Germline variants in tumor suppressor FBXW7 lead to impaired ubiquitination and a neurodevelopmental syndrome.

Neurodevelopmental disorders are highly heterogenous conditions resulting from abnormalities of brain architecture and/or function. FBXW7 (F-box and WD-repeat-domain-containing 7), a recognized developmental regulator and tumor suppressor, has been shown to regulate cell-cycle progression and cell growth and survival by targeting substrates including CYCLIN E1/2 and NOTCH for degradation via the ubiquitin proteasome system. We used a genotype-first approach and global data-sharing platforms to identify 35 individuals harboring de novo and inherited FBXW7 germline monoallelic chromosomal deletions and nonsense, frameshift, splice-site, and missense variants associated with a neurodevelopmental syndrome. The FBXW7 neurodevelopmental syndrome is distinguished by global developmental delay, borderline to severe intellectual disability, hypotonia, and gastrointestinal issues. Brain imaging detailed variable underlying structural abnormalities affecting the cerebellum, corpus collosum, and white matter. A crystal-structure model of FBXW7 predicted that missense variants were clustered at the substrate-binding surface of the WD40 domain and that these might reduce FBXW7 substrate binding affinity. Expression of recombinant FBXW7 missense variants in cultured cells demonstrated impaired CYCLIN E1 and CYCLIN E2 turnover. Pan-neuronal knockdown of the Drosophila ortholog, archipelago, impaired learning and neuronal function. Collectively, the data presented herein provide compelling evidence of an F-Box protein-related, phenotypically variable neurodevelopmental disorder associated with monoallelic variants in FBXW7.

TNPO2 variants associate with human developmental delays, neurologic deficits, and dysmorphic features and alter TNPO2 activity in Drosophila.

Transportin-2 (TNPO2) mediates multiple pathways including non-classical nucleocytoplasmic shuttling of >60 cargoes, such as developmental and neuronal proteins. We identified 15 individuals carrying de novo coding variants in TNPO2 who presented with global developmental delay (GDD), dysmorphic features, ophthalmologic abnormalities, and neurological features. To assess the nature of these variants, functional studies were performed in Drosophila. We found that fly dTnpo (orthologous to TNPO2) is expressed in a subset of neurons. dTnpo is critical for neuronal maintenance and function as downregulating dTnpo in mature neurons using RNAi disrupts neuronal activity and survival. Altering the activity and expression of dTnpo using mutant alleles or RNAi causes developmental defects, including eye and wing deformities and lethality. These effects are dosage dependent as more severe phenotypes are associated with stronger dTnpo loss. Interestingly, similar phenotypes are observed with dTnpo upregulation and ectopic expression of TNPO2, showing that loss and gain of Transportin activity causes developmental defects. Further, proband-associated variants can cause more or less severe developmental abnormalities compared to wild-type TNPO2 when ectopically expressed. The impact of the variants tested seems to correlate with their position within the protein. Specifically, those that fall within the RAN binding domain cause more severe toxicity and those in the acidic loop are less toxic. Variants within the cargo binding domain show tissue-dependent effects. In summary, dTnpo is an essential gene in flies during development and in neurons. Further, proband-associated de novo variants within TNPO2 disrupt the function of the encoded protein. Hence, TNPO2 variants are causative for neurodevelopmental abnormalities.

Biallelic CRELD1 variants cause a multisystem syndrome, including neurodevelopmental phenotypes, cardiac dysrhythmias, and frequent infections.

