Metabolic disorders and mental retardation

Intellectual Disabilities and Neurocognitive Impairment in Adult Patients with Inherited Metabolic Diseases: A UK Single Centre Experience

Inherited metabolic diseases (IMDs) are a group of heterogeneous genetic disorders resulting in substrate accumulation, energy deficiency, or complex molecular defects due to the failure of specific molecules to act as enzymes, cofactors, transporters, or receptors in specific metabolic pathways. The pathophysiological changes seen in IMDs are sometimes associated with intellectual disability (ID) or neurocognitive decline, necessitating multidisciplinary input. We here describe our experience at one tertiary metabolic centre in the UK. We reviewed the case prevalence and existing service provision in one adult IMD service covering a multi-ethnic population of 10 million in North England. In our cohort of 2268 IMD patients, 1598 patients had general metabolic conditions (70.5%), and 670 had lysosomal storage disease/disorders (LSD)s (29.5%). The overall prevalence of ID and neurocognitive decline was found to be 15.7% (n = 357), with patients with LSDs accounting for 23.5% (n = 84) of affected patients. Given the prevalence of ID in adults with IMDs, access to multidisciplinary input from neuropsychology and neuropsychiatry services is important. Education of healthcare professionals to diagnose IMDs in patients with ID, in addition to neurocognitive and neuropsychiatric presentations, will avoid missed diagnoses of IMD and will have a positive effect on patient outcomes.

Suppression of exaggerated NMDAR activity by memantine treatment ameliorates neurological and behavioral deficits in aminopeptidase P1-deficient mice

Inborn errors of metabolism (IEMs) are common causes of neurodevelopmental disorders, including microcephaly, hyperactivity, and intellectual disability. However, the synaptic mechanisms of and pharmacological interventions for the neurological complications of most IEMs are unclear. Here, we report that metabolic dysfunction perturbs neuronal NMDA receptor (NMDAR) homeostasis and that the restoration of NMDAR signaling ameliorates neurodevelopmental and cognitive deficits in IEM model mice that lack aminopeptidase P1. Aminopeptidase P1-deficient (Xpnpep1^–/–) mice, with a disruption of the proline-specific metalloprotease gene Xpnpep1, exhibit hippocampal neurodegeneration, behavioral hyperactivity, and impaired hippocampus-dependent learning. In this study, we found that GluN1 and GluN2A expression, NMDAR activity, and the NMDAR-dependent long-term potentiation (LTP) of excitatory synaptic transmission were markedly enhanced in the hippocampi of Xpnpep1^–/– mice. The exaggerated NMDAR activity and NMDAR-dependent LTP were reversed by the NMDAR antagonist memantine. A single administration of memantine reversed hyperactivity in adult Xpnpep1^–/– mice without improving learning and memory. Furthermore, chronic administration of memantine ameliorated hippocampal neurodegeneration, hyperactivity, and impaired learning and memory in Xpnpep1^–/– mice. In addition, abnormally enhanced NMDAR-dependent LTP and NMDAR downstream signaling in the hippocampi of Xpnpep1^–/– mice were reversed by chronic memantine treatment. These results suggest that the metabolic dysfunction caused by aminopeptidase P1 deficiency leads to synaptic dysfunction with excessive NMDAR activity, and the restoration of synaptic function may be a potential therapeutic strategy for the treatment of neurological complications related to IEMs.

Addressing neurological symptoms may offer new treatments for inborn errors of metabolism (IEMs) affecting neurodevelopment. In such IEMs, mutation of an enzyme disrupts a metabolic pathway, causing buildup or lack of key molecules, with symptoms including hyperactivity, developmental delay, and intellectual disability. Because the detailed pathological mechanisms of most IEMs are unknown, there are no treatments for resulting neurological issues. Myoung-Hwan Kim at Seoul National University and co-workers investigated whether they could treat the neurological symptoms of the IEM, aminopeptidase P1 (APP1) deficiency. They found that APP1 deficiency in mice caused an increase in the neural receptor NMDAR. Suppressing NMDAR reduced both neurological and behavioral symptoms. These findings suggest potential treatments for APP1 deficiency, and indicate that neurodevelopmental disorders in IEMs may be treated by repairing the neural circuitry instead of the root metabolic cause.

Whole exome sequencing identified a novel nonsense INPP4A mutation in a family with intellectual disability

Intellectual disability (ID) is characterized by significant deficits in adaptive behaviors and cognitive functioning. The involvement of both genetic and environmental factors in pathogenesis of the ID, makes the diagnosis of the disease more complicated. Nowadays, the entrance of next generation sequencing (NGS) approaches has facilitated the discovery of causative genes in this genetically heterogeneous disease. Here, we report a novel nonsense mutation (c.115 C > T, p.Gln39X) of INPP4A gene in a family with inherited ID using whole exome sequencing (WES). The mutation was completely co-segregated with disease phenotype in all affected members, and unaffected members of family were either homozygous or heterozygous. In silico analysis predicted the c.115 C > T; p.Gln39X as probably pathogenic variant. It seems that mutated transcript would degrade through nonsense-mediated decay (NMD) or potentially form strongly truncated protein lacking functionally important domain like C2A_copine. The INPP4A is an important neuroprotective protein which is preferentially detected in brain. The variant c.115C > T; p.Gln39X is the third reported mutation of INPP4A gene in neurological diseases. Such variants further expand the mutation spectrum in INPP4A and substantiate its role in the pathogenesis of ID. However, more experimental data are needed for considering these mutations in genetic counseling.

