Biochemical correlates of neuropsychiatric illness in maple syrup urine disease

The interplay of psychosis and non-compliance with fatal outcome in an adult with MSUD

Significant progress has been achieved in enhancing early outcomes for individuals with maple syrup urine disease (MSUD), a rare metabolic disorder that leads to the accumulation of branched-chain amino acids leucine, isoleucine, and valine, where leucine is known as the primary neurotoxic metabolite. Newborn screening is helpful in early diagnosis and implementation of dietary treatment, thus reducing neurological deterioration and complications in young children. However, patients face the life-long challenge of maintaining metabolic control through adherence to a strict low-leucine diet to avoid long-term consequences of chronic hyperleucinemia, which include cognitive deficits, mood disorders, and movement disorders. This case report exemplifies the complex involvement of MSUD in adult survivors. Despite presenting early in life, the patient thrived until the onset of psychiatric symptoms. The subject of this case is a 25-year-old woman with MSUD, who remained in her usual state of health until presentation to the emergency department (ED) with psychosis and altered mental status. However, due to a lack of medical records and poor communication, there was a delay in considering MSUD as a primary cause of her psychiatric symptoms. Although a genetics consultation was later arranged and efforts were made to decrease plasma leucine to the therapeutic range, these interventions proved inadequate in halting her deterioration in health. Her condition worsened within 72 h, culminating in her untimely death. This case emphasizes the comorbidity of psychiatric involvement in MSUD, which contributes to metabolic decompensation that can lead to cerebral edema and death. This case also highlights the pressing need for enhanced strategies for the acute management and long-term care of MSUD patients with psychiatric involvement, particularly in scenarios where mental disturbance could lead to noncompliance.

Treatment Outcomes for Maple Syrup Urine Disease Detected by Newborn Screening

OBJECTIVE

Maple syrup urine disease (MSUD), a life-threatening metabolic disorder, is included in newborn screening (NBS) programs worldwide. The study aims to evaluate the impact of NBS on the long-term outcome of MSUD patients.

METHODS

We performed a prospective, national, multicenter, observational study.

RESULTS

In the studied NBS cohort (N = 33; 22 classic MSUD [cMSUD], 11 variant MSUD [vMSUD]; median age at last visit 10.4 years), 32 (97%) patients survived, 58% of them had normal cognitive functions (median IQ 87). Initial peak leucine increased linearly with age in cMSUD (median: 1712 µmol/L), but not in vMSUD. Global IQ correlated inversely with the initial peak leucine concentration (P = .04; β = -0.0081) and the frequency of decompensations (P = .02; β = -9.133). A cluster analysis identified 2 subgroups differing in their long-term metabolic control (median leucine concentration: 162 vs 278 µmol/L; P < .001). In cMSUD, lower leucine concentrations were associated with a higher IQ (95.5 vs 80; P = .008). Liver transplantation (median age 5.8 years) was not associated with better cognitive outcome. NBS is highly sensitive for cMSUD, but vMSUD might be missed (N = 2 missed by NBS).

CONCLUSIONS

NBS and the early start of treatment improve survival and long-term outcome in individuals with cMSUD. Disease severity is an important modifier of outcome; however, the time to NBS report and the quality of long-term metabolic control had an independent impact on cognitive outcome, highlighting the importance of an early diagnosis and the quality of treatment.

Liver gene transfer for metabolite detoxification in inherited metabolic diseases

Inherited metabolic disorders (IMDs) are a growing group of genetic diseases caused by defects in enzymes that mediate cellular metabolism, often resulting in the accumulation of toxic substrates. The liver is a highly metabolically active organ that hosts several thousands of chemical reactions. As such, it is an organ frequently affected in IMDs. In this article, we review current approaches for liver-directed gene-based therapy aimed at metabolite detoxification in a variety of IMDs. Moreover, we discuss current unresolved challenges in gene-based therapies for IMDs.

In Vivo Intracerebral Administration of α-Ketoisocaproic Acid to Neonate Rats Disrupts Brain Redox Homeostasis and Promotes Neuronal Death, Glial Reactivity, and Myelination Injury

Maple syrup urine disease (MSUD) is caused by severe deficiency of branched-chain α-keto acid dehydrogenase complex activity, resulting in tissue accumulation of branched-chain α-keto acids and amino acids, particularly α-ketoisocaproic acid (KIC) and leucine. Affected patients regularly manifest with acute episodes of encephalopathy including seizures, coma, and potentially fatal brain edema during the newborn period. The present work investigated the ex vivo effects of a single intracerebroventricular injection of KIC to neonate rats on redox homeostasis and neurochemical markers of neuronal viability (neuronal nuclear protein (NeuN)), astrogliosis (glial fibrillary acidic protein (GFAP)), and myelination (myelin basic protein (MBP) and 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase)) in the cerebral cortex and striatum. KIC significantly disturbed redox homeostasis in these brain structures 6 h after injection, as observed by increased 2',7'-dichlorofluorescein oxidation (reactive oxygen species generation), malondialdehyde levels (lipid oxidative damage), and carbonyl formation (protein oxidative damage), besides impairing the antioxidant defenses (diminished levels of reduced glutathione and altered glutathione peroxidase, glutathione reductase, and superoxide dismutase activities) in both cerebral structures. Noteworthy, the antioxidants N-acetylcysteine and melatonin attenuated or normalized most of the KIC-induced effects on redox homeostasis. Furthermore, a reduction of NeuN, MBP, and CNPase, and an increase of GFAP levels were observed at postnatal day 15, suggesting neuronal loss, myelination injury, and astrocyte reactivity, respectively. Our data indicate that disruption of redox homeostasis, associated with neural damage caused by acute intracerebral accumulation of KIC in the neonatal period may contribute to the neuropathology characteristic of MSUD patients.

Memantine Improves Memory and Neurochemical Damage in a Model of Maple Syrup Urine Disease

Maple Syrup Urine Disease (MSUD) is a metabolic disease characterized by the accumulation of branched-chain amino acids (BCAA) in different tissues due to a deficit in the branched-chain alpha-ketoacid dehydrogenase complex. The most common symptoms are poor feeding, psychomotor delay, and neurological damage. However, dietary therapy is not effective. Studies have demonstrated that memantine improves neurological damage in neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. Therefore, we hypothesize that memantine, an NMDA receptor antagonist can ameliorate the effects elicited by BCAA in an MSUD animal model. For this, we organized the rats into four groups: control group (1), MSUD group (2), memantine group (3), and MSUD + memantine group (4). Animals were exposed to the MSUD model by the administration of BCAA (15.8 µL/g) (groups 2 and 4) or saline solution (0.9%) (groups 1 and 3) and treated with water or memantine (5 mg/kg) (groups 3 and 4). Our results showed that BCAA administration induced memory alterations, and changes in the levels of acetylcholine in the cerebral cortex. Furthermore, induction of oxidative damage and alterations in antioxidant enzyme activities along with an increase in pro-inflammatory cytokines were verified in the cerebral cortex. Thus, memantine treatment prevented the alterations in memory, acetylcholinesterase activity, 2',7'-Dichlorofluorescein oxidation, thiobarbituric acid reactive substances levels, sulfhydryl content, and inflammation. These findings suggest that memantine can improve the pathomechanisms observed in the MSUD model, and may improve oxidative stress, inflammation, and behavior alterations.

