Dodecyl creatine ester therapy: from promise to reality.

Pathogenic variants in SLC6A8, the gene which encodes creatine transporter SLC6A8, prevent creatine uptake in the brain and result in a variable degree of intellectual disability, behavioral disorders (e.g., autism spectrum disorder), epilepsy, and severe speech and language delay. There are no treatments to improve neurodevelopmental outcomes for creatine transporter deficiency (CTD). In this spotlight, we summarize recent advances in innovative molecules to treat CTD, with a focus on dodecyl creatine ester, the most promising drug candidate.

A multiomics approach reveals evidence for phenylbutyrate as a potential treatment for combined D,L-2- hydroxyglutaric aciduria.

PURPOSE: To identify therapies for combined D, L-2-hydroxyglutaric aciduria (C-2HGA), a rare genetic disorder caused by recessive variants in the SLC25A1 gene. METHODS: Patients C-2HGA were identified and diagnosed by whole exome sequencing and biochemical genetic testing. Patient derived fibroblasts were then treated with phenylbutyrate and the functional effects assessed by metabolomics and RNA-sequencing. RESULTS: In this study, we demonstrated that C-2HGA patient derived fibroblasts exhibited impaired cellular bioenergetics. Moreover, Fibroblasts form one patient exhibited worsened cellular bioenergetics when supplemented with citrate. We hypothesized that treating patient cells with phenylbutyrate (PB), an FDA approved pharmaceutical drug that conjugates glutamine for renal excretion, would reduce mitochondrial 2-ketoglutarate, thereby leading to improved cellular bioenergetics. Metabolomic and RNA-seq analyses of PB-treated fibroblasts demonstrated a significant decrease in intracellular 2-ketoglutarate, 2-hydroxyglutarate, and in levels of mRNA coding for citrate synthase and isocitrate dehydrogenase. Consistent with the known action of PB, an increased level of phenylacetylglutamine in patient cells was consistent with the drug acting as 2-ketoglutarate sink. CONCLUSION: Our pre-clinical studies suggest that citrate supplementation has the possibility exacerbating energy metabolism in this condition. However, improvement in cellular bioenergetics suggests phenylbutyrate might have interventional utility for this rare disease.

X-linked creatine transporter (SLC6A8) deficiency in females: Difficult to recognize, but a potentially treatable disease.

Creatine transporter deficiency (CTD), caused by pathogenic variants in SLC6A8, is the second most common cause of X-linked intellectual disability. Symptoms include intellectual disability, epilepsy, and behavioral disorders and are caused by reduced cerebral creatine levels. Targeted treatment with oral supplementation is available, however the treatment efficacy is still being investigated. There are clinical and theoretical indications that heterozygous females with CTD respond better to supplementation treatment than hemizygous males. Unfortunately, heterozygous females with CTD often have more subtle and uncharacteristic clinical and biochemical phenotypes, rendering diagnosis more difficult. We report a new female case who presented with learning disabilities and seizures. After determining the diagnosis with molecular genetic testing confirmed by proton magnetic resonance spectroscopy (1H-MRS), the patient was treated with supplementation treatment including creatine, arginine, and glycine. After 28 months of treatment, the patient showed prominent clinical improvement and increased creatine levels in the brain. Furthermore, we provide a review of the 32 female cases reported in the current literature including a description of phenotypes, genotypes, diagnostic approaches, and effects of supplementation treatment. Based on this, we find that supplementation treatment should be tested in heterozygous female patients with CTD, and a prospective treatment underlines the importance of diagnosing these patients. The diagnosis should be suspected in a broad clinical spectrum of female patients and can only be made by molecular genetic testing. 1H-MRS of cerebral creatine levels is essential for establishing the diagnosis in females, and especially valuable when assessing variants of unknown significance.

Current and potential new treatment strategies for creatine deficiency syndromes.