The anxiolytic effects of atorvastatin and simvastatin on dietary-induced increase in homocysteine levels in rats

The aim of this study was to evaluate the effects of atorvastatin and simvastatin on behavioral manifestations that followed hyperhomocysteinemia induced by special dietary protocols enriched in methionine and deficient in B vitamins (B6, B9, B12) by means of alterations in anxiety levels in rats. Simultaneously, we investigated the alterations of oxidative stress markers in rat hippocampus induced by applied dietary protocols. Furthermore, considering the well-known antioxidant properties of statins, we attempted to assess their impact on major markers of oxidative stress and their possible beneficial role on anxiety-like behavior effect in rats. The 4-week-old male Wistar albino rats were divided (eight per group) according to basic dietary protocols: standard chow, methionine-enriched, and methionine-enriched vitamins B (B6, B9, B12) deficient. Each dietary protocol (30 days) included groups with atorvastatin (3 mg/kg/day i.p.) and simvastatin (5 mg/kg/day i.p.). The behavioral testing was performed in the open field and elevated plus maze tests. Parameters of oxidative stress (index of lipid peroxidation, superoxide dismutase, catalase activity, glutathione) were determined in hippocampal tissue samples following decapitation after anesthesia. Methionine-load dietary protocols induced increased oxidative stress in rat hippocampus, which was accompanied by anxiogenic behavioral manifestations. The methionine-enriched diet with restricted vitamins B intake induced more pronounced anxiogenic effect, as well as increased oxidative stress compared to the methionine-load diet with normal vitamins B content. Simultaneous administration of statins showed beneficial effects by means of both decreased parameters of oxidative stress and attenuation of anxiety. The results obtained with simvastatin were more convincible compared to atorvastatin.

Surgical resection versus transarterial chemoembolization for BCLC intermediate stage hepatocellular carcinoma: a systematic review and meta-analysis

BACKGROUND & OBJECTIVE

Transarterial chemoembolization (TACE) is recommended as the first-line therapy for intermediate stage hepatocellular carcinoma (HCC) according to the Barcelona Clinic Liver Cancer (BCLC) algorithm. However, in clinical practice, many such patients undergo surgical resection. A meta-analysis with a systematic search of the medical literature was conducted to compare these two procedures for BCLC intermediate stage HCC.

METHODS

PubMed, Embase, Medline and Cochrane library were searched for studies comparing surgical resection with TACE for BCLC intermediate stage HCC that were published before December 2016. The primary outcome was overall survival, and the secondary outcomes were postoperative complications and 30-day mortality.

RESULTS

This meta-analysis included 9 studies with 2619 patients (surgical resection, n = 1204 (46%) and TACE, n = 1415 (54%)). When compared with the TACE group, the pooled hazard ratio (HR) for the 1, 3 and 5-year OS rates in patients who underwent surgical resection were 0.62 (95% CI 0.51-0.75, P = 0.39; I2 = 6%, P < 0.001), 0.58 (95% CI 0.51-0.67, P = 0.25; I2 = 22%, P < 0.001) and 0.59 (95% CI 0.54-0.64, P = 0.18; I2 = 20%, P < 0.001). No significant differences in the pooled odds ratios (OR) were found between surgical resection and TACE in postoperative complications and 30-day mortality [OR 1.23 (95% CI 0.87 to 1.74, P = 0.390; I2 = 0%, P = 0.240) and OR 1.11 (95% CI 0.60 to 2.04, P = 0.89; I2 = 0%, P = 0.740), respectively].

CONCLUSION

This meta-analysis on studies on Asian HCC patients demonstrated surgical resection had better overall survival than TACE for patients with intermediate stage HCC, without any significant increase in postoperative complication or 30-day mortality rates. Further studies are needed to validate these results on Western patients, moreover, a reappraisal of the recommended treatments for BCLC intermediate stage HCC should be considered.

Deficiency of aminopeptidase P1 causes behavioral hyperactivity, cognitive deficits, and hippocampal neurodegeneration

Metabolic diseases affect various organs including the brain. Accumulation or depletion of substrates frequently leads to brain injury and dysfunction. Deficiency of aminopeptidase P1, a cytosolic proline-specific peptidase encoded by the Xpnpep1 gene, causes an inborn error of metabolism (IEM) characterized by peptiduria in humans. We previously reported that knockout of aminopeptidase P1 in mice causes neurodevelopmental disorders and peptiduria. However, little is known about the pathophysiological role of aminopeptidase P1 in the brain. Here, we show that loss of aminopeptidase P1 causes behavioral and neurological deficits in mice. Mice deficient in aminopeptidase P1 (Xpnpep1^-/- ) display abnormally enhanced locomotor activities in both the home cage and open-field box. The aminopeptidase P1 deficiency in mice also resulted in severe impairments in novel-object recognition, the Morris water maze task, and contextual, but not cued, fear memory. These behavioral dysfunctions were accompanied by epileptiform electroencephalogram activity and neurodegeneration in the hippocampus. However, mice with a heterozygous mutation for aminopeptidase P1 (Xpnpep1^+/- ) exhibited normal behaviors and brain structure. These results suggest that loss of aminopeptidase P1 leads to behavioral, cognitive and neurological deficits. This study may provide insight into new pathogenic mechanisms for brain dysfunction related to IEMs.

Creatine Enhances Mitochondrial-Mediated Oligodendrocyte Survival After Demyelinating Injury

Chronic oligodendrocyte loss, which occurs in the demyelinating disorder multiple sclerosis (MS), contributes to axonal dysfunction and neurodegeneration. Current therapies are able to reduce MS severity, but do not prevent transition into the progressive phase of the disease, which is characterized by chronic neurodegeneration. Therefore, pharmacological compounds that promote oligodendrocyte survival could be beneficial for neuroprotection in MS. Here, we investigated the role of creatine, an organic acid involved in adenosine triphosphate (ATP) buffering, in oligodendrocyte function. We found that creatine increased mitochondrial ATP production directly in oligodendrocyte lineage cell cultures and exerted robust protection on oligodendrocytes by preventing cell death in both naive and lipopolysaccharide-treated mixed glia. Moreover, lysolecithin-mediated demyelination in mice deficient in the creatine-synthesizing enzyme guanidinoacetate-methyltransferase (Gamt) did not affect oligodendrocyte precursor cell recruitment, but resulted in exacerbated apoptosis of regenerated oligodendrocytes in central nervous system (CNS) lesions. Remarkably, creatine administration into Gamt-deficient and wild-type mice with demyelinating injury reduced oligodendrocyte apoptosis, thereby increasing oligodendrocyte density and myelin basic protein staining in CNS lesions. We found that creatine did not affect the recruitment of macrophages/microglia into lesions, suggesting that creatine affects oligodendrocyte survival independently of inflammation. Together, our results demonstrate a novel function for creatine in promoting oligodendrocyte viability during CNS remyelination.SIGNIFICANCE STATEMENT We report that creatine enhances oligodendrocyte mitochondrial function and protects against caspase-dependent oligodendrocyte apoptosis during CNS remyelination. This work has important implications for the development of therapeutic targets for diseases characterized by oligodendrocyte death, including multiple sclerosis.