Successful treatment of severe MSUD in Bckdhb-/- mice with neonatal AAV gene therapy

Maple syrup urine disease (MSUD) is rare autosomal recessive metabolic disorder caused by the dysfunction of the mitochondrial branched-chain 2-ketoacid dehydrogenase (BCKD) enzyme complex leading to massive accumulation of branched-chain amino acids and 2-keto acids. MSUD management, based on a life-long strict protein restriction with nontoxic amino acids oral supplementation represents an unmet need as it is associated with a poor quality of life, and does not fully protect from acute life-threatening decompensations or long-term neuropsychiatric complications. Orthotopic liver transplantation is a beneficial therapeutic option, which shows that restoration of only a fraction of whole-body BCKD enzyme activity is therapeutic. MSUD is thus an ideal target for gene therapy. We and others have tested AAV gene therapy in mice for two of the three genes involved in MSUD, BCKDHA and DBT. In this study, we developed a similar approach for the third MSUD gene, BCKDHB. We performed the first characterization of a Bckdhb-/- mouse model, which recapitulates the severe human phenotype of MSUD with early-neonatal symptoms leading to death during the first week of life with massive accumulation of MSUD biomarkers. Based on our previous experience in Bckdha-/- mice, we designed a transgene carrying the human BCKDHB gene under the control of a ubiquitous EF1α promoter, encapsidated in an AAV8 capsid. Injection in neonatal Bckdhb-/- mice at 1014  vg/kg achieved long-term rescue of the severe MSUD phenotype of Bckdhb-/- mice. These data further validate the efficacy of gene therapy for MSUD opening perspectives towards clinical translation.

Oral enzyme therapy for maple syrup urine disease (MSUD) suppresses plasma leucine levels in intermediate MSUD mice and healthy nonhuman primates

Maple syrup urine disease (MSUD) is an inborn error of branched-chain amino acid metabolism affecting several thousand individuals worldwide. MSUD patients have elevated levels of plasma leucine and its metabolic product α-ketoisocaproate (KIC), which can lead to severe neurotoxicity, coma, and death. Patients must maintain a strict diet of protein restriction and medical formula, and periods of noncompliance or illness can lead to acute metabolic decompensation or cumulative neurological impairment. Given the lack of therapeutic options for MSUD patients, we sought to develop an oral enzyme therapy that can degrade leucine within the gastrointestinal tract prior to its systemic absorption and thus enable patients to maintain acceptable plasma leucine levels while broadening their access to natural protein. We identified a highly active leucine decarboxylase enzyme from Planctomycetaceae bacterium and used directed evolution to engineer the enzyme for stability to gastric and intestinal conditions. Following high-throughput screening of over 12 000 enzyme variants over 9 iterative rounds of evolution, we identified a lead variant, LDCv10, which retains activity following simulated gastric or intestinal conditions in vitro. In intermediate MSUD mice or healthy nonhuman primates given a whey protein meal, oral treatment with LDCv10 suppressed the spike in plasma leucine and KIC and reduced the leucine area under the curve in a dose-dependent manner. Reduction in plasma leucine correlated with decreased brain leucine levels following oral LDCv10 treatment. Collectively, these data support further development of LDCv10 as a potential new therapy for MSUD patients.

Treatment of maple syrup urine disease: Benefits, risks, and challenges of liver transplantation

Maple syrup urine disease (MSUD) is caused by a deficiency in the activity of the branched-chain α-ketoacid dehydrogenase (BCKD) complex, promoting the accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine, and valine, as well as their respective α-keto acids. MSUD is an autosomal recessive hereditary metabolic disorder characterized by ketoacidosis, ataxia, coma, and mental and psychomotor retardation. The mechanisms involved in the brain damage caused by MSUD are not fully understood. Early diagnosis and treatment, as well as proper control of metabolic decompensation crises, are crucial for patients' survival and for a better prognosis. The recommended treatment consists of a high-calorie diet with restricted protein intake and specific formulas containing essential amino acids, except those accumulated in MSUD. This treatment will be maintained throughout life, being adjusted according to the patients' nutritional needs and BCAA concentration. Because dietary treatment may not be sufficient to prevent neurological damage in MSUD patients, other therapeutic strategies have been studied, including liver transplantation. With transplantation, it is possible to obtain an increase of about 10% of the normal BCKD in the body, an amount sufficient to maintain amino acid homeostasis and reduce metabolic decompensation crises. However, the experience related to this practice is very limited when considering the shortage of liver for transplantation and the risks related to the surgical procedure and immunosuppression. Thus, the purpose of this review is to survey the benefits, risks, and challenges of liver transplantation in the treatment of MSUD.

Melatonin improves behavioral parameters and oxidative stress in zebrafish submitted to a leucine-induced MSUD protocol

Maple syrup urine disease (MSUD) is an inherited metabolic disorder caused by a deficiency in branched-chain alpha-ketoacid dehydrogenase complex (BCKAC). The treatment is a standard therapy based on a protein-restricted diet with low branched-chain amino acids (BCAA) content to reduce plasma levels and, consequently, the effects of accumulating their metabolites, mainly in the central nervous system. Although the benefits of dietary therapy for MSUD are undeniable, natural protein restriction may increase the risk of nutritional deficiencies, resulting in a low total antioxidant status that can predispose and contribute to oxidative stress. As MSUD is related to redox and energy imbalance, melatonin can be an important adjuvant treatment. Melatonin directly scavenges the hydroxy radical, peroxyl radical, nitrite anion, and singlet oxygen and indirectly induces antioxidant enzyme production. Therefore, this study assesses the role of melatonin treatment on oxidative stress in brain tissue and behavior parameters of zebrafish (Danio rerio) exposed to two concentrations of leucine-induced MSUD: leucine 2 mM and 5mM; and treated with 100 nM of melatonin. Oxidative stress was assessed through oxidative damage (TBARS, DCF, and sulfhydryl content) and antioxidant enzyme activity (SOD and CAT). Melatonin treatment improved redox imbalance with reduced TBARS levels, increased SOD activity, and normalized CAT activity to baseline. Behavior was analyzed with novel object recognition test. Animals exposed to leucine improved object recognition due to melatonin treatment. With the above, we can suggest that melatonin supplementation can protect neurologic oxidative stress, protecting leucine-induced behavior alterations such as memory impairment.