Creatine deficiency syndromes (CDS) are inherited metabolic disorders caused by mutations in GATM, GAMT and SLC6A8 and mainly affect central nervous system (CNS). AGAT- and GAMT-deficient patients lack the functional brain endogenous creatine (Cr) synthesis pathway but express the Cr transporter SLC6A8 at blood-brain barrier (BBB), and can thus be treated by oral supplementation of high doses of Cr. For Cr transporter deficiency (SLC6A8 deficiency or CTD), current treatment strategies benefit one-third of patients. However, as their phenotype is not completely reversed, and for the other two-thirds of CTD patients, the development of novel more effective therapies is needed. This article aims to review the current knowledge on Cr metabolism and CDS clinical aspects, highlighting their current treatment possibilities and the most recent research perspectives on CDS potential therapeutics designed, in particular, to bring new options for the treatment of CTD.

Cerebral folate deficiency: Analytical tests and differential diagnosis.

Cerebral folate deficiency is typically defined as a deficiency of the major folate species 5-methyltetrahydrofolate in the cerebrospinal fluid (CSF) in the presence of normal peripheral total folate levels. However, it should be noted that cerebral folate deficiency is also often used to describe conditions where CSF 5-MTHF is low, in the presence of low or undefined peripheral folate levels. Known defects of folate transport are deficiency of the proton coupled folate transporter, associated with systemic as well as cerebral folate deficiency, and deficiency of the folate receptor alpha, leading to an isolated cerebral folate deficiency associated with intractable seizures, developmental delay and/or regression, progressive ataxia and choreoathetoid movement disorders. Inborn errors of folate metabolism include deficiencies of the enzymes methylenetetrahydrofolate reductase, dihydrofolate reductase and 5,10-methenyltetrahydrofolate synthetase. Cerebral folate deficiency is potentially a treatable condition and so prompt recognition of these inborn errors and initiation of appropriate therapy is of paramount importance. Secondary cerebral folate deficiency may be observed in other inherited metabolic diseases, including disorders of the mitochondrial oxidative phosphorylation system, serine deficiency, and pyridoxine dependent epilepsy. Other secondary causes of cerebral folate deficiency include the effects of drugs, immune response activation, toxic insults and oxidative stress. This review describes the absorption, transport and metabolism of folate within the body; analytical methods to measure folate species in blood, plasma and CSF; inherited and acquired causes of cerebral folate deficiency; and possible treatment options in those patients found to have cerebral folate deficiency.

Response to medical and a novel dietary treatment in newborn screen identified patients with ethylmalonic encephalopathy.

Ethylmalonic encephalopathy (EE) is a devastating neurodegenerative disease caused by mutations in the ETHE1 gene critical for hydrogen sulfide (H2S) detoxification. Patients present in infancy with hypotonia, developmental delay, diarrhea, orthostatic acrocyanosis and petechiae. Biochemical findings include elevated C4, C5 acylcarnitines and lactic and ethylmalonic acid (EMA) in body fluids. Current treatment modalities include metronidazole and N-acetylcysteine (NAC) to lower the production and promote detoxification of toxic H2S. Patients are typically identified after the onset of clinical symptoms and there is limited information about long term response to treatment. We report the findings of two unrelated patients with EE, identified through newborn screening, who were managed with conventional treatment (NAC, metronidazole alternated with neomycin) and in patient 2, a novel dietary treatment restricting sulfur containing amino acids. Pathogenic mutations were confirmed in the ETHE1 gene (homozygous splice site mutation in patient 1, c.505 + 1G > A; compound heterozygous mutations in patient 2, c.131_132delAG + c.566delG). Both patients were started on metronidazole and NAC by 10 weeks of age and treated for 23 months. Patient 1 did not accept the metabolic formula due to palatability and parental refusal for gastrostomy tube placement. She demonstrated improved biomarkers (EMA, lactic acid and thiosulfate) and an attenuated clinical course. Patient 2 was started on a low methionine and cysteine diet at 8 months of age utilizing SOD Anamix® Early Years, (Nutricia). Baseline EMA levels were (642 mg/g Cr; n = 2) and decreased with medical treatment by 38% to a mean of 399 (n = 4, SD = 71, p 0.0013). With dietary treatment EMA levels were further reduced by 42% to a mean of 233 (n = 8, SD = 52, p 0.0030). Lactic acid, thiosulfates and clinical outcomes were also improved. Our long-term follow-up confirms previous reports of clinical improvement with NAC and metronidazole treatment. Additionally, our studies suggest that a diet restricted in sulfur-containing amino acids results in further improvement in clinical outcomes and biochemical markers.

