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Editorial overview: Neurodevelopment Diseases and Neurogenetics pivot towards mechanisms and therapies

Geschwind DH, Gleeson JG.

Curr Opin Genet Dev. 2020 Dec;65:iii-vii. doi: 10.1016/j.gde.2020.09.001. Epub 2020 Nov 8. NO ABSTRACT PMID:33176916 | DOI:10.1016/j.gde.2020.09.001

November 12, 2020

A founder mutation in PEX12 among Egyptian patients in peroxisomal biogenesis disorder

Zaki MS, Issa MY, Thomas MM, Elbendary HM, Rafat K, Al Menabawy NM, Selim LA, Ismail S, Abdel-Salam GM, Gleeson JG. 

Neurol Sci. 2020 Oct 29. doi: 10.1007/s10072-020-04843-2. Online ahead of print. ABSTRACT At least 14 distinctive PEX genes function in the biogenesis of peroxisomes. Biallelic alterations in the peroxisomal biogenesis factor 12 (PEX12) gene lead to Zellweger syndrome spectrum (ZSS) with variable clinical expressivity ranging from early lethality to mildly affected with long-term survival. Herein, we define 20 patients derived from 14 unrelated Egyptian families, 19 of which show a homozygous PEX12 in-frame (c.1047_1049del p.(Gln349del)) deletion. This founder mutation, reported rarely outside of Egypt, was associated with a uniformly severe phenotype. Patients showed developmental delay in early life followed by motor and mental regression, progressive hypotonia, unsteadiness, and lack of speech. Seventeen patients had sparse hair or partial alopecia, a striking feature that was not noted previously in PEX12. Neonatal cholestasis was manifested in 2 siblings. Neurodiagnostics showed consistent cerebellar atrophy and variable white matter demyelination, axonal neuropathy in about half, and cardiomyopathy in 10% of patients. A single patient with a compound heterozygous PEX12 mutation exhibited milder features with late childhood onset with gait disturbance and learning disability. Thus, the PEX12 relatively common founder mutation accounts for the majority of PEX12-related disease in Egypt and delineates a uniform clinical and radiographic phenotype. PMID:33123925 | DOI:10.1007/s10072-020-04843-2

October 30, 2020

Insight into developmental mechanisms of global and focal migration disorders of cortical development

Castello MA, Gleeson JG. 

Curr Opin Neurobiol. 2020 Oct 21;66:77-84. doi: 10.1016/j.conb.2020.10.005. Online ahead of print. ABSTRACT Cortical development involves neurogenesis followed by migration, maturation, and myelination of immature neurons. Disruptions in these processes can cause malformations of cortical development (MCD). Radial glia (RG) are the stem cells of the brain, both generating neurons and providing the scaffold upon which immature neurons radially migrate. Germline mutations in genes required for cell migration, or cell-cell contact, often lead to global MCDs. Somatic mutations in RG in genes involved in homeostatic function, like mTOR signaling, often lead to focal MCDs. Two different mutations occurring in the same patient can combine in ways we are just beginning to understand. Our growing knowledge about MCD suggests mTOR inhibitors may have expanded utility in treatment-resistant epilepsy, while imaging techniques can better delineate the type and extent of these lesions. PMID:33099181 | DOI:10.1016/j.conb.2020.10.005

October 25, 2020

A relatively common homozygous TRAPPC4 splicing variant is associated with an early-infantile neurodegenerative syndrome

Ghosh SG, Scala M, Beetz C, Helman G, Stanley V, Yang X, Breuss MW, Mazaheri N, Selim L, Hadipour F, Pais L, Stutterd CA, Karageorgou V, Begtrup A, Crunk A, Juusola J, Willaert R, Flore LA, Kennelly K, Spencer C, Brown M, Trapane P, Hurst ACE, Lane Rutledge S, Goodloe DH, McDonald MT, Shashi V, Schoch K; Undiagnosed Diseases Network, Tomoum H, Zaitoun R, Hadipour Z, Galehdari H, Pagnamenta AT, Mojarrad M, Sedaghat A, Dias P, Quintas S, Eslahi A, Shariati G, Bauer P, Simons C, Houlden H, Issa MY, Zaki MS, Maroofian R, Gleeson JG. 