PURPOSE: We sought to delineate a multisystem disorder caused by recessive cysteine-rich with epidermal growth factor-like domains 1 (CRELD1) gene variants. METHODS: The impact of CRELD1 variants was characterized through an international collaboration utilizing next-generation DNA sequencing, gene knockdown, and protein overexpression in Xenopus tropicalis, and in vitro analysis of patient immune cells. RESULTS: Biallelic variants in CRELD1 were found in 18 participants from 14 families. Affected individuals displayed an array of phenotypes involving developmental delay, early-onset epilepsy, and hypotonia, with about half demonstrating cardiac arrhythmias and some experiencing recurrent infections. Most harbored a frameshift in trans with a missense allele, with 1 recurrent variant, p.(Cys192Tyr), identified in 10 families. X tropicalis tadpoles with creld1 knockdown displayed developmental defects along with increased susceptibility to induced seizures compared with controls. Additionally, human CRELD1 harboring missense variants from affected individuals had reduced protein function, indicated by a diminished ability to induce craniofacial defects when overexpressed in X tropicalis. Finally, baseline analyses of peripheral blood mononuclear cells showed similar proportions of immune cell subtypes in patients compared with healthy donors. CONCLUSION: This patient cohort, combined with experimental data, provide evidence of a multisystem clinical syndrome mediated by recessive variants in CRELD1.

Clinical, biochemical and molecular characterization of 12 patients with pyruvate carboxylase deficiency treated with triheptanoin.

Pyruvate carboxylase (PC) deficiency is a rare autosomal recessive mitochondrial neurometabolic disorder of energy deficit resulting in high morbidity and mortality, with limited therapeutic options. The PC homotetramer has a critical role in gluconeogenesis, anaplerosis, neurotransmitter synthesis, and lipogenesis. The main biochemical and clinical findings in PC deficiency (PCD) include lactic acidosis, ketonuria, failure to thrive, and neurological dysfunction. Use of the anaplerotic agent triheptanoin on a limited number of individuals with PCD has had mixed results. We expand on the potential utility of triheptanoin in PCD by examining the clinical, biochemical, molecular, and health-related quality-of-life (HRQoL) findings in a cohort of 12 individuals with PCD (eight with Type A and two each with Types B and C) treated with triheptanoin ranging for 6 days to about 7 years. The main endpoints were changes in blood lactate and HRQoL scores, but collection of useful data was limited to about half of subjects. An overall trend of lactate reduction with time on triheptanoin was noted, but with significant variability among subjects and only one subject reaching close to statistical significance for this endpoint. Parent reported HRQoL assessments with treatment showed mixed results, with some subjects showing no change, some improvement, and some worsening of overall scores. Subjects with buried amino acids in the pyruvate carboxyltransferase domain of PC that undergo destabilizing replacements may be more likely to respond (with lactate reduction or HRQoL improvement) to triheptanoin compared to those with replacements that disrupt tetramerization or subunit-subunit interface contacts. The reason for this difference is unclear and requires further validation. We observed significant variability but an overall trend of lactate reduction with time on triheptanoin and mixed parent reported outcome changes by HRQoL assessments for subjects with PCD on long-term triheptanoin. The mixed results noted with triheptanoin therapy in this study could be due to endpoint data limitation, variability of disease severity between subjects, limitation of the parent reported HRQoL tool, or subject genotype variability. Alternative designed trials and more study subjects with PCD will be needed to validate important observations from this work.

Variants in GNAI1 cause a syndrome associated with variable features including developmental delay, seizures, and hypotonia.

PURPOSE: Neurodevelopmental disorders (NDDs) encompass a spectrum of genetically heterogeneous disorders with features that commonly include developmental delay, intellectual disability, and autism spectrum disorders. We sought to delineate the molecular and phenotypic spectrum of a novel neurodevelopmental disorder caused by variants in the GNAI1 gene. METHODS: Through large cohort trio-based exome sequencing and international data-sharing, we identified 24 unrelated individuals with NDD phenotypes and a variant in GNAI1, which encodes the inhibitory Gαi1 subunit of heterotrimeric G-proteins. We collected detailed genotype and phenotype information for each affected individual. RESULTS: We identified 16 unique variants in GNAI1 in 24 affected individuals; 23 occurred de novo and 1 was inherited from a mosaic parent. Most affected individuals have a severe neurodevelopmental disorder. Core features include global developmental delay, intellectual disability, hypotonia, and epilepsy. CONCLUSION: This collaboration establishes GNAI1 variants as a cause of NDDs. GNAI1-related NDD is most often characterized by severe to profound delays, hypotonia, epilepsy that ranges from self-limiting to intractable, behavior problems, and variable mild dysmorphic features.

