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

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

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

Intellectual disability: A potentially treatable condition

The application of genomics has greatly increased the diagnosis of specific monogenic causes of intellectual disability and improved our understanding of the neuronal processes that result in cognitive impairment. Meanwhile, families are building rare disease communities and seeking disease-specific treatments to change the trajectory of health and developmental outcomes for their children. To date, treatments for intellectual disability have focussed on metabolic disorders, where early treatment has improved cognition and neurodevelopmental outcomes. In this article, we discuss the treatment strategies that may be possible to change the neurodevelopmental outcome in a broader range of genetic forms of intellectual disability. These strategies include substrate modification, enzyme replacement therapy, gene therapy and molecular therapies. We argue that intellectual disability should now be considered a potentially treatable condition and a strong candidate for precision medicine.

The Mendelian disorders of chromatin machinery: Harnessing metabolic pathways and therapies for treatment

The Mendelian disorders of chromatin machinery (MDCMs) represent a distinct subgroup of disorders that present with neurodevelopmental disability. The chromatin machinery regulates gene expression by a range of mechanisms, including by post-translational modification of histones, responding to histone marks, and remodelling nucleosomes. Some of the MDCMs that impact on histone modification may have potential therapeutic interventions. Two potential treatment strategies are to enhance the intracellular pool of metabolites that can act as substrates for histone modifiers and the use of medications that may inhibit or promote the modification of histone residues to influence gene expression. In this article we discuss the influence and potential treatments of histone modifications involving histone acetylation and histone methylation. Genomic technologies are facilitating earlier diagnosis of many Mendelian disorders, providing potential opportunities for early treatment from infancy. This has parallels with how inborn errors of metabolism have been afforded early treatment with newborn screening. Before this promise can be fulfilled, we require greater understanding of the biochemical fingerprint of these conditions, which may provide opportunities to supplement metabolites that can act as substrates for chromatin modifying enzymes. Importantly, understanding the metabolomic profile of affected individuals may also provide disorder-specific biomarkers that will be critical for demonstrating efficacy of treatment, as treatment response may not be able to be accurately assessed by clinical measures.

Diagnostic Yield of CSF Testing in Infants for Disorders of Biogenic Amine Neurotransmitter Metabolism

BACKGROUND AND OBJECTIVES

Biochemical testing of CSF for neurotransmitter metabolites and their cofactors is often used in the diagnostic evaluation of infants with neurologic disorders but requires an invasive, labor-intensive procedure with many potential sources of error. Our aim was to determine the diagnostic yield of CSF testing for biogenic amines (serotonin, norepinephrine, epinephrine, and dopamine) and their cofactors in identifying inborn errors of neurotransmitter metabolism among infants.

METHODS

We evaluated all infants aged 1 year or younger who underwent CSF biogenic amine neurotransmitter (CSFNT) testing at Children's Hospital of Philadelphia (CHOP) and Boston Children's Hospital (BCH) between 2008 and 2017 in this cross-sectional study. The primary outcome was the proportion of individuals who received a diagnostic result from CSFNT testing. Secondary assessments included the proportion of infants who obtained a diagnostic result from other types of diagnostic testing.

RESULTS

The cohort included 323 individuals (191 from CHOP and 232 from BCH). The median age at presentation was 110 days (range 36-193). The most common presenting features were seizures (71%), hypotonia (47%), and developmental delay (43%). The diagnostic yield of CSFNT testing was zero. When CSF pyridoxal-5-phosphate level was assayed with CSFNT testing, 1 patient had a diagnostic result. An etiologic diagnosis was identified in 163 patients (50%) of the cohort, with genetic testing having the highest yield (120 individuals, 37%).

DISCUSSION

Our findings support the case for deimplementation of CSFNT testing as a standard diagnostic test of etiology in infants aged 1 year or younger presenting with neurologic disorders.

Real-world diagnostic outcomes and cost-effectiveness of genome-wide sequencing for developmental and seizure disorders: Evidence from Canada

PURPOSE

To determine real-world diagnostic rates, cost trajectories, and cost-effectiveness of exome sequencing (ES) and genome sequencing (GS) for children with developmental and/or seizure disorders in British Columbia, Canada.

METHODS

Based on medical records review, we estimated real-world costs and outcomes for 491 patients who underwent standard of care (SOC) diagnostic testing at British Columbia Children's Hospital. Results informed a state-transition Markov model examining cost-effectiveness of 3 competing diagnostic strategies: (1) SOC with last-tier access to ES, (2) streamlined ES access, and (3) first-tier GS.

RESULTS

Through SOC, 49.4% (95% CI: 40.6, 58.2) of patients were diagnosed at an average cost of C$11,683 per patient (95% CI: 9200, 14,166). Compared with SOC, earlier ES or GS access yielded similar or improved diagnostic rates and shorter times to genetic diagnosis, with 94% of simulations demonstrating cost savings for streamlined ES and 60% for first-tier GS. Net benefit from the perspective of the health care system was C$2956 (95% CI: -608, 6519) for streamlined ES compared with SOC.

CONCLUSION

Using real-world data, we found earlier access to ES may yield more rapid genetic diagnosis of childhood developmental and seizure disorders and cost savings compared with current practice in a Canadian health care system.

Cholic acid increases plasma cholesterol in Smith-Lemli-Opitz syndrome: A pilot study

Background

Smith-Lemli-Opitz syndrome (SLOS) is an inherited disorder of cholesterol biosynthesis associated with congenital malformations, growth delay, intellectual disability and behavior problems. SLOS is caused by bi-allelic mutations in DHCR7, which lead to reduced activity of 7-dehydrocholesterol reductase that catalyzes the last step in cholesterol biosynthesis. Symptoms of SLOS are thought to be due to cholesterol deficiency and accumulation of its precursor 7-dehydrocholesterol (7-DHC) and 8-dehydrocholesterol (8-DHC), and toxic oxysterols. Therapy for SLOS often includes dietary cholesterol supplementation, but lipids are poorly absorbed from the diet, possibly due to impaired bile acid synthesis. We hypothesized that bile acid supplementation with cholic acid would improve dietary cholesterol absorption and raise plasma cholesterol levels.

Methods

Twelve SLOS subjects (10 M, 2F, ages 2-27 years) who had plasma cholesterol ≤125 mg/dL were treated with cholic acid (10 mg/kg/day) divided twice daily for 2 months. Plasma cholesterol, 7-DHC and 8-DHC were measured by GC-MS. Oxysterols were measured by ultra-high-performance LC-MS/MS. Data were analyzed using paired t-tests.

Results

At baseline, plasma cholesterol was 75 ± 24 mg/dL (mean ± SD; range 43-125, n = 12). After 2 months on cholic acid, mean plasma cholesterol increased to 97 ± 29 mg/dL (p = 0.011). Eleven of 12 subjects showed an increase in plasma cholesterol that varied from 3.8% to 85.7% (mean 38.7 ± 23.3%). 7-Hydroxycholesterol decreased by 20.6% on average (p = 0.013) but no significant changes were seen in 7-DHC or 8-DHC. Mean body weight tended to increase (3.6% p = 0.069). Subjects tolerated cholic acid well and experienced no drug-related adverse events.