Exposure to leucine alters glutamate levels and leads to memory and social impairment in zebrafish

Maple Syrup Urine Disease (MSUD) is a metabolic disorder characterized by high levels in blood and urine of branched-chain amino acids leucine, isoleucine, and valine and their alpha-ketoacids, by a partial or total blockade in the activity of branched-chain complex alpha-keto acids dehydrogenase. The main symptoms in MSUD occur in the central nervous system, including cognitive deficits, locomotor, poor feeding, seizures, psychomotor delay, and mental retardation, but the mechanisms of neurotoxicity and behavior alteration due to this disease are poorly understood, thus this study aimed at showing the effects of leucine exposure on glutamate levels and behavior in zebrafish. For this, we analyzed the behavior using the social preference test and novel object recognition test, moreover, we analyse the glutamate levels and uptake using scintillation and high-performance liquid chromatography methods. Our results demonstrated a decrease in glutamate levels and uptake, accompanied by memory and social impairment. In conclusion, these results suggest that alterations in glutamate levels can be associated with behavior impairment, however, more studies are necessary to understand the mechanisms for brain damage in MSUD.

Genomic and biochemical analysis of repeatedly observed variants in DBT in individuals with maple syrup urine disease of Central American ancestry

Maple syrup urine disease (MSUD) is an intoxication-type inherited metabolic disorder in which hyperleucinemia leads to brain swelling and death without treatment. MSUD is caused by branched-chain alpha-ketoacid dehydrogenase deficiency due to biallelic loss of the protein products from the genes BCKDHA, BCKDHB, or DBT, while a distinct but related condition is caused by loss of DLD. In this case series, eleven individuals with MSUD caused by two pathogenic variants in DBT are presented. All eleven individuals have a deletion of exon 2 (delEx2, NM_001918.3:c.48_171del); six individuals are homozygous and five individuals are compound heterozygous with a novel missense variant (NM_001918.5:c.916 T > C [p.Ser306Pro]) confirmed to be in trans. Western Blot indicates decreased amount of protein product in delEx2;c.916 T > C liver cells and absence of protein product in delEx2 homozygous hepatocytes. Ultrahigh performance liquid chromatography-tandem mass spectrometry demonstrates an accumulation of branched-chain amino acids and alpha-ketoacids in explanted hepatocytes. Individuals with these variants have a neonatal-onset, non-thiamine-responsive, classical form of MSUD. Strikingly, the entire cohort is derived from families who immigrated to the Washington, DC, metro area from Honduras or El Salvador suggesting the possibility of a founder effect.

Maple syrup urine disease decompensation misdiagnosed as a psychotic event

Maple syrup urine disease (MSUD) is an autosomal recessive metabolic disease resulting in impaired or absent breakdown of branched-chain amino acids (BCAA) valine, isoleucine, and leucine. Classic MSUD often presents in post-natal periods, at times before newborn screening results, and is treated with a protein restricted diet supplemented with medical food and close follow up to prevent toxic buildup of blood leucine.

Acute episodes of decompensation are prevented by early recognition and treatment. Acute episodes of metabolic decompensation in patients with MSUD are medical emergencies that require immediate treatments as cerebral edema may lead to brain-stem compression resulting in death. As the early outcomes improve for MSUD patients, the long-term sequelae of chronic hyperleucemia are being elucidated and include cognitive impairment, mental health disorders, and movement disorders.

In this report we present an adult patient with MSUD with attention deficit, hyperactivity type (ADHD) and depression due to prolonged exposure to elevated leucine managed with community support services who presented to the emergency department with new onset of acute hallucinations. He was held in the emergency department awaiting involuntary commitment to a psychiatric facility and underwent psychiatric treatments for suspected new onset hallucinations without improvement. Upon notification of metabolic specialists and initiation of appropriate therapy of MSUD, his leucine level normalized rapidly with resolution of his acute psychosis.

This case describes the acute presentation of psychosis in the setting of long-term toxicity of leucine. This case also highlights the importance of transition of care, education and planning in patients with inborn errors of metabolism.

Novel Gene-Correction-Based Therapeutic Modalities for Monogenic Liver Disorders

The majority of monogenic liver diseases are autosomal recessive disorders, with few being sex-related or co-dominant. Although orthotopic liver transplantation (LT) is currently the sole therapeutic option for end-stage patients, such an invasive surgical approach is severely restricted by the lack of donors and post-transplant complications, mainly associated with life-long immunosuppressive regimens. Therefore, the last decade has witnessed efforts for innovative cellular or gene-based therapeutic strategies. Gene therapy is a promising approach for treatment of many hereditary disorders, such as monogenic inborn errors. The liver is an organ characterized by unique features, making it an attractive target for in vivo and ex vivo gene transfer. The current genetic approaches for hereditary liver diseases are mediated by viral or non-viral vectors, with promising results generated by gene-editing tools, such as CRISPR-Cas9 technology. Despite massive progress in experimental gene-correction technologies, limitations in validated approaches for monogenic liver disorders have encouraged researchers to refine promising gene therapy protocols. Herein, we highlighted the most common monogenetic liver disorders, followed by proposed genetic engineering approaches, offered as promising therapeutic modalities.

Neonatal gene therapy achieves sustained disease rescue of maple syrup urine disease in mice

Maple syrup urine disease (MSUD) is a rare recessively inherited metabolic disorder causing accumulation of branched chain amino acids leading to neonatal death, if untreated. Treatment for MSUD represents an unmet need because the current treatment with life-long low-protein diet is challenging to maintain, and despite treatment the risk of acute decompensations and neuropsychiatric symptoms remains. Here, based on significant liver contribution to the catabolism of the branched chain amino acid leucine, we develop a liver-directed adeno-associated virus (AAV8) gene therapy for MSUD. We establish and characterize the Bckdha (branched chain keto acid dehydrogenase a)^−/− mouse that exhibits a lethal neonatal phenotype mimicking human MSUD. Animals were treated at P0 with intravenous human BCKDHA AAV8 vectors under the control of either a ubiquitous or a liver-specific promoter. BCKDHA gene transfer rescued the lethal phenotype. While the use of a ubiquitous promoter fully and sustainably rescued the disease (long-term survival, normal phenotype and correction of biochemical abnormalities), liver-specific expression of BCKDHA led to partial, though sustained rescue. Here we show efficacy of gene therapy for MSUD demonstrating its potential for clinical translation.

Maple syrup urine disease (MSUD) is a rare inborn error of metabolism, which is currently treated with life-long low-protein diet that can be challenging to maintain. Here the authors develop an AAV8-directed gene therapy providing sustainable disease rescue in a mouse model of MSUD.

Coadministration of tianeptine alters behavioral parameters and levels of neurotrophins in a chronic model of Maple Syrup Urine disease

Maple Syrup Urine Disease (MSUD) is caused by the deficiency in the activity of the branched-chain α-ketoacid dehydrogenase complex (BCKDC), resulting in the accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine, and valine, and their respective branched-chain α-keto acids. Patients with MSUD are at high risk of developing chronic neuropsychiatric disorders; however, the pathophysiology of brain damage in these patients remains unclear. We hypothesize that MSUD can cause depressive symptoms in patients. To test our hypothesis, Wistar rats were submitted to the BCAA and tianeptine (antidepressant) administration for 21 days, starting seven days postnatal. Depression-like symptoms were assessed by testing for anhedonia and forced swimming after treatments. After the last test, the brain structures were dissected for the evaluation of neutrophins. We demonstrate that chronic BCAA administration induced depressive-like behavior, increased BDNF levels, and decreased NGF levels, suggesting a relationship between BCAA toxicity and brain damage, as observed in patients with MSUD. However, the administration of tianeptine was effective in preventing behavioral changes and restoring neurotrophins levels.