Successful treatment of a patient with ethylmalonic encephalopathy by intravenous N-acetylcysteine.

Ethylmalonic encephalopathy (EE) is an autosomal recessive devastating metabolic disorder affecting the brain, gastrointestinal tract, peripheral vessels and rarely the other vascular organs. We report a 10-month-old girl who presented as a meningococcemia clinic but later diagnosed ethylmalonic encephalopathy. Molecular analyses revealed a homozygous c.554 T > G; p. L185R mutation in ETHE1 gene. She was only partially benefited from riboflavine, coenzyme Q10, metronidazole, N-acetylcysteine and symptomatic treatment and discharged from hospital with the sequela of oxygene dependance and developmental delay. We observed N-acetylcysteine 100 mg/kg/day intravenous infusion theraphy may be the most important drug especially in comatous EE patients.

Challenges for Worldwide Harmonization of Newborn Screening Programs.

BACKGROUND: Inherited metabolic disorders (IMDs) are caused by a defect in a metabolic pathway, leading to malfunctioning metabolism and/or the accumulation of toxic intermediate metabolites. To date, hundreds of IMDs have been identified. Many of these diseases are potentially fatal conditions that are not apparent at birth. Newborn screening (NBS) programs involve the clinical and laboratory examination of neonates who exhibit no health problems, with the aim of discovering those infants who are, in fact, suffering from a treatable condition. CONTENT: In recent years, the introduction of tandem mass spectrometry has allowed the expansion of screening programs. However, this expansion has brought a high degree of heterogeneity in the IMDs tested among different NBS programs. An attempt to harmonize the metabolic conditions recommended to be screened has been carried out. Two uniform screening panels have been proposed in the US and European Union, by knowledgeable organizations. Here, we review current evidence-based processes to assess and expand NBS programs. We also discuss the IMDs that have recently been introduced in some screening programs, such as severe combined immunodeficiencies, lysosomal storage disorders, and adrenoleukodystrophy. SUMMARY: NBS programs have been an established public health function for more than 50 years to efficiently and cost-effectively identify neonates with severe conditions. However, NBS is not yet optimal. This review is intended to elucidate the current degree of harmonization of NBS programs worldwide as well as to describe the major controversial points and discuss the multiple challenges that must be confronted in expanded NBS strategies.

A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model.

D-2-hydroxyglutaric aciduria (D2HGA) type II is a rare neurometabolic disorder caused by germline gain-of-function mutations in isocitrate dehydrogenase 2 (IDH2), resulting in accumulation of D-2-hydroxyglutarate (D2HG). Patients exhibit a wide spectrum of symptoms including cardiomyopathy, epilepsy, developmental delay and limited life span. Currently, there are no effective therapeutic interventions. We generated a D2HGA type II mouse model by introducing the Idh2R140Q mutation at the native chromosomal locus. Idh2R140Q mice displayed significantly elevated 2HG levels and recapitulated multiple defects seen in patients. AGI-026, a potent, selective inhibitor of the human IDH2R140Q-mutant enzyme, suppressed 2HG production, rescued cardiomyopathy, and provided a survival benefit in Idh2R140Q mice; treatment withdrawal resulted in deterioration of cardiac function. We observed differential expression of multiple genes and metabolites that are associated with cardiomyopathy, which were largely reversed by AGI-026. These findings demonstrate the potential therapeutic benefit of an IDH2R140Q inhibitor in patients with D2HGA type II.

