A severity scoring tool to assess the neurological features of neuronopathic Gaucher disease

Type III Gaucher disease is one of the three recognized subtypes of Gaucher disease, an inherited deficiency of lysosomal glucocerebrosidase. Phenotypically there is a wide spectrum of visceral and neurological manifestations. Enzyme replacement is effective in managing the visceral disease; however, the neurological manifestations remain a more challenging obstacle. There is an unfulfilled need to reliably monitor neurological disease and its response to treatment. A severity scoring tool was developed through neurological domain identification, item generation and tool formation. Domain identification was established based on a retrospective single centre study (n = 15) and a systematic review of publications. Forty-seven patients with neuronopathic Gaucher disease were then assessed using the tool to establish the clinical and statistical reliability of each domain. Judgement quantification of the tool was established through a process of content validity involving five European experts. Content validity is considered to be most effective when undertaken systematically. Concurrent validity and feasibility of the tool was also highlighted. This process allowed a revised and validated version of the tool to be developed.

GAMT deficiency: Features, treatment, and outcome in an inborn error of creatine synthesis

BACKGROUND

Guanidinoactetate methyltransferase (GAMT) deficiency is an autosomal recessive disorder of creatine synthesis. The authors analyzed clinical, biochemical, and molecular findings in 27 patients.

METHODS

The authors collected data from questionnaires and literature reports. A score including degree of intellectual disability, epileptic seizures, and movement disorder was developed and used to classify clinical phenotype as severe, moderate, or mild. Score and biochemical data were assessed before and during treatment with oral creatine substitution alone or with additional dietary arginine restriction and ornithine supplementation.

RESULTS

Intellectual disability, epileptic seizures, guanidinoacetate accumulation in body fluids, and deficiency of brain creatine were common in all 27 patients. Twelve patients had severe, 12 patients had moderate, and three patients had mild clinical phenotype. Twenty-one of 27 (78%) patients had severe intellectual disability (estimated IQ 20 to 34). There was no obvious correlation between severity of the clinical phenotype, guanidinoacetate accumulation in body fluids, and GAMT mutations. Treatment resulted in almost normalized cerebral creatine levels, reduced guanidinoacetate accumulation, and in improvement of epilepsy and movement disorder, whereas the degree of intellectual disability remained unchanged.

CONCLUSION

Guanidinoactetate methyltransferase deficiency should be considered in patients with unexplained intellectual disability, and urinary guanidinoacetate should be determined as an initial diagnostic approach.

Influenza virus associated encephalopathy

Perspective on the paper by Hosoya et al (see page 469)

Disorders of intermediary metabolism: toxic leukoencephalopathies

Myelination starts in the latter half of gestation. It is initiated by oligodendrocyte progenitor cells. Three sequential steps can be distinguished: (1) initial ensheathment of axons by premyelin sheaths generated by oligodendrocyte progenitor cells; (2) initial insertion of myelin basic protein (MBP) into transitional sheaths; and (3) generation of mature MBP-rich myelin. Different inborn errors of metabolism can interfere with different stages of these physiological processes, causing white-matter diseases, i.e. toxic leukoencephalopathies. Some inborn errors of metabolism disturb the formation of myelin by being toxic to oligodendrocytes or by interference with the biosynthesis of cholesterol and lipids, e.g. globoid cell leukodystrophy and phenylketonuria. Remethylation defects, e.g. methylenetetrahydrofolate reductase deficiency, cobalamin C, D, E, F and G defects, interfere with the expression, processing and insertion of MBP. The concept of excitotoxicity, which has been developed in neurons, has recently been modified and has been extended to the oligodendroglial lineage. Mitochondriopathies and cerebral organic acid disorders may cause secondary excitotoxicity resulting in toxic encephalopathies, which may affect both neurons and oligodendrocytes. This review aims to present relevant diseases, summarizing recent knowledge on mechanisms and formulating testable hypotheses of pathophysiology leading to new and improved treatment strategies.

The effect of genotype on the natural history of eIF2B-related leukodystrophies

BACKGROUND

Recessive mutations in the five eucaryotic initiation factor 2B (eIF2B) subunits have been found in leukodystrophies of variable age at onset and severity.

OBJECTIVES

To evaluate the clinical spectrum of eIF2B-related disorders and search for a phenotype-genotype correlation.

METHODS

Ninety-three individuals (78 families) with an undetermined leukodystrophy were selected on MRI-based criteria of childhood ataxia with central hypomyelination/vanishing white matter (CACH/VWM) for EIF2B genes analysis.

RESULTS

Eighty-nine percent of individuals with MRI criteria of CACH/VWM have a mutation in one of the eIF2B beta to epsilon subunits. For 83 individuals (68 families), 46 distinct mutations (90% missense) in four of the five eIF2B subunits (beta, gamma, delta, epsilon) were identified. Sixty-four percent were in the epsilon subunit, a R113H substitution was found in 71% of eIF2B epsilon-mutated families. A large clinical spectrum was observed from rapidly fatal infantile to asymptomatic adult forms. Disease severity was correlated with age at onset (p < 0.0001) but not with the type of the mutated subunit nor with the position of the mutation within the protein. Mutations R113H in the epsilon subunit and E213G in the beta subunit were significantly associated with milder forms.

