Asparagine synthetase deficiency detected by whole exome sequencing causes congenital microcephaly, epileptic encephalopathy and psychomotor delay

L-Cysteine: A promising nutritional supplement for alleviating anxiety disorders

Anxiety disorders are prevalent chronic psychological disease with complex pathogenic mechanisms. Current anxiolytics have limited efficacy and numerous side effects in many anxiety patients, highlighting the urgent need for new therapies. Recent research has been focusing on nutritional supplements, particularly amino acids, as potential therapies for anxiety disorders. Among these, L-Cysteine plays a crucial role in various biological processes. L-Cysteine exhibits antioxidant properties that can enhance the antioxidant functions of the central nervous system (CNS). Furthermore, metabolites of L-cysteine, such as glutathione and hydrogen sulfide have been shown to alleviate anxiety through distinct molecular mechanisms. Long-term administration of L-Cysteine has anxiolytic, antidepressant, and memory-improving effects. L-Cysteine depletion can lead to increased oxidative stress in the brain. This review delves into the potential mechanisms of L-Cysteine and its main products, glutathione (GSH) and hydrogen sulfide (H2S) in the management of anxiety and related diseases.

Utility of AlphaMissense predictions in Asparagine Synthetase deficiency variant classification

AlphaMissense is a recently developed method that is designed to classify missense variants into pathogenic, benign, or ambiguous categories across the entire human proteome. Asparagine Synthetase Deficiency (ASNSD) is a developmental disorder associated with severe symptoms, including congenital microcephaly, seizures, and premature death. Diagnosing ASNSD relies on identifying mutations in the asparagine synthetase (ASNS) gene through DNA sequencing and determining whether these variants are pathogenic or benign. Pathogenic ASNS variants are predicted to disrupt the protein's structure and/or function, leading to asparagine depletion within cells and inhibition of cell growth. AlphaMissense offers a promising solution for the rapid classification of ASNS variants established by DNA sequencing and provides a community resource of pathogenicity scores and classifications for newly diagnosed ASNSD patients. Here, we assessed AlphaMissense's utility in ASNSD by benchmarking it against known critical residues in ASNS and evaluating its performance against a list of previously reported ASNSD-associated variants. We also present a pipeline to calculate AlphaMissense scores for any protein in the UniProt database. AlphaMissense accurately attributed a high average pathogenicity score to known critical residues within the two ASNS active sites and the connecting intramolecular tunnel. The program successfully categorized 78.9% of known ASNSD-associated missense variants as pathogenic. The remaining variants were primarily labeled as ambiguous, with a smaller proportion classified as benign. This study underscores the potential role of AlphaMissense in classifying ASNS variants in suspected cases of ASNSD, potentially providing clarity to patients and their families grappling with ongoing diagnostic uncertainty.

Case report: A compound heterozygous mutations in ASNS broadens the spectrum of asparagine synthetase deficiency in the prenatal diagnosis

Asparagine synthetase deficiency (ASNSD) is a rare congenital disorder characterized by severe progressive microcephaly, global developmental delay, spastic quadriplegia, and refractory seizures. ASNSD is caused by variations of the ASNS gene. The present study showed a Chinese family with a fetus suffering microcephaly. Whole-exome sequencing and Sanger sequencing were used to identify the disease-associated genetic variants. Compound heterozygous variants c.97C>T p. (R33C) and c.1031-2_1033del were identified in the ASNS gene and the variants were inherited from the parents. The mutation site c.97C>T was highly conserved across a wide range of species and predicted to alter the local electrostatic potential. The variant c.1031-2_1033del was classified pathogenic. However, there is no case report of prenatal diagnosis of ASNSD. This is the first description of fetal compound mutations in the ASNS gene leading to ASNSD, which expanded the spectrum of ASNSD.

Amino acid metabolism in health and disease

Amino acids are the building blocks of protein synthesis. They are structural elements and energy sources of cells necessary for normal cell growth, differentiation and function. Amino acid metabolism disorders have been linked with a number of pathological conditions, including metabolic diseases, cardiovascular diseases, immune diseases, and cancer. In the case of tumors, alterations in amino acid metabolism can be used not only as clinical indicators of cancer progression but also as therapeutic strategies. Since the growth and development of tumors depend on the intake of foreign amino acids, more and more studies have targeted the metabolism of tumor-related amino acids to selectively kill tumor cells. Furthermore, immune-related studies have confirmed that amino acid metabolism regulates the function of effector T cells and regulatory T cells, affecting the function of immune cells. Therefore, studying amino acid metabolism associated with disease and identifying targets in amino acid metabolic pathways may be helpful for disease treatment. This article mainly focuses on the research of amino acid metabolism in tumor-oriented diseases, and reviews the research and clinical research progress of metabolic diseases, cardiovascular diseases and immune-related diseases related to amino acid metabolism, in order to provide theoretical basis for targeted therapy of amino acid metabolism.