ADHD symptoms in neurometabolic diseases: Underlying mechanisms and clinical implications

Neurometabolic diseases (NMDs) are typically caused by genetic abnormalities affecting enzyme functions, which in turn interfere with normal development and activity of the nervous system. Although the individual disorders are rare, NMDs are collectively relatively common and often lead to lifelong difficulties and high societal costs. Neuropsychiatric manifestations, including ADHD symptoms, are prominent in many NMDs, also when the primary biochemical defect originates in cells and tissues outside the nervous system. ADHD symptoms have been described in phenylketonuria, tyrosinemias, alkaptonuria, succinic semialdehyde dehydrogenase deficiency, X-linked ichthyosis, maple syrup urine disease, and several mitochondrial disorders, but are probably present in many other NMDs and may pose diagnostic and therapeutic challenges. Here we review current literature linking NMDs with ADHD symptoms. We cite emerging evidence that many NMDs converge on common neurochemical mechanisms that interfere with monoamine neurotransmitter synthesis, transport, metabolism, or receptor functions, mechanisms that are also considered central in ADHD pathophysiology and treatment. Finally, we discuss the therapeutic implications of these findings and propose a path forward to increase our understanding of these relationships.

Metabolic Control and "Ideal" Outcomes in Liver Transplantation for Maple Syrup Urine Disease

OBJECTIVES

To assess outcomes following liver transplantation for maple syrup urine disease by determining attainment and sustainability of metabolic control and apply an "ideal" outcome composite in long-term survivors.

STUDY DESIGN

A single center, retrospective review collected clinical data including branched-chain amino acid (leucine, isoleucine, and valine) levels following liver transplant and determined achievement of an ideal long-term outcome profile of a first allograft stable on immunosuppression monotherapy, normal growth, and absence of common transplant-related sequelae.

RESULTS

Of 77 patients meeting inclusion criteria identified, 23 were long-term (≥10-year) survivors and were additionally assessed for ideal outcome attainment. Patient and graft survival were 100% and 99%, respectively, and all patients were on an unrestricted protein intake diet. Although significant variation was noted in mean isoleucine (P < .01) and leucine (P < .05) levels postliver transplantation, no difference was seen in valine (P = .29) and overall clinical impact was likely negligible as metabolic stability was achieved and sustained beyond 3 years postliver transplantation and no metabolic crises were identified. Of 23 long-term survivors with available data, 9 (39%) achieved all composite metrics determined to define "ideal" outcomes in pediatric postliver transplantation populations.

CONCLUSIONS

Liver transplant enables long-term metabolic stability for patients with maple syrup urine disease. A combination of experience and improvement in both pre- and postliver transplantation care has enabled excellent survival and minimal comorbidities following transplant.

Orthopaedic Manifestations of Inborn Errors of Metabolism

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Inborn errors of metabolism are disorders of carbohydrate, amino acid, organic acid, or purine and pyrimidine metabolism; disorders of fatty acid oxidation; disorders of metal metabolism; and lysosomal storage defects that can cause metabolic derangements that have secondary musculoskeletal effects.

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Orthopaedic surgeons should be aware that patients with inborn errors of metabolism may be at high risk for spasticity, which may cause joint subluxations, scoliosis, and contractures, as well as poor bone quality, which is caused by malnutrition or disordered bone growth.

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Multidisciplinary care and follow-up are important to identify musculoskeletal problems in a timely manner in order to provide effective treatment.

Orthopaedic Problems in 35 Patients With Organic Acid Disorders

INTRODUCTION

Organic acid disorders (OADs) are a subset of inborn errors of metabolism that result in a toxic accumulation of organic acids in the body, which can lead to metabolic derangements and encephalopathy. Patients with these disorders are managed by a team of biochemical geneticists and metabolic nutritionists. However, subspecialists such as neurologists and orthopaedic surgeons are often needed to help manage the sequelae of the metabolic derangements. The breadth of orthopaedic sequelae of these disease states is poorly understood. Herein, we describe orthopaedic problems associated with 5 types of OAD most commonly seen at our institution: maple syrup urine disease, methylmalonic aciduria, propionic aciduria, pyruvate dehydrogenase deficiency, and glutaric aciduria type 1.

METHODS

We retrospectively reviewed medical records of 35 patients with an OAD who were seen at our academic tertiary care center from May 1999 to May 2020. Patients were grouped into cohorts according to OAD type and analyzed for orthopaedic presentations of hip, knee, or foot disorders, presence and severity of scoliosis, history of fracture, movement disorders, and osteopenia/osteoporosis.

RESULTS

Of the 35 patients, 13 had maple syrup urine disease, 12 had methylmalonic aciduria, 4 had propionic aciduria, 4 had pyruvate dehydrogenase deficiency, and 2 had glutaric aciduria type 1. Associated orthopaedic problems included spasticity causing neuromuscular scoliosis and/or hip subluxation or dislocation (10 patients), fractures (7 patients), and osteopenia/osteoporosis (7 patients). Overall, 22 of 35 patients had some orthopaedic condition.

CONCLUSIONS

Most in this cohort of patients with OAD also had an orthopaedic abnormality. It is important for physicians treating these patients to understand their propensity for musculoskeletal problems. When treating patients with OAD, it is important to initiate and maintain communication with specialists in several disciplines and to develop collaborative treatments for this unique population.

LEVEL OF EVIDENCE

Level IV-prognostic study.

Maternal and cord plasma branched-chain amino acids and child risk of attention-deficit hyperactivity disorder: a prospective birth cohort study

BACKGROUND

Branched-chain amino acids (BCAA: leucine, isoleucine, and valine) are essential amino acids involved in biological functions of brain development and recently linked with autism. However, their role in attention-deficit hyperactivity disorder (ADHD) is not well-studied. We investigated individual and combined relationships of maternal plasma and newborn cord plasma BCAAs with childhood development of ADHD.

METHODS

We utilized the Boston Birth Cohort, a predominantly urban, low-income, US minority population. Child developmental outcomes were defined in three mutually exclusive groups - ADHD, neurotypical (NT), or other developmental disabilities based on physician diagnoses per ICD-9 or 10 in medical records. The final sample included 626 children (299 ADHD, 327 NT) excluding other developmental disabilities. BCAAs were measured by liquid chromatography-tandem mass spectrometry. We used factor analysis to create composite scores of maternal and cord BCAA, which we divided into tertiles. Logistic regressions analyzed relationships between maternal or cord BCAA tertiles with child ADHD risk, controlling for maternal race, age, parity, smoking, education, low birth weight, preterm birth, and child sex. Additionally, we analyzed maternal and cord plasma BCAAs jointly on child ADHD risk.

RESULTS

Adjusted logistic regression found significantly increased odds of child ADHD diagnosis for the second (OR 1.63, 95% CI: 1.04, 2.54, p = .032) and third tertiles (OR 2.01, 95% CI: 1.28, 3.15, p = .002) of cord BCAA scores compared to the first tertile. This finding held for the third tertile when further adjusting for maternal BCAA score. There was no significant association between maternal BCAA score and child ADHD risk, nor a significant interaction between maternal and cord BCAA scores.