CONCLUSIONS

The degree of eIF2B dysfunction, which is involved in the regulation of protein synthesis during cellular stress, may play a role in the clinical expression of eIF2B-related disorders.

Glutaric aciduria type I and kynurenine pathway metabolites: a modified hypothesis

Glutaric aciduria type I is an inborn error of organic acid metabolism that demonstrates a particular temporal vulnerability (acute encephalopathic episodes in infancy) and a spatial vulnerability (acute striatal necrosis, focused on the putamen). Excitotoxic mechanisms involving 3-hydroxyglutaric acid as the major neurotoxin have been suggested. This paper proposes a role for metabolites of the kynurenine pathway in the pathogenic process and modifies the hypothesis of Heyes. Deficiency of glutaryl-CoA dehydrogenase blocking the glutarate pathway and activation of indoleamine 2,3-dioxygenase in macrophages/monocytes by intercurrent inflammation may increase flux down the kynurenine pathway towards the production of quinolinic acid. Quinolinic acid is neurotoxic and is an endogenous agonist at N-methyl-D-aspartate receptors. Synergistic excitation of these receptors by quinolinic acid and 3-hydroxyglutaric acid, which alone does not have sufficient potency, may be involved in the pathogenesis of striatal necrosis.

A comparison between parents?? and therapists?? views of their child??s individual seating systems

Children with cerebral palsy are often prescribed adaptive seating systems for use in their wheelchairs for the purposes of improving posture and to help prevent the development of long-term deformity. However, clinical experience indicates that parents and the therapists who advocate the use of these systems do not always agree about the wheelchairs. This study discusses the development of questionnaires for both parents and therapists to measure differences in their opinions about the wheelchairs. The questions were developed through clinical experience, validation was through interviews to discuss topics important to the participants, and repeated application of the questionnaire ensured consistency. The reliability of the questions appears satisfactory and the interview responses demonstrate that the questions selected are important to both groups of stakeholders. However, it was found that parental concerns over their children's seating systems concentrated on functional and day-to-day management issues, whereas therapist concerns focused on technical issues and postural management. Both groups of stakeholders agreed that the questionnaires would be a useful precursor to attending a seating clinic appointment, as it could aid communication between the parent and provider and improve the efficiency and satisfaction of such an appointment. It appears the questionnaire has potential as an outcome measurement tool.

Neurological outcome of patients with ornithine carbamoyltransferase deficiency

BACKGROUND

Ornithine carbamoyltransferase (OCT) deficiency is the commonest of the inherited urea cycle disorders.

AIMS

To determine the long term neurological and cognitive outcome of continuously treated surviving patients.

METHODS

Twenty eight surviving children (five boys) with OCT deficiency who had been treated continuously with a low protein diet and alternative pathway therapy were identified. Those aged 5-16 years had a detailed neurological examination and psychometric testing.

RESULTS

Four presented in the neonatal period and four were treated prospectively following antenatal diagnosis. Median (range) age at diagnosis for the later onset group was 19 (2-144) months; median time between onset of symptoms and diagnosis was 10 (2-48) months. Nine children had had less than three episodes of hyperammonaemic encephalopathy, the others more. Seven had focal abnormalities on neurological examination; 14 had global cognitive impairment; four had a normal IQ but specific learning difficulties. Sixteen underwent neuroimaging which was normal in three, showed focal abnormalities of the cerebral hemispheres in six, and global cerebral atrophy in seven.

CONCLUSION

Eighteen of 28 surviving children with OCT deficiency had disabling neurological complications. Plasma ammonia at diagnosis was the only factor that predicted this outcome. While most neurological complications could be attributed to hyperammonaemic encephalopathy, other mechanisms may also contribute to the neurological abnormalities.

Infantile Alexander disease: spectrum of GFAP mutations and genotype-phenotype correlation

Heterozygous, de novo mutations in the glial fibrillary acidic protein (GFAP) gene have recently been reported in 12 patients affected by neuropathologically proved Alexander disease. We searched for GFAP mutations in a series of patients who had heterogeneous clinical symptoms but were candidates for Alexander disease on the basis of suggestive neuroimaging abnormalities. Missense, heterozygous, de novo GFAP mutations were found in exons 1 or 4 for 14 of the 15 patients analyzed, including patients without macrocephaly. Nine patients carried arginine mutations (four had R79H; four had R239C; and one had R239H) that have been described elsewhere, whereas the other five had one of four novel mutations, of which two affect arginine (2R88C and 1R88S) and two affect nonarginine residues (1L76F and 1N77Y). All mutations were located in the rod domain of GFAP, and there is a correlation between clinical severity and the affected amino acid. These results confirm that GFAP mutations are a reliable molecular marker for the diagnosis of infantile Alexander disease, and they also form a basis for the recommendation of GFAP analysis for prenatal diagnosis to detect potential cases of germinal mosaicism.

