brain methionine-homocysteine transmethylation cycle. S-Adenosylmethionine (SAM) is the main methyl donor in several transmethylation reactions. The demethylated product of SAM, S-adenosylhomocysteine (SAH), is hydrolyzed to yield homocysteine, which can be remethylated to methionine by transfer of a methyl group of 5-methyltetrahydrofolate (5-MTHF). A reduced activity of the transmethylation cycle in the brain may result in hypomethylation of the promoter of the presenilin 1 (PS1) gene, which will lead to overexpression of presenilin 1 and, consequently, to increased Abeta(1-42) (Abeta42) formation. Brain transmethylation was studied in 30 patients with 'probable' AD and 28 age-matched non-demented controls by measuring the cerebrospinal fluid (CSF) levels of SAM, SAH and 5-MTHF. 5-MTHF was determined by HPLC with electrochemical detection, while SAM and SAH were assayed by stable isotope dilution tandem mass spectrometry. We found no statistical differences between AD patients and controls for 5-MTHF, SAM and SAH levels, and the SAM/SAH-ratio in CSF. These findings argue against a possible change in methylation of the promoter and expression of PS1.

Mutations in phenotypically mild D-2-hydroxyglutaric aciduria.

D-2-hydroxyglutaric aciduria is a neurometabolic disorder with mild and severe phenotypes. Recently, we reported pathogenic mutations in the D-2-hydroxyglutarate dehydrogenase gene as the cause of the severe phenotype of D-2-hydroxyglutaric aciduria in two patients. Here, we report two novel pathogenic mutations in this gene in one patient with a mild presentation and two asymptomatic siblings with D-2-hydroxyglutaric aciduria from two unrelated consanguineous Palestinian families: a splice error (IVS4-2A-->G) and a missense mutation (c.1315A-->G;p.Asn439Asp). Overexpression of this mutant protein showed marked reduction of the enzyme activity.

Metaphyseal enchondrodysplasia with 2-hydroxy-glutaric aciduria: observation of a third case and further delineation.

In the course of evaluating a 17 months old boy with waddling gait and swollen joints, we found generalized, severe ossification defects in the metaphyses of his long bones. The differential diagnosis included nutritional or genetic rickets, metaphyseal dysplasia, and enchondrodysplasia. Calcium, phosphate and alkaline phosphatase were normal, while targeted analysis of urinary organic acids repeatedly revealed excretion of 2-hydroxy-glutaric acid. Thus, this child appears to have an unusual combination of findings described in just two other patients so far, a girl and a boy, and called 'spondyloenchondrodysplasia with D-2-hydroxy-glutaric aciduria'. These three cases are similar in terms of severe metaphyseal lesions, mild vertebral involvement, and presence of 2-hydroxy-glutaric acid in the urine. We consider this a radiographically and biochemically distinct entity, for which we suggest the name of 'metaphyseal enchondrodysplasia with 2-hydroxy-glutaric aciduria'.

Mutations in the D-2-hydroxyglutarate dehydrogenase gene cause D-2-hydroxyglutaric aciduria.

d-2-hydroxyglutaric aciduria is a neurometabolic disorder with both a mild and a severe phenotype and with unknown etiology. Recently, a novel enzyme, d-2-hydroxyglutarate dehydrogenase, which converts d-2-hydroxyglutarate into 2-ketoglutarate, and its gene were identified. In the genes of two unrelated patients affected with d-2-hydroxyglutaric aciduria, we identified disease-causing mutations. One patient was homozygous for a missense mutation (c.1331T-->C; p.Val444Ala). The other patient was compound heterozygous for a missense mutation (c.440T-->G; p.Ile147Ser) and a splice-site mutation (IVS1-23A-->G) that resulted in a null allele. Overexpression studies in HEK-293 cells of proteins containing the missense mutations showed a marked reduction of d-2-hydroxyglutarate dehydrogenase activity, proving that mutations in the d-2-hydroxyglutarate dehydrogenase gene cause d-2-hydroxyglutaric aciduria.

Age related reference values for urine creatine and guanidinoacetic acid concentration in children and adolescents by gas chromatography-mass spectrometry.

A new gas chromatography-mass spectrometry method for routine quantification of urine creatine and guanidinoacetic acid (GAA) has been developed to provide a fast, reliable and inexpensive metabolic screening. Our method uses a two-step derivatization procedure which involves a reaction with hexafluoroacetylacetone followed by a reaction with mono-trimethylsilyltrifluoroacetamide. The standard curves showed linearity over a range of 43-4269 micromol/l for GAA and 38-7325 micromol/l for creatine, which covers the range of GAA and creatine normally found in urine. The lower detection limit is 1.54 micromol/l for GAA and 1.22 micromol/l for creatine, whereas the lower quantification limit is 5.04 micromol/l for GAA and 4.19 micromol/l for creatine. This method was also employed to establish reference values for GAA and creatine in healthy infants, children and adolescents based on the analysis of 169 urine samples. Although no sex differences were observed, normal GAA urinary levels and creatine excretion are distinct in age-related subgroups. We identified a statistically significant age difference in two major groups for GAA (children under 4 years, 18-159 micromol/mmol creatinine; and subjects of 5-16 years, 18-130 micromol/mmol creatinine) whereas three groups were discriminated for creatine (children under 4 years, 0.04-1.51 mmol/mmol creatinine; subjects of 5-11 years, 0.04-1.07 mmol/mmol creatinine; and subjects of 12-16 years, 0.04-0.56 mmol/mmol creatinine).

Creatine and guanidinoacetate: diagnostic markers for inborn errors in creatine biosynthesis and transport.

In this study, measurements of guanidinoacetate (GAA) and creatine (Cr) in urine, plasma, and cerebrospinal fluid (CSF) were performed using stable isotope dilution gas chromatography-mass spectrometry. Both compounds were analyzed in a single analysis. Reference values were established for GAA and Cr. These values were age dependent. No differences with gender were observed. Eight guanidinoacetate methyltransferase (GAMT) deficient patients and eight creatine transporter SLC6A8 deficient patients were investigated. In urine, plasma, and CSF of GAMT deficient patients increased levels of GAA are present. The SLC6A8 deficient patients all show increased creatine/creatinine (Cr/Crn) ratio in urine demonstrating the importance of the Cr/Crn ratio as a pathognomonic marker of the SLC6A8 deficiency.