CONCLUSIONS

In this prospective US birth cohort, higher cord BCAA levels were associated with a greater risk of developing ADHD in childhood. These results have implications for further research into mechanisms of ADHD development and possible early life screening and interventions.

Brain magnetic resonance imaging findings and radiologic review of maple syrup urine disease: Report of three cases

BACKGROUND

Maple syrup urine disease (MSUD) is a rare autosomal-recessive disorder that affects branched-chain amino acid (BCAA) metabolism and is named after the distinctive sweet odor of affected infants’ urine. This disease is characterized by the accumulation of BCAAs and corresponding branched-chain ketoacids of leucine, isoleucine, and valine in the plasma, urine, and cerebrospinal fluid. However, the mechanisms of MSUD-induced brain damage remain poorly defined. The accumulation of BCAAs in the brain inhibits the activity of pyruvate dehydrogenase and α-ketoglutarate, disrupting the citric acid cycle and consequently impacting the synthesis of amino acids, causing cerebral edema and abnormal myelination.

CASE SUMMARY

We report three neonates admitted to our hospital with the classic subtype of MSUD. All three patients, with a transient normal period, presented with poor feeding, vomiting, poor weight gain, and increasing lethargy after birth. Laboratory testing revealed metabolic acidosis. The serum tandem mass spectrometry amino acid profile showed elevated plasma levels of BCAAs (leucine, isoleucine, and valine). Brain magnetic resonance imaging (MRI) presented abnormal signals mainly involving the globus pallidus, thalamus, internal capsule, brainstem, and cerebellar white matter, which represent the typical myelinated areas in normal full-term neonates.

CONCLUSION

In our patients, MRI showed typical features, in concordance with the available literature. Early detection and timely treatment are very helpful for the prognosis of MSUD patients. Therefore, we discuss the neuroimaging features of MSUD to enhance the knowledge of pediatricians about this disease.

International classification of functioning, disability and health framework (ICF) based adaptive functioning outcomes of children with organic acidemias from a middle-income country

OBJECTIVE

The World Health Organization International Classification of Functioning, Disability and Health Framework (ICF) states that a child's health conditions, functions, activities, participation in life and contextual factors shape disability. Research on the development of children with organic acidemias (OA) mostly focused on cognitive and medical outcomes. This study aimed to examine adaptive functioning of children with OAs based on ICF.

METHODS

In this cross-sectional study, children with propionic academia, methylmalonic acidemia and maple syrup urine disease receiving care at Ankara University School of Medicine, Department of Pediatrics, Pediatric Metabolism Division were recruited. Comprehensive developmental assessments included ICF-based methods. Adaptive functioning was measured with Vineland Adaptive Behavior Scales-Second Edition.

RESULTS

The sample comprised 22 children with a median age of 47.5 months (IQR: 35-73.5). Most mothers (64%) had less than 5 years of education, half had depression. Two children (9%) were attending to school, 14 (64%) were not regularly playing with friends. Fourteen children (64%) had significant communication delays, 12 (55%) had significant problems in daily living skills, and 12 (55%) in social skills. Mean adaptive behavior composite score was 65.5 ± 16.8 (low), children with feeding disorders had significantly more low adaptive behavior composite scores than children with no feeding disorder diagnosis (p = 0.001).

CONCLUSIONS

Our results imply that children with OAs from Turkey, a middle-income country had major difficulties in functioning, activities, participation and contextual factors. Feeding problems appeared as a risk factor for lower adaptive functioning. ICF-based assessments and interventions are urgently needed in the management of children with OAs.

Administration of branched-chain amino acids alters epigenetic regulatory enzymes in an animal model of Maple Syrup Urine Disease

Maple Syrup Urine Disease (MSUD) is an autosomal recessive inherited disorder that affects the activity of the branched-chainα-keto acid dehydrogenase complex (BCDK). This deficiency on BCDK complex results in the accumulation of branched-chain amino acids (BCAA) leucine, isoleucine, valine, and their corresponding α-keto acids. Epigenetic changes can negatively affect the metabolism of BCAA. These changes are catalyzed by the epigenetic regulatory enzymes, e.g., DNA methyltransferase (DNMT), histone deacetylases (HDAC), and histone acetyltransferases (HAT). However, the impacts of BCAA administration on the activity of epigenetic regulatory enzymes in the brain of MSUD patients are still unknown. In this study, we aimed to demonstrate the impact of BCAA administration on the activity of DNMT, HDAC, and HAT in the brain structures of infant rats, an animal model of MSUD. For that, we administered a BCAA pool to infant rats for 21 days. We demonstrated that BCAA administration significantly increased the DNMT and HDAC activities in the hippocampus and striatum, but not in the cerebral cortex of MSUD infant rats. A positive correlation was observed between HDAC and DNMT activities in the hippocampus and striatum of animals exposed to BCAA injections. Our results showed that the BCAA administration could modulate epigenetic regulatory enzymes, mainly DNMT and HDAC, in the brains of infant rats. Therefore, we suggest that the increase in the activity of DNMT and HDAC in the hippocampus and striatum could partially explain the neurological impairments presented in animal models of MSUD.

Aberrant BCAA and glutamate metabolism linked to regional neurodegeneration in a mouse model of Leigh syndrome

The dysfunction of respiratory chain complex I (CI) is the most common form of mitochondrial disease that most often presents as Leigh syndrome (LS) in children - a severe neurometabolic disorder defined by progressive focal lesions in specific brain regions. The mechanisms underlying this region-specific vulnerability to CI deficiency, however, remain elusive. Here, we examined brain regional respiratory chain enzyme activities and metabolic profiles in a mouse model of LS with global CI deficiency to gain insight into regional vulnerability to neurodegeneration. One lesion-resistant and three lesion-prone brain regions were investigated in Ndufs4 knockout (KO) mice at the late stage of LS. Enzyme assays confirmed significantly decreased (60-80%) CI activity in all investigated KO brain regions, with the lesion-resistant region displaying the highest residual CI activity (38% of wild type). A higher residual CI activity, and a less perturbed NADH/NAD⁺ ratio, correlate with less severe metabolic perturbations in KO brain regions. Moreover, less perturbed BCAA oxidation and increased glutamate oxidation seem to distinguish lesion-resistant from -prone KO brain regions, thereby identifying key areas of metabolism to target in future therapeutic intervention studies.