Homozygous thermolabile variant of the methylenetetrahydrofolate reductase gene: a potential risk factor for hyperhomocysteinaemia, CVD, and stroke in childhood

In this study of 118 children (median age 5.1 years; range 6 months to 17 years) with ischaemic stroke or transient ischaemic attack (TIA), 22 children (19%) were homozygous for the thermolabile variant of the methylenetetrahydrofolate reductase allele (t-MTHFR), compared with nine of 78 (12%) of a reference population (p=0.18, OR 1.76, 95% CI 0.76 to 4.04). Of those with cerebrovascular disease (CVD), 17 of 84 were homozygous for the t-MTHFR allele (p=0.13 compared with the reference population (OR 1.95, 95% CI 0.81 to 4.65). There was a significant (p<0.025) increment of plasma total homocysteine concentration in homozygotes for the t-MTHFR allele compared with heterozygotes, negatives for the t-MTHFR allele, and control children with no history of stroke. In four of 12 homozygotes for the t-MTHFR allele, plasma homocysteine levels were raised, compared with three of 38 of those who were negative or heterozygous (p=0.047; OR 5.8, 95% CI 1.1 to 31.2). Homozygotes for the t-MTHFR allele were significantly more likely to have a recurrent event than those who were negative or heterozygous (Cox regression p=0.031, hazard ratio 2.18, 95% CI 1.08 to 4.42). These data suggest that homozygosity for the t-MTHFR allele is associated with raised homocysteine levels in children and is a risk factor for primary and secondary stroke and TIA.

Mitochondrial DNA point mutation T9176C in Leigh syndrome

Leigh syndrome is a progressive neurodegenerative disease frequently associated with mitochondrial abnormalities. The mitochondrial DNA T9176C mutation in the adenosine triphosphatase 6 gene has recently been described as a cause of Leigh syndrome. Leukocyte DNA from 59 children with Leigh syndrome was screened for the T9176C mutation by conventional polymerase chain reaction methods. Two unrelated patients were found to be homoplasmic for this mutation in blood. Both patients had similar clinical and biochemical features. They had first presented acutely at 3 and 5 years, respectively, with ataxia and slurred speech. Magnetic resonance imaging changes were consistent with Leigh syndrome, and the cerebrospinal fluid lactate was elevated. They have both had relatively stable disease since the time of diagnosis. The mother of one of the children had presented at age 29 years with sudden onset of ataxia, headache, and blurred vision. She was heteroplasmic for the T9176C mutation. The T1976C is an important cause of Leigh syndrome especially in the subgroup of patients with more stable disease and normal respiratory chain enzyme analysis.

Inherited ion channel disorders

The inherited ion channel disorders (channelopathies) are a group of disorders caused by mutations in genes encoding ion channels. Ion channel disorders can affect any tissue, but the majority affect skeletal muscle or the central nervous system. These disorders include skeletal muscle sodium channelopathies causing hyperkalaemic periodic paralysis, paramyotonia congenita and potassium-aggravated myotonia. Skeletal muscle calcium channelopathies can cause hypokalaemic periodic paralysis, malignant hyperthermia and central core disease. Skeletal muscle chloride channelopathies can cause Thomsen and Becker myotonia. A neuronal sodium channelopathy causes the generalised epilepsy febrile seizures plus syndrome. Neuronal potassium channelopathies can cause familial benign neonatal convulsions and episodic ataxia type 1. Finally, neuronal calcium channelopathies can cause episodic ataxia type 2, familial hemiplegic migraine and spinocerebellar ataxia type 6.

CONCLUSION

The clinical features, aetiology and pathogenesis of inherited voltage-gated ion channel disorders affecting muscle and the central nervous system are reviewed here.

Cerebellar ataxia, anterior horn cell disease, learning difficulties, and dystonia: a new syndrome

The following case reports describe a new condition of cerebellar ataxia, anterior horn cell disease, dystonia, and learning difficulties. Four cases are described. The condition appears to be of autosomal recessive inheritance as the group is made up of two pairs of sisters. All cases were evident by 3 years of age. Anterior horn cell disease was of a type not previously described at this age in association with cerebellar ataxia. Further genetic studies suggest the condition is not allelic with spinal muscular atrophy having no evidence of deletion of the survival motor neurone gene.

The neurochemistry of phenylketonuria

The mechanisms by which deficiency of hepatic phenylalanine hydroxylase causes central nervous system disease are reviewed. The neurological disease appears to be secondary to increased concentrations of phenylalanine and a decrease in the concentrations of other large neutral amino acids, especially methionine and tyrosine, within the central nervous system. This causes a deficiency of the neurotransmitter dopamine, reduced protein synthesis and demyelination. Similar mechanisms appear to be operating when blood phenylalanine concentrations are in the range expected for early continuously treated phenylketonuria.

CONCLUSION

The severe brain disease found in phenylketonuria is caused by a raised blood phenylalanine content which increases the brain free phenylalanine and decreases the concentration of other large neutral amino acids. Brain protein synthesis is decreased, myelin turnover is increased and there are abnormalities in amine neurotransmitter systems.

Cerebrospinal fluid studies in children with cerebral malaria: an excitotoxic mechanism?