Conclusions

In this pilot study, cholic acid supplementation was well tolerated and safe and resulted in an increase in plasma cholesterol in most SLOS subjects. Further controlled longitudinal studies are needed to look for the sustainability of the biochemical effect and possible clinical benefits.

A Delphi Survey Study to Formulate Statements on the Treatability of Inherited Metabolic Disorders to Decide on Eligibility for Newborn Screening

The Wilson and Jungner (W&J) and Andermann criteria are meant to help select diseases eligible for population-based screening. With the introduction of next-generation sequencing (NGS) methods for newborn screening (NBS), more inherited metabolic diseases (IMDs) can technically be included, and a revision of the criteria was attempted. This study aimed to formulate statements and investigate whether those statements could elaborate on the criterion of treatability for IMDs to decide on eligibility for NBS. An online Delphi study was started among a panel of Dutch IMD experts (EPs). EPs evaluated, amended, and approved statements on treatability that were subsequently applied to 10 IMDs. After two rounds of Delphi, consensus was reached on 10 statements. Application of these statements selected 5 out of 10 IMDs proposed for this study as eligible for NBS, including 3 IMDs in the current Dutch NBS. The statement: 'The expected benefit/burden ratio of early treatment is positive and results in a significant health outcome' contributed most to decision-making. Our Delphi study resulted in 10 statements that can help to decide on eligibility for inclusion in NBS based on treatability, also showing that other criteria could be handled in a comparable way. Validation of the statements is required before these can be applied as guidance to authorities.

Where Do Neurodevelopmental Disorders Go? Casting the Eye Away from Childhood towards Adulthood

Neurodevelopmental disorders (NDDs) encompass a group of complex conditions with onset during the early developmental period. Such disorders are frequently associated with a number of neuropsychiatric features, the most prevalent ones being autism spectrum disorder, attention-deficit/hyperactivity disorder, intellectual disability, communication and specific learning disorders, and motor disorders. These conditions are characterized by wide genetic and clinical variability, and although they were previously conceptualized as childhood-limited disorders, NDDs are progressively being recognized as persistent conditions with a potentially relevant impact on the quality of life and overall functioning during adult life. In addition, emerging evidence seems to point towards the hypothesis of a neurodevelopmental continuum, according to which NNDs could portray different time-dependent outcomes, depending on the severity of the altered brain development. Despite representing lifelong phenotypes, they are often not promptly identified and/or managed in adulthood. In this regard, specific guidelines on clinical and therapeutic approaches for these conditions have not yet been delineated. In this view, future research investigations should be encouraged to broaden available knowledge, characterize the clinical course of NDDs across an individual’s lifespan, and better understand the patterns of aging-related concerns in adults with an NDD diagnosis. Additionally, considering the difficulties many young adults encounter while transitioning from childhood to adult mental health services, new, specific programs should be developed and existing programs should be implemented to improve the transition process and for the management of NDDs in adulthood.

Reduced resource utilization with early use of next-generation sequencing in rare genetic diseases in an Asian cohort

Children with genetic diseases endure a prolonged and costly "diagnostic odyssey." The use of whole exome sequencing (WES) and whole genome sequencing (WGS) has improved the diagnosis rate, ending the odyssey. However, the additional costs associated WES/WGS has impeded their adoption in Asian settings. We aim to estimate the expected change to the mean number of diagnostic tests used, and the associated costs from a decision to use WES early in the diagnostic pathways of pediatric phenotypes, as compared to Existing Practice. Retrospective data from a patient cohort recruited under the Singapore Undiagnosed Disease Program from a tertiary hospital in Singapore, for the period October 2004 to September 2020, was analyzed. Four phenotype-specific subgroups were used: multiple congenital anomalies (MCA) without developmental delay; global developmental delay (GDD); neuromuscular disorder (NMD) and primary immunodeficiency disorder (PID). Patients had undergone a traditional diagnostic pathway and received a diagnosis either through clinical exome or WES or WGS. A costs only analysis was performed, by tabulating the outcomes "test quantity" and "test costs" incurred by patients. The outcomes were compared with alternate diagnostic pathways which incorporates the early introduction of WES trio testing. To include uncertainty in cost outcomes, simulation studies were done on uncertain parameters. Cost outcomes are reported in Singapore dollars (S$). The 92 included patients had MCA (n = 48), GDD (n = 29), NMD (n = 10), or PID (n = 5). Patients were aged between 18 days and 26 years, 52.2% were males. The majority were of Chinese ethnicity (81.5%). If patients had access to WES directly, test quantity reduced by 97.38% for MCA, 96.98% for GDD, 96.56% for NMD, and 99.84% for PID. The expected cost savings per patient were $5940 for MCA (US$4433), $5342 for GDD (US$3986), $4622 for NMD (US$3449), and $58,497 for PID (US$43,654). Uncertainty assessment for MCA and GDD patients showed a respective likelihood of 86.9% and 97.4% for cost savings. Adoption of alternate diagnostic pathways with early WES in selected pediatric subgroups are likelt to reduce costs, when compared to Existing Practice. Benefits arising from earlier diagnosis, and the potential cost savings could mitigate the large initial cost of implementing WES in Asian settings.

Role of Psychologists in Pediatric Metabolic Disorders

Metabolic disorders or inborn errors of metabolism (IEMs) can have a wide range of neurodevelopmental and behavioral presentations. These can vary with age and/or management or stressors from common childhood/intercurrent illnesses/procedures/interventions. Collaborative care models such as multidisciplinary metabolic clinics or colocated models with behavioral health clinics and metabolic clinics in the same location can be valuable resources in improving long-term outcomes in patients with IEM. Psychologists' expertise using behavioral interventions, screening, or adaptive/cognitive measures can help with diagnosis, treatment adherence, school performance, family support, community resources, transition to adolescence and young adulthood using health belief concepts to improve outcomes.

How paediatricians investigate early developmental impairment in the UK: a qualitative descriptive study

Background

Early developmental impairment (EDI) is common and has many aetiologies and, therefore, potential investigations. There are several published guidelines recommending aetiological investigations, and paediatricians’ views of them varies. Little is known on the thought processes underlying clinical decisions in investigating EDI. This study aimed to describe the thought processes affecting clinical decisions on the investigation of EDI within a nationalised health care system.

Methods

A qualitative descriptive study using semi-structured qualitative interviews performed in person or via video link with paediatricians who see children with EDI in England. As part of the interview, a case study of a fictional disease, Cavorite deficiency, modelled on biotinidase deficiency, was given to participants with the cost of testing, incidence and likelihood it would respond to treatment. This allowed exploration of cost without encumbrance from predisposing views and training on the condition. Thematic analysis was performed by iterative approach. Where participants stated they wanted to redirect money from investigations to treatment, were that even possible, we asked which services they would like to be better funded in their area.

