Phosphoglycerate dehydrogenase (PHGDH) deficiency without epilepsy mimicking primary microcephaly

Precision diagnosis and treatment of vitamin metabolism-related epilepsy

Epilepsy is a chronic disorder of the nervous system caused by abnormal discharges from brain cells. Structural, infectious, metabolic, immunologic, and unknown causes can contribute to the development of seizures. In recent years, there has been increasing attention on epilepsy caused by genetic metabolic disorders. More than two hundred inherited metabolic disorders have been identified as potential cause of seizures, and they are mainly associated with energy deficiency in the brain, accumulation of toxic substances, abnormal neurotransmitter transmission, and deficiency of cofactors. Vitamins play a crucial role as components of several enzymes or coenzymes. Impaired metabolism of thiamine, biotin, vitamin B6, vitamin B12 and folic acid can contribute to early-onset seizures and developmental abnormalities in infants. However, timely supplementation therapy can significantly improve patient prognosis of affected patients. Therefore, a thorough understanding and investigation of the metabolic basis of epilepsy is essential for the development of precise therapeutic approaches, which could provide significant therapeutic benefits for patients.

Activation of nicotinic acetylcholine receptor α7 subunit limits Zika viral infection via promoting autophagy and ferroptosis

Vagus nerve regulates viral infection and inflammation via the alpha 7 nicotinic acetylcholine receptor (α7 nAChR); however, the role of α7 nAChR in ZIKA virus (ZIKV) infection, which can cause severe neurological diseases such as microcephaly and Guillain-Barré syndrome, remains unknown. Here, we first examined the role of α7 nAChR in ZIKV infection in vitro. A broad effect of α7 nAChR activation was identified in limiting ZIKV infection in multiple cell lines. Combined with transcriptomics analysis, we further demonstrated that α7 nAChR activation promoted autophagy and ferroptosis pathways to limit cellular ZIKV viral loads. Additionally, activation of α7 nAChR prevented ZIKV-induced p62 nucleus accumulation, which mediated an enhanced autophagy pathway. By regulating proteasome complex and an E3 ligase NEDD4, activation of α7 nAChR resulted in increased amount of cellular p62, which further enhanced the ferroptosis pathway to reduce ZIKV infection. Moreover, utilizing in vivo neonatal mouse models, we showed that α7 nAChR is essential in controlling the disease severity of ZIKV infection. Taken together, our findings identify an α7 nAChR-mediated effect that critically contributes to limiting ZIKV infection, and α7 nAChR activation offers a novel strategy for combating ZIKV infection and its complications.

Mild phenotypes of phosphoglycerate dehydrogenase deficiency by a novel mutation of PHGDH gene: Case report and literature review

Phosphoglycerate dehydrogenase (PHGDH) deficiency is a rare autosomal recessive genetic disease of serine biosynthesis. Its typical features are congenital microcephaly, epileptic seizures, and psychomotor developmental delay. Here, we reported the first Chinese familial cases with genetically confirmed PHGDH deficiency and reviewed several previous reports. Two siblings in this family presented with microcephaly, psychomotor retardation, and epilepsy in early juvenile. Brain magnetic resonance imaging (MRI) showed only a slight change of enlarged ventricle. Biochemical investigations revealed low serum serine and glycine concentrations. The whole-exome sequencing (WES) results identified a missense variant in the PHGDH gene (NM_006623.4: exon11: c.1211T>A, p. Val404Asp). Although two patients in this Chinese family carried the same pathogenic mutation in the PHGDH, their symptoms and responses to treatment were not exactly the same. We found a novel variant in the PHGDH gene and expanded the genotypic and phenotypic spectrum of serine biosynthesis disorders.

Serine biosynthesis defect due to haploinsufficiency of PHGDH causes retinal disease

Macular telangiectasia type 2 (MacTel) is a progressive, late-onset retinal degenerative disease linked to decreased serum levels of serine that elevate circulating levels of a toxic ceramide species, deoxysphingolipids (deoxySLs); however, causal genetic variants that reduce serine levels in patients have not been identified. Here we identify rare, functional variants in the gene encoding the rate-limiting serine biosynthetic enzyme, phosphoglycerate dehydrogenase (PHGDH), as the single locus accounting for a significant fraction of MacTel. Under a dominant collapsing analysis model of a genome-wide enrichment analysis of rare variants predicted to impact protein function in 793 MacTel cases and 17,610 matched controls, the PHGDH gene achieves genome-wide significance (P = 1.2 × 10-13) with variants explaining ~3.2% of affected individuals. We further show that the resulting functional defects in PHGDH cause decreased serine biosynthesis and accumulation of deoxySLs in retinal pigmented epithelial cells. PHGDH is a significant locus for MacTel that explains the typical disease phenotype and suggests a number of potential treatment options.