Eur J Hum Genet. 2021 Feb;29(2):271-279. doi: 10.1038/s41431-020-00717-5. Epub 2020 Sep 8. ABSTRACT Trafficking protein particle (TRAPP) complexes, which include the TRAPPC4 protein, regulate membrane trafficking between lipid organelles in a process termed vesicular tethering. TRAPPC4 was recently implicated in a recessive neurodevelopmental condition in four unrelated families due to a shared c.454+3A>G splice variant. Here, we report 23 patients from 17 independent families with an early-infantile-onset neurodegenerative presentation, where we also identified the homozygous variant hg38:11:119020256 A>G (NM_016146.5:c.454+3A>G) in TRAPPC4 through exome or genome sequencing. No other clinically relevant TRAPPC4 variants were identified among any of over 10,000 patients with neurodevelopmental conditions. We found the carrier frequency of TRAPPC4 c.454+3A>G was 2.4-5.4 per 10,000 healthy individuals. Affected individuals with the homozygous TRAPPC4 c.454+3A>G variant showed profound psychomotor delay, developmental regression, early-onset epilepsy, microcephaly and progressive spastic tetraplegia. Based upon RNA sequencing, the variant resulted in partial exon 3 skipping and generation of an aberrant transcript owing to use of a downstream cryptic splice donor site, predicting a premature stop codon and nonsense mediated decay. These data confirm the pathogenicity of the TRAPPC4 c.454+3A>G variant, and refine the clinical presentation of TRAPPC4-related encephalopathy. PMID:32901138 | PMC:PMC7868361 | DOI:10.1038/s41431-020-00717-5

September 9, 2020

Loss of NARS1 impairs progenitor proliferation in cortical brain organoids and leads to microcephaly

Wang L, Li Z, Sievert D, Smith DEC, Mendes MI, Chen DY, Stanley V, Ghosh S, Wang Y, Kara M, Aslanger AD, Rosti RO, Houlden H, Salomons GS, Gleeson JG. 

Nat Commun. 2020 Aug 12;11(1):4038. doi: 10.1038/s41467-020-17454-4. ABSTRACT Asparaginyl-tRNA synthetase1 (NARS1) is a member of the ubiquitously expressed cytoplasmic Class IIa family of tRNA synthetases required for protein translation. Here, we identify biallelic missense and frameshift mutations in NARS1 in seven patients from three unrelated families with microcephaly and neurodevelopmental delay. Patient cells show reduced NARS1 protein, impaired NARS1 activity and impaired global protein synthesis. Cortical brain organoid modeling shows reduced proliferation of radial glial cells (RGCs), leading to smaller organoids characteristic of microcephaly. Single-cell analysis reveals altered constituents of both astrocytic and RGC lineages, suggesting a requirement for NARS1 in RGC proliferation. Our findings demonstrate that NARS1 is required to meet protein synthetic needs and to support RGC proliferation in human brain development. PMID:32788587 | PMC:PMC7424529 | DOI:10.1038/s41467-020-17454-4

August 14, 2020

Pathogenic ARH3 mutations result in ADP-ribose chromatin scars during DNA strand break repair

Hanzlikova H, Prokhorova E, Krejcikova K, Cihlarova Z, Kalasova I, Kubovciak J, Sachova J, Hailstone R, Brazina J, Ghosh S, Cirak S, Gleeson JG, Ahel I, Caldecott KW.

Nat Commun. 2020 Jul 7;11(1):3391. doi: 10.1038/s41467-020-17069-9. ABSTRACT Neurodegeneration is a common hallmark of individuals with hereditary defects in DNA single-strand break repair; a process regulated by poly(ADP-ribose) metabolism. Recently, mutations in the ARH3 (ADPRHL2) hydrolase that removes ADP-ribose from proteins have been associated with neurodegenerative disease. Here, we show that ARH3-mutated patient cells accumulate mono(ADP-ribose) scars on core histones that are a molecular memory of recently repaired DNA single-strand breaks. We demonstrate that the ADP-ribose chromatin scars result in reduced endogenous levels of important chromatin modifications such as H3K9 acetylation, and that ARH3 patient cells exhibit measurable levels of deregulated transcription. Moreover, we show that the mono(ADP-ribose) scars are lost from the chromatin of ARH3-defective cells in the prolonged presence of PARP inhibition, and concomitantly that chromatin acetylation is restored to normal. Collectively, these data indicate that ARH3 can act as an eraser of ADP-ribose chromatin scars at sites of PARP activity during DNA single-strand break repair. PMID:32636369 | PMC:PMC7341855 | DOI:10.1038/s41467-020-17069-9