Results

Interviews were conducted with 14 consultant paediatricians: 9 Community / Neurodisability, 2 General paediatricians, and 3 Paediatric Neurologists. Two themes were identified: the value of an aetiological diagnosis to families and managing risk and probability when investigating EDI. The latter contained 4 subthemes: ‘circumspection’ involved blanket investigations chosen irrespective of phenotype and high regard for guidelines; ‘accepting appropriate risk’ involved participants choosing investigations based on clinical phenotype, recognising some aetiologies would be missed; consultants found they ‘transitioned between practices’ during their career; and ‘improved practice’ was thought possible with better evidence on how to stratify investigations based on phenotype. Services that were most frequently reported to need additional funding were therapy services, early community developmental services, management of behaviour, sleep and mental health, and educational support.

Conclusions

There are many factors that influence paediatricians’ choice of aetiological investigation in EDI, but clinical factors are the most important. Paediatricians want better evidence to allow them to select the right investigations for each child without a significant risk of missing an important diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-022-03233-1.

Towards Next-Generation Sequencing (NGS)-Based Newborn Screening: A Technical Study to Prepare for the Challenges Ahead

Newborn screening (NBS) aims to identify neonates with severe conditions for whom immediate treatment is required. Currently, a biochemistry-first approach is used to identify these disorders, which are predominantly inherited meta1bolic disorders (IMD). Next-generation sequencing (NGS) is expected to have some advantages over the current approach, for example the ability to detect IMDs that meet all screening criteria but lack an identifiable biochemical footprint. We have now designed a technical study to explore the use of NGS techniques as a first-tier approach in NBS. Here, we describe the aim and set-up of the NGS-first for the NBS (NGSf4NBS) project, which will proceed in three steps. In Step 1, we will identify IMDs eligible for NGS-first testing, based on treatability. In Step 2, we will investigate the feasibility, limitations and comparability of different technical NGS approaches and analysis workflows for NBS, eventually aiming to develop a rapid NGS-based workflow. Finally, in Step 3, we will prepare for the incorporation of this workflow into the existing Dutch NBS program and propose a protocol for referral of a child after a positive NGS test result. The results of this study will be the basis for an additional analytical route within NBS that will be further studied for its applicability within the NBS program, e.g., regarding the ethical, legal, financial and social implications.

Diagnosis and Workup of Intellectual Disability in Adults: Suggested Strategies for the Adult Neurologist

Purpose of Review

Etiologic investigations for adults with intellectual disability (ID) pose a special challenge to many adult neurologists. The adaptability of pediatric guidelines for workup of ID to adult populations has not been clearly established. We review the current recommendations on etiologic workup of ID in children and adults and provide initial guidance for adult neurologists who care for individuals with ID of unknown etiology.

Recent Findings

Etiologic workup, including genetic testing, is recommended in individuals with ID of unknown origin. Workup should be guided by a thoughtful history and physical examination, which can help identify certain causes of ID.

Summary

Specific diagnoses may help guide management and surveillance of comorbid conditions in individuals with ID. Etiologic investigations of adults with ID include genetic and metabolic testing and brain imaging in the appropriate clinical setting.

Diagnostic yield from routine metabolic screening tests in evaluation of global developmental delay and intellectual disability

Global developmental delay and intellectual disability (GDD/ID) affect 3% of the paediatric population. Although inborn errors of metabolism (IEM) are not a common cause of GDD/ID, early therapeutic intervention can improve neurodevelopmental manifestations. In 2012, a first-tier test panel, including specialized metabolic and routine chemistry tests, was piloted to community-based paediatricians in British Columbia with aims to achieve earlier diagnosis of treatable IEM.

Objective

The aim of this retrospective review was to evaluate the diagnostic yield from these first-tier tests in the 7 years before (2006 to 2012) and after (2013 to 2019) implementation at the community paediatrician level.

Results

Prior and postimplementation diagnostic yield of an IEM from first-tier metabolic testing was 9 out of 986 (0.91%) and 11 out of 4,345 children (0.25%), respectively. Disorders of creatine metabolism and organic acidurias were the most frequently established diagnoses in both time periods. No diagnoses were established through acylcarnitine copper/ceruloplasmin, lactate, or ammonia testing. Twenty out of 24 patients had specific neurological or other red flag signs in addition to GDD/ID. Four boys diagnosed with an x-linked creatine transporter defect (CTD) had speech-language delay as the most prominent finding.

Conclusions

The expansion of first-tier metabolic testing to community-based paediatricians in BC did not yield an increase in IEM diagnoses. A modified first-tier test panel should be offered to patients with GDD/ID, neurologic, and/or red flag signs. Urine creatine testing in boys with speech-language delay warrants consideration to detect CTD.

Secondary biogenic amine deficiencies: genetic etiology, therapeutic interventions, and clinical effects

Monoamine neurotransmitter disorders present predominantly with neurologic features, including dystonic or dyskinetic cerebral palsy and movement disorders. Genetic conditions that lead to secondary defects in the synthesis, catabolism, transport, and metabolism of biogenic amines can lead to neurotransmitter abnormalities, which can present with similar features. Eleven patients with secondary neurotransmitter abnormalities were enrolled between 2011 and 2015. All patients underwent research-based whole exome and/or whole genome sequencing (WES/WGS). A trial of treatment with levodopa/carbidopa and 5-hydroxytryptophan was initiated. In six families with abnormal neurotransmitter profiles and neurological phenotypes, variants in known disease-causing genes (KCNJ6, SCN2A, CSTB in 2 siblings, NRNX1, KIF1A and PAK3) were identified, while one patient had a variant of uncertain significance in a candidate gene (DLG4) that may explain her phenotype. In 3 patients, no compelling candidate genes were identified. A trial of neurotransmitter replacement therapy led to improvement in motor and behavioral symptoms in all but two patients. The patient with KCNJ6 variant did not respond to L-dopa therapy, but rather experienced increased dyskinetic movements even at low dose of medication. The patient's symptoms harboring the NRNX1 deletion remained unaltered. This study demonstrates the utility of genome-wide sequencing in further understanding the etiology and pathophysiology of neurometabolic conditions, and the potential of secondary neurotransmitter deficiencies to serve as novel therapeutic targets. As there was a largely favorable response to therapy in our case series, a careful trial of neurotransmitter replacement therapy should be considered in patients with cerebrospinal fluid (CSF) monoamines below reference range.

Brief Report: Delayed Diagnosis of Treatable Inborn Errors of Metabolism in Children with Autism and Other Neurodevelopmental Disorders

The objective of our study was to evaluate the frequency of treatable inborn errors of metabolism (IEM) in a clinical sample of Mexican children and adolescents with neurodevelopmental disorders (NDD). Amino acids and acylcarnitines in blood samples of 51 unrelated children and adolescents were analyzed by tandem mass spectrometry to detect treatable IEM of small molecules. One patient with isovaleric acidemia and autism spectrum disorder (ASD) and another with beta-ketothiolase deficiency and ASD/intellectual disability/attention-deficit/hyperactivity disorder (ADHD) were diagnosed, indicating an IEM frequency of 3.9% (1:26 subjects). The high frequency of treatable IEM indicates the need to perform a minimum metabolic screening as part of the diagnostic approach for patient with NDD, particularly when newborn screening programs are limited to a few disorders.