Characterizing asparagine synthetase deficiency variants in lymphoblastoid cell lines

Asparagine synthetase (ASNS) catalyzes the synthesis of asparagine (Asn) from aspartate and glutamine. Biallelic mutations in the ASNS gene result in ASNS Deficiency (ASNSD). Children with ASNSD exhibit congenital microcephaly, epileptic-like seizures, and continued brain atrophy, often leading to premature mortality. This report describes a 4-year-old male with global developmental delay and seizures with two novel mutations in the ASNS gene, c.614A > C (maternal) and c.1192dupT (paternal) encoding p.H205P and p.Y398Lfs*4 variants, respectively. We employed the novel use of immortalized lymphoblastoid cell lines (LCL) to show that the proliferation of the heterozygotic parental LCL was not severely affected by culture in Asn-free medium, but growth of the child's cells was suppressed by about 50%. Asn production by the LCL from both the father and the child was significantly decreased relative to the mother's cells. mRNA and protein analysis of the paternal LCL cells for the Y398Lfs*4 variant revealed reductions in both. Attempts to ectopically express the truncated Y398Lfs*4 variant in either HEK293T or ASNS-null cells resulted in little or no detectable protein. Expression and purification of the H205P variant from HEK293T cells revealed enzymatic activity similar to wild-type ASNS. Stable expression of WT ASNS rescued the growth of ASNS-null JRS cells in Asn-free medium and the H205P variant was only slightly less effective. However, the Y398Lfs*4 variant appeared to be unstable in JRS cells. These results indicate that co-expression of the H205P and Y398Lfs*4 variants leads to a significant reduction in Asn synthesis and cellular growth.

Monoallelic and biallelic mutations in RELN underlie a graded series of neurodevelopmental disorders

Reelin, a large extracellular protein, plays several critical roles in brain development and function. It is encoded by RELN, first identified as the gene disrupted in the reeler mouse, a classic neurological mutant exhibiting ataxia, tremors and a 'reeling' gait. In humans, biallelic variants in RELN have been associated with a recessive lissencephaly variant with cerebellar hypoplasia, which matches well with the homozygous mouse mutant that has abnormal cortical structure, small hippocampi and severe cerebellar hypoplasia. Despite the large size of the gene, only 11 individuals with RELN-related lissencephaly with cerebellar hypoplasia from six families have previously been reported. Heterozygous carriers in these families were briefly reported as unaffected, although putative loss-of-function variants are practically absent in the population (probability of loss of function intolerance = 1). Here we present data on seven individuals from four families with biallelic and 13 individuals from seven families with monoallelic (heterozygous) variants of RELN and frontotemporal or temporal-predominant lissencephaly variant. Some individuals with monoallelic variants have moderate frontotemporal lissencephaly, but with normal cerebellar structure and intellectual disability with severe behavioural dysfunction. However, one adult had abnormal MRI with normal intelligence and neurological profile. Thorough literature analysis supports a causal role for monoallelic RELN variants in four seemingly distinct phenotypes including frontotemporal lissencephaly, epilepsy, autism and probably schizophrenia. Notably, we observed a significantly higher proportion of loss-of-function variants in the biallelic compared to the monoallelic cohort, where the variant spectrum included missense and splice-site variants. We assessed the impact of two canonical splice-site variants observed as biallelic or monoallelic variants in individuals with moderately affected or normal cerebellum and demonstrated exon skipping causing in-frame loss of 46 or 52 amino acids in the central RELN domain. Previously reported functional studies demonstrated severe reduction in overall RELN secretion caused by heterozygous missense variants p.Cys539Arg and p.Arg3207Cys associated with lissencephaly suggesting a dominant-negative effect. We conclude that biallelic variants resulting in complete absence of RELN expression are associated with a consistent and severe phenotype that includes cerebellar hypoplasia. However, reduced expression of RELN remains sufficient to maintain nearly normal cerebellar structure. Monoallelic variants are associated with incomplete penetrance and variable expressivity even within the same family and may have dominant-negative effects. Reduced RELN secretion in heterozygous individuals affects only cortical structure whereas the cerebellum remains intact. Our data expand the spectrum of RELN-related neurodevelopmental disorders ranging from lethal brain malformations to adult phenotypes with normal brain imaging.

Increased glycine contributes to synaptic dysfunction and early mortality in Nprl2 seizure model

Targeted therapies for epilepsies associated with the mTORC1 signaling negative regulator GATOR1 are lacking. NPRL2 is a subunit of the GATOR1 complex and mutations in GATOR1 subunits, including NPRL2, are associated with epilepsy. To delineate the mechanisms underlying NPRL2-related epilepsies, we created a mouse (Mus musculus) model with neocortical loss of Nprl2. Mutant mice have increased mTORC1 signaling and exhibit spontaneous seizures. They also display abnormal synaptic function characterized by increased evoked and spontaneous EPSC and decreased evoked and spontaneous IPSC frequencies, respectively. Proteomic and metabolomics studies of Nprl2 mutants revealed alterations in known epilepsy-implicated proteins and metabolic pathways, including increases in the neurotransmitter, glycine. Furthermore, glycine actions on the NMDA receptor contribute to the electrophysiological and survival phenotypes of these mice. Taken together, in this neuronal Nprl2 model, we delineate underlying molecular, metabolic, and electrophysiological mechanisms contributing to mTORC1-related epilepsy, providing potential therapeutic targets for epilepsy.