Autosomal recessive variants in TUBGCP2 alter the γ-tubulin ring complex leading to neurodevelopmental disease

Microtubules help building the cytoskeleton of neurons and other cells. Several components of the gamma-tubulin (γ-tubulin) complex have been previously reported in human neurodevelopmental diseases. We describe two siblings from a consanguineous Turkish family with dysmorphic features, developmental delay, brain malformation, and epilepsy carrying a homozygous mutation (p.Glu311Lys) in TUBGCP2 encoding the γ-tubulin complex 2 (GCP2) protein. This variant is predicted to disrupt the electrostatic interaction of GCP2 with GCP3. In primary fibroblasts carrying the variant, we observed a faint delocalization of γ-tubulin during the cell cycle but normal GCP2 protein levels. Through mass spectrometry, we observed dysregulation of multiple proteins involved in the assembly and organization of the cytoskeleton and the extracellular matrix, controlling cellular adhesion and of proteins crucial for neuronal homeostasis including axon guidance. In summary, our functional and proteomic studies link TUBGCP2 and the γ-tubulin complex to the development of the central nervous system in humans.

L-serine synthesis via the phosphorylated pathway in humans

L-serine is a nonessential amino acid in eukaryotic cells, used for protein synthesis and in producing phosphoglycerides, glycerides, sphingolipids, phosphatidylserine, and methylenetetrahydrofolate. Moreover, L-serine is the precursor of two relevant coagonists of NMDA receptors: glycine (through the enzyme serine hydroxymethyltransferase), which preferentially acts on extrasynaptic receptors and D-serine (through the enzyme serine racemase), dominant at synaptic receptors. The cytosolic "phosphorylated pathway" regulates de novo biosynthesis of L-serine, employing 3-phosphoglycerate generated by glycolysis and the enzymes 3-phosphoglycerate dehydrogenase, phosphoserine aminotransferase, and phosphoserine phosphatase (the latter representing the irreversible step). In the human brain, L-serine is primarily found in glial cells and is supplied to neurons for D-serine synthesis. Serine-deficient patients show severe neurological symptoms, including congenital microcephaly, psychomotor retardation, and intractable seizures, thus highlighting the relevance of de novo production of this amino acid in brain development and morphogenesis. Indeed, the phosphorylated pathway is strictly linked to cancer. Moreover, L-serine has been suggested as a ready-to-use treatment, as also recently proposed for Alzheimer's disease. Here, we present our current state of knowledge concerning the three mammalian enzymes of the phosphorylated pathway and known mutations related to pathological conditions: although the structure of these enzymes has been solved, how enzyme activity is regulated remains largely unknown. We believe that an in-depth investigation of these enzymes is crucial to identify the molecular mechanisms involved in modulating concentrations of the serine enantiomers and for studying the interplay between glial and neuronal cells and also to determine the most suitable therapeutic approach for various diseases.

No 380 - Évaluation et prise en charge de la microcéphalie détectée avant la naissance

OBJECTIF

Informer les fournisseurs canadiens de soins de santé périnatale des critères diagnostiques de la microcéphalie fœtale et fournir l'information sur les analyses pertinentes, le pronostic, et la prise en charge prénatale et périnatale en lien avec a cette observation prénatale.