Treatable inherited metabolic disorders causing intellectual disability: 2021 review and digital app

BACKGROUND

The Treatable ID App was created in 2012 as digital tool to improve early recognition and intervention for treatable inherited metabolic disorders (IMDs) presenting with global developmental delay and intellectual disability (collectively 'treatable IDs'). Our aim is to update the 2012 review on treatable IDs and App to capture the advances made in the identification of new IMDs along with increased pathophysiological insights catalyzing therapeutic development and implementation.

METHODS

Two independent reviewers queried PubMed, OMIM and Orphanet databases to reassess all previously included disorders and therapies and to identify all reports on Treatable IDs published between 2012 and 2021. These were included if listed in the International Classification of IMDs (ICIMD) and presenting with ID as a major feature, and if published evidence for a therapeutic intervention improving ID primary and/or secondary outcomes is available. Data on clinical symptoms, diagnostic testing, treatment strategies, effects on outcomes, and evidence levels were extracted and evaluated by the reviewers and external experts. The generated knowledge was translated into a diagnostic algorithm and updated version of the App with novel features.

RESULTS

Our review identified 116 treatable IDs (139 genes), of which 44 newly identified, belonging to 17 ICIMD categories. The most frequent therapeutic interventions were nutritional, pharmacological and vitamin and trace element supplementation. Evidence level varied from 1 to 3 (trials, cohort studies, case-control studies) for 19% and 4-5 (case-report, expert opinion) for 81% of treatments. Reported effects included improvement of clinical deterioration in 62%, neurological manifestations in 47% and development in 37%.

CONCLUSION

The number of treatable IDs identified by our literature review increased by more than one-third in eight years. Although there has been much attention to gene-based and enzyme replacement therapy, the majority of effective treatments are nutritional, which are relatively affordable, widely available and (often) surprisingly effective. We present a diagnostic algorithm (adjustable to local resources and expertise) and the updated App to facilitate a swift and accurate workup, prioritizing treatable IDs. Our digital tool is freely available as Native and Web App (www.treatable-id.org) with several novel features. Our Treatable ID endeavor contributes to the Treatabolome and International Rare Diseases Research Consortium goals, enabling clinicians to deliver rapid evidence-based interventions to our rare disease patients.

Systematic Review of N-of-1 Studies in Rare Genetic Neurodevelopmental Disorders: The Power of 1

OBJECTIVE

To improve the use of N-of-1 studies in rare genetic neurodevelopmental disorders, we systematically reviewed the literature and formulated recommendations for future studies.

METHODS

The systematic review protocol was registered in the PROSPERO International Prospective Register of Systematic Reviews (CRD42020154720). EMBASE and MEDLINE were searched for relevant studies. Information was recorded on types of interventions, outcome measures, validity, strengths, and limitations using standard reporting guidelines and critical appraisal tools. Qualitative and descriptive analyses were performed.

RESULTS

Twelve studies met the N-of-1 inclusion criteria, including both single trials and series. Interventions were mainly directed to neuropsychiatric manifestations. Main strengths were the use of personalized and clinically relevant outcomes in most studies. Generalizability was compromised due to limited use of validated and generalizable outcome measures.

CONCLUSION

N-of-1 studies are sporadically reported in rare genetic neurodevelopmental disorders. Properly executed N-of-1 studies may provide a powerful alternative to larger randomized controlled trials in rare disorders and a much needed bridge between practice and science. We provide recommendations for future N-of-1 studies in rare genetic neurodevelopmental disorders, ultimately optimizing evidence-based and personalized care.

Genetic and metabolic investigations for individuals with neurodevelopmental disorders: A survey of Canadian geneticists' practices

Neurodevelopmental disorders (NDDs) are genetically heterogeneous. There are many possible etiological investigations for NDDs, and a lack of clear and current guidelines for such testing. Here we characterize the practices of genetic and metabolic physicians in Canada as it pertains to etiological investigation of patients with NDDs, by means of an online questionnaire. The survey response rate was 30% (n = 46). The most commonly ordered first-line tests for patients with non-syndromic NDDs are chromosomal microarray (98%) and Fragile X testing (85%). The most commonly ordered second-line test for non-syndromic NDDs is a multi-gene panel (78%) or exome sequencing (29%). Biochemical screening is ordered as a first line test by 33% of respondents, second line by 31%, and rarely or never by 36% of respondents. Those respondents with metabolics fellowship training were more likely to order biochemical screening than those without. The number of years of clinical experience generally did not affect the types of tests ordered. For patients with NDDs, test-ordering practice among Canadian clinical geneticists is highly variable, in particular with respect to biochemical screening and use of next-generation sequencing technologies. Evidence-based guidelines should be developed to facilitate best practices in Canada.

Case Report: Rapid Treatment of Uridine-Responsive Epileptic Encephalopathy Caused by CAD Deficiency

We present two unrelated Chinese patients with CAD deficiency manifesting with a triad of infantile-onset psychomotor developmental delay with regression, drug-refractory epilepsy, and anaemia with anisopoikilocytosis. Timely translation into uridine supplementation, within 2-months of disease onset, allowed us to stop conventional anti-epileptic drugs and led to dramatic improvement in the clinical symptoms, with prompt cessation of seizures, resolution of anaemia, developmental progress, and prevention of development of severe and non-reversible manifestations. The remarkable recovery and prevention of advanced disease with prompt treatment, highlights the need to act immediately upon genetic diagnosis of a treatable disease. This further reinforces CAD deficiency as a treatable neurometabolic disorder and emphasises the need for a biomarker or genetic new born screening for early identification.

Inhibiting phosphoglycerate dehydrogenase counteracts chemotherapeutic efficacy against MYCN-amplified neuroblastoma

Here we sought metabolic alterations specifically associated with MYCN amplification as nodes to indirectly target the MYCN oncogene. Liquid chromatography-mass spectrometry-based proteomics identified seven proteins consistently correlated with MYCN in proteomes from 49 neuroblastoma biopsies and 13 cell lines. Among these was phosphoglycerate dehydrogenase (PHGDH), the rate-limiting enzyme in de novo serine synthesis. MYCN associated with two regions in the PHGDH promoter, supporting transcriptional PHGDH regulation by MYCN. Pulsed stable isotope-resolved metabolomics utilizing ¹³ C-glucose labeling demonstrated higher de novo serine synthesis in MYCN-amplified cells compared to cells with diploid MYCN. An independence of MYCN-amplified cells from exogenous serine and glycine was demonstrated by serine and glycine starvation, which attenuated nucleotide pools and proliferation only in cells with diploid MYCN but did not diminish these endpoints in MYCN-amplified cells. Proliferation was attenuated in MYCN-amplified cells by CRISPR/Cas9-mediated PHGDH knockout or treatment with PHGDH small molecule inhibitors without affecting cell viability. PHGDH inhibitors administered as single-agent therapy to NOG mice harboring patient-derived MYCN-amplified neuroblastoma xenografts slowed tumor growth. However, combining a PHGDH inhibitor with the standard-of-care chemotherapy drug, cisplatin, revealed antagonism of chemotherapy efficacy in vivo. Emergence of chemotherapy resistance was confirmed in the genetic PHGDH knockout model in vitro. Altogether, PHGDH knockout or inhibition by small molecules consistently slows proliferation, but stops short of killing the cells, which then establish resistance to classical chemotherapy. Although PHGDH inhibition with small molecules has produced encouraging results in other preclinical cancer models, this approach has limited attractiveness for patients with neuroblastoma.