Increased apoptosis and hypomyelination in cerebral white matter of macular mutant mouse brain

Hypomyelination in developing brain is often accompanied by congenital metabolic disorders. Menkes kinky hair disease is an X-linked neurodegenerative disease of impaired copper transport, resulting from a mutation of the Menkes disease gene, a transmembrane copper-transporting p-type ATPase gene (ATP7A). In a macular mutant mouse model, the murine ortholog of Menkes gene (mottled gene) is mutated, and widespread neurodegeneration and subsequent death are observed. Although some biochemical analysis of myelin protein in macular mouse has been reported, detailed histological study of myelination in this mouse model is currently lacking. Since myelin abnormality is one of the neuropathologic findings of human Menkes disease, in this study early myelination in macular mouse brain was evaluated by immunohistochemistry. Two-week-old macular mice and normal littermates were perfused with 4% paraformaldehyde. Immunohistochemical staining of paraffin embedded and vibratome sections was performed using antibodies against either CNPase, cleaved caspase-3 or O4 (marker of immature oligodendrocytes). This staining showed that cerebral myelination in macular mouse was generally hypoplastic and that hypomyelination was remarkable in internal capsule, corpus callosum, and cingulate cortex. In addition, an increased number of cleaved caspase-3 positive cells were observed in corpus callosum and internal capsule. Copper deficiency induced by low copper diet has been reported to induce oligodendrocyte dysfunction and leads to hypomyelination in this mouse model. Taken together, hypomyelination observed in this study in a mouse model of Menkes disease is assumed to be induced by increased apoptosis of immature oligodendrocytes in developing cerebrum, through deficient intracellular copper metabolism.

The metabolic evaluation of the child with an intellectual developmental disorder: diagnostic algorithm for identification of treatable causes and new digital resource

Intellectual developmental disorders (IDD), characterized by significant impairment of cognitive functions, with limitations of learning, adaptive behavior and skills, are frequent (2.5% of the population affected) and present with significant co-morbidity. The burden of IDD, in terms of emotional suffering and associated health care costs, is significant; prevention and treatment therefore are important. A systematic literature review, updated in 2013, identified 89 inborn errors of metabolism (IEMs), which present with IDD as prominent feature and are amenable to causal therapy. Therapeutic effects include improvement and/or stabilization of psychomotor/cognitive development, behavior/psychiatric disturbances, seizures, neurologic and systemic manifestations. The levels of available evidence for the various treatments range from Level 1b, c (n=5); Level 2a, b, c (n=14); Level 4 (n=53), and Levels 4-5 (n=27). For a target audience comprising clinical and biochemical geneticists, child neurologists and developmental pediatricians, five experts translated....this data into a 2-tiered diagnostic algorithm: The first tier comprises metabolic "screening" tests in urine and blood, which are relatively accessible, affordable, less invasive, and have the potential to identify 60% of all treatable IEMs. The second tier investigations for the remaining disorders are ordered based on individual clinical signs and symptoms. This algorithm is supported by an App www.treatable-id.org, which comprises up-to-date information on all 89 IEMs, relevant diagnostic tests, therapies and a search function based on signs and symptoms. These recommendations support the clinician in early identification of treatable IEMs in the child with IDD, allowing for timely initiation of therapy with the potential to improve neurodevelopmental outcomes. The need for future studies to determine yield and usefulness of these recommendations, with subsequent updates and improvements to developments in the field, is outlined.

Developmental retardation, microcephaly, and peptiduria in mice without aminopeptidase P1

Cytosolic aminopeptidase P1 (APP1) is one of the three known mammalian aminopeptidase Ps (APPs) that cleave the N-terminal amino acid residue of peptides in which the penultimate amino acid is proline. In mammals, many biologically active peptides have a highly conserved N-terminal penultimate proline. However, little is known about the physiological role of APP1. In addition, there is no direct evidence to associate a deficiency in APP1 with metabolic diseases. Although two human subjects with reduced APP activity exhibited peptiduria, it is unclear which of the three APP isoforms is responsible for this disorder. In this study, we generated APP1-deficient mice by knocking out Xpnpep1. Mouse APP1 deficiency causes severe growth retardation, microcephaly, and modest lethality. In addition, imino-oligopeptide excretion was observed in urine samples from APP1-deficient mice. These results suggest an essential role for APP1-mediated peptide metabolism in body and brain development, and indicate a strong causal link between APP1 deficiency and peptiduria.

Treatable inborn errors of metabolism causing intellectual disability: a systematic literature review

BACKGROUND

Intellectual disability ('developmental delay' at age<5 years) affects 2.5% of population worldwide. Recommendations to investigate genetic causes of intellectual disability are based on frequencies of single conditions and on the yield of diagnostic methods, rather than availability of causal therapy. Inborn errors of metabolism constitute a subgroup of rare genetic conditions for which an increasing number of treatments has become available. To identify all currently treatable inborn errors of metabolism presenting with predominantly intellectual disability, we performed a systematic literature review.

METHODS

We applied Cochrane Collaboration guidelines in formulation of PICO and definitions, and searched in Pubmed (1960-2011) and relevant (online) textbooks to identify 'all inborn errors of metabolism presenting with intellectual disability as major feature'. We assessed levels of evidence of treatments and characterised the effect of treatments on IQ/development and related outcomes.

RESULTS

We identified a total of 81 'treatable inborn errors of metabolism' presenting with intellectual disability as a major feature, including disorders of amino acids (n=12), cholesterol and bile acid (n=2), creatine (n=3), fatty aldehydes (n=1); glucose homeostasis and transport (n=2); hyperhomocysteinemia (n=7); lysosomes (n=12), metals (n=3), mitochondria (n=2), neurotransmission (n=7); organic acids (n=19), peroxisomes (n=1), pyrimidines (n=2), urea cycle (n=7), and vitamins/co-factors (n=8). 62% (n=50) of all disorders are identified by metabolic screening tests in blood (plasma amino acids, homocysteine) and urine (creatine metabolites, glycosaminoglycans, oligosaccharides, organic acids, pyrimidines). For the remaining disorders (n=31) a 'single test per single disease' approach including primary molecular analysis is required. Therapeutic modalities include: sick-day management, diet, co-factor/vitamin supplements, substrate inhibition, stemcell transplant, gene therapy. Therapeutic effects include improvement and/or stabilisation of psychomotor/cognitive development, behaviour/psychiatric disturbances, seizures, neurologic and systemic manifestations. The levels of available evidence for the various treatments range from Level 1b,c (n=5); Level 2a,b,c (n=14); Level 4 (n=45), Level 4-5 (n=27). In clinical practice more than 60% of treatments with evidence level 4-5 is internationally accepted as 'standard of care'.