Diagnostic methods and recommendations for the cerebral creatine deficiency syndromes.

Primary care pediatricians and a variety of specialist physicians strive to define an accurate diagnosis for children presenting with impairment of expressive speech and delay in achieving developmental milestones. Within the past two decades, a group of disorders featuring this presentation have been identified as cerebral creatine deficiency syndromes (CCDS). Patients with these disorders were initially discerned using proton magnetic resonance spectroscopy of the brain within a magnetic resonance imaging (MRI) examination. The objective of this review is to provide the clinician with an overview of the current information available on identifying and treating these conditions. We explain the salient features of creatine metabolism, synthesis, and transport required for normal development. We propose diagnostic approaches for confirming a CCDS diagnosis. Finally, we describe treatment approaches for managing patients with these conditions.

Treatment of X-linked creatine transporter (SLC6A8) deficiency: systematic review of the literature and three new cases.

BACKGROUND: Creatine transporter deficiency (CTD) is an X-linked inborn error of creatine metabolism characterized by reduced intra-cerebral creatine, developmental delay/intellectual disability, (ID), behavioral disturbance, seizures, and hypotonia in individuals harboring mutations in the SLC6A8 gene. Treatment for CTD includes supplementation with creatine, either alone or in combination with creatine precursors (arginine or glycine). Unlike other disorders of creatine metabolism, the efficacy of its treatment remains controversial. METHODS: We present our systematic literature review (2001-2013) comprising 7 publications (case series/reports), collectively describing 25 patients who met the inclusion criteria, and 3 additional cases treated at our institution. Definitions were established and extracted data analyzed for cognitive ability, psychiatric and behavioral disturbances, epilepsy, and cerebral proton magnetic resonance spectroscopy measurements at pre- and post-treatment. RESULTS: Treatment regimens varied among the 28 cases: 2 patients received creatine-monohydrate supplementation; 7 patients received L-arginine; 2 patients received creatine-monohydrate and L-arginine; and 17 patients received a combination of creatine-monohydrate, L-arginine and glycine. Median treatment duration was 34.6 months (range 3 months-5 years). Level of evidence was IV. A total of 10 patients (36%) demonstrated response to treatment, manifested by either an increase in cerebral creatine, or improved clinical parameters. Seven of the 28 patients had quantified pre- and post-treatment creatine, and it was significantly increased post-treatment. All of the patients with increased cerebral creatine also experienced clinical improvement. In addition, the majority of patients with clinical improvement had detectable cerebral creatine prior to treatment. 90% of the patients who improved were initiated on treatment before nine years of age. CONCLUSIONS: Acknowledging the limitations of this systematic review, we conclude that a proportion of CTD patients show amenability to treatment-particularly milder cases with residual brain creatine, and therefore probable residual protein function. We propose systematic screening for CTD in patients with ID, to allow early initiation of treatment, which currently comprises oral creatine, arginine and/or glycine supplementation. Standardized monitoring for safety and evaluation of treatment effects are required in all patients. This study provides effectiveness on currently available treatment, which can be used to discern effectiveness of future interventions (e.g. cyclocreatine).

Combined D2-/L2-hydroxyglutaric aciduria (SLC25A1 deficiency): clinical course and effects of citrate treatment.