Brain Branched-Chain Amino Acids in Maple Syrup Urine Disease: Implications for Neurological Disorders

Maple syrup urine disease (MSUD) is an autosomal recessive disorder caused by decreased activity of the branched-chain α-ketoacid dehydrogenase complex (BCKDC), which catalyzes the irreversible catabolism of branched-chain amino acids (BCAAs). Current management of this BCAA dyshomeostasis consists of dietary restriction of BCAAs and liver transplantation, which aims to partially restore functional BCKDC activity in the periphery. These treatments improve the circulating levels of BCAAs and significantly increase survival rates in MSUD patients. However, significant cognitive and psychiatric morbidities remain. Specifically, patients are at a higher lifetime risk for cognitive impairments, mood and anxiety disorders (depression, anxiety, and panic disorder), and attention deficit disorder. Recent literature suggests that the neurological sequelae may be due to the brain-specific roles of BCAAs. This review will focus on the derangements of BCAAs observed in the brain of MSUD patients and will explore the potential mechanisms driving neurologic dysfunction. Finally, we will discuss recent evidence that implicates the relevance of BCAA metabolism in other neurological disorders. An understanding of the role of BCAAs in the central nervous system may facilitate future identification of novel therapeutic approaches in MSUD and a broad range of neurological disorders.

Loss of the Drosophila branched-chain α-ketoacid dehydrogenase complex results in neuronal dysfunction

Maple syrup urine disease (MSUD) is an inherited error in the metabolism of branched-chain amino acids (BCAAs) caused by a severe deficiency of the branched-chain α-ketoacid dehydrogenase (BCKDH) complex, which ultimately leads to neurological disorders. The limited therapies, including protein-restricted diets and liver transplants, are not as effective as they could be for the treatment of MSUD due to the current lack of molecular insights into the disease pathogenesis. To address this issue, we developed a Drosophila model of MSUD by knocking out the dDBT gene, an ortholog of the human gene encoding the dihydrolipoamide branched chain transacylase (DBT) subunit of BCKDH. The homozygous dDBT mutant larvae recapitulate an array of MSUD phenotypes, including aberrant BCAA accumulation, developmental defects, poor mobile behavior and disrupted L-glutamate homeostasis. Moreover, the dDBT mutation causes neuronal apoptosis during the developmental progression of larval brains. The genetic and functional evidence generated by in vivo depletion of dDBT expression in the eye indicates severe impairment of retinal rhabdomeres. Further, the dDBT mutant shows elevated oxidative stress and higher lipid peroxidation accumulation in the larval brain. Therefore, we conclude from in vivo evidence that the loss of dDBT results in oxidative brain damage that may lead to neuronal cell death and contribute to aspects of MSUD pathology. Importantly, when the dDBT mutants were administrated with Metformin, the aberrances in BCAA levels and motor behavior were ameliorated. This intriguing outcome strongly merits the use of the dDBT mutant as a platform for developing MSUD therapies.This article has an associated First Person interview with the joint first authors of the paper.

Ibuprofen during gestation prevents some changes in physical and reflex development in offspring in a model of hyperleucinemia and maternal inflammation

Maple Syrup Urine Disease (MSUD) is caused by a severe deficiency in the branched-chain ketoacid dehydrogenase complex activity. Patients MSUD accumulate the branched-chain amino acids leucine (Leu), isoleucine, valine in blood, and other tissues. Leu and/or their branched-chain α-keto acids are linked to neurological damage in MSUD. When immediately diagnosed and treated, patients develop normally. Inflammation in MSUD can elicit a metabolic decompensation crisis. There are few cases of pregnancy in MSUD women, and little is known about the effect of maternal hyperleucinemia on the neurodevelopment of their babies. During pregnancy, some intercurrences like maternal infection or inflammation may affect fetal development and are linked to neurologic diseases. Lipopolysaccharide is widely accepted as a model of maternal inflammation. We analyzed the effects of maternal hyperleucinemia and inflammation and the possible positive impact the use of ibuprofen in Wistar rats on a battery of physics (ear unfolding, hair growing, incisors eruption, eye-opening, and auditive channel opening) and neurological reflexes (palmar grasp, surface righting, negative geotaxis, air-righting, and auditory-startle response) maturation parameters in the offspring. Maternal hyperleucinemia and inflammation delayed some physical parameters and neurological reflexes, indicating that both situations may be harmful to fetuses, and ibuprofen reversed some settings.

Clues and challenges in the diagnosis of intermittent maple syrup urine disease

BACKGROUND

Maple syrup urine disease is a rare autosomal-recessive aminoacidopathy, caused by deficient branched-chain 2-keto acid dehydrogenase (BCKD), with subsequent accumulation of branched-chain amino acids (BCAAs): leucine, isoleucine and valine. While most cases of MSUD are classic, some 20% of cases are non-classic variants, designated as intermediate- or intermittent-types. Patients with the latter form usually develop normally and are cognitively intact, with normal BCAA levels when asymptomatic. However, intercurrent febrile illness and catabolism may cause metabolic derailment with life-threatening neurological sequelae. Thus, early detection and dietary intervention are warranted in intermittent MSUD.

PATIENTS AND METHODS

We describe eight patients from four unrelated families, diagnosed with intermittent MSUD. Their presenting symptoms during metabolic crises varied from confusion and decreased consciousness, to ataxia, and acute psychosis. Molecular confirmation of MSUD was pursued via sequencing of the BCKDHA, BCKDHB and DBT genes.

RESULTS

All affected individuals were found to harbor bi-allelic pathogenic variants in either BCKDHB or DBT. Of the seven variants, four variants in BCKDHB (p.G101D, p. V103A, p. A221D, p. Y195C) and one variant in DBT (p.K427E) were not previously described.

CONCLUSIONS

While newborn screening programs allow for early detection of classic MSUD, cases of the intermittent form might go undetected, and present later in childhood following metabolic derailment, with an array of non-specific symptoms. Our experience with the families reported herein adds to the current knowledge regarding the phenotype and mutational spectrum of this unique inborn error of branched-chain amino acid metabolism, and underscore the high index of suspicion required for its diagnosis.

Branched-chain α-ketoacid dehydrogenase deficiency (maple syrup urine disease): Treatment, biomarkers, and outcomes

Over the past three decades, we studied 184 individuals with 174 different molecular variants of branched-chain α-ketoacid dehydrogenase activity, and here delineate essential clinical and biochemical aspects of the maple syrup urine disease (MSUD) phenotype. We collected data about treatment, survival, hospitalization, metabolic control, and liver transplantation from patients with classic (i.e., severe; n = 176), intermediate (n = 6) and intermittent (n = 2) forms of MSUD. A total of 13,589 amino acid profiles were used to analyze leucine tolerance, amino acid homeostasis, estimated cerebral amino acid uptake, quantitative responses to anabolic therapy, and metabolic control after liver transplantation. Standard instruments were used to measure neuropsychiatric outcomes. Despite advances in clinical care, classic MSUD remains a morbid and potentially fatal disorder. Stringent dietary therapy maintains metabolic variables within acceptable limits but is challenging to implement, fails to restore appropriate concentration relationships among circulating amino acids, and does not fully prevent cognitive and psychiatric disabilities. Liver transplantation eliminates the need for a prescription diet and safeguards patients from life-threatening metabolic crises, but is associated with predictable morbidities and does not reverse pre-existing neurological sequelae. There is a critical unmet need for safe and effective disease-modifying therapies for MSUD which can be implemented early in life. The biochemistry and physiology of MSUD and its response to liver transplantation afford key insights into the design of new therapies based on gene replacement or editing.