Microcephaly in Neurometabolic Diseases

Neurometabolic disorders are an important group of diseases that mostly occur in neonates and infants. They are mainly due to the lack or dysfunction of an enzyme or cofactors necessary for a specific biochemical reaction, which leads to a deficiency of essential metabolites in the brain. This, in turn, can cause certain neurometabolic diseases. Disruption of metabolic pathways, and the inhibition at earlier stages, may lead to the storage of reaction intermediates, which are often toxic to the developing brain. Symptoms are caused by the progressive deterioration of mental, motor, and perceptual functions. The authors review the diseases with microcephaly, which may be one of the most visible signs of neurometabolic disorders.

Asparagine Synthetase Deficiency with Intracranial Hemorrhage Can Mimic Molybdenum Cofactor Deficiency

Here we report a consanguineous Egyptian family with two siblings presented with congenital microcephaly, early-onset epileptic encephalopathy, feeding difficulties, and early lethality. The condition was initially diagnosed as molybdenum cofactor deficiency as the brain imaging for one of them showed brain edema and intracranial hemorrhage in addition to the hypoplastic corpus callosum, vermis hypoplasia, and small-sized pons. Subsequently, whole exome sequencing identified a novel homozygous missense variant in exon 4 of ASNS gene c.397_398GT > CA (p.Val133Gln) confirming the diagnosis of asparagine synthetase deficiency syndrome. No discernible alternative cause for the intracranial hemorrhage was found. Our patient is the second to show asparagine synthetase deficiency and intracranial hemorrhage, thus confirming the involvement of ASNS gene. As such, it is important to consider asparagine synthetase deficiency syndrome in patients with microcephaly, brain edema, and neonatal intracranial hemorrhage.

Effects of A6E Mutation on Protein Expression and Supramolecular Assembly of Yeast Asparagine Synthetase

Simple Summary

Certain mutations causing extremely low abundance of asparagine synthetase (the enzyme responsible for producing asparagine, one of the amino acids required for normal growth and development) have been identified in humans with neurological problems and small head and brain size. Currently, yeast is becoming more popular in modeling many human diseases. In this study, we incorporate a mutation, associated with human asparagine synthetase deficiency, into the yeast asparagine synthetase gene to demonstrate that this mutation can also show similar effects as those observed in humans, leading to very low abundance of yeast asparagine synthetase and slower yeast growth rate. This suggests that our yeast system can be alternatively used to initially screen for any drugs that can help rescue the protein levels of asparagine synthetase before applying them to further studies in mammals and humans. Furthermore, this mutation might specifically be introduced into the asparagine synthetase gene of the target cancer cells in order to suppress the overproduction of asparagine synthetase within these abnormal cells, therefore inhibiting the growth of cancer, which might be helpful for patients with blood cancer to prevent them developing any resistance to the conventional asparaginase treatment.

Abstract

Asparagine synthetase deficiency (ASD) has been found to be caused by certain mutations in the gene encoding human asparagine synthetase (ASNS). Among reported mutations, A6E mutation showed the greatest reduction in ASNS abundance. However, the effect of A6E mutation has not yet been tested with yeast asparagine synthetase (Asn1/2p). Here, we constructed a yeast strain by deleting ASN2 from its genome, introducing the A6E mutation codon to ASN1, along with GFP downstream of ASN1. Our mutant yeast construct showed a noticeable decrease of Asn1p(A6E)-GFP levels as compared to the control yeast expressing Asn1p(WT)-GFP. At the stationary phase, the A6E mutation also markedly lowered the assembly frequency of the enzyme. In contrast to Asn1p(WT)-GFP, Asn1p(A6E)-GFP was insensitive to changes in the intracellular energy levels upon treatment with sodium azide during the log phase or fresh glucose at the stationary phase. Our study has confirmed that the effect of A6E mutation on protein expression levels of asparagine synthetase is common in both unicellular and multicellular eukaryotes, suggesting that yeast could be a model of ASD. Furthermore, A6E mutation could be introduced to the ASNS gene of acute lymphoblastic leukemia patients to inhibit the upregulation of ASNS by cancer cells, reducing the risk of developing resistance to the asparaginase treatment.

Rapid exome sequencing and adjunct RNA studies confirm the pathogenicity of a novel homozygous ASNS splicing variant in a critically ill neonate

Rapid genomic diagnosis programs are transforming rare disease diagnosis in acute pediatrics. A ventilated newborn with cerebellar hypoplasia underwent rapid exome sequencing (75 h), identifying a novel homozygous ASNS splice-site variant (NM_133436.3:c.1476+1G>A) of uncertain significance. Rapid ASNS splicing studies using blood-derived messenger RNA from the family trio confirmed a consistent pattern of abnormal splicing induced by the variant (cryptic 5' splice-site or exon 12 skipping) with absence of normal ASNS splicing in the proband. Splicing studies reported within 10 days led to reclassification of c.1476+1G>A as pathogenic at age 27 days. Intensive care was redirected toward palliation. Cost analyses for the neonate and his undiagnosed, similarly affected deceased sibling, demonstrate that early diagnosis reduced hospitalization costs by AU$100,828. We highlight the diagnostic benefits of adjunct RNA testing to confirm the pathogenicity of splicing variants identified via rapid genomic testing pipelines for precision and preventative medicine.