Combined D,L-2-hydroxyglutaric aciduria (DL-2HGA; OMIM #615182) is a rare neurometabolic disorder clinically characterized by muscular hypotonia, severe neurodevelopmental dysfunction, and intractable seizures associated with respiratory distress. Biochemically, DL-2HGA patients excrete increased amounts of D- and L-2-hydroxyglutarate (D2HG and L2HG, respectively), with predominance of D2HG, and α-ketoglutarate, and show a decrease in urinary citrate. Impaired function of the mitochondrial citrate carrier (CIC) due to pathogenic mutations within the SLC25A1 gene has been identified as the underlying molecular cause of the disease. CIC mediates efflux of the mitochondrial tricarboxylic acid (TCA) cycle intermediates citrate and isocitrate in exchange for cytosolic malate. Thus, depletion of cytosolic citrate as well as accumulation of citrate inside mitochondria have been considered to play a role in the pathophysiology of DL-2HGA. Here, we report for the first time on a patient with a genetically confirmed diagnosis of DL-2HGA and treatment with either malate or citrate. During malate treatment, urinary malate concentration increased, but beyond that, neither biochemical nor clinical alterations were observed. In contrast, treatment with citrate led to an increased urinary excretion of TCA cycle intermediates malate and succinate, and by trend to an increased concentration of urinary citrate. Furthermore, excretion of D2HG and L2HG was reduced during citrate treatment. Clinically, the patient showed stabilization with regard to frequency and severity of seizures. Treating DL-2HGA with citrate should be considered in other DL-2HGA patients, and its effects should be studied systematically.

Diagnosis and management of cerebral folate deficiency. A form of folinic acid-responsive seizures.

Folinic acid-responsive seizures (FARS) are a rare treatable cause of neonatal epilepsy. They have characteristic peaks on CSF monoamine metabolite analysis, and have mutations in the ALDH7A1 gene, characteristically found in pyridoxine-dependent epilepsy. There are case reports of patients presenting with seizures at a later age, and with folate deficiency due to different mechanisms with variable response to folinic acid supplementation. Here, we report 2 siblings who presented with global developmental delay and intractable seizures who responded clinically to folinic acid therapy. Their work-up included metabolic and genetic testing. The DNA sequencing was carried out for the ALDH7A1 gene, and the folate receptor 1 (FOLR1) gene. They had very low 5-methyltetrahydrofolate (5-MTHF) in CSF with no systemic folate deficiency and no characteristic peaks on neurotransmitter metabolite chromatogram. A novel mutation in the FOLR1 gene was found. The mutation in this gene is shown to affect CSF folate transport leading to cerebral folate deficiency. The response to treatment with folinic acid was dramatic with improvement in social interaction, mobility, and complete seizure control. We should consider the possibility of this treatable condition in appropriate clinical circumstances early, as diagnosis with favorable outcome depends on the specialized tests.

A novel missense variant in the L2HGDH gene in a cat with L-2-hydroxyglutaric aciduria and multicystic cerebral lesions.

CASE DESCRIPTION: A 9-month-old intact male domestic shorthair cat was evaluated for increasing frequency of generalized tonic-clonic seizures. CLINICAL FINDINGS: The cat was reported to have had episodes of circling between the seizures. Upon examination, the cat had bilateral inconsistent menace response but otherwise normal physical and neurological examinations. DIAGNOSTICS: Magnetic resonance imaging (MRI) of the brain identified multifocal, small, rounded intra-axial lesions within the subcortical white matter containing fluid with similar characteristics as cerebrospinal fluid. Evaluation of urine organic acids showed increased excretion of 2-hydroxyglutaric acid. An XM_023255678.2:c.397C>T nonsense variant in the L2HGDH gene encoding L-2-hydroxyglutarate dehydrogenase was identified using whole genome sequencing. TREATMENT AND OUTCOME: Levetiracetam treatment was initiated at 20 mg/kg PO q8h, but the cat died after a seizure 10 days later. CLINICAL RELEVANCE: We report the second pathogenic gene variant in L-2-hydroxyglutaric aciduria in cats and describe for the first time multicystic cerebral lesions on MRI.

Cervical catheter placement for intrathecal baclofen test dose: is it safe?