CONCLUSION

This literature review generated the evidence to prioritise treatability in the diagnostic evaluation of intellectual disability. Our results were translated into digital information tools for the clinician (www.treatable-id.org), which are part of a diagnostic protocol, currently implemented for evaluation of effectiveness in our institution. Treatments for these disorders are relatively accessible, affordable and with acceptable side-effects. Evidence for the majority of the therapies is limited however; international collaborations, patient registries, and novel trial methodologies are key in turning the tide for rare diseases such as these.

Aspectos clínicos e demográficos da fenilcetonúria no Estado da Bahia

OBJETIVO: Descrever as características clínicas e demográficas dos pacientes com diagnóstico de hiperfenilalaninemia acompanhados no Serviço de Referência em Triagem Neonatal da Bahia. MÉTODOS: Estudo transversal de 99 famílias (111 afetados) com fenótipo bioquímico de hiperfenilalaninemia, com coleta de dados em prontuários e em banco de dados laboratorial, incluindo aspectos demográficos e clínicos. RESULTADOS: A incidência de hiperfenilalaninemia na Bahia foi de um caso a cada 16.334 nascidos vivos, com cobertura de 91%. Dentre os pacientes acompanhados, 82% foram diagnosticados pela triagem neonatal e, em 11 famílias, havia mais de um caso. O fenótipo clássico da fenilcetonúria foi diagnosticado em 63 (57%) pacientes. Entre os triados, a mediana de idade na primeira consulta foi 39,5 dias e, deles, 34% apresentavam sintomatologia nesse momento; nenhum com atraso no desenvolvimento neuropsicomotor. A consanguinidade foi descrita em 32% dos casos e houve predomínio de pacientes classificados como brancos (63%). Os pais tinham baixa escolaridade e baixa renda. Dos 417 municípios da Bahia, 15% apresentavam pelo menos um caso, com concentração na região nordeste (10%) e na capital do Estado (14%). CONCLUSÕES: Os resultados evidenciaram idade tardia ao início do tratamento, o que pode comprometer os resultados do programa. Observou-se também presença de consanguinidade e recorrência familiar, reforçando a importância da investigação familiar para diagnosticar indivíduos com deficiência mental de etiologia não esclarecida que podem se beneficiar de tratamento.

A long-term study of bone mineral density in patients with phenylketonuria under diet therapy

INTRODUCTION

Dietary control of classic phenylketonuria (PKU) needs restriction of natural proteins; adequate protein intake is achieved by adding low phenylalanine (phe) formulae. The adequacy of this diet for normal bone mineralization had not been sufficiently evaluated. Our aim was to evaluate and follow up bone mineral density (BMD) in children and adolescents with PKU within a 2-year time interval to assess the adequacy of a phenylalanine restricted diet for bone mineralization and to search for a possible relationship between BMD, dietary control and blood phenylalanine (phe) concentrations.

MATERIAL AND METHODS

Thirty-two patients with classic PKU (3-19 years) were evaluated for their bone mineral status using dual energy X-ray absorptiometry (DEXA) both at the beginning (baseline) and the end (follow-up) of the study.

RESULTS

Low BMD was detected in 31.25% at the start and in 6.25% of patients after 2 years follows-up. No relationship was found between BMD and the duration of diet compliance and phe level as well.

CONCLUSIONS

In this study the low BMD detected in our patients was both at baseline and follow-up independent of diet restriction. A yearly DEXA would be highly beneficial for early detection and treatment, thus preventing osteoporosis and decreasing the risk of fractures. We also suggest the importance of searching for new emerging therapies such as enzyme substitution or gene therapy as low protein diet compliance was not enough to maintain normal bone mineral density.

Effects of creatine and β-guanidinopropionic acid and alterations in creatine transporter and creatine kinases expression in acute seizure and chronic epilepsy models

Background

In order to confirm the roles of creatine (Cr) in epilepsy, we investigated the anti-convulsive effects of Cr, creatine transporter (CRT) and creatine kinases (CKs) against chemical-induced acute seizure activity and chronic epileptic seizure activity.

Results

Two hr after pilocarpine (PILO)-seizure induction, ubiquitous mitochondrial CK (uMtCK) immunoreactivity was unaltered as compared to control level. However, brain-type cytoplasm CK (BCK) immunoreactivity was decreased to 70% of control level. CRT immunoreactivity was decreased to 60% of control level. Following Cr or Tat-CK treatment, uMtCK or CRT immunoreactivity was unaffected, while BCK immunoreactivity in Cr treated group was increased to 3.6-fold of control levels. β-Guanidinopropionic acid (GPA, a competitive CRT inhibitor) reduced BCK and CRT expression. In addition, Cr and tat-BCK treatment delayed the beginning of seizure activity after PILO injection. However, GPA treatment induced spontaneous seizure activity without PILO treatment. In chronic epilepsy rats, both uMtCK and CRT immunoreactivities were reduced in the hippocampus. In contrast, BCK immunoreactivity was similar to that observed in control animals. Cr-, GPA and tat-BCK treatment could not change EEG.

Conclusion

Cr/CK circuit may play an important role in sustaining or exacerbating acute seizure activity, but not chronic epileptic discharge.