July 9, 2020

Failure to thrive – an overlooked manifestation of KMT2B-related dystonia: a case presentation

Ng A, Galosi S, Salz L, Wong T, Schwager C, Amudhavalli S, Gelineau-Morel R, Chowdhury S; Rady Children’s Institute for Genomic Medicine Investigators, Friedman J.

BMC Neurol. 2020 Jun 16;20(1):246. doi: 10.1186/s12883-020-01798-x. ABSTRACT BACKGROUND: KMT2B-related dystonia is a recently described form of childhood onset dystonia that may improve with deep brain stimulation. Prior reports have focused on neurologic features including prominent bulbar involvement without detailing general health consequences that may result from orolingual dysfunction. We describe a family with novel KMT2B mutation with several members with failure to thrive to highlight this non-neurologic, but consequential impact of mutation in this gene. CASE PRESENTATION: We present a case of a 15-year old female who was admitted and evaluated for failure to thrive. On exam, she had severe speech dysfluency, limited ability to protrude the tongue, and generalized dystonia involving the oromandibular region, right upper and left lower extremity with left foot inversion contracture. The proband and her parents underwent whole genome sequencing. A previously undescribed variant, c.4960 T > C (p.Cys1654Arg), was identified in the KMT2B gene in the proband and mother, and this variant was subsequently confirmed in two maternal cousins, one with failure to thrive. Literature review identified frequent reports of prominent bulbar involvement but failure to thrive is rarely mentioned. CONCLUSION: Failure to thrive is a common pediatric clinical condition that has consequences for growth and development. In the presence of an abnormal neurologic exam, a search for a specific underlying genetic etiology should be pursued. With this case series, we highlight an unusual potentially treatable cause of failure to thrive, reinforce the importance of precise molecular diagnosis for patients with failure to thrive and an abnormal neurologic exam, and underscore the importance of cascade screening of family members. PMID:32546208 | PMC:PMC7296679 | DOI:10.1186/s12883-020-01798-x

June 18, 2020
Genetic Neurologic DiseaseNeurogenomicsRare Disease

Consensus guideline for the diagnosis and treatment of tetrahydrobiopterin (BH4) deficiencies

Opladen T, López-Laso E, Cortès-Saladelafont E, Pearson TS, Sivri HS, Yildiz Y, Assmann B, Kurian MA, Leuzzi V, Heales S, Pope S, Porta F, García-Cazorla A, Honzík T, Pons R, Regal L, Goez H, Artuch R, Hoffmann GF, Horvath G, Thöny B, Scholl-Bürgi S, Burlina A, Verbeek MM, Mastrangelo M, Friedman J, Wassenberg T, Jeltsch K, Kulhánek J, Kuseyri Hübschmann O; International Working Group on Neurotransmitter related Disorders (iNTD).

Orphanet J Rare Dis. 2020 May 26;15(1):126. doi: 10.1186/s13023-020-01379-8. ABSTRACT BACKGROUND: Tetrahydrobiopterin (BH4) deficiencies comprise a group of six rare neurometabolic disorders characterized by insufficient synthesis of the monoamine neurotransmitters dopamine and serotonin due to a disturbance of BH4 biosynthesis or recycling. Hyperphenylalaninemia (HPA) is the first diagnostic hallmark for most BH4 deficiencies, apart from autosomal dominant guanosine triphosphate cyclohydrolase I deficiency and sepiapterin reductase deficiency. Early supplementation of neurotransmitter precursors and where appropriate, treatment of HPA results in significant improvement of motor and cognitive function. Management approaches differ across the world and therefore these guidelines have been developed aiming to harmonize and optimize patient care. Representatives of the International Working Group on Neurotransmitter related Disorders (iNTD) developed the guidelines according to the SIGN (Scottish Intercollegiate Guidelines Network) methodology by evaluating all available evidence for the diagnosis and treatment of BH4 deficiencies. CONCLUSION: Although the total body of evidence in the literature was mainly rated as low or very low, these consensus guidelines will help to harmonize clinical practice and to standardize and improve care for BH4 deficient patients. PMID:32456656 | PMC:PMC7251883 | DOI:10.1186/s13023-020-01379-8