INTRODUCTION: Intrathecal baclofen testing is usually performed via a catheter inserted at the lumbar spine. However, in patients with scoliosis, the distorted anatomy and bone fusion from corrective spinal surgery obviates access at the lumbar spine. PATIENTS AND METHODS: We report a method for inserting the intrathecal catheter via a posterior cervical approach and discuss our outcome. We describe our experience in 20 patients in whom intrathecal baclofen test catheter was inserted at the lower cervical spine. Data was collected prospectively. DISCUSSION: The procedure was successful in all 20 patients. There were no complications as a result of surgery or from baclofen test dose administration via a cervical catheter. Of the 20 patients, 15 went on to have baclofen pump implantation via a cervical catheter. In one patient, subsequent pump implantation procedure was unsuccessful due to presence of extradural scar tissue. In the remaining four patients pump implantation was declined due impending corrective spinal surgery or social reasons. CONCLUSION: Our experience shows that low cervical catheter insertion for administration of a test dose of intrathecal baclofen and feasible and safe to perform via the method described.

Exploring triheptanoin as treatment for short chain enoyl CoA hydratase deficiency.

We explored the benefits of triheptanoin as a treatment for Short Chain Enoyl Co-A Hydratase (SCEH) deficiency. One child with early onset, severe SCEH Deficiency was treated with triheptanoin, an odd chain oil with anapleurotic properties, for 37 months. Blood and urine chemistry safety measures, motor skills assessment, physical exam, and neurological assessment were monitored over a 27 month period. Modest sustained gains in motor skills, attention, muscle bulk, and strength were observed without any significant adverse effects. Triheptanoin appears to be a promising effective treatment for SCEH Deficiency.

L2HGDH Missense Variant in a Cat with L-2-Hydroxyglutaric Aciduria.

A 7-month-old, spayed female, domestic longhair cat with L-2-hydroxyglutaric aciduria (L-2-HGA) was investigated. The aim of this study was to investigate the clinical signs, metabolic changes and underlying genetic defect. The owner of the cat reported a 4-month history of multiple paroxysmal seizure-like episodes, characterized by running around the house, often in circles, with abnormal behavior, bumping into obstacles, salivating and often urinating. The episodes were followed by a period of disorientation and inappetence. Neurological examination revealed an absent bilateral menace response. Routine blood work revealed mild microcytic anemia but biochemistry, ammonia, lactate and pre- and post-prandial bile acids were unremarkable. MRI of the brain identified multifocal, bilaterally symmetrical and T2-weighted hyperintensities within the prosencephalon, mesencephalon and metencephalon, primarily affecting the grey matter. Urinary organic acids identified highly increased levels of L-2-hydroxyglutaric acid. The cat was treated with the anticonvulsants levetiracetam and phenobarbitone and has been seizure-free for 16 months. We sequenced the genome of the affected cat and compared the data to 48 control genomes. L2HGDH, coding for L-2-hydroxyglutarate dehydrogenase, was investigated as the top functional candidate gene. This search revealed a single private protein-changing variant in the affected cat. The identified homozygous variant, XM_023255678.1:c.1301A>G, is predicted to result in an amino acid change in the L2HGDH protein, XP_023111446.1:p.His434Arg. The available clinical and biochemical data together with current knowledge about L2HGDH variants and their functional impact in humans and dogs allow us to classify the p.His434Arg variant as a causative variant for the observed neurological signs in this cat.

Attention deficit hyperactivity disorder: a rare clinical presentation of L-2-hydroxyglutaric aciduria.

L-2-hydroxyglutaric aciduria (L2HGA) is a rare autosomal recessive neurometabolic disorder caused by the deficiency of L-2-hydroxyglutarate dehydrogenase (L2HGDH) enzyme. Dystonia, ataxia, pyramidal involvement and seizures are the common clinical manifestations. Coexisting behavioural problems and intellectual disability are also seen, however attention deficit hyperactivity disorder (ADHD) as the presenting clinical feature in L2HGA is rarely described. Here, we report a 5-year-old boy with behavioural problems and mild language delay. On clinical assessment, he fulfilled the diagnostic criteria for ADHD. His MR brain sequences showed classical finding of L2HGA-bilateral symmetrical T2-weighted hyperintensity involving subcortical white matter, basal ganglia and dentate nucleus. Urine analysis showed increased levels of 2-hydroxyglutaric acid and exome sequencing (targeted leukodystrophy panel) revealed homozygous likely pathogenic mutation in L2HGDH He was started on high dose of riboflavin and levocarnitine and rehabilitative measures with which he had improvement in behavioural symptoms. This case illustrates the pivotol role of MR brain imaging in the diagnosis of inborn errors of metabolism.