Discovery of Biomarker Panels for Neural Dysfunction in Inborn Errors of Amino Acid Metabolism

Patients with inborn errors of amino acid metabolism frequently show neuropsychiatric symptoms despite accurate metabolic control. This study aimed to gain insight into the underlying mechanisms of neural dysfunction. Here we analyzed the expression of brain-derived neurotrophic factor (BDNF) and 10 genes required for correct brain functioning in plasma and blood of patients with Urea Cycle Disorders (UCD), Maple Syrup Urine Disease (MSUD) and controls. Receiver-operating characteristic (ROC) analysis was used to evaluate sensitivity and specificity of potential biomarkers. CACNA2D2 (α2δ2 subunit of voltage-gated calcium channels) and MECP2 (methyl-CpG binding protein 2) mRNA and protein showed an excellent neural function biomarker signature (AUC ≥ 0,925) for recognition of MSUD. THBS3 (thrombospondin 3) mRNA and AABA gave a very good biomarker signature (AUC 0,911) for executive-attention deficits. THBS3, LIN28A mRNA, and alanine showed a perfect biomarker signature (AUC 1) for behavioral and mood disorders. Finally, a panel of BDNF protein and at least two large neural AAs showed a perfect biomarker signature (AUC 1) for recognition of psychomotor delay, pointing to excessive protein restriction as central causative of psychomotor delay. To conclude, our study has identified promising biomarker panels for neural function evaluation, providing a base for future studies with larger samples.

Biomarkers for major depressive and bipolar disorders using metabolomics: A systematic review

Major depressive disorder (MDD) and bipolar disorder (BD) lack robust biomarkers useful for screening purposes in a clinical setting. A systematic review of the literature was conducted on metabolomic studies of patients with MDD or BD through the use of analytical platforms such as in vivo brain imaging, mass spectrometry, and nuclear magnetic resonance. Our search identified a total of 7,590 articles, of which 266 articles remained for full-text revision. Overall, 249 metabolites were found to be dysregulated with 122 of these metabolites being reported in two or more of the studies included. A list of biomarkers for MDD and BD established from metabolites found to be abnormal, along with the number of studies supporting each metabolite and a comparison of which biological fluids they were reported in, is provided. Metabolic pathways that may be important in the pathophysiology of MDD and BD were identified and predominantly center on glutamatergic metabolism, energy metabolism, and neurotransmission. Using online drug registries, we also illustrate how metabolomics can facilitate the discovery of novel candidate drug targets.

Evaluation of plasma biomarkers of inflammation in patients with maple syrup urine disease

Maple syrup urine disease (MSUD) is an autosomal recessive inherited disorder that affects branched-chain amino acid (BCAA) catabolism and is associated with acute and chronic brain dysfunction. Recent studies have shown that inflammation may be involved in the neuropathology of MSUD. However, these studies have mainly focused on single or small subsets of proteins or molecules. Here we performed a case-control study, including 12 treated-MSUD patients, in order to investigate the plasmatic biomarkers of inflammation, to help to establish a possible relationship between these biomarkers and the disease. Our results showed that MSUD patients in treatment with restricted protein diets have high levels of pro-inflammatory cytokines [IFN-γ, TNF-α, IL-1β and IL-6] and cell adhesion molecules [sICAM-1 and sVCAM-1] compared to the control group. However, no significant alterations were found in the levels of IL-2, IL-4, IL-5, IL-7, IL-8, and IL-10 between healthy controls and MSUD patients. Moreover, we found a positive correlation between number of metabolic crisis and IL-1β levels and sICAM-1 in MSUD patients. In conclusion, our findings in plasma of patients with MSUD suggest that inflammation may play an important role in the pathogenesis of MSUD, although this process is not directly associated with BCAA blood levels. Overall, data reported here are consistent with the working hypothesis that inflammation may be involved in the pathophysiological mechanism underlying the brain damage observed in MSUD patients.

Impact of pregnancy on inborn errors of metabolism

Once based mainly in paediatrics, inborn errors of metabolism (IEM), or inherited metabolic disorders (IMD) represent a growing adult medicine specialty. Individually rare these conditions have currently, a collective estimated prevalence of >1:800. Diagnosis has improved through expanded newborn screening programs, identification of potentially affected family members and greater awareness of symptomatic presentations in adolescence and in adulthood. Better survival and reduced mortality from previously lethal and debilitating conditions means greater numbers transition to adulthood. Pregnancy, once contraindicated for many, may represent a challenging but successful outcome. Successful pregnancies are now reported in a wide range of IEM. Significant challenges remain, given the biological stresses of pregnancy, parturition and the puerperium. Known diagnoses allow preventive and pre-emptive management. Unrecognized metabolic disorders especially, remain a preventable cause of maternal and neonatal mortality and morbidity. Increased awareness of these conditions amongst all clinicians is essential to expedite diagnosis and manage appropriately. This review aims to describe normal adaptations to pregnancy and discuss how various types of IEM may be affected. Relevant translational research and clinical experience will be reviewed with practical management aspects cited. Based on current literature, the impact of maternal IEM on mother and/or foetus, as well as how foetal IEM may affect the mother, will be considered. Insights gained from these rare disorders to more common conditions will be explored. Gaps in the literature, unanswered questions and steps to enhance further knowledge and systematically capture experience, such as establishment of an IEM-pregnancy registry, will be summarized.

Adult ADHD and Comorbid Somatic Disease: A Systematic Literature Review

OBJECTIVE

To systematically review, synthesize, and appraise available evidence, connecting adult ADHD with somatic disease.

METHOD

Embase, Psychinfo, and Medline databases were searched for studies published from 1994 to 2015 addressing adult ADHD and somatic comorbidity. Somatic conditions were classified according to International Classification of Diseases (ICD-10) codes. Levels of evidence were graded as inconclusive, tentative, or well documented.

RESULTS

Most of the 126 studies included in the qualitative synthesis were small and of modest quality. Obesity, sleep disorders, and asthma were well-documented comorbidities in adult ADHD. Tentative evidence was found for an association between adult ADHD and migraine and celiac disease. In a large health registry study, cardiovascular disease was not associated with adult ADHD.

CONCLUSION

There are few large systematic studies using standardized diagnostic criteria evaluating adult ADHD and somatic comorbidities. Significant associations are found between adult ADHD and several somatic diseases, and these are important to consider when assessing and treating either adult ADHD or the somatic diseases.

Long-term metabolic follow-up and clinical outcome of 35 patients with maple syrup urine disease

BACKGROUND

Maple syrup urine disease (MSUD) is a rare disease that requires a protein-restricted diet for successful management. Little is known, however, about the psychosocial outcome of MSUD patients. This study investigates the relationship between metabolic and clinical parameters and psychosocial outcomes in a cohort of patients with neonatal-onset MSUD.

METHODS

Data on academic achievement, psychological care, family involvement, and biochemical parameters were collected from the medical records of neonatal MSUD patients treated at Necker Hospital (Paris) between 1964 and 2013.