The pathogenesis of cerebral malaria is poorly understood. One hypothesis is that activation of microglia and astrocytes in the brain might cause the cerebral symptoms by excitotoxic mechanisms. Cerebrospinal fluid was sampled in 97 Kenyan children with cerebral malaria, 85% within 48 hr of admission. When compared with an age-matched reference range, there were large increases in concentrations of the excitotoxin quinolinic acid (geometric mean ratio cerebral malaria/reference population [95% confidence limits] = 14.1 [9.8-20.4], P < 0.001) and total neopterin (10.9 [9.1-13.0], P < 0.001) and lesser increases in tetra-hydrobiopterin, di-hydrobiopterin, and 5-hydroxyindoleacetic acid. There was no change in tryptophan concentration. In contrast, nitrate plus nitrite concentrations were decreased (geometric mean ratio = 0.45 [0.35-0.59], P < 0.001). There was a graded increment in quinolinic acid concentration across outcome groups of increasing severity. The increased concentration of quinolinic acid suggests that excitotoxic mechanisms may contribute to the pathogenesis of cerebral malaria.

Inborn errors of neurotransmitter receptors

Inborn errors of neurotransmitter receptors are recently described gene mutations that directly affect receptor function. Currently three conditions are known to be caused by this mechanism: hyperekplexia; two forms of congenital inherited myasthenic syndromes; and autosomal dominant nocturnal frontal lobe epilepsy. Here, neurotransmitters, their receptors and known inborn errors of receptor function are reviewed.

GTP cyclohydrolase deficiency; intrafamilial variation in clinical phenotype, including levodopa responsiveness

A family with a dominant form of partial GTP cyclohydrolase deficiency is described. Clinical severity varied from mild involvement with complete responsiveness to levodopa to severe dystonia precluding any voluntary activity including talking, progressive contractures, and only partial responsiveness to levodopa. Although there are several possible reasons for intrafamilial variability, any patient with dystonia, the cause of which is not clearly identified, should receive a trial of levodopa.

Cerebrospinal fluid concentrations of nitrate plus nitrite during the treatment of acute lymphoblastic leukaemia in childhood

To investigate the hypothesis that acute lymphoblastic leukaemia (ALL) and its treatment disturb central nervous system nitric oxide metabolism, 11 patients were studied. Serial cerebrospinal fluid (CSF) samples were collected throughout treatment and the concentration of nitrate plus nitrite (NOx) was measured. Compared to an age-matched reference population, CSF NOx was significantly increased before treatment and rose further during the induction phase of treatment. Concentrations remained high during consolidation treatment, but fell during continuing treatment and normalised by the end of treatment. In conclusion, ALL and its treatment cause an increase in central nervous system nitric oxide production. reserved.

Clinical and laboratory findings in referrals for mitochondrial DNA analysis

BACKGROUND

Increasingly, mutations of mitochondrial DNA (mtDNA) are being considered when investigating the aetiology of neurological diseases in childhood. However, they are often difficult to predict clinically.

METHOD

Mitochondrial DNA analysis was carried out on 190 children from 1992 to 1996. Most patients were screened for large scale rearrangements and point mutations at nucleotide positions 3243, 3271, 8344, and 8993.

RESULTS

Mutations were found in only 15 patients (7.9%) and were either large scale rearrangements (seven patients) or point mutations at nucleotide position 3243 (eight patients). Other point mutations were screened for depending on the clinical picture. The age of symptom onset was significantly older in children with an mtDNA mutation (mean 7.0 years) compared with children without a mutation (mean 2.8 years). Neither Leigh's syndrome (28 cases) nor severe infantile lactic acidosis (12 cases) was associated with mtDNA mutation. Only three clinical features were significantly associated with an mtDNA mutation: progressive external ophthalmoplegia, myopathy, and pigmentary retinopathy. Family history was valuable: the point mutation at nucleotide 3243 (but not the large scale rearrangements) was associated with maternal inheritance; and consanguinity was not associated with mtDNA mutations. The only investigation that provided specific evidence of an underlying mtDNA mutation was histochemical staining of muscle biopsy specimens. The large scale mutations associated with Kearns-Sayre syndrome and progressive external ophthalmoplegia were found in DNA from muscle only, not leucocyte DNA; whereas point mutations were found in leucocyte DNA.

CONCLUSIONS

Even among children seen at a neurogenetic referral centre, mtDNA mutations were very uncommon. Muscle biopsy was the only investigation to provide evidence of mtDNA abnormality.

Neurological outcome of methylmalonic acidaemia

OBJECTIVE

To assess the long term outcome of patients with methylmalonic acidaemia in a cross sectional study.

PATIENTS

All 35 patients with methylmalonic acidaemia seen at Great Ormond Street Hospital for Children in London, UK between 1970 and 1996 were studied. They were divided into cobalamin responsive (n = 6) and non-responsive (n = 29), and early and late onset groups.

RESULTS

There was a significant difference between cobalamin responsive and non-responsive groups in severity, survival, and incidence of neurological sequelae. Cobalamin responsive patients had mild disease, irrespective of age at presentation, their neurological complications were less severe, and they are all alive. The cobalamin non-responsive group comprised 19 early and nine late onset patients. The early onset patients had more severe disease at presentation and 14 have died; all late onset patients are alive. There was no significant difference in abnormal neurological signs, although early onset patients had a significantly reduced full scale intelligence quotient and poor cognitive outcome. In both groups, abnormal neurological signs continue to increase with age.