Congenital microcephaly with early onset epileptic encephalopathy caused by ASNS gene mutation: A case report

RATIONALE

Asparagine synthetase deficiency (ASNSD) refers to a congenital metabolic abnormality caused by mutation in the asparagine synthetase (ASNS) gene encoded by chromosome 7q21. Herein, we report the first case of ASNSD in China, in which novel ASNS mutations were identified.

PATIENT CONCERNS

A 6-month-old boy presented with a 4-month history of microcephaly and psychomotor developmental retardation and a 2-month history of epilepsy. Four months after birth, magnetic resonance imaging demonstrated a giant cyst in the right lateral ventricle, and a ventriculoperitoneal shunt was placed. Video electroencephalography showed a hypsarrhythmia pattern with a string of tonic-clonic and myoclonic seizures. On admission, physical examination showed microcephaly. Neurologic examination showed a decreased tension in the trunk muscles and an increased tension in the extremity muscles; tendon hyperreflexia was noted, and bilateral pathologic reflexes were positive.

DIAGNOSIS

A diagnosed of congenital microcephaly was made. Whole-exome sequencing revealed a heterozygous deletion mutation c.666_667delCT (p.L2221Lfs*5) in exon 6 of the ASNS gene and a heterozygous missense mutation c.1424C>T (p.T457I) in exon 13 of the ASNS gene.

INTERVENTIONS

After admission, intravenous adrenocorticotropic hormone and oral topiramate was administrated for 4 weeks, while the seizures persisted. Then, levetiracetam and clonazepam were added.

OUTCOMES

After the follow-up period of 18 months, video electroencephalography showed that complex episodes disappeared with changes in multiple focal spike and sharp waves; 1 focal attack arising from the left occipital region and 2 focal attacks arising from the right middle temporal and the right occipital region were recorded.

LESSONS

This is the first case of ASNSD in China. We identified 2 novel mutations (c.666_667delCT and c.1424C>T) in the ASNS gene, which expands the ASNS gene mutation profile and will be beneficial for genetic diagnosis.

High Expression of Asparagine Synthetase Is Associated with Poor Prognosis of Breast Cancer in Chinese Population

Aims: This study aimed to determine the expression of asparagine synthetase (ASNS) in breast cancer (BC) tissues and estimate its prognostic value for BC patients. Besides, the roles of ASNS in the proliferation of BC cells were also examined in the study. Methods: Quantitative real-time PCR was conducted to detect the expression of ASNS mRNA in BC tissues and normal controls. The relationship between ASNS expression and clinical characteristics of BC patients was analyzed using χ-square test. MTT assay was performed to explore the effect of ASNS expression on the proliferation of BC cells. Kaplan-Meier curves were plotted to describe the overall survival rate of BC patients. Cox regression analyses were implemented to investigate prognostic factors. Results: ASNS mRNA overexpression was observed in BC tissues (p < 0.05). High expression of ASNS was significantly related to histological grade (p = 0.017), vascular invasion (p = 0.009), and PR status (p = 0.014). The downregulation of ASNS affected the proliferation of BC cells (p < 0.05). Kaplan-Meier survival showed that patients with high ASNS expression lived shorter than those with low expressions (p < 0.001). Finally, Cox regression analyses revealed that ASNS could act as a prognostic marker for BC patients (p < 0.001, HR = 3.293, 95% CI = 1.790-6.058). Conclusion: Taken together, ASNS is a valuable prognostic biomarker for BC patients.

A novel compound heterozygous missense mutation in ASNS broadens the spectrum of asparagine synthetase deficiency

Background

Asparagine synthetase deficiency (ASNSD) is a rare pediatric congenital disorder that clinically manifests into severe progressive microcephaly, global developmental delay, spastic quadriplegia, and refractory seizures. ASNSD is caused by inheritable autosomal recessive mutations in the asparagine synthetase (ASNS) gene.

Methods

We performed whole‐exome sequencing using the patient's peripheral blood, and newly discovered mutations were subsequently verified in the patient's parents via Sanger sequencing. Software‐based bioinformatics analyses (protein sequence conservation analysis, prediction of protein phosphorylation sites, protein structure modeling, and protein stability prediction) were performed to investigate and deduce their downstream effects.

Results

In this article, we summarized all the previously reported cases of ASNSD and that of a Chinese girl who was clinically diagnosed with ASNSD, which was later confirmed via genetic testing. Whole‐exome sequencing revealed two compound heterozygous missense mutations within the ASNS (c.368T > C, p.F123S and c.1649G > A, p.R550H). The origin of the two mutations was also verified in the patient's parents via Sanger sequencing. The mutation c.368T > C (p.F123S) was discovered and confirmed to be novel and previously unreported. Using software‐based bioinformatics analyses, we deduced that the two mutation sites are highly conserved across a wide range of species, with the ability to alter different phosphorylation sites and destabilize the ASNS protein structure. The newly identified p.F123S mutation was predicted to be the most significantly destabilizing and detrimental mutation to the ASNS protein structure, compared to all other previously reported mutations.

Conclusion

Evidently, the presence of these compound heterozygous mutations could lead to severe clinical phenotypes and serve as a potential indicator for considerably higher risk with less optimistic prognosis in ASNSD patients.