Brain-derived neurotrophic factor inhibits phenylalanine-induced neuronal apoptosis by preventing RhoA pathway activation

Phenylketonuria (PKU) is neuropathologically characterized by neuronal cell loss, white matter abnormalities, dendritic simplification, and synaptic density reduction. The neuropathological effect may be due to the 'toxicity' of the high concentration of phenylalanine, while little is known about the related treatments to block this effect. In this study, we reported that brain-derived growth factor (BDNF) protected neurons from phenylalanine-induced apoptosis and inhibition of Trk receptor by K252a or downregulation of TrkB abrogated the effect of BDNF. We further demonstrated that phenylalanine-induced RhoA activation and myosin light chain phosphorylation were inhibited by pretreatment with BDNF, while phenylalanine activates the mitochondria-mediated apoptosis through the RhoA/Rho-associated kinase pathway. Thus our studies indicate that the protective effect of BDNF against phenylalanine-induced neuronal apoptosis is probably mediated by suppression of RhoA signaling pathway via TrkB receptor. Taken together, these findings suggest a potential neuroprotective action of BDNF in prevention and treatment of PKU brain injury.

Mental retardation and inborn errors of metabolism

In countries where clinical phenylketonuria is detected by newborn screening inborn errors of metabolism are rare causes of isolated mental retardation. There is no international agreement about what type of metabolic tests must be applied in patients with unspecific mental retardation. However, and although infrequent, there are a number of inborn errors of metabolism that can present in this way. Because of the high recurrence risk and the possibility of specific therapies, guidelines need to be developed and adapted to different populations. The application of a universal protocol may result in a low diagnostic performance in individual ethnic populations. Consideration of associated signs (extraneurological manifestations, psychiatric signs, autistic traits, cerebellar dysfunction, epilepsy or dysmorphic traits) greatly improves the diagnostic fulfilment.

Pilot use of the early motor repertoire in infants with inborn errors of metabolism: outcomes in early and middle childhood

BACKGROUND

Predicting later outcome in neonates presenting with severe inborn errors of metabolism (IEM) is difficult. The assessment of the early motor repertoire is a reliable method of evaluating the integrity of the central nervous system in young infants. This method is based on an age-specific qualitative assessment of general movements (GMs, 0-8 weeks of age), fidgety movements (FMs) and the concurrent motor repertoire (9-20 weeks of age).

AIM

To determine the quality of the early motor repertoire (at 0-20 weeks post term age) in relation to later neurological outcome in infants with severe IEM.

STUDY DESIGN

Prospective cohort study. The quality of the motor repertoire was assessed from serial videotape recordings.

SUBJECTS

Five infants with IEM. Four presented with a severe IEM in the neonatal period: an undefined gluconeogenesis defect, propionic acidemia, arginosuccinate synthetase and arginosuccinate lyase deficiency. One neonate was antenatally diagnosed with arginosuccinate synthetase deficiency.

OUTCOME MEASURES

Outcome at the age of at least 18 m was determined by neurological examination and developmental tests.

RESULTS

All infants initially had abnormal GMs: hypokinesia, followed by GMs of a poor repertoire. The quality of the early motor repertoire normalised in 3 infants, and remained abnormal in 2. The more severe and persistent abnormalities of the motor repertoire were considered with the more abnormal neurological and developmental scores, later on.

CONCLUSIONS

The quality of the early motor repertoire might be related to later neurological outcome in infants with inborn errors of metabolism.

Yield of additional metabolic studies in neurodevelopmental disorders

The timing and yield of metabolic studies for patients with neurodevelopmental disorders is a matter of continuing debate. We determined the yield of additional or repeated metabolic studies in patients with neurodevelopmental disorders. Patients referred to a tertiary diagnostic center for patients with unexplained neurodevelopmental disorders were included. Initial metabolic studies had been performed in most patients (87%) before referral. Additional/repeated metabolic studies were individually tailored. Twelve metabolic diseases of 433 patients studied (2.8%) were diagnosed, despite normal initial metabolic studies before referral. Specific metabolic investigations lead to a greater diagnostic yield in patients with neurodevelopmental disorders.

XLMR genes: update 2007

X-linked mental retardation (XLMR) is a common cause of inherited intellectual disability with an estimated prevalence of approximately 1/1000 males. Most XLMR conditions are inherited as X-linked recessive traits, although female carriers may manifest usually milder symptoms. We have listed 215 XLMR conditions, subdivided according to their clinical presentation: 149 with specific clinical findings, including 98 syndromes and 51 neuromuscular conditions, and 66 nonspecific (MRX) forms. We also present a map of the 82 XLMR genes cloned to date (November 2007) and a map of the 97 conditions that have been positioned by linkage analysis or cytogenetic breakpoints. We briefly consider the molecular function of known XLMR proteins and discuss the possible strategies to identify the remaining XLMR genes. Final remarks are made on the natural history of XLMR conditions and on diagnostic issues.

Metabolomics identifies perturbations in human disorders of propionate metabolism

BACKGROUND

We applied untargeted mass spectrometry-based metabolomics to the diseases methylmalonic acidemia (MMA) and propionic acidemia (PA).

METHODS

We used a screening platform that used untargeted, mass-based metabolomics of methanol-extracted plasma to find significantly different molecular features in human plasma samples from MMA and PA patients and from healthy individuals. Capillary reverse phase liquid chromatography (4 microL/min) was interfaced to a TOF mass spectrometer, and data were processed using nonlinear alignment software (XCMS) and an online database (METLIN) to find and identify metabolites differentially regulated in disease.

RESULTS

Of the approximately 3500 features measured, propionyl carnitine was easily identified as the best biomarker of disease (P value 1.3 x 10(-18)), demonstrating the proof-of-concept use of untargeted metabolomics in clinical chemistry discovery. Five additional acylcarnitine metabolites showed significant differentiation between plasma from patients and healthy individuals, and gamma-butyrobetaine was highly increased in a subset of patients. Two acylcarnitine metabolites and numerous unidentified species differentiate MMA and PA. Many metabolites that do not appear in any public database, and that remain unidentified, varied significantly between normal, MMA, and PA, underscoring the complex downstream metabolic effects resulting from the defect in a single enzyme.

CONCLUSIONS

This proof-of-concept study demonstrates that metabolomics can expand the range of metabolites associated with human disease and shows that this method may be useful for disease diagnosis and patient clinical evaluation.