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.

The diagnosis of inborn errors of metabolism in previously undiagnosed adults referred for medical genetics evaluation

Traditionally thought of as a pediatric diagnostic and therapeutic dilemma, the diagnostic rate and spectrum of inborn errors of metabolism (IEM) in the adult population is largely unknown. A retrospective chart review of patients seen by the Michigan Medicine Adult Medical Genetics Clinic for clinical evaluation from 2014 to 2018 was conducted. Patients referred for a primary indication possibly consistent with an IEM were considered. Variables included age at genetic evaluation, symptom onset age, sex, clinical course, organ systems involved, developmental history, family history and prior genetic testing. Of patients evaluated during the study period, 112 were referred for an indication possibly consistent with an IEM and underwent a complete biochemical workup with an IEM diagnostic rate of 9.8% achieved. An additional 9.8% were diagnosed with a non-IEM genetic diagnosis. Management changes were implemented in all IEM diagnoses. Metabolic disorders in the adult population are under-recognized and under-diagnosed. This report demonstrates the need for clinicians to consider these diagnoses in adults and either refer to a genetics clinic or initiate a biochemical workup. As advances in diagnosis, treatment, and life expectancy of patients with IEMs increases, recognizing and diagnosing these conditions can significantly impact care.

A diagnostic approach to syndromic retinal dystrophies with intellectual disability

Inherited retinal dystrophies are a group of monogenic disorders that, as a whole, contribute significantly to the burden of ocular disease in both pediatric and adult patients. In their syndromic forms, retinal dystrophies can be observed in association with intellectual disability, frequently alongside other systemic manifestations. There are now over 80 genes implicated in syndromic retinal dystrophies with intellectual disability. Identifying and accurately characterizing these disorders allows the clinician to narrow the differential diagnosis, evaluate for relevant associated features, arrive at a timely and accurate diagnosis, and address both sight-threatening ocular manifestations and morbidity-causing systemic manifestations. The co-occurrence of retinal dystrophy and intellectual disability in an individual can be challenging to investigate, diagnose, and counsel given the considerable phenotypic and genotypic heterogeneity that exists within this broad group of disorders. We performed a review of the current literature and propose an algorithm to facilitate the evaluation, and clinical and mechanistic classification, of these individuals.

Intellectual disability and nutrition-related health

Intellectual disability (ID) is a condition that affects approximately 1% of the population (Maulik et al, 2011). The numbers may differ across nations, owing to different systems and diagnosis entries or lack of such, but usually range between 0.6 and 3% (Stromme & Valvatne, 1998). Persons with ID are a heterogeneous group with different diagnoses and different levels of intellectual ability. These range from profound (IQ < 20) and serious ID (IQ 20–34) to moderate (IQ 35–49) and light ID (IQ 50–69); this roughly translates into the intellectual capacity of children between 3–12 years of age. More than 75% of persons with ID have the mild form and their intellectual capacity and potential may be underestimated in some cases if IQ is the only diagnostic criteria. However, the range in itself is an important factor to take into account when addressing nutrition and health issues. It is further important to recognize that ID is also a feature of several rare disorders, and many disorders not yet identified, adding to the complexity of this group.

Vascular Homeostasis and Inflammation in Health and Disease-Lessons from Single Cell Technologies

The vascular system is critical infrastructure that transports oxygen and nutrients around the body, and dynamically adapts its function to an array of environmental changes. To fulfil the demands of diverse organs, each with unique functions and requirements, the vascular system displays vast regional heterogeneity as well as specialized cell types. Our understanding of the heterogeneity of vascular cells and the molecular mechanisms that regulate their function is beginning to benefit greatly from the rapid development of single cell technologies. Recent studies have started to analyze and map vascular beds in a range of organs in healthy and diseased states at single cell resolution. The current review focuses on recent biological insights on the vascular system garnered from single cell analyses. We cover the themes of vascular heterogeneity, phenotypic plasticity of vascular cells in pathologies such as atherosclerosis and cardiovascular disease, as well as the contribution of defective microvasculature to the development of neurodegenerative disorders such as Alzheimer's disease. Further adaptation of single cell technologies to study the vascular system will be pivotal in uncovering the mechanisms that drive the array of diseases underpinned by vascular dysfunction.

Neural metabolic imbalance induced by MOF dysfunction triggers pericyte activation and breakdown of vasculature

Mutations in chromatin-modifying complexes and metabolic enzymes commonly underlie complex human developmental syndromes affecting multiple organs. A major challenge is to determine how disease-causing genetic lesions cause deregulation of homeostasis in unique cell types. Here we show that neural-specific depletion of three members of the non-specific lethal (NSL) chromatin complex-Mof, Kansl2 or Kansl3-unexpectedly leads to severe vascular defects and brain haemorrhaging. Deregulation of the epigenetic landscape induced by the loss of the NSL complex in neural cells causes widespread metabolic defects, including an accumulation of free long-chain fatty acids (LCFAs). Free LCFAs induce a Toll-like receptor 4 (TLR4)-NFκB-dependent pro-inflammatory signalling cascade in neighbouring vascular pericytes that is rescued by TLR4 inhibition. Pericytes display functional changes in response to LCFA-induced activation that result in vascular breakdown. Our work establishes that neurovascular function is determined by the neural metabolic environment.

Utility of metabolic screening in neurological presentations of infancy

Background

The first‐line use of specialized metabolic screening laboratories in the investigation of hypotonia and/or developmental delay remains a standard practice despite lack of supporting evidence. Our study aimed to address the utility of such testing by determining the proportion of patients whose diagnosis was directly supported by metabolic screening.

Methods

We performed a retrospective chart review study of 164 patients under age one who had screening metabolic laboratory testing done within the time period of one calendar year.

Results

Of patients screened, 9/164 (5.5%) had diagnoses supported by metabolic testing (two with nonketotic hyperglycinemia, three with ornithine transcarbamylase deficiency, one with propionic acidemia, one with a congenital disorder of glycosylation, one with D‐bifunctional protein deficiency, and one with GM1 Gangliosidosis). Of patients specifically evaluated for hypotonia and/or developmental delay, 5/79 (6.3%) were diagnosed with the aid of metabolic testing. All patients with positive screens presented with acute decompensation. Outside of this subgroup of high‐risk patients, no patients were diagnosed using metabolic testing. Screening laboratories were also ineffective in an outpatient setting, identifying only one of the seven outpatients who was ultimately diagnosed with an inborn error of metabolism.

Conclusions

These findings demonstrate that the yield of specialized metabolic screening testing is extremely low in infants with hypotonia and/or developmental delay, approaching zero outside of the specific setting of clinical decompensation or multi‐system involvement. Furthermore, many outpatient cases of IEM are not identified by screening studies. This information will help guide the diagnostic evaluation of hypotonia and/or global developmental delay.