Asparagine synthetase deficiency: A novel case with an unusual molecular mechanism

We report the case of a girl with Asparagine synthetase deficiency, an autosomal recessive metabolic disorder characterized by severe microcephaly and epileptic encephalopathy secondary to pathogenic variants in the ASNS gene. Genetic explorations found a deletion of ASNS and a missense variant on the other allele detected respectively by array comparative genomic hybridization (CGH) and Sanger sequencing. Amino acid analysis provided a biochemical confirmation. Previous cases of Asparagine synthetase deficiency were diagnosed though exome Sequencing. The combination of several techniques (array CGH, sequencing, and biochemical analysis) improves the opportunity to provide accurate diagnosis.

Clinical outcomes of two patients with a novel pathogenic variant in ASNS: response to asparagine supplementation and review of the literature

Asparagine synthetase deficiency (ASNSD, OMIM #615574) is a rare autosomal recessive neurometabolic inborn error that leads to severe cognitive impairment. It manifests with microcephaly, intractable seizures, and progressive cerebral atrophy. Currently, there is no established treatment for this condition. In our pediatric cohort, we discovered, by whole-exome sequencing in two siblings from Turkey, a novel homozygous missense mutation in asparagine synthetase at NM_133436.3 (ASNS_v001): c.1108C>T that results in an amino acid exchange p.(Leu370Phe), in the C-terminal domain. After identification of the metabolic defect, treatment with oral asparagine supplementation was attempted in both patients for 24 months. Asparagine supplementation was well tolerated, and no further disease progression was observed during treatment. One of our patients showed mild developmental progress with increased levels of attention and improved nonverbal communication. These results support our hypothesis that asparagine supplementation should be further investigated as a treatment option for ASNSD. We further reviewed all previously reported ASNSD cases with regard for their clinical phenotypes and brain imaging findings to provide an essential knowledge base for rapid diagnosis and future clinical studies.

Molecular diagnosis of asparagine synthetase (ASNS) deficiency in two Indian families and literature review of 29 ASNS deficient cases

In the current study, we report three cases of Asparagine Synthetase (ASNS) Deficiency from two consanguineous families. Family 1 had two early neonatal deaths due to a novel mutation in the ASNS gene c.788C > T (p.S263F) and both the children presented with microcephaly and one of them had severe intracranial haemorrhage. The proband from the second family was homozygous for c.146G > A (p.R49Q) and manifested myoclonic seizures, developmental delay, coarse hair and diffuse cortical atrophy. Molecular docking studies of both the mutations revealed alteration in the ligand binding site. Till date, 26 mutations were reported in ASNS gene in 29 affected children indicating high degree of genetic heterogeneity and high mortality. Although asparagine depletion is not of diagnostic utility, multiple linear regression model suggested that asparagine levels vary to the extent of 20.6% based on glutamine and aspartate levels and ASNS deficiency results in depletion of asparagine synthesis. ASNS deficiency should be suspected in any neonate with microcephaly and epileptic encephalopathy.

Cyst-Peritoneal Shunt for the Treatment of a Progressive Intracerebral Cyst Associated with ASNS Mutation: Case Report and Literature Review

BACKGROUND

Congenital microcephaly could result from a gene mutation. Asparagine synthetase deficiency, which is caused by the asparagine synthetase (ASNS) mutation, is a rare autosomal-recessive neurometabolic disorder. It is characterized by severe developmental delay, congenital microcephaly, and seizures.

CASE DESCRIPTION

Here we present the first report on a progressive intracerebral cyst associated with ASNS mutation, which caused neurodevelopmental dysplasia. ASNS mutation was confirmed by whole-exome sequencing and is the most likely reason for the neurodevelopmental dysplasia, which results in microcephaly, refractory seizures, and congenital visual impairment. Antiepileptic drugs have limited therapeutic effect on these epileptic seizures.

CONCLUSIONS

Although there is no cure for this disorder so far, the huge progressive intracerebral cyst can be cured by a cyst-peritoneal shunt.

Unravelling the genetic architecture of autosomal recessive epilepsy in the genomic era

The technological advancement of next-generation sequencing has greatly accelerated the pace of variant discovery in epilepsy. Despite an initial focus on autosomal dominant epilepsy due to the tractable nature of variant discovery with trios under a de novo model, more and more variants are being reported in families with epilepsies consistent with autosomal recessive (AR) inheritance. In this review, we touch on the classical AR epilepsy variants such as the inborn errors of metabolism and malformations of cortical development. However, we also highlight recently reported genes that are being identified by next-generation sequencing approaches and online 'matchmaking' platforms. Syndromes mainly characterized by seizures and complex neurodevelopmental disorders comorbid with epilepsy are discussed as an example of the wide phenotypic spectrum associated with the AR epilepsies. We conclude with a foray into the future, from the application of whole-genome sequencing to identify elusive epilepsy variants, to the promise of precision medicine initiatives to provide novel targeted therapeutics specific to the individual based on their clinical genetic testing.