Differential effects of phenylalanine on Rac1, Cdc42, and RhoA expression and activity in cultured cortical neurons

Phenylketonuria (PKU) is characterized by a high concentration of phenylalanine, which can lead to mental retardation. One of the characteristic pathologic changes in untreated phenylketonuria patients is a reduction in the number of axons, dendrites, and synapses in the brain. This is thought to be due to the toxic effects of phenylalanine and/or its metabolites, however, the underlying mechanism remains unclear. In this study, we observed that phenylalanine reduced the number of dendrites and dendritic spines in cultured neurons. We further demonstrated that phenylalanine down-regulated Rac1, Cdc42, and RhoA mRNA and protein expression. Pull-down assays indicated that phenylalanine caused a decrease in Rac1/Cdc42 activity but increased RhoA activity. Expression of a dominant negative RhoA or treatment with a Rho-associated kinase specific inhibitor, Y-27632, partly inhibited the phenylalanine-induced decrease in dendrite numbers. In conclusion, we have demonstrated that phenylalanine affects the expression and activity of Rac1, Cdc42, and RhoA. Furthermore, RhoA signaling is involved in the inhibitory effect of phenylalanine on dendritic branching. These results may provide an important insight into the molecular mechanism underlying phenylalanine-induced abnormalities of dendrites, specifically in phenylketonuria neuronal injury.

Phenylalanine activates the mitochondria-mediated apoptosis through the RhoA/Rho-associated kinase pathway in cortical neurons

Phenylketonuria (PKU) is caused by deficiency of phenylalanine hydroxylase, resulting in an accumulation of phenylalanine in brain tissue and cerebrospinal fluid of phenylketonuria patients. Phenylketonuria is neuropathologically characterized by neuronal cell loss, white matter abnormalities, dendritic simplification, and synaptic density reduction. The neuropathological effect may be due to the "toxicity" of the high concentration of phenylalanine, while the underlying mechanism remains unclear. In this study, we found that cultured cerebral cortical neurons underwent mitochondria-mediated apoptosis when exposed to phenylalanine. We further demonstrated that phenylalanine induced RhoA activation. Phenylalanine also promoted myosin light chain (MLC) phosphorylation, which might be the result of the activation of Rho-associated kinase (ROCK). The RhoA antagonist, C3 transferase (C3), Rho-associated kinase specific inhibitor, Y-27632, and the overexpression of either dominant negative RhoA or dominant negative Rho-associated kinase inhibited phenylalanine-induced caspase-3 activation and rescued neurons from apoptosis, indicating that the RhoA/Rho-associated kinase signalling pathway plays an important role in phenylalanine-induced neuronal apoptosis.

Peak bone mass in patients with phenylketonuria

OBJECTIVE

Several studies have suggested a compromised bone mass in phenylketonuria patients but most reported on heterogeneous or small patient groups. Our aim was to evaluate peak bone mass in adult PKU patients and to relate BMD to nutritional parameters.

PATIENTS AND METHODS

BMD was measured by dual-energy x-ray absorptiometry in 31 adult PKU patients (18 female), mean age 25 +/- 5.3 years. Nutritional intake was calculated based on food diaries. Diet adherence was determined based on patients' report.

RESULTS

Mean blood phenylalanine (Phe) concentration was 968 +/- 526 micromol/L (16 +/- 8.7 mg/dl). Eight patients (32.2%) met the recommended blood Phe concentration of <726 micromol/L (<12 mg/dl), and there was no significant difference in Phe concentrations between diet-adherent and non-adherent patients. Osteopenia was detected in 11 patients (38.7%), while osteoporosis was detected in 2 patients (6.5%). No correlation was found between BMD and age, blood minerals, Phe, vitamin D and alkaline phosphatase levels, calcium and protein intake, body mass index, and body fat percentage.

CONCLUSIONS

Peak bone mass is decreased in PKU patients. Possible explanations include long-standing dietary deficiency in protein, calcium, vitamin D or trace elements, or a primary defect in bone turnover inherent to the disease itself. Our data do not favour any of these hypotheses. Further studies are needed to elucidate the cause of low bone density in PKU patients.

Proteomic analysis of γ-butyrolactone-treated mouse thalamus reveals dysregulated proteins upon absence seizure

Absence seizure has been of interest because the symptom is related to sensory processing. However, the mechanism that causes the disease is not understood yet. To better understand the molecular mechanism related to the disease progress at protein level, we performed proteomic studies using the thalamus of mice for which absence seizure was induced by gamma-butyrolactone (GBL). Differential proteome expression between GBL-treated mice and control mice was examined by fluorescence 2D difference gel electrophoresis (DIGE) at three different time points (5, 10, and 30 min) after GBL-administration. We identified 16 proteins differentially expressed by >1.4-fold at any of the three time points. All proteins besides the serine protease inhibitor EIA were down-regulated in absence seizure-induced mice. The down-regulated proteins can be classified into five groups by their biological functions: cytoskeleton rearrangement, neuroprotection, neurotransmitter secretion, calcium binding, and metabolism. The maximum level of change was reached by 10 min after GBL-treatment, with the expression level returning back to the original at 30 min when mice were awakened from absence seizure thereby demonstrating the proteomic response is reversible. Our results suggest that absence seizures are associated with restricted functional sets of proteins, whose down-regulation may interfere with general function of neuronal cells.

A novel relationship between creatine transport at the blood-brain and blood-retinal barriers, creatine biosynthesis, and its use for brain and retinal energy homeostasis

Evidence is increasing that the creatine/phosphocreatine shuttle system plays an essential role in energy homeostasis in the brain and retina to ensure proper development and function. Thus, our understanding of the mechanism of creatine supply and creatine usage in the brain and retina and of creatine supplementation in patients with creatine deficiency syndromes is an important step towards improved therapeutic strategies for brain and retinal disorders. Our recent research provides novel molecular-anatomical evidence that (i) at the blood-brain barrier and the inner blood-retinal barrier, the creatine transporter (CRT/SLC6AS) functions as a major pathway for supplying creatine to the brain and retina, and that (ii) local creatine is preferentially synthesized in the glial cells, e.g., oligodendrocytes, astrocytes, and Müller cells, in the brain and retina. Thus, the blood-brain barrier and inner blood-retinal barrier play important roles not only in supplying energy sources (glucose and lactate), but also in supplying an energy 'buffer' (creatine). These findings lead to the novel insight that the creatine/phosphocreatine shuttle system is based on an intricate relationship between the blood-brain barrier, inner blood-retinal barrier, glia, and neurons (photoreceptor cells) to maintain and ensure energy homeostasis in the brain and retina.