Consideration of a metabolic disorder in the differential of mild developmental delay: A case of nonketotic hyperglycinemia revisited 36 years later.

We present a 53-year-old male with nonketotic hyperglycinemia (NKH) who presented in decompensated state to our university hospital several months prior to a primary diagnosis of multifocal pneumonia accompanied by reports of seizure-like activity, altered mental status, tremors, and fever. He was initially diagnosed with NKH in his preschool years, over 40 years previously, along with his younger sister. At that time, he had developmental and physical delays (which his sister also experienced). His health course has been relatively uneventful otherwise, as regards decompensation of his disease, and he has not been on the standard regimens of reduced dietary glycine intake along with dextromethorphan and sodium benzoate. Recent molecular confirmation of NKH was completed and both he and his sibling likely have an attenuated form of NKH mediated by the combined effects of their variants. This paper presents what we believe to be report of the oldest surviving individuals with attenuated NKH.

1H NMR metabolomics study of age profiling in children.

Metabolic profiling of urine provides a fingerprint of personalized endogenous metabolite markers that correlate to a number of factors such as gender, disease, diet, toxicity, medication, and age. It is important to study these factors individually, if possible to unravel their unique contributions. In this study, age-related metabolic changes in children of age 12 years and below were analyzed by (1)H NMR spectroscopy of urine. The effect of age on the urinary metabolite profile was observed as a distinct age-dependent clustering even from the unsupervised principal component analysis. Further analysis, using partial least squares with orthogonal signal correction regression with respect to age, resulted in the identification of an age-related metabolic profile. Metabolites that correlated with age included creatinine, creatine, glycine, betaine/TMAO, citrate, succinate, and acetone. Although creatinine increased with age, all the other metabolites decreased. These results may be potentially useful in assessing the biological age (as opposed to chronological) of young humans as well as in providing a deeper understanding of the confounding factors in the application of metabolomics.

Hyperammonemia in the ICU.

Patients experiencing acute elevations of ammonia present to the ICU with encephalopathy, which may progress quickly to cerebral herniation. Patient survival requires immediate treatment of intracerebral hypertension and the reduction of ammonia levels. When hyperammonemia is not thought to be the result of liver failure, treatment for an occult disorder of metabolism must begin prior to the confirmation of an etiology. This article reviews ammonia metabolism, the effects of ammonia on the brain, the causes of hyperammonemia, and the diagnosis of inborn errors of metabolism in adult patients.

An atypical case of Canavan disease with stroke-like presentation.

BACKGROUND: Canavan disease is an autosomal recessive leukodystrophy caused by a deficiency of aspartoacylase. The disease has a severe course, with death occurring in the first few years of life. Atypical patients with mild courses have been reported, but acute presentations similar to stroke have not been well described. PATIENT DESCRIPTION: We present a boy who presented at 4 months of age with seizures after an episode of cardiopulmonary arrest is discussed. RESULTS: He was initially thought to have an ischemic watershed stroke based on his initial clinical presentation and magnetic resonance imaging. However, biochemical and follow-up radiologic evaluation were consistent with mild Canavan disease. DNA sequencing of the ASPA gene indicated one known mutation (A305E) and a novel mutation, L30V. Follow-up magnetic resonance imaging did not reveal the atrophy which would have been expected with watershed ischemia. Magnetic resonance spectroscopy demonstrated elevated N-acetyl aspartate to creatinine and N-acetyl aspartate to choline ratios. At 4 years of age, he was normocephalic, with mild clumsiness, speech delay, and seizures. CONCLUSIONS: This child's unusual acute presentation, along with his prolonged mild course, raises questions about the relationship between biochemical signs of abnormal aspartoacylase function and clinical findings. This patient highlights the need for long-term clinical follow-up of children with mild Canavan disease to clarify the significance of these biochemical abnormalities.