Whole Exome Sequencing Identifies a Novel Mutation of TPK1 in a Chinese Family with Recurrent Ataxia

TPK deficiency, also known as thiamine metabolism dysfunction syndrome 5, is a rare autosomal recessive disorder of inborn error of metabolism caused by TPK1 gene mutation. Its clinical manifestation is highly variable, ranging from spontaneous remission to fatal metabolic crisis. Here, we describe two affected siblings in a Chinese family presenting with recurrent episodes of acute ataxia. Whole exome sequencing identified a homozygous missense variant c.382C > T (p.Leu128Phe) in the TPK gene, which is located in the thiamine binding domain and affects a highly conserved amino acid. Besides, a review of the 18 previously reported patients provides a better understanding of the clinical and genetic features of this disorder. TPK deficiency may be an under-diagnosed cause of acute encephalopathy and ataxia. Given the potential benefit of early intervention, TPK deficiency should be considered in patients with episodic encephalopathy or ataxia, especially those associated with lactic acidosis and α-ketoglutaric aciduria. Significant decreased TPP in the blood is a strong hint of the disease. WES (whole exome sequencing) can help to further identify the molecular diagnosis.

Genetic Counseling in Neurodevelopmental Disorders

Neurodevelopmental disorders (NDDs), including global developmental delay (GDD), intellectual disability (ID), and autism spectrum disorder (ASD), represent a continuum of developmental brain dysfunction. Although the etiology of NDD is heterogeneous, genetic variation represents the largest contribution, strongly supporting the recommendation for genetic evaluation in individuals with GDD/ID and ASD. Technological advances now allow for a specific genetic diagnosis to be identified in a substantial portion of affected individuals. This information has important ramifications for treatment, prognosis, and recurrence risk, as well as psychological and social benefits for the family. Genetic counseling is a vital service to enable patients and their families to understand and adapt to the genetic contribution to NDDs. As the demand for genetic evaluation for NDDs increases, genetic counselors will have a predominant role in the ongoing evaluation of NDDs, especially as identification of genetic etiologies has the potential to lead to targeted treatments for NDDs in the future.

Genetic Counseling and Genome Sequencing in Pediatric Rare Disease

Both genome sequencing (GS) and exome sequencing (ES) have proven to be revolutionary in the diagnosis of pediatric rare disease. The diagnostic potential and increasing affordability make GS and ES more accessible as a routine clinical test in some centers. Herein, I review aspects of rare disease in pediatrics associated with the use of genomic technologies with an emphasis on the benefits and limitations of both ES and GS, complexities of variant classification, and the importance of genetic counseling. Indications for testing, the role of genetic counselors in genomic test selection, and the diagnostic potential of ES and GS in various pediatric multisystem disorders are discussed. The neonatal population represents an important cohort in pediatric rare disease. Rapid ES and GS in critically ill neonates can have an immediate impact on medical management and present unique genetic counseling challenges. This work includes reviews of recommendations for genetic counseling for families considering genome-wide sequencing, and issues of access to genetic counseling that affect clinical use and will necessitate implementation of innovative methods such as online decision aids. Finally, this work will also review the challenges of having a child with a rare disease, the impact of results from ES and GS on these families, and the role of various support agencies.

A Scoping Review of Inborn Errors of Metabolism Causing Progressive Intellectual and Neurologic Deterioration (PIND)

Background: Progressive intellectual and neurological deterioration (PIND) is a rare but severe childhood disorder characterized by loss of intellectual or developmental abilities, and requires quick diagnosis to ensure timely treatment to prevent possible irreversible neurological damage. Inborn errors of metabolism (IEMs) constitute a group of more than 1,000 monogenic conditions in which the impairment of a biochemical pathway is intrinsic to the pathophysiology of the disease, resulting in either accumulation of toxic metabolites and/or shortage of energy and building blocks for the cells. Many IEMs are amenable to treatment with the potential to improve outcomes. With this literature review we aim to create an overview of IEMs presenting with PIND in children, to aid clinicians in accelerating the diagnostic process.

Methods: We performed a PubMed search on IEMs presenting with PIND in individuals aged 0–18 years. We applied stringent selection criteria and subsequently derived information on encoding genes, pathways, clinical and biochemical signs and diagnostic tests from IEMbase (www.iembase.org) and other sources.

Results: The PubMed search resulted in a total of 2,152 articles and a review of references added another 19 articles. After applying our selection criteria, a total of 85 IEMs presenting with PIND remained, of which 57 IEMs were reported in multiple unrelated cases and 28 in single families. For 44 IEMs (52%) diagnosis can be achieved through generally accessible metabolic blood and urine screening tests; the remainder requires enzymatic and/or genetic testing. Treatment targeting the underlying pathophysiology is available for 35 IEMs (41%). All treatment strategies are reported to achieve stabilization of deterioration, and a subset improved seizure control and/or neurodevelopment.

Conclusions: We present the first comprehensive overview of IEMs presenting with PIND, and provide a structured approach to diagnosis and overview of treatability. Clearly IEMs constitute the largest group of genetic PIND conditions and have the advantage of detectable biomarkers as well as amenability to treatment. Thus, the clinician should keep IEMs at the forefront of the diagnostic workup of a child with PIND. With the ongoing discovery of new IEMs, expanded phenotypes, and novel treatment strategies, continuous updates to this work will be required.

Personalized medicine in genetic epilepsies - possibilities, challenges, and new frontiers

Identifying the optimal treatment based on specific characteristics of each patient is the main promise of precision medicine. In the field of epilepsy, the identification of more than 100 causative genes provides the enticing possibility of treatments targeted to specific disease etiologies. These conditions include classical examples, such as the use of vitamin B6 in antiquitin deficiency or the ketogenic diet in GLUT1 deficiency, where the disease mechanism can be directly addressed by the selection of a specific therapeutic compound. For epilepsies caused by channelopathies there have been advances in understanding how the selection of existing medications can be targeted to the functional consequences of genetic alterations. We discuss the examples of the use of sodium channel blockers such as phenytoin and oxcarbazepine in the sodium channelopathies, quinidine in KCNT1-related epilepsies, and strategies in GRIN-related epilepsies as examples of epilepsy precision medicine. Assessing the clinical response to targeted treatments of these conditions has been complicated by genetic and phenotypic heterogeneity, as well as by various neurological and non-neurological comorbidities. Moving forward, the development of standardized outcome measures will be critical to successful precision medicine trials in complex and heterogeneous disorders like the epilepsies. Finally, we address new frontiers in epilepsy precision medicine, including the need to match the growing volume of genetic data with high-throughput functional assays to assess the functional consequences of genetic variants and the ability to extract clinical data at large scale from electronic medical records and apply quantitative methods based on standardized phenotyping language.

Inborn Errors of Metabolism in the Era of Untargeted Metabolomics and Lipidomics

Inborn errors of metabolism (IEMs) are a group of inherited diseases with variable incidences. IEMs are caused by disrupting enzyme activities in specific metabolic pathways by genetic mutations, either directly or indirectly by cofactor deficiencies, causing altered levels of compounds associated with these pathways. While IEMs may present with multiple overlapping symptoms and metabolites, early and accurate diagnosis of IEMs is critical for the long-term health of affected subjects. The prevalence of IEMs differs between countries, likely because different IEM classifications and IEM screening methods are used. Currently, newborn screening programs exclusively use targeted metabolic assays that focus on limited panels of compounds for selected IEM diseases. Such targeted approaches face the problem of false negative and false positive diagnoses that could be overcome if metabolic screening adopted analyses of a broader range of analytes. Hence, we here review the prospects of using untargeted metabolomics for IEM screening. Untargeted metabolomics and lipidomics do not rely on predefined target lists and can detect as many metabolites as possible in a sample, allowing to screen for many metabolic pathways simultaneously. Examples are given for nontargeted analyses of IEMs, and prospects and limitations of different metabolomics methods are discussed. We conclude that dedicated studies are needed to compare accuracy and robustness of targeted and untargeted methods with respect to widening the scope of IEM diagnostics.