CONCLUSIONS

Cobalamin responsive patients have a better long term outcome. The outcome in the non-responsive patients, particularly the early onset group, remains poor and alternative treatments should therefore be considered early in this group.

Demyelination and single-carbon transfer pathway metabolites during the treatment of acute lymphoblastic leukemia: CSF studies

PURPOSE

To investigate the hypothesis that methotrexate causes demyelination due to a deficiency in S-adenosylmethionine (SAM) during the treatment of acute lymphoblastic leukemia (ALL).

PATIENTS AND METHODS

Twenty-four patients treated on the Medical Research Council United Kingdom ALL trial no. 11 (MRC UKALL XI) were studied. The trial randomized patients at the presymptomatic CNS treatment (PCNS) phase to receive (1) intrathecal methotrexate and cranial radiotherapy (CRTX); (2) high-dose intravenous methotrexate with folinic acid rescue and continuing intrathecal methotrexate (HDMTX); and (3) continuing intrathecal methotrexate alone (ITMTX). Serial CSF samples were collected throughout treatment and concentrations of 5-methyltetrahydrofolate (MTF), methionine (MET), SAM, and myelin basic protein (MBP) were measured. The results were grouped into treatment milestones and compared with an age-matched reference population.

RESULTS

There was a highly significant effect of both treatment milestones and trial arm on the metabolite and MBP concentrations. CSF MTF reached a nadir during the induction phase of treatment, while SAM and MET reached their nadir during the consolidation phase. CSF MBP mirrored SAM concentration and there was a significant inverse relationship between the two. MTF, SAM, and MBP returned to normal values by the end of treatment, while MET was increased significantly. The effect of treatment was decremental across the ITMTX, HDMTX, and CRTX groups.

CONCLUSION

Treatment of ALL causes marked abnormalities in the single-carbon transfer pathway and subclinical demyelination. Methotrexate is one cause of this. Whether these abnormalities contribute to the late cognitive deficits requires further study.

Demyelination and inborn errors of the single carbon transfer pathway

Inborn errors of the single-carbon transfer pathway are rare disorders of folate and cobalamin metabolism. They may be complicated by demyelination resembling subacute combined degeneration of the cord and brain. The study of CSF metabolites in children with serial errors affecting the single-carbon transfer pathway has suggested that S-adenosylmethionine deficiency is a cause of the demyelination. This deficiency is corrected by treatment that causes clinical improvement and remyelination. Some treatments can only have an indirect effect on the brain and this is discussed with other evidence that the liver may produce factors that are necessary for the maintenance of central myelin.

Cerebrospinal fluid and plasma total homocysteine and related metabolites in children with cystathionine beta-synthase deficiency: the effect of treatment

The neurologic complications of cystathionine beta-synthase deficiency are thought to be secondary to accumulation of homocyst(e)ine in the CNS. Treatment of this disorder with betaine has been shown to improve the behavior of individuals, to reduce plasma total homocysteine, and to correct secondary abnormalities of serine. To test the hypothesis that homocyst(e)ine accumulates within the CNS and that this can be reduced by treatment with betaine, we measured total homocysteine and related metabolites in the plasma of 10 children with cystathionine beta-synthase deficiency and cerebrospinal fluid of five children before and during betaine therapy. In plasma, betaine significantly lowered total homocysteine (but not to the normal range) and had a variable effect on methionine. In the cerebrospinal fluid, total homocysteine was raised before treatment (mean 1.2 microM) and was significantly reduced by betaine (mean 0.32 microM) but not to the normal range (<0.10 microM). Cerebrospinal fluid methionine was raised before and during treatment, but betaine did not cause a significant further increase. Cerebrospinal fluid serine was significantly reduced before treatment and rose to the normal range with betaine. Cerebrospinal fluid S-adenosylmethionine was normal before treatment and rose significantly with treatment; there were no significant changes in cerebrospinal fluid 5-methyltetrahydrofolate. The demonstration of accumulation of homocysteine within the CNS lends support to the hypothesis that this may be one cause of the neurologic complications of cystathionine beta-synthase deficiency. Betaine is effective in reducing cerebrospinal fluid homocysteine, but concentrations are still significantly raised during treatment.

Missense mutation clustering in the survival motor neuron gene: a role for a conserved tyrosine and glycine rich region of the protein in RNA metabolism?

The Survival Motor Neuron (SMN) gene shows deletions in the majority of patients with Spinal Muscular Atrophy (SMA), a disease of motor neuron degeneration. To date only two missense mutations have been reported in SMN in patients with SMA. The fact that no SMN-homologues have been forthcoming from data-base searching has resulted in a lack of hypotheses concerning the structural and functional consequences of these mutations. Recently SMN has been shown to interact with heterogeneous nuclear ribonucleoproteins (hnRNPs) suggesting a role in mRNA metabolism. We describe a novel missense mutation and the subsequent identification of a triplicated tyrosine-glycine (Y-G) peptide sequence at the C-terminal of SMN which encompasses each of the three predicted amino acid sequence substitutions. We have identified apparent orthologues of SMN in Caenorhabditis elegans and Schizosaccharomyces pombe. These sequences retain the highly conserved Y-G motif and provide additional support for a role of SMN in mRNA metabolism.