Novel Mutations in the Asparagine Synthetase Gene (ASNS) Associated With Microcephaly

Microcephaly is a devastating condition defined by a small head and small brain compared to the age- and sex-matched population. Mutations in a number of different genes causative for microcephaly have been identified, e.g., MCPH1, WDR62, and ASPM. Recently, mutations in the gene encoding the enzyme asparagine synthetase (ASNS) were associated to microcephaly and so far 24 different mutations in ASNS causing microcephaly have been described. In a family with two affected girls, we identified novel compound heterozygous variants in ASNS (c.1165G > C, p.E389Q and c.601delA, p.M201Wfs^∗28). The first mutation (E389Q) is a missense mutation resulting in the replacement of a glutamate residue evolutionary conserved from Escherichia coli to Homo sapiens by glutamine. Protein modeling based on the known crystal structure of ASNS of E. coli predicted a destabilization of the protein by E389Q. The second mutation (p.M201Wfs^∗28) results in a premature stop codon after amino acid 227, thereby truncating more than half of the protein. The novel variants expand the growing list of microcephaly causing mutations in ASNS.

Characterization of a novel variant in siblings with Asparagine Synthetase Deficiency

Asparagine Synthetase Deficiency (ASD) is a recently described inborn error of metabolism caused by bi-allelic pathogenic variants in the asparagine synthetase (ASNS) gene. ASD typically presents congenitally with microcephaly and severe, often medically refractory, epilepsy. Development is generally severely affected at birth. Tone is abnormal with axial hypotonia and progressive appendicular spasticity. Hyperekplexia has been reported. Neuroimaging typically demonstrates gyral simplification, abnormal myelination, and progressive cerebral atrophy. The present report describes two siblings from consanguineous parents with a homozygous Arg49Gln variant associated with a milder form of ASD that is characterized by later onset of symptoms. Both siblings had a period of normal development before onset of seizures, and development regression. Primary fibroblast studies of the siblings and their parents document that homozygosity for Arg49Gln blocks cell growth in the absence of extracellular asparagine. Functional studies with these cells suggest no impact of the Arg49Gln variant on basal ASNS mRNA or protein levels, nor on regulation of the gene itself. Molecular modelling of the ASNS protein structure indicates that the Arg49Gln variant lies near the substrate binding site for glutamine. Collectively, the results suggest that the Arg49Gln variant affects the enzymatic function of ASNS. The clinical, cellular, and molecular observations from these siblings expand the known phenotypic spectrum of ASD.

Asparagine synthetase: Function, structure, and role in disease

Asparagine synthetase (ASNS) converts aspartate and glutamine to asparagine and glutamate in an ATP-dependent reaction. ASNS is present in most, if not all, mammalian organs, but varies widely in basal expression. Human ASNS activity is highly responsive to cellular stress, primarily by increased transcription from a single gene located on chromosome 7. Elevated ASNS protein expression is associated with resistance to asparaginase therapy in childhood acute lymphoblastic leukemia. There is evidence that ASNS expression levels may also be inversely correlated with asparaginase efficacy in certain solid tumors as well. Children with mutations in the ASNS gene exhibit developmental delays, intellectual disability, microcephaly, intractable seizures, and progressive brain atrophy. Thus far, 15 unique mutations in the ASNS gene have been clinically associated with asparagine synthetase deficiency (ASD). Molecular modeling using the Escherichia coli ASNS-B structure has revealed that most of the reported ASD substitutions are located near catalytic sites or within highly conserved regions of the protein. For some ASD patients, fibroblast cell culture studies have eliminated protein and mRNA synthesis or stability as the basis for decreased proliferation.

Asparagine Synthetase deficiency-report of a novel mutation and review of literature

Asparagine synthetase deficiency is a rare inborn error of metabolism caused by a defect in ASNS, a gene encoding asparagine synthetase. It manifests with a severe neurological phenotype manifesting as severe developmental delay, congenital microcephaly, spasticity and refractory seizures. To date, nineteen patients from twelve unrelated families have been identified. Majority of the mutations are missense and nonsense mutations in homozygous or compound heterozygous state. We add another case from India which harbored a novel homozygous missense variation in exon 11 and compare the current case with previously reported cases.

Amino acid synthesis deficiencies

In recent years the number of disorders known to affect amino acid synthesis has grown rapidly. Nor is it just the number of disorders that has increased: the associated clinical phenotypes have also expanded spectacularly, primarily due to the advances of next generation sequencing diagnostics. In contrast to the "classical" inborn errors of metabolism in catabolic pathways, in which elevated levels of metabolites are easily detected in body fluids, synthesis defects present with low values of metabolites or, confusingly, even completely normal levels of amino acids. This makes the biochemical diagnosis of this relatively new group of metabolic diseases challenging. Defects in the synthesis pathways of serine metabolism, glutamine, proline and, recently, asparagine have all been reported. Although these amino acid synthesis defects are in unrelated metabolic pathways, they do share many clinical features. In children the central nervous system is primarily affected, giving rise to (congenital) microcephaly, early onset seizures and varying degrees of mental disability. The brain abnormalities are accompanied by skin disorders such as cutis laxa in defects of proline synthesis, collodion-like skin and ichthyosis in serine deficiency, and necrolytic erythema in glutamine deficiency. Hypomyelination with accompanying loss of brain volume and gyration defects can be observed on brain MRI in all synthesis disorders. In adults with defects in serine or proline synthesis, spastic paraplegia and several forms of polyneuropathy with or without intellectual disability appear to be the major symptoms in these late-presenting forms of amino acid disorders. This review provides a comprehensive overview of the disorders in amino acid synthesis.