Diagnostic contribution of metabolic workup for neonatal inherited metabolic disorders in the absence of expanded newborn screening

Inherited metabolic disorders (IMDs) in neonates are a diagnostic and therapeutic challenge for the neonatologist, with the priority being to rapidly flag the treatable diseases. The objective of this study was to evaluate the contribution of targeted metabolic testing for diagnosing suspected IMDs on the basis of suggestive clinical setting or family history in neonates. We conducted an observational study over five years, from January 1st, 2010 to December 31, 2014 in the neonatal intensive care unit (NICU) at Robert Debré University Hospital, Paris, France. We assessed the number of neonates for whom a metabolic testing was performed, the indication for each metabolic test and the diagnostic yield of this selected metabolic workup for diagnosing an IMD. Metabolic testing comprised at least one of the following testings: plasma, urine or cerebrospinal fluid amino acids, urine organic acids, plasma acylcarnitine profile, and urine mucopolysaccharides and oligosaccharides. 11,301 neonates were admitted at the neonatal ICU during the study period. One hundred and ninety six neonates underwent metabolic testing. Eleven cases of IMDs were diagnosed. This diagnostic approach allowed the diagnosis, treatment and survival of 4 neonates (maple syrup urine disease, propionic acidemia, carnitine-acylcarnitine translocase deficiency and type 1 tyrosinemia). In total, metabolic testing was performed for 1.7% of the total number of neonates admitted in the NICU over the study period. These included 23% finally unaffected neonates with transient abnormalities, 5.6% neonates suffering from an identified IMD, 45.4% neonates suffering from a non-metabolic identified disease and 26% neonates with chronic abnormalities but for whom no final causal diagnosis could be made. In conclusion, as expected, such a metabolic targeted workup allowed the diagnosis of classical neonatal onset IMDs in symptomatic newborns. However, this workup remained normal or unspecific for 94.4% of the tested patients. It allowed excluding an IMD in 68.4% of the tested neonates. In spite of the high rate of normal results, such a strategy seems acceptable due to the severity of the symptoms and the need for immediate treatment when available in neonatal IMDs. However, its cost-effectiveness remains low especially in a clinically targeted population in a country where newborn screening is still unavailable for IMDs except for phenylketonuria in 2019.

Glutaminase Deficiency Caused by Short Tandem Repeat Expansion in GLS

We report an inborn error of metabolism caused by an expansion of a GCA-repeat tract in the 5' untranslated region of the gene encoding glutaminase (GLS) that was identified through detailed clinical and biochemical phenotyping, combined with whole-genome sequencing. The expansion was observed in three unrelated patients who presented with an early-onset delay in overall development, progressive ataxia, and elevated levels of glutamine. In addition to ataxia, one patient also showed cerebellar atrophy. The expansion was associated with a relative deficiency of GLS messenger RNA transcribed from the expanded allele, which probably resulted from repeat-mediated chromatin changes upstream of the GLS repeat. Our discovery underscores the importance of careful examination of regions of the genome that are typically excluded from or poorly captured by exome sequencing.

P4 medicine for epilepsy and intellectual disability: nutritional therapy for inherited metabolic disease

Early identification and treatment of inherited metabolic diseases (IMDs) are essential to prevent and minimize intellectual disability (ID) and epilepsy. The oldest form of treatment, nutritional modulation, has proved beneficial for many IMDs. These conditions represent a promising model for P4 medicine - predictive, preventive, personalized, and participatory - specifically through the interpretation of individual genetic, pathophysiological, and clinical characteristics. More than 1000 IMDs have been described, and for these different nutritional modulation strategies are applied, varying from substrate reduction, supplementation of vitamins for catalyzation of enzymatic reactions or supplementation of amino acids or other nutrients, to substitution for deficient or inactivated products. This review provides an overview of all IMDs presenting with epilepsy and/or ID amenable to nutritional modulation; these are 85 in number, belonging to 27 categories. Therapeutic strategies include protein-restricted diet, ketogenic diet, fat-restricted diet, lactose-restricted diet; supplementation of amino acids, carbohydrates, or others; and supplementation of vitamins or cofactors as well as a sick-day protocol. Nutritional therapies are generally safe, affordable, and accessible, but compliance is an issue. Three different types of response exist: (1) a positive effect on seizure control and/or psychomotor development; (2) efficacy in prevention of decompensation but ongoing damage occurs; and (3) insufficient insights or evidence to establish the treatment as effective. For the latter category, we describe pyridoxine-dependent epilepsy as a case vignette for P4 medicine, discuss the benefits and challenges of nutritional modulation in IMDs, and outline novel approaches and solutions.

Metabolic Evaluation of Epilepsy: A Diagnostic Algorithm With Focus on Treatable Conditions

Although inborn errors of metabolism do not represent the most common cause of seizures, their early identification is of utmost importance, since many will require therapeutic measures beyond that of common anti-epileptic drugs, either in order to control seizures, or to decrease the risk of neurodegeneration. We translate the currently-known literature on metabolic etiologies of epilepsy (268 inborn errors of metabolism belonging to 21 categories, with 74 treatable errors), into a 2-tiered diagnostic algorithm, with the first-tier comprising accessible, affordable, and less invasive screening tests in urine and blood, with the potential to identify the majority of treatable conditions, while the second-tier tests are ordered based on individual clinical signs and symptoms. This resource aims to support the pediatrician, neurologist, biochemical, and clinical geneticists in early identification of treatable inborn errors of metabolism in a child with seizures, allowing for timely initiation of targeted therapy with the potential to improve outcomes.

The role of integrated behavioral health in caring for patients with metabolic disorders

This review of integrated behavioral health (IBH) provides a background on IBH models, and the benefits of IBH in pediatric practice with an emphasis on how IBH specialists can collaborate with families and clinicians. An overview of intellectual disability (ID) and psychiatric disorders focused on disorders of inborn errors of metabolism (IEM) highlights issues in assessment and monitoring of these patients with implications for clinical practice and the role of IBH in caring for patients with IEM disorders.