Neonatal Graves' disease associated with severe metabolic abnormalities.

Neonatal Graves' disease is a rare condition that is sometimes associated with multisystem abnormalities that can mimic infection or inborn errors of metabolism. Here we describe the cases of 2 infants who had serious metabolic derangements including conjugated hyperbilirubinemia and hyperammonemia.

Class selection of amino acid metabolites in body fluids using chemical derivatization and their enhanced 13C NMR.

We report a chemical derivatization method that selects a class of metabolites from a complex mixture and enhances their detection by 13C NMR. Acetylation of amines directly in aqueous medium with 1,1'-13C(2) acetic anhydride is a simple method that creates a high sensitivity and quantitative label in complex biofluids with minimal sample pretreatment. Detection using either 1D or 2D 13C NMR experiments produces highly resolved spectra with improved sensitivity. Experiments to identify and compare amino acids and related metabolites in normal human urine and serum samples as well as in urine from patients with the inborn errors of metabolism tyrosinemia type II, argininosuccinic aciduria, homocystinuria, and phenylketonuria demonstrate the method. The use of metabolite derivatization and 13C NMR spectroscopy produces data suitable for metabolite profiling analysis of biofluids on a time scale that allows routine use. Extension of this approach to enhance the NMR detection of other classes of metabolites has also been accomplished. The improved detection of low-concentration metabolites shown here creates opportunities to improve the understanding of the biological processes and develop improved disease detection methodologies.

Principal component analysis of urine metabolites detected by NMR and DESI-MS in patients with inborn errors of metabolism.

Urine metabolic profiles of patients with inborn errors of metabolism were examined with nuclear magnetic resonance (NMR) and desorption electrospray ionization mass spectrometry (DESI-MS) methods. Spectra obtained from the study of urine samples from individual patients with argininosuccinic aciduria (ASA), classic homocystinuria (HCY), classic methylmalonic acidemia (MMA), maple syrup urine disease (MSUD), phenylketonuria (PKU) and type II tyrosinemia (TYRO) were compared with six control patient urine samples using principal component analysis (PCA). Target molecule spectra were identified from the loading plots of PCA output and compared with known metabolic profiles from the literature and metabolite databases. Results obtained from the two techniques were then correlated to obtain a common list of molecules associated with the different diseases and metabolic pathways. The combined approach discussed here may prove useful in the rapid screening of biological fluids from sick patients and may help to improve the understanding of these rare diseases.

Lethal neonatal and severe late infantile forms of carnitine palmitoyltransferase II deficiency associated with compound heterozygosity for different protein truncation mutations.

We describe a lethal neonatal form of carnitine palmitoyltransferase II (CPT II) deficiency with compound heterozygosity for 2 truncation mutations (Q413fs and 109AGC --> GCAGC). A new phenotype for a severe late infantile form of CPT II deficiency with hypoglycemia is associated with compound heterozygosity for the severe Q413fs mutation and a mild point mutation (P50H).

Pyruvate carboxylase deficiency--insights from liver transplantation.

Pyruvate carboxylase deficiency, complex form, presents in early infancy with lethal metabolic acidosis, resulting from ketoacidosis and lactic acidemia. Renal tubular acidosis, hyperammonemia, and citrullinemia complete the picture. In an infant with this disease, large amounts of glucose ameliorated the ketoacidosis, but worsened the lactic acidosis. Orthotopic hepatic transplantation completely reversed the ketoacidosis and the renal tubular abnormality and ameliorated the lactic acidemia. Concentrations of glutamine in cerebrospinal fluid were low and did not improve with liver transplantation.