PIF* promotes brain re-myelination locally while regulating systemic inflammation- clinically relevant multiple sclerosis M.smegmatis model

Neurologic disease diagnosis and treatment is challenging. Multiple Sclerosis (MS) is a demyelinating autoimmune disease with few clinical forms and uncertain etiology. Current studies suggest that it is likely caused by infection(s) triggering a systemic immune response resulting in antigen/non-antigen-related autoimmune response in central nervous system (CNS). New therapeutic approaches are needed. Secreted by viable embryos, PreImplantation Factor (PIF) possesses a local and systemic immunity regulatory role. Synthetic PIF (PIF) duplicates endogenous peptide's protective effect in pre-clinical autoimmune and transplantation models. PIF protects against brain hypoxia-ischemia by directly targeting microglia and neurons. In chronic experimental autoimmune encephalitis (EAE) model PIF reverses paralysis while promoting neural repair. Herein we report that PIF directly promotes brain re-myelination and reverses paralysis in relapsing remitting EAE MS model. PIF crosses the blood-brain barrier targeting microglia. Systemically, PIF decreases pro-inflammatory IL23/IL17 cytokines, while preserving CNS-specific T-cell repertoire. Global brain gene analysis revealed that PIF regulates critical Na+/K+/Ca++ ions, amino acid and glucose transport genes expression. Further, PIF modulates oxidative stress, DNA methylation, cell cycle regulation, and protein ubiquitination while regulating multiple genes. In cultured astrocytes, PIF promotes BDNF-myelin synthesis promoter and SLC2A1 (glucose transport) while reducing deleterious E2F5, and HSP90ab1 (oxidative stress) genes expression. In cultured microglia, PIF increases anti-inflammatory IL10 while reducing pro-inflammatory IFNγ expression. Collectively, PIF promotes brain re-myelination and neuroprotection in relapsing remitting EAE MS model. Coupled with ongoing, Fast-Track FDA approved clinical trial, NCT#02239562 (immune disorder), current data supports PIF's translation for neurodegenerative disorders therapy.

The first report of Japanese patients with asparagine synthetase deficiency

BACKGROUND

Asparagine synthetase (ASNS) deficiency was recently discovered as a metabolic disorder of non-essential amino acids, and presents as severe progressive microcephaly, intellectual disorder, dyskinetic quadriplegia, and intractable seizures.

METHODS

Two Japanese children with progressive microcephaly born to unrelated patients were analyzed by whole exome sequencing and novel ASNS mutations were identified. The effects of the ASNS mutations were analyzed by structural evaluation and in silico predictions.

RESULTS

We describe the first known Japanese patients with ASNS deficiency. Their clinical manifestations were very similar to reported cases of ASNS deficiency. Progressive microcephaly was noted during the prenatal period in patient 1 but only after birth in patient 2. Both patients had novel ASNS mutations: patient 1 had p.L145S transmitted from his mother and p.L247W which was absent from his mother, while patient 2 carried p.V489D and p.W541Cfs*5, which were transmitted from his mother and father, respectively. Three of the four mutations were predicted to affect protein folding, and in silico analyses suggested that they would be pathogenic.

CONCLUSION

We report the first two Japanese patients with ASNS deficiency. Disease severity appears to vary among patients, as is the case for other non-essential amino acid metabolic disorders.

Diaphragmatic Eventration in Sisters with Asparagine Synthetase Deficiency: A Novel Homozygous ASNS Mutation and Expanded Phenotype

BACKGROUND

Asparagine Synthetase Deficiency (ASNSD; OMIM #615574) is a newly described rare autosomal recessive neurometabolic disorder, characterised by congenital microcephaly, severe psychomotor delay, encephalopathy and progressive cerebral atrophy. To date, seven families and seven missense mutations in the ASNSD disease causing gene, ASNS, have been published.

METHODS

We report two further affected infant sisters from a consanguineous Indian family, who in addition to the previously described features had diaphragmatic eventration. Both girls died within the first 6 months of life. Whole exome sequencing (WES) was performed for both sisters to identify the pathogenic mutation. The clinical and biochemical parameters of our patient are compared to previous reports.

RESULTS

WES demonstrated a homozygous novel missense ASNS mutation, c.1019G > A, resulting in substitution of the highly conserved arginine residue by histidine (R340H).

CONCLUSION

This report expands the phenotypic and mutation spectrum of ASNSD, which should be considered in neonates with congenital microcephaly, seizures and profound neurodevelopmental delay. The presence of diaphragmatic eventration suggests extracranial involvement of the central nervous system in a disorder that was previously thought to exclusively affect the brain. Like all previously reported patients, these cases were diagnosed with WES, highlighting the clinical utility of next generation sequencing in the diagnosis of rare, difficult to recognise disorders.