DESTINATAIRES

Tous les fournisseurs de soins de maternité (fournisseurs principaux de soins de santé) et de soins de pédiatrie; les conseiller(e)s en génétique; les infirmièr(e)s en soins de maternité; les infirmièr(e)s practicien(ne)s, les administrateur(trice)s provinciaux de soins de maternité; les étudiant(e)s, en médecine; les résident(e)s postdoctoraux et les stagiaires (fellows). RéSULTATS: Fournir de meilleurs conseils et une prise en charge clinique adéquate aux femmes et aux familles qui ont reçu un diagnostic prénatal de microcéphalie fœtale. DONNéES PROBANTES: La documentation publiée est tirée de recherches effectuées en 2018 dans le moteur PubMed et les bases de données Medline, CINAHL et Cochrane Library au moyen de mots-clés anglais pertinents (prenatal ultrasound, prenatal imaging, fetal, antenatal ou prenatal microcephaly). Des publications supplémentaires ont été sélectionnées à partir des notices bibliographiques de ces articles. PéRIODE DE RECHERCHE: Sept ans (2010-2018); la dernière recherche a été effectuée le 19 avril 2018. L'auteur principal a terminé la validation des articles. AVANTAGES, PRéJUDICES ET COûTS: Le présent document renseigne les lecteurs au sujet (1) des critères diagnostiques de la microcéphalie fœtale, (2) de ses étiologies potentielles et (3) des analyses et options de prise en charge avant et après la naissance. Il propose une méthode fondée sur des données probantes pour établir le diagnostic et déterminer la prise en charge de la microcéphalie détectée avant la naissance. Ces recommandations sont fondées sur l'opinion d'experts, mais n'ont pas fait l'objet d'une évaluation économique de la santé. Une mise en œuvre aux échelles locale ou provinciale sera requise. Les auteurs reconnaissent que l'accès aux services et ressources mentionnés varie au Canada. Par conséquent, ces recommandations ont été formulées dans la perspective de promouvoir l'accès et de fournir une orientation pour toutes les provinces et tous les territoires du pays. CRITèRES: La solidité des données probantes indiquées s'appuie sur les critères décrits dans le rapport du Groupe d'étude canadien sur les soins de santé préventifs. RECOMMANDATIONS.

No. 380-Investigation and Management of Prenatally Identified Microcephaly

OBJECTIVE

To update Canadian maternity care and reproductive health care providers on the diagnostic criteria of fetal microcephaly and provide information on the relevant investigations, prognosis, and pre- and perinatal management of this prenatal finding.

INTENDED USERS

All maternity care (most responsible health provider [MRHP]) and pediatric providers; genetic counsellors; maternity nurses; nurse practitioners; provincial maternity care administrators; medical students; postgraduate residents, and fellows.

OUTCOMES

To provide better counselling and appropriate clinical management to women and families who have received a prenatal diagnosis of fetal microcephaly.

EVIDENCE

Published literature was retrieved through searches of PubMed or Medline, CINAHL, and The Cochrane Library in 2018, using appropriate key words (prenatal ultrasound, prenatal imaging, fetal, antenatal, or prenatal microcephaly). Additional publications were identified from the bibliographies of these articles.

SEARCH PERIOD

Seven years (2010-2018); completed final search April 19, 2018. The primary author completed validation of the articles.

BENEFITS, HARMS, AND COSTS

This document educates readers about (1) the diagnostic criteria for fetal microcephaly, (2) its potential etiologies, (3) investigation and management options both pre- and postnatally. It proposes an evidence-based approach to the diagnosis and management of prenatally detected microcephaly. These recommendations are based on expert opinion and have not been subjected to a health economics assessment. Local or provincial implementation will be required. The authors recognize that there is variability across Canada in access to the cited services and resources. As such, these recommendations were developed in an attempt to promote access and to provide guidance for all provinces and territories across the country.

VALUES

The quality of evidence was rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care.

RECOMMENDATIONS

Expanding the genotypic and phenotypic spectrum of severe serine biosynthesis disorders

Serine biosynthesis disorders comprise a spectrum of very rare autosomal recessive inborn errors of metabolism with wide phenotypic variability. Neu-Laxova syndrome represents the most severe expression and is characterized by multiple congenital anomalies and pre- or perinatal lethality. Here, we present the mutation spectrum and a detailed phenotypic analysis in 15 unrelated families with severe types of serine biosynthesis disorders. We identified likely disease-causing variants in the PHGDH and PSAT1 genes, several of which have not been reported previously. Phenotype analysis and a comprehensive review of the literature corroborates the evidence that serine biosynthesis disorders represent a continuum with varying degrees of phenotypic expression and suggest that even gradual differences at the severe end of the spectrum may be correlated with particular genotypes. We postulate that the individual residual enzyme activity of mutant proteins is the major determinant of the phenotypic variability, but further functional studies are needed to explore effects at the enzyme protein level.