Retention and loss of amino acid biosynthetic pathways based on analysis of whole-genome sequences

Plants and fungi can synthesize each of the 20 amino acids by using biosynthetic pathways inherited from their bacterial ancestors. However, the ability to synthesize nine amino acids (Phe, Trp, Ile, Leu, Val, Lys, His, Thr, and Met) was lost in a wide variety of eukaryotes that evolved the ability to feed on other organisms. Since the biosynthetic pathways and their respective enzymes are well characterized, orthologs can be recognized in whole genomes to understand when in evolution pathways were lost. The pattern of pathway loss and retention was analyzed in the complete genomes of three early-diverging protist parasites, the amoeba Dictyostelium, and six animals. The nine pathways were lost independently in animals, Dictyostelium, Leishmania, Plasmodium, and Cryptosporidium. Seven additional pathways appear to have been lost in one or another parasite, demonstrating that they are dispensable in a nutrition-rich environment. Our predictions of pathways retained and pathways lost based on computational analyses of whole genomes are validated by minimal-medium studies with mammals, fish, worms, and Dictyostelium. The apparent selective advantages of retaining biosynthetic capabilities for amino acids available in the diet are considered.

Aspectos clínicos da fenilcetonúria em serviço de referência em triagem neonatal da Bahia

OBJETIVOS: descrever as características clínicas dos pacientes com hiperfenilalaninemia acompanhados no Serviço de Referência em Triagem Neonatal (SRTN) do estado da Bahia. MÉTODOS: estudo descritivo transversal, tendo como amostra todos os pacientes com diagnóstico conhecido de Hiperfenilalaninemia residentes no estado da Bahia e acompanhados no SRTN até setembro de 2005. Tal população é composta de 46 famílias, num total de 51 pacientes. A análise dos dados foi descritiva, incluindo medidas de tendência central e dispersão. RESULTADOS: houve discreto predomínio do gênero feminino (52,9%). A maioria dos pacientes (78,4%) teve seu diagnóstico estabelecido através da triagem neonatal, tendo, portanto, tratamento precoce. Consangüinidade foi registrada em 32,6% das famílias. A média de início do tratamento entre os pacientes diagnosticados pela triagem neonatal foi de 56,6 37,8 dias, enquanto que entre os pacientes com diagnóstico tardio, foi de 7,1 anos. CONCLUSÕES: o estudo descreve um grupo de pacientes representativo de uma patologia incluída no Programa Nacional de Triagem Neonatal (PNTN), sendo, portanto, de relevância para a saúde pública. Entre os dados clínicos, chama a atenção a média de idade do início do tratamento, superior ao recomendado na literatura, alertando para a necessidade de um maior enfoque no diagnóstico precoce.

Neurodevelopmental disabilities: beyond the diagnosis

Increasingly clinicians are taking more active roles in the management of children with neurodevelopmental disorders. Management of these children extends beyond traditional boundaries of health. The purpose of this review is to provide clinicians with an approach to the management of children with neurodevelopmental disorders. Patient advocacy is crucial for effective practice when working with children with neurodevelopmental disabilities. An effective advocate understands how a child's impairments relate to his/her limitations and works to prevent barriers to participation. The advocate recognizes the multiple domains in a child's health and life that must be addressed. An overall management program should be developed in cooperation with the child's primary advocates, his/her family. There are multiple different therapies, each with its own goals, that should be coordinated and prioritized as part of this plan. Federal programs can provide some of these therapies for children.

Two novel mutations in SLC6A8 cause creatine transporter defect and distinctive X-linked mental retardation in two unrelated Dutch families

Four Dutch male patients, two brothers from unrelated families were referred for investigation of psychomotor and severe language/speech delay. All four patients showed growth deficiency over the years. Facial features and poor body habitus were quite similar in the patients and in their mothers. Brain MRI showed nonspecific periventricular white matter lesions. In all the patients neuropsychological tests revealed moderate mental retardation, attention deficit and hyperactivity with impulsivity, a semantic-pragmatic language disorder, and oral dyspraxia. This specific cognitive profile is different from other children with mental retardation syndromes and seems to be unique. Excretion of creatine to creatinine ratio in urine of the four boys was increased compared to controls and their creatine uptake in fibroblasts was deficient. In the two brothers from the first pedigree, DNA sequence analysis revealed a novel mutation in the splice donor site in intron 10 (IVS10 + 5G>C, c.1495 + 5G>C) of the SLC6A8 gene leading to skipping of exon 10. In the other sib pair a novel missense mutation (c. 1361C>T; p.Pro544Leu) was found. These are the first families reported, in which the clinical suspicion of a creatine transporter disorder was raised on clinical grounds, before a brain 1H-MRS suggested the diagnosis. Screening of apparently X-linked mental retarded patients with this somatic and behavioral phenotype by the biochemical assay of creatine to creatinine ratio in the urine or DNA sequence analysis of SLC6A8 is worthwhile even when 1H-MRS is not available.

Molecular and comparative genetics of mental retardation

Affecting 1-3% of the population, mental retardation (MR) poses significant challenges for clinicians and scientists. Understanding the biology of MR is complicated by the extraordinary heterogeneity of genetic MR disorders. Detailed analyses of >1000 Online Mendelian Inheritance in Man (OMIM) database entries and literature searches through September 2003 revealed 282 molecularly identified MR genes. We estimate that hundreds more MR genes remain to be identified. A novel test, in which we distributed unmapped MR disorders proportionately across the autosomes, failed to eliminate the well-known X-chromosome overrepresentation of MR genes and candidate genes. This evidence argues against ascertainment bias as the main cause of the skewed distribution. On the basis of a synthesis of clinical and laboratory data, we developed a biological functions classification scheme for MR genes. Metabolic pathways, signaling pathways, and transcription are the most common functions, but numerous other aspects of neuronal and glial biology are controlled by MR genes as well. Using protein sequence and domain-organization comparisons, we found a striking conservation of MR genes and genetic pathways across the approximately 700 million years that separate Homo sapiens and Drosophila melanogaster. Eighty-seven percent have one or more fruit fly homologs and 76% have at least one candidate functional ortholog. We propose that D. melanogaster can be used in a systematic manner to study MR and possibly to develop bioassays for therapeutic drug discovery. We selected 42 Drosophila orthologs as most likely to reveal molecular and cellular mechanisms of nervous system development or plasticity relevant to MR.