Hyperekplexia, microcephaly and simplified gyral pattern caused by novel ASNS mutations, case report

Background

Asparagine synthetase deficiency (OMIM# 615574) is a very rare newly described neurometabolic disorder characterized by congenital microcephaly and severe global developmental delay, associated with intractable seizures or hyperekplexia. Brain MRI typically shows cerebral atrophy with simplified gyral pattern and delayed myelination. Only 12 cases have been described to date. The disease is caused by homozygous or compound heterozygous mutations in the ASNS gene on chromosome 7q21.

Case presentation

Family 1 is a multiplex consanguineous family with five affected members, while Family 2 is simplex. One affected from each family was available for detailed phenotyping. Both patients (Patients 1 and 2) presented at birth with microcephaly and severe hyperekplexia, and were found to have gross brain malformation characterized by simplified gyral pattern, and hypoplastic cerebellum and pons. EEG showed no epileptiform discharge in Patient 2 but multifocal discharges in patient 1. Patient 2 is currently four years old with severe neurodevelopmental delay, quadriplegia and cortical blindness. Whole exome sequencing (WES) revealed a novel homozygous mutation in ASNS (NM_001178076.1) in each patient (c.970C > T:p.(Arg324*) and c.944A > G:p.(Tyr315Cys)).

Conclusion

Our results expand the mutational spectrum of the recently described asparagine synthetase deficiency and show a remarkable clinical homogeneity among affected individuals, which should facilitate its recognition and molecular confirmation for pertinent and timely genetic counseling.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-016-0633-0) contains supplementary material, which is available to authorized users.

Worsening of Seizures After Asparagine Supplementation in a Child with Asparagine Synthetase Deficiency

OBJECTIVE

Asparagine synthetase deficiency is an autosomal recessive neurometabolic disorder characterized clinically by severe congenital microcephaly, global developmental delay, intractable epilepsy, and motor impairment in the form of spastic quadriparesis. Diagnosis is confirmed by findings of low cerebral spinal fluid or plasma asparagine in addition to a mutation of the subsequently in ASNS gene. There is no documented trial of asparagine as a treatment for this disorder.

PATIENT DESCRIPTION

We present a child with asparagine synthetase deficiency whose mental status improved slightly from a vegetative state to a minimally conscious state after starting asparagine supplementation. He subsequently became irritable, developed sleep disturbance, and experienced worsening seizures, requiring discontinuation of the asparagine supplements.

CONCLUSIONS

Asparagine supplementation may be not effective in controlling the seizures in asparagine synthetase deficiency, and it is likely to make them worse.

Neuropädiatrische Differenzialdiagnostik der Mikrozephalie im Kindesalter

Eine Mikrozephalie betrifft 2–3 % der Bevölkerung und geht oftmals mit einer Intelligenzminderung einher. Die zugrunde liegende Reduktion des Gehirnvolumens kann sowohl durch exogene Faktoren als auch durch genetische Ursachen bedingt sein. Problematisch sind sowohl die uneinheitliche Klassifikation als auch die große Heterogenität der hinter dem klinischen Zeichen Mikrozephalie stehenden Erkrankungen. Im vorliegenden Artikel stellen wir unseren Vorschlag für die diagnostische Herangehensweise an ein Kind mit Mikrozephalie aus neuropädiatrischer Sicht vor.

Asparagine Synthetase Deficiency causes reduced proliferation of cells under conditions of limited asparagine

Asparagine Synthetase Deficiency is a recently described cause of profound intellectual disability, marked progressive cerebral atrophy and variable seizure disorder. To date there has been limited functional data explaining the underlying pathophysiology. We report a new case with compound heterozygous mutations in the ASNS gene (NM_183356.3:c. [866G>C]; [1010C>T]). Both variants alter evolutionarily conserved amino acids and were predicted to be pathogenic based on in silico protein modelling that suggests disruption of the critical ATP binding site of the ASNS enzyme. In patient fibroblasts, ASNS expression as well as protein and mRNA stability are not affected by these variants. However, there is markedly reduced proliferation of patient fibroblasts when cultured in asparagine-limited growth medium, compared to parental and wild type fibroblasts. Restricting asparagine replicates the physiology within the blood-brain-barrier, with limited transfer of dietary derived asparagine, resulting in reliance of neuronal cells on intracellular asparagine synthesis by the ASNS enzyme. These functional studies offer insight into the underlying pathophysiology of the dramatic progressive cerebral atrophy associated with Asparagine Synthetase Deficiency.

Asparagine Synthetase Deficiency: New Inborn Errors of Metabolism

BACKGROUND

Asparagine synthetase deficiency (ASD) is a newly identified neurometabolic disorder characterized by severe congenital microcephaly, severe global developmental delay, intractable seizure disorder, and spastic quadriplegia. Brain MRI showed brain atrophy, delayed myelination, and simplified gyriform pattern.

METHODS

We report ASD deficiency in a 2- and 4-year-old sibling. On them, we described clinical, biochemical, and molecular findings, and we compared our results with previously reported cases.

RESULTS

We identified a homozygous novel missense mutation in ASNS gene in both probands and we demonstrated low CSF and plasma asparagine in both patients.

CONCLUSIONS

Clinicians should suspect ASD deficiency in any newborn presented with severe congenital microcephaly followed by severe epileptic encephalopathy and global developmental delay. CSF asparagine level is low in this disorder while plasma may be low.