L’évaluation de l’enfant ayant un retard global du développement ou un handicap intellectuel

Le retard global du développement (RGD) et le handicap intellectuel (HI) font partie des problèmes courants en milieu pédiatrique. Leur étiologie est très hétérogène. L’American Academy of Pediatrics , l’American Academy of Neurology et le protocole Treatable Intellectual Disability Endeavor (TIDE) de la Colombie-Britannique préconisent des explorations du RGD et du HI en plusieurs étapes, afin d’orienter les médecins vers une recherche étiologique qui optimise le rendement thérapeutique. Le présent document de principes propose un cadre pour l’exploration clinique du RGD et du HI chez les enfants, de même qu’une mise à jour du protocole d’exploration étiologique que peuvent suivre les médecins canadiens. Le protocole révisé repose sur les connaissances à jour et les lignes directrices en place. Les principaux éléments de l’exploration comprennent des tests de la vision et de l’ouïe en bonne et due forme, l’analyse chromosomique sur micropuce, le test d’ADN du gène de l’X fragile et les tests de niveau 1 de dépistage des erreurs innées du métabolisme traitables. En cas de manifestations neurologiques particulières, l’imagerie cérébrale est recommandée.

Evaluation of the Child With Developmental Impairments

PURPOSE OF REVIEW

This article discusses the diagnostic evaluation of intellectual developmental disorder, comprising global developmental delay and intellectual disability in children.

RECENT FINDINGS

With a prevalence of 1% to 3% and substantial comorbidity, high lifetime costs, and emotional burden, intellectual developmental disorder is characterized by limitations in both intellectual functioning (IQ less than 70) and adaptive behavior starting before 18 years of age. Pinpointing the precise genetic cause is important, as it allows for accurate genetic counseling, avoidance of unnecessary testing, prognostication, and tailored management, which, for an increasing number of genetic conditions, targets the pathophysiology and improves outcomes.

SUMMARY

The etiology of intellectual developmental disorder is heterogeneous, which mandates a structured approach that considers family situation, test costs, yield, and potential therapeutic tractability of the identified condition. Diagnosis of an underlying genetic cause is increasingly important with the advent of new treatments. Still, in many cases, the cause remains unknown, and research is needed to elucidate its complex molecular basis.

Evaluation of the child with global developmental delay and intellectual disability

Global developmental delay (GDD) and intellectual disability (ID) are common concerns in the paediatric setting. Etiologies of both conditions are highly heterogeneous. The American Academy of Pediatrics, the American Academy of Neurology and the British Columbia-based Treatable Intellectual Disability Endeavor (TIDE) protocol have each proposed multitiered investigations of GDD/ID to guide physicians toward an understanding of etiology that optimizes therapeutic yield. This statement provides a framework for the clinical investigation of GDD/ID in children, along with an updated protocol for Canadian physicians to follow in the etiological investigation of GDD/ID. The revised protocol is based on current knowledge and existing guidelines. Key elements of investigation include formal vision and hearing testing, chromosomal microarray, Fragile-X DNA testing and first-tier testing for treatable inborn errors of metabolism. Brain imaging is recommended in the presence of specific neurological findings.

The Genomic Consultation Service: A clinical service designed to improve patient selection for genome-wide sequencing in British Columbia

BACKGROUND

Access to clinical diagnostic genome-wide sequencing (GWS; exome or whole genome sequencing) is limited in British Columbia. The establishment of a translational research initiative (CAUSES) to provide diagnostic genome-wide sequencing for 500 children necessitated the development of a genomic consultation service, a clinical service established to provide consultation for physicians considering GWS for their pediatric patients throughout British Columbia. The Genomic Consultation Service provides patient-specific genomic advice that may include: GWS, multi-gene panel, single gene test, referral to medical genetics for clinical evaluation, or no genetic testing. Here, we describe and evaluate this service.

METHODS

We analyzed referral patterns, patient demographics, clinical indications, and genomic advice provided during the first year of this service. Comparison of outcomes from the first 6 months versus the last 6 months was performed.

RESULTS

A total of 407 referrals (238 males and 169 females [p = .0006]) were processed in the first year. Only children were eligible for referral and average patient age was 8 years. Medical genetics was the most frequent referring discipline, followed by biochemical disease and pediatric neurology, respectively. Most patients (68%) had syndromic intellectual disability. There was a significant difference in the frequency of referrals not appropriate for GWS in the first versus the second 6 months of the service (75/220 vs. 42/187; p = .01) suggesting increasing awareness of testing criteria by referring physicians.

CONCLUSION

This triage service is utilized throughout the province and appears to be an important factor in the high diagnostic rate (>40%) achieved in our GWS program.

Gain-of-function KCNJ6 Mutation in a Severe Hyperkinetic Movement Disorder Phenotype

Here, we describe a fourth case of a human with a de novo KCNJ6 (GIRK2) mutation, who presented with clinical findings of severe hyperkinetic movement disorder and developmental delay, similar to the Keppen-Lubinsky syndrome but without lipodystrophy. Whole-exome sequencing of the patient's DNA revealed a heterozygous de novo variant in the KCNJ6 (c.512T>G, p.Leu171Arg). We conducted in vitro functional studies to determine if this Leu-to-Arg mutation alters the function of GIRK2 channels. Heterologous expression of the mutant GIRK2 channel alone produced an aberrant basal inward current that lacked G protein activation, lost K⁺ selectivity and gained Ca²⁺ permeability. Notably, the inward current was inhibited by the Na⁺ channel blocker QX-314, similar to the previously reported weaver mutation in murine GIRK2. Expression of a tandem dimer containing GIRK1 and GIRK2(p.Leu171Arg) did not lead to any currents, suggesting heterotetramers are not functional. In neurons expressing p.Leu171Arg GIRK2 channels, these changes in channel properties would be expected to generate a sustained depolarization, instead of the normal G protein-gated inhibitory response, which could be mitigated by expression of other GIRK subunits. The identification of the p.Leu171Arg GIRK2 mutation potentially expands the Keppen-Lubinsky syndrome phenotype to include severe dystonia and ballismus. Our study suggests screening for dominant KCNJ6 mutations in the evaluation of patients with severe movement disorders, which could provide evidence to support a causal role of KCNJ6 in neurological channelopathies.

The role of the clinician in the multi-omics era: are you ready?

Since Garrod's first description of alkaptonuria in 1902, and newborn screening for phenylketonuria introduced in the 1960s, P4 medicine (preventive, predictive, personalized, and participatory) has been a reality for the clinician serving patients with inherited metabolic diseases. The era of high-throughput technologies promises to accelerate its scale dramatically. Genomics, transcriptomics, epigenomics, proteomics, glycomics, metabolomics, and lipidomics offer an amazing opportunity for holistic investigation and contextual pathophysiologic understanding of inherited metabolic diseases for precise diagnosis and tailored treatment. While each of the -omics technologies is important to systems biology, some are more mature than others. Exome sequencing is emerging as a reimbursed test in clinics around the world, and untargeted metabolomics has the potential to serve as a single biochemical testing platform. The challenge lies in the integration and cautious interpretation of these big data, with translation into clinically meaningful information and/or action for our patients. A daunting but exciting task for the clinician; we provide clinical cases to illustrate the importance of his/her role as the connector between physicians, laboratory experts and researchers in the basic, computer, and clinical sciences. Open collaborations, data sharing, functional assays, and model organisms play a key role in the validation of -omics discoveries. Having all the right expertise at the table when discussing the diagnostic approach and individualized management plan according to the information yielded by -omics investigations (e.g., actionable mutations, novel therapeutic interventions), is the stepping stone of P4 medicine. Patient participation and the adjustment of the medical team's plan to his/her and the family's wishes most certainly is the capstone. Are you ready?