Dopa-responsive dystonia in British patients: new mutations of the GTP-cyclohydrolase I gene and evidence for genetic heterogeneity

Dopa-responsive dystonia (DRD) was originally described in a series of Japanese patients, but is now increasingly recognized in other countries. Recently the GTP cyclohydrolase I (GTPCH) gene was isolated as the first causative gene for dopa-responsive dystonia (DRD). Mutations were identified in three Japanese families with autosomal dominantly inherited DRD and in one sporadic Japanese patient. Characterisation of the exon-intron boundaries of this gene has now allowed the analysis of mutations at the level of genomic DNA. Amplifying all six exons, we analyzed the GTPCH gene in nine British families with 33 affected family members and in three sporadic cases and found six new mutations. Only point mutations were found, causing a stop codon in one family and an amino acid change in highly conserved regions of the gene in a further four families and in one sporadic case. None of these mutations were detected more than once and none of the mutations previously described were found in our patients. No mutations were identified in four families and in two sporadic cases.

Association of cerebrospinal fluid deficiency of 5-methyltetrahydrofolate, but not S-adenosylmethionine, with reduced concentrations of the acid metabolites of 5-hydroxytryptamine and dopamine

1. Folate deficiency, or inborn errors of folate metabolism, cause reduced turnover of 5-hydroxytryptamine (serotonin), and perhaps dopamine, in the central nervous system. The mechanism by which this occurs are not known. One possibility is that this is mediated by deficiency of the methyl-donor S-adenosylmethionine. 2. To test this in humans, we have measured cerebrospinal fluid concentrations of 5-hydroxyindoleacetic acid and homovanillic acid, metabolites of 5-hydroxytryptamine and dopamine, respectively, in children with inborn errors of the methyl-transfer pathway. These children are naturally deficient in 5-methyltetrahydrofolate, S-adenosylmethionine or both before treatment, and replete with S-adenosylmethionine, but not necessarily with 5-methyltetrahydrofolate, during treatment. 3. Children with subnormal cerebrospinal fluid concentrations of 5-methyltetrahydrofolate had significantly reduced concentrations of 5-hydroxyindoleacetic acid and homovanillic acid. Children with subnormal cerebrospinal fluid concentrations of S-adenosylmethionine did not have significantly reduced concentrations of these metabolites. 4. We conclude that the mechanism by which deficiency of 5-methyltetrahydrofolate causes reduced 5-hydroxytryptamine and dopamine turnover is unlikely to be mediated by S-adenosylmethionine.

The psychiatric, psychological and behavioural functioning of a boy with terminal deletion of the long arm of chromosome 10

The developmental and behavioural functioning of a six-year-old boy with deletion of the long arm of chromosome 10 was evaluated using reliable, standardised, psychological inventories. The information obtained clarified his complex pattern of strengths and needs; it also contributes scientifically derived data to the literature on behavioural correlates of this condition.

Physiology and pathophysiology of organic acids in cerebrospinal fluid

Concentrations of organic acids in cerebrospinal fluid (CSF) appear to be directly dependent upon their rate of production in the brain. There is evidence that the net release of short-chain monocarboxylic acids from the brain is a major route for removing these products of cerebral metabolism. Concentrations of organic acids in blood and CSF are largely independent of each other. Quantitative reference values for the concentrations of organic acids in CSF and plasma as well as ratios of individual organic acids between CSF and plasma were determined in 35 pairs of samples from paediatric patients. Over 25 organic acids were quantifiable in all or in the majority of CSF and/or plasma specimens (limit of detection 1 mumol/L). There were substantial differences in the CSF/plasma ratios between subgroups of organic acids. Metabolites related to fatty-acid oxidation were present in CSF in substantially less amounts than in plasma. Organic acids related to carbohydrate and energy metabolism and to amino acid degradation were present in CSF in the same amounts as or slightly smaller amounts than in plasma. Finally, some organic acids were found in substantially higher amounts in CSF than in plasma, e.g. glycolate, glycerate, 2,4-dihydroxybutyrate, citrate and isocitrate. Studies of organic acids in CSF and plasma samples are presented from patients with 'cerebral' lactic acidosis, disorders of propionate and methylmalonate metabolism, glutaryl-CoA dehydrogenase deficiency and L-2-hydroxy-glutaric aciduria. It became apparent that derangements of organic acids in the CSF may occur independently of the systemic metabolism. Quantitative organic acid analysis in CSF will yield new information on the pathophysiology in the central nervous system (CNS) of these disorders and may prove necessary for successful monitoring of treatment of organoacidopathies, which present mainly with neurological disease. For example, in glutaryl-CoA dehydrogenase deficiency the urinary excretion of glutarate appears to be an inadequate parameter for monitoring the effect of dietary therapy, without plasma and CSF determinations. In L-2-hydroxyglutaric aciduria the elevation of L-2-hydroxyglutarate was found to be greater in CSF than in plasma. In addition, some other organic acids, glycolate, glycerate, 2,4-dihydroxybutyrate, citrate and isocitrate, were also elevated in the CSF of the patients out of proportion to normal levels in plasma and urine. High concentrations of an unknown compound, which was tentatively identified as 2,4-dihydroxyglutarate, were found in the CSF of patients with L-2-hydroxyglutaric aciduria.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemical pathogenesis of subacute combined degeneration of the spinal cord and brain