RESULTS

Thirty-five MSUD patients with a mean age of 16.3 (2.1-49.0) years participated. Metabolic decompensations (plasma leucine >380 μmol/L) were more frequent during the first year of life and after 15 years, mainly due to infection and dietary noncompliance, respectively. Leucine levels increased significantly in adulthood: 61.5% of adults were independent and achieved adequate social and professional integration; 56% needed occasional or sustained psychological or psychiatric care (8/19, with externalizing, mood, emotional, and anxiety disorders being the most common). Patients needing psychiatric care were significantly older [mean and standard deviation (SD) 22.6 (7.7) years] than patients needing only psychological follow-up [mean (SD) 14.3 (8.9) years]. Patients with psychological follow-up experienced the highest lifetime number of decompensations; 45% of families had difficulty coping with the chronic disease. Parental involvement was negatively associated with the number of lifetime decompensations.

CONCLUSION

Adults had increased levels of plasma leucine, consistent with greater chronic toxicity. Psychological care was associated with age and number of decompensations. In addition, parental involvement appeared to be crucial in the management of MSUD patients.

Maple syrup urine disease: mechanisms and management

Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by defects in the branched-chain α-ketoacid dehydrogenase complex, which results in elevations of the branched-chain amino acids (BCAAs) in plasma, α-ketoacids in urine, and production of the pathognomonic disease marker, alloisoleucine. The disorder varies in severity and the clinical spectrum is quite broad with five recognized clinical variants that have no known association with genotype. The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine, and can lead to irreversible neurological complications, including stereotypical movements, metabolic decompensation, and death if left untreated. Treatment consists of dietary restriction of BCAAs and close metabolic monitoring. Clinical outcomes are generally good in patients where treatment is initiated early. Newborn screening for MSUD is now commonplace in the United States and is included on the Recommended Uniform Screening Panel (RUSP). We review this disorder including its presentation, screening and clinical diagnosis, treatment, and other relevant aspects pertaining to the care of patients.

Two homozygous mutations in the exon 5 of BCKDHB gene that may cause the classic form of maple syrup urine disease

Maple syrup urine disease (MSUD) is a rare autosomal recessive genetic disorder caused by defects in the catabolism of the branched-chain amino acids (BCAAs). Classic form of MSUD (CMSUD) is caused by mutations in BCKDHA, BCKDHB, DBT genes mostly. In this study, we analyzed the clinical and genetic characteristics of two patients with CMSUD. Two homozygous mutations, c.517G > T (p.Asp173Tyr) and c.503G > A (p.Arg168His), both in the exon 5 of BCKDHB were detected respectively. The novel mutation p.Asp173Tyr of patient A, inherited from his parents, is predicted to affect conformation of protein by computer analysis. The reported mutation p.Arg168His observed in patient B seemed to occur in a maternal uniparental disomy inheritance manner. Review of related literature revealed that most missense mutations in exon 5 of BCKDHB in homozygous genotype often result in CMSUD because of its incorrect conformation, and exon 5 of BCKDHB might be a susceptible region. Thus the novel homozygous mutation p.Asp173Tyr and the founder homozygous mutation p.Arg168His may be responsible for the clinical presentation of the two CMSUD patients, facilitating the future genetic counselling and prenatal diagnosis.

Neurocognitive profiles in MSUD school-age patients

Maple syrup urine disease (MSUD), an inborn error of amino acids catabolism is characterized by accumulation of branched chain amino acids (BCAAs) leucine, isoleucine, valine and their corresponding alpha-ketoacids. Impact on the cognitive development has been reported historically, with developmental delays of varying degree. Currently, earlier diagnosis and improved management allow a better neurodevelopment, without requirement of special education. However, specific impairments can be observed, and so far, results of detailed neurocognitive assessments are not available. The aim of this study was to analyse neurocognitive profiles of French MSUD patients. This was a multicentre retrospective study on MSUD patients who underwent neurocognitive evaluation at primary school age. Twenty-one patients with classical neonatal onset MSUD were included. The patients' mean age at the time of evaluation was 8.7 years. The mean intellectual quotient (IQ) score was in the normal range (95.1 ± 12.6). In a subset of eight patients, a consistent developmental pattern of higher verbal than performance IQ was observed (mean of the difference 25.7 ± 8.7, p < 0.0001). No correlation could be established between this pattern and long-term metabolic balance (BCAA blood levels), or severity of acute metabolic imbalances, or leucine blood levels at diagnosis and time to toxin removal procedure. These data show that some MSUD patients may exhibit an abnormal neurocognitive profile with higher verbal than performance abilities. This might suggest an executive dysfunction disorder that would need to be further investigated by specialized testing. This pattern is important to detect in MSUD, as appropriate neuropsychological treatment strategies should be proposed.

Interactions in the Metabolism of Glutamate and the Branched-Chain Amino Acids and Ketoacids in the CNS

Glutamatergic neurotransmission entails a tonic loss of glutamate from nerve endings into the synapse. Replacement of neuronal glutamate is essential in order to avoid depletion of the internal pool. In brain this occurs primarily via the glutamate-glutamine cycle, which invokes astrocytic synthesis of glutamine and hydrolysis of this amino acid via neuronal phosphate-dependent glutaminase. This cycle maintains constancy of internal pools, but it does not provide a mechanism for inevitable losses of glutamate N from brain. Import of glutamine or glutamate from blood does not occur to any appreciable extent. However, the branched-chain amino acids (BCAA) cross the blood-brain barrier swiftly. The brain possesses abundant branched-chain amino acid transaminase activity which replenishes brain glutamate and also generates branched-chain ketoacids. It seems probable that the branched-chain amino acids and ketoacids participate in a "glutamate-BCAA cycle" which involves shuttling of branched-chain amino acids and ketoacids between astrocytes and neurons. This mechanism not only supports the synthesis of glutamate, it also may constitute a mechanism by which high (and potentially toxic) concentrations of glutamate can be avoided by the re-amination of branched-chain ketoacids.

Autism in patients with propionic acidemia

Certain inborn errors of metabolism have been suggested to increase the risk of autistic behavior. In an animal model, propionic acid ingestion triggered abnormal behavior resembling autism. So far only a few cases were reported with propionic acidemia and autistic features. From a series of twelve consecutively diagnosed cases with propionic acidemia, we report on eight patients with autistic features. The patients were followed 2-4 times a year and underwent regular clinical, dietary and laboratory investigations. Psychological evaluation was performed every second to fourth year. All patients were compliant with the standard diet and carnitine supplementation. None of the patients had frequent metabolic decompensations. From the metabolic factors known to impact neuropsychological outcome we detected chronically decreased valine levels and altered valine to leucine ratios in five out of the eight patients. Recurrent lactic acid elevations were present in six out of the eight patients. Five of the eight patients were diagnosed with Autism Spectrum Disorder, four of them had pathogenic variants in PCCB. Disorder according to DSM-IV and/or DSM-5 criteria. One of the patients diagnosed with propionic acidemia by newborn screening had the most significant behavioral features and another was diagnosed with Autism Spectrum Disorder prior to propionic acidemia. We hypothesize that chronic suboptimal intracellular metabolic balance may be responsible for the increased risk for autistic features in propionic acidemia. We propose that patients diagnosed with propionic acidemia should be screened for Autism Spectrum Disorder.