Distinct cellular expressions of creatine synthetic enzyme GAMT and creatine kinases uCK-Mi and CK-B suggest a novel neuron-glial relationship for brain energy homeostasis

The creatine/phosphocreatine shuttle system, as catalysed reversibly by creatine kinases, is thought to be essential for the storing and buffering of high phosphate-bound energy in tissues with high energy demand. In the present study, we aimed to clarify the cellular system of creatine biosynthesis and its energy metabolism in the mouse brain by immunohistochemistry for creatine biosynthetic enzyme S-adenosylmethionine:guanidinoacetate N-methyltransferase (GAMT), ubiquitous mitochondrial creatine kinase (uCK-Mi) and brain-type cytoplasmic creatine kinase (CK-B). GAMT was expressed highly in oligodendrocytes and olfactory ensheathing glia and moderately in astrocytes, whereas GAMT was very low in neurons and microglia. By contrast, uCK-Mi was expressed selectively in neurons and localized in their mitochondria in dendrites, cell bodies, axons and terminals. The distinct and almost complementary distribution of GAMT and uCK-Mi suggests that the creatine in neuronal mitochondria is derived not only from the circulation, but also from local glial cells associated with these neuronal elements. By contrast, CK-B was selective to astrocytes among glial populations, and was exclusive to inhibitory neurons among neuronal populations. Interestingly, these cells with high CK-B immunoreactivity are known to be highly resistant to acute energy loss, such as hypoxia and hypoglycemia. Considering that phosphocreatine generates ATP much faster than the processes of glycolysis and oxidative phosphorylation, the highly regulated cellular expressions of creatine biosynthetic and metabolic enzymes suggest that the creatine/phosphocreatine shuttle system plays a role in brain energy homeostasis through a novel neuron-glial relationship.

Dysmorphology diagnosis

A patient with multiple malformations poses a diagnostic dilemma to the pediatrician. There are thousands of malformation syndromes described and diagnosis of a syndrome appears a daunting task. An approach to diagnosis of a malformation syndrome is presented. Relevant details in the history and examination, important investigations, the process of differential diagnosis, and search engines used to aid in diagnosis of a malformation syndrome are described.

Temporal and regional differences in the olfactory proteome as a consequence of MeCP2 deficiency

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the gene encoding MeCP2. By binding to methylated CpG dinucleotide promoter regions, MeCP2 acts as a transcriptional repressor, predicting that its absence might result in widespread aberrant gene transcription, leading to the RTT phenotype. Considering this potentially broad action of MeCP2 on expression and the complexity of the brain, especially during development, we approached the consequences of MeCP2 deficiency in a mouse model by using a temporal and regional proteomic strategy. We used the olfactory system (olfactory epithelium and bulb) because its attributes make it an excellent developmental model system. We find evidence of temporal and regional proteomic pattern differences between WT and MeCP2-deficient mice. It was possible to segregate these changes in protein expression into five biological function groups: cytoskeleton arrangement, chromatin modeling, energy metabolism, cell signaling, and neuroprotection. By combining the proteomic results with the RNA levels of the identified proteins, we show that protein expression changes are the consequence of differences in mRNA level or posttranslational modifications. We conclude that brain regions and ages must be carefully considered when investigating MeCP2 deficiency, and that not only transcription should be taken into account as a source for these changes, but posttranslational protein modifications as well.

Molecular and Comparative Genetics of Mental Retardation

Affecting 1-3% of the population, mental retardation (MR) poses significant challenges for clinicians and scientists. Understanding the biology of MR is complicated by the extraordinary heterogeneity of genetic MR disorders. Detailed analyses of &gt;1000 Online Mendelian Inheritance in Man (OMIM) database entries and literature searches through September 2003 revealed 282 molecularly identified MR genes. We estimate that hundreds more MR genes remain to be identified. A novel test, in which we distributed unmapped MR disorders proportionately across the autosomes, failed to eliminate the well-known X-chromosome overrepresentation of MR genes and candidate genes. This evidence argues against ascertainment bias as the main cause of the skewed distribution. On the basis of a synthesis of clinical and laboratory data, we developed a biological functions classification scheme for MR genes. Metabolic pathways, signaling pathways, and transcription are the most common functions, but numerous other aspects of neuronal and glial biology are controlled by MR genes as well. Using protein sequence and domain-organization comparisons, we found a striking conservation of MR genes and genetic pathways across the ∼700 million years that separate Homo sapiens and Drosophila melanogaster. Eighty-seven percent have one or more fruit fly homologs and 76% have at least one candidate functional ortholog. We propose that D. melanogaster can be used in a systematic manner to study MR and possibly to develop bioassays for therapeutic drug discovery. We selected 42 Drosophila orthologs as most likely to reveal molecular and cellular mechanisms of nervous system development or plasticity relevant to MR.

Diagnostic evaluation of developmental delay/mental retardation: An overview

Mental retardation (MR) is one of the few clinically important disorders for which the etiopathogenesis is still poorly understood. It is a condition of great concern for public health and society. MR is currently defined as a significant impairment of cognitive and adaptive functions, with onset before age 18 years. It may become evident during infancy or early childhood as developmental delay (DD), but it is best diagnosed during the school years. MR is estimated to occur in 1-10% of the population, and research on its etiology has always been a challenge in medicine. The etiopathogenesis encompasses so many different entities that the attending physician can sometimes feel a "virtual panic," starting a wide-range diagnostic evaluation. The Consensus Conference of the American College of Medical Genetics has recently established guidelines regarding the evaluation of patients with MR [Curry et al., 1997], emphasizing the high diagnostic utility of cytogenetic studies and neuroimaging in certain clinical settings. However, since then there has been substantial progress in molecular cytogenetics and neuroimaging techniques, the use of which has allowed recognition and definition of new disorders, thus increasing the diagnostic yield. This review will focus on the most appropriate investigations shown to be, at present, necessary to define the etiology of DD/MR, in the context of recommendations for the clinical evaluation of the patient with undiagnosed MR.