Novel NAXE variants as a cause for neurometabolic disorder: implications for treatment.

Neurometabolic disorders are often inherited and complex disorders that result from abnormalities of enzymes important for development and function of the nervous system. Recently, biallelic mutations in NAXE (APOA1BP) were found in patients with an infantile, lethal, neurometabolic disease. Here, exome sequencing was performed in two affected sisters and their healthy parents. The best candidate, NAXE, was tested for replication in exome sequencing data from 4351 patients with neurodevelopmental disorders. Quantitative RT-PCR, western blot and form factor analysis were performed to assess NAXE expression, protein levels and to analyze mitochondrial morphology in fibroblasts. Vitamin B3 was administered to one patient. Compound heterozygous missense (c.757G>A: p.Gly253Ser) and splicing (c.665-1G>A) variants in NAXE were identified in both affected sisters. In contrast to the previously reported patients with biallelic NAXE variants, our patients showed a milder phenotype with disease onset in early adulthood with psychosis, cognitive impairment, seizures, cerebellar ataxia and spasticity. The symptoms fluctuated. Additional screening of NAXE identified three novel homozygous missense variants (p.Lys245Gln, p.Asp218Asn, p.Ile214Val) in three patients with overlapping phenotype (fluctuating disease course, respiratory insufficiency, movement disorder). Lastly, patients with the c.665-1G>A splicing variant showed a significant reduction of NAXE expression compared to control fibroblasts and undetectable NAXE protein levels compared to control fibroblasts. Based on the metabolic pathway, vitamin B3 and coenzyme Q treatment was introduced in one patient in addition to antiepileptic treatment. This combination and avoidance of triggers was associated with continuous motor and cognitive improvement. The NAXE variants identified in this study suggest a loss-of-function mechanism leading to an insufficient NAD(P)HX repair system. Importantly, symptoms of patients with NAXE variants may improve with vitamin B3/coenzyme Q administration.

Creatine Transporter Deficiency Presenting as Autism Spectrum Disorder.

Autism spectrum disorder (ASD) is the most common disability-causing neurodevelopmental disorder in childhood. Although inborn errors of metabolism (IEM) are rare causes of ASD, they are significant for several reasons, including implications in genetic counseling and determination of prognosis. In this article, we present a 6-year-old boy who presented to us with ASD and was diagnosed with creatine transporter deficiency. Physical and neurologic examination of this patient had not previously raised suspicion of IEM, but twin pregnancy, prematurity, NICU stay due to necrotizing enterocolitis, transient infantile hypotonia, gross-motor delay, breath-holding spells, and a single febrile seizure complicated the history. MRI revealed mild T2-hyperintensity in posterior periventricular white matter. Further evaluation with magnetic resonance spectroscopy, which showed a decreased creatine peak, led to diagnostic investigations for disorders of creatine metabolism, revealing increased urinary creatine:creatinine ratio and a de novo, novel hemizygous frameshift variant in SLC6A8 Clinicians are advised to maintain a high index of suspicion for IEM and to evaluate patients with ASD for syndromic features. Although current guidelines from relevant organizations differ in their recommendations regarding the necessity and the extent of metabolic screening in ASD, there is a growing trend toward screening for treatable IEM. In this case report, we present challenges and pitfalls in the diagnostic journey for creatine transporter deficiency and underline the significance of a thorough history and physical examination in the evaluation of a child with ASD.