In humans, subacute combined degeneration of the spinal cord and brain, a primary demyelinating disease, is caused by cobalamin or methyltetrahydrofolate deficiency. Experimental studies into its pathogenesis suggest that dysfunction of the methyl-transfer pathway may be the cause. Compelling evidence for this comes from the study of inborn errors of cobalamin metabolism where deficiency of methylcobalamin, but not deoxyadenosylcobalamin, is associated with demyelination. Recent studies have focused upon inborn errors of the methyl-transfer pathway. Cerebrospinal fluid concentrations of metabolites of the methyl-transfer pathway have been measured in humans with sequential errors of the pathway and correlated with demyelination demonstrated on magnetic resonance imaging of the brain. This has provided new data suggesting that deficiency of S-adenosylmethionine is critical to the development of demyelination in cobalamin deficiency.

Distal motor axonopathy and central nervous system myelin vacuolation caused by cycloleucine, an inhibitor of methionine adenosyltransferase

Cycloleucine (CL), an inhibitor of methionine adenosyltransferase, has previously been used to produce an experimental model of subacute combined degeneration of the spinal cord. A re-investigation of its effects on the morphology of the nervous system and on brain concentrations of methionine and S-adenosylmethionine (SAM) was undertaken. Cycloleucine was administered as a single dose intraperitoneally (2 mg/g body weight) to young mice aged 21 d and adults aged 6 or 10 wks. The 21-day-old mice showed clinical evidence of toxicity within 24 h and thereafter developed progressive muscle weakness and ataxia. Animals did not survive longer than 1 wk. Light and electron microscopic examination of the central and peripheral nervous systems showed that intramyelinic vacuolation developed in the white matter of brain and cord within 12 h. The intramyelinic vacuolation in the white matter of brain and cord became more severe with longer survival, vacuoles coalescing and secondary axonal degeneration becoming evident. There was no myelin vacuolation in peripheral nerves. Axonal lesions occurred in the distal parts of motor nerves within 12-24 h resulting in degeneration of intramuscular nerve fibres and terminals. Later there was evidence of axonal degeneration in tibial and sciatic nerves. Many dorsal root ganglion cells became vacuolated or necrotic and numerous degenerated fibres were noted in the white matter of the spinal cord, particularly in the gracile funiculus. The optic nerves were not affected at any stage. In adult mice the pathology consisted of distal motor axonal degeneration which developed at 1-2 d. Little or no intramyelinic vacuolation in white matter was noted. Brain concentrations of SAM were reduced and levels of methionine became greatly elevated. The morphological effects of CL are considered to be the result of SAM deficiency impairing transmethylation processes known to be important in the formation and stabilization of myelin through the methylation of myelin basic protein. The immature developing central nervous system is much more vulnerable than the fully myelinated adult brain and spinal cord. The distal, predominantly motor axonopathy is a new observation and may be a reflection of the importance of transmethylation processes in the maintenance of axonal terminal membranes and the mechanisms of release of acetylcholine at the neuromuscular junction.

Association of demyelination with deficiency of cerebrospinal-fluid S-adenosylmethionine in inborn errors of methyl-transfer pathway

Long-term deficiency of cobalamin or folate causes a demyelinating disease of the brain and spinal cord. A reduced supply of methyl groups has been implicated as its cause. To examine the mechanisms of demyelination in human beings, we have studied three children with sequential inborn errors of the methyl-transfer pathway. One child had abnormal methylfolate metabolism, one abnormal methylcobalamin metabolism, and one hypermethioninaemia probably caused by methionine adenosyltransferase deficiency. Magnetic resonance imaging of the brain and measurement of cerebrospinal-fluid concentrations of 5-methyltetrahydrofolate, methionine, and S-adenosylmethionine were carried out before and after 6-12 months of appropriate treatment. Each patient had abnormal myelination before treatment; the scans suggested demyelination. The only consistent biochemical abnormality in the cerebrospinal fluid was a low concentration of S-adenosylmethionine. Treatment led to substantial clinical improvement, apparent remyelination, and increases in cerebrospinal-fluid S-adenosylmethionine concentration into the normal range. Cerebrospinal-fluid concentrations of S-adenosylmethionine and methionine were significantly lower in eight other children with errors of the methyl-transfer pathway than in an age-matched reference population (mean [95% confidence interval] standard deviation score -1.81 [0.57], p less than 0.001 for S-adenosyl methionine and -1.82 [0.19], p less than 0.001 for methionine). The concentrations of these metabolites increased to within the reference range on treatment. We have shown that demyelination is associated with cerebrospinal-fluid S-adenosylmethionine deficiency and that restoration of S-adenosylmethionine is associated with remyelination.

Cerebrospinal fluid concentrations of S-adenosylmethionine, methionine, and 5-methyltetrahydrofolate in a reference population: cerebrospinal fluid S-adenosylmethionine declines with age in humans

Cerebrospinal fluid concentrations of S-adenosylmethionine, methionine, and 5-methyltetrahydrofolate were measured in 80 children and young adults in whom there was no disturbance of the methyl transfer pathway. Cerebrospinal fluid was collected under standardized conditions and analyzed by high-performance liquid chromatography. S-Adenosylmethionine, but not methionine nor 5-methyltetrahydrofolate, concentrations declined sharply during the first year of life. There was no correlation between concentrations of S-adenosylmethionine and methionine or 5-methyltetrahydrofolate. Reference ranges for the three metabolites are given.