May 28, 2020
Genetic Neurologic DiseaseNeurogenomicsRare Disease

Closing in on Mechanisms of Open Neural Tube Defects

Lee S, Gleeson JG. 

Trends Neurosci. 2020 Jul;43(7):519-532. doi: 10.1016/j.tins.2020.04.009. Epub 2020 May 15. ABSTRACT Neural tube defects (NTDs) represent a failure of the neural plate to complete the developmental transition to a neural tube. NTDs are the most common birth anomaly of the CNS. Following mandatory folic acid fortification of dietary grains, a dramatic reduction in the incidence of NTDs was observed in areas where the policy was implemented, yet the genetic drivers of NTDs in humans, and the mechanisms by which folic acid prevents disease, remain disputed. Here, we discuss current understanding of human NTD genetics, recent advances regarding potential mechanisms by which folic acid might modify risk through effects on the epigenome and transcriptome, and new approaches to study refined phenotypes for a greater appreciation of the developmental and genetic causes of NTDs. PMID:32423763 | PMC:PMC7321880 | DOI:10.1016/j.tins.2020.04.009

May 20, 2020

Molecular diagnosis in recessive pediatric neurogenetic disease can help reduce disease recurrence in families

Issa MY, Chechlacz Z, Stanley V, George RD, McEvoy-Venneri J, Belandres D, Elbendary HM, Gaber KR, Nabil A, Abdel-Hamid MS, Zaki MS, Gleeson JG.

BMC Med Genomics. 2020 May 13;13(1):68. doi: 10.1186/s12920-020-0714-1. ABSTRACT BACKGROUND: The causes for thousands of individually rare recessive diseases have been discovered since the adoption of next generation sequencing (NGS). Following the molecular diagnosis in older children in a family, parents could use this information to opt for fetal genotyping in subsequent pregnancies, which could inform decisions about elective termination of pregnancy. The use of NGS diagnostic sequencing in families has not been demonstrated to yield benefit in subsequent pregnancies to reduce recurrence. Here we evaluated whether genetic diagnosis in older children in families supports reduction in recurrence of recessive neurogenetic disease. METHODS: Retrospective study involving families with a child with a recessive pediatric brain disease (rPBD) that underwent NGS-based molecular diagnosis. Prenatal molecular testing was offered to couples in which a molecular diagnosis was made, to help couples seeking to prevent recurrence. With this information, families made decisions about elective termination. Pregnancies that were carried to term were assessed for the health of child and mother, and compared with historic recurrence risk of recessive disease. RESULTS: Between 2010 and 2016, 1172 families presented with a child a likely rPBD, 526 families received a molecular diagnosis, 91 families returned to the clinic with 101 subsequent pregnancies, and 84 opted for fetal genotyping. Sixty tested negative for recurrence for the biallelic mutation in the fetus, and all, except for one spontaneous abortion, carried to term, and were unaffected at follow-up. Of 24 that genotyped positive for the biallelic mutation, 16 were electively terminated, and 8 were carried to term and showed features of disease similar to that of the older affected sibling(s). Among the 101 pregnancies, disease recurrence in living offspring deviated from the expected 25% to the observed 12% ([95% CI 0·04 to 0·20], p = 0·011). CONCLUSIONS: Molecular diagnosis in an older child, coupled with prenatal fetal genotyping in subsequent pregnancies and genetic counselling, allows families to make informed decisions to reduce recessive neurogenetic disease recurrence. PMID:32404165 | PMC:PMC7218834 | DOI:10.1186/s12920-020-0714-1

May 15, 2020

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