L-3,4-dihydroxyphenylalanine (levodopa) lowers central nervous system S-adenosylmethionine concentrations in humans

To determine whether levodopa reduces the levels of S-adenosylmethionine in the human central nervous system, cerebrospinal fluid (CSF) concentrations of S-adenosylmethionine, methionine, 3-methoxytyrosine, levodopa and 5-methyltetrahydrofolate were measured in six children with dopamine deficiency before and after treatment. In four, the lack of dopamine was secondary to a reduction in concentration of levodopa and these were treated with levodopa together with a peripheral dopa-decarboxylase inhibitor. In the other two, levodopa in the central nervous system naturally accumulated due to a congenital deficiency of aromatic-L-amino acid decarboxylase and these were treated with pyridoxine (which in this condition lowers central levodopa concentrations). Raising levodopa concentrations in the central nervous system caused a fall in CSF S-adenosyl-methionine concentration and a rise in CSF 3-methoxytyrosine concentration. No change was observed in CSF methionine concentration and in all patients CSF 5-methyltetrahydrofolate concentration was normal. With one exclusion there was a linear relationship between CSF S-adenosylmethionine and 3-methoxytyrosine concentrations. This is the first demonstration of such effects in humans and the implications upon levodopa therapy are discussed.

Central-nervous-system methyl-group metabolism in children with neurological complications of HIV infection

To assess methyl-group metabolism in the central nervous system in infection with human immunodeficiency virus (HIV), levels of 5-methyltetrahydrofolate, methionine, and S-adenosylmethionine were measured by high-performance liquid chromatography in cerebrospinal fluid (CSF) from six children with congenital HIV infection and neurological complications. Total neopterins were also measured, as a marker of macrophage activation. In all six children concentrations of one or more methyl-group carriers were lower than those in a reference population of children, and all of the five in whom CSF neopterins were measured had higher than normal levels. Defective methylation may play a part in the neurological damage caused by HIV infection.

A method for the measurement of S-adenosylmethionine in small volume samples of cerebrospinal fluid or brain using high-performance liquid chromatography-electrochemistry

A method for the measurement of S-adenosylmethionine in cerebrospinal fluid and brain using high-performance liquid chromatography with electrochemical detection is described. The method is based upon the catechol O-methyltransferase-catalyzed methylation of dihydroxybenzylamine to its 3- and 4-methoxy derivatives and measurement of the latter. Detection limits are 0.1 pmol for 3- and 4-methoxyhydroxybenzylamine, recovery is 100%, and variability is less than 8%. HPLC measurement of 3- and 4-methoxyhydroxybenzylamine is linear up to at least 100 pmol injected. The use of a nonbiological catechol in the assay minimizes interference from endogenous and exogenous catechols and the wide limits of linearity allows the assay of small volumes of cerebrospinal fluid or brain extract without further concentration or dilution.

Acute metabolic encephalopathy: a review of causes, mechanisms and treatment

Acute encephalopathy is a relatively common problem: one of the causes is metabolic disorders. A detailed history, examination and investigations performed during the acute illness (blood sugar, blood gases, plasma ammonia, blood lactate, plasma ketones, plasma amino acids, liver function tests, and urinary organic acids) should identify those patients in whom a metabolic disorder is likely. More detailed studies may be needed to establish a precise diagnosis. The mechanism of the acute brain dysfunction is multifactorial. Factors that contribute include changes in blood flow and, initially, a disturbance in neurotransmitter function followed by failure of energy metabolism and cellular depolarization. Treatment of these conditions is largely supportive, with special attention to the management of cerebral perfusion pressure.

Association of adverse perinatal events with an empty sella turcica in children with growth hormone deficiency

High-resolution computed tomography (HR-CT) of the hypothalamo-pituitary region was performed in 26 consecutive children presenting with growth hormone deficiency (GHD) at one clinic. 58% had an empty sella turcica (ES) and 42% a full sella turcica (FS). There was no difference between the ES and FS groups for mean (+/- 95% confidence limits) presentation age (ES 6.7 (+/- 1.8) years, FS 5.6 (+/- 2.2) years), height standard deviation score (SDS) (ES -3.9 (+/- 0.8), FS -3.3 (+/- 0.5] nor head circumference SDS (ES -1.9 (+/- 1.1), FS -0.7 (+/- 1.1]. There were significant associations between the ES group and a history of adverse perinatal events (p less than 0.001) and multiple pituitary deficiency (p = 0.014). Growth hormone response to an acute growth hormone releasing factor test showed no association with HR-CT diagnosis. Sella turcica volumes were calculated from the HR-CT scans. All sella volumes were small; mean SDS for height was -2.6 (+/- 0.2). There was no difference in sella volume SDS between the ES and FS groups (ES -2.9 (+/- 0.3), FS -2.5 (+/- 0.4]. Adverse perinatal events may cause an ES and GHD by compromising the blood supply to the pituitary gland or infundibulum.