title: GLRB is the third major gene of effect in hyperekplexia.
abstract: Glycinergic neurotransmission is a major inhibitory influence in the CNS and its disruption triggers a paediatric and adult startle disorder, hyperekplexia. The postsynaptic α(1)-subunit (GLRA1) of the inhibitory glycine receptor (GlyR) and the cognate presynaptic glycine transporter (SLC6A5/GlyT2) are well-established genes of effect in hyperekplexia. Nevertheless, 52% of cases (117 from 232) remain gene negative and unexplained. Ligand-gated heteropentameric GlyRs form chloride ion channels that contain the α(1) and β-subunits (GLRB) in a 2α(1):3β configuration and they form the predominant population of GlyRs in the postnatal and adult human brain, brainstem and spinal cord. We screened GLRB through 117 GLRA1- and SLC6A5-negative hyperekplexia patients using a multiplex-polymerase chain reaction and Sanger sequencing approach. The screening identified recessive and dominant GLRB variants in 12 unrelated hyperekplexia probands. This primarily yielded homozygous null mutations, with nonsense (n = 3), small indel (n = 1), a large 95 kb deletion (n = 1), frameshifts (n = 1) and one recurrent splicing variant found in four cases. A further three cases were found with two homozygous and one dominant GLRB missense mutations. We provide strong evidence for the pathogenicity of GLRB mutations using splicing assays, deletion mapping, cell-surface biotinylation, expression studies and molecular modelling. This study describes the definitive assignment of GLRB as the third major gene for hyperekplexia and impacts on the genetic stratification and biological causation of this neonatal/paediatric disorder. Driven principally by consanguineous homozygosity of GLRB mutations, the study reveals long-term additive phenotypic outcomes for affected cases such as severe apnoea attacks, learning difficulties and developmental delay.
authors.affiliation: Neurology Research and Molecular Neuroscience, Institute of Life Science, Swansea University, Swansea SA2 8PP, UK. s.chung@swansea.ac.uk
authors.forename: Seo-Kyung
authors.initials: SK
authors.lastname: Chung
authors.forename: Anna
authors.initials: A
authors.lastname: Bode
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Cushion
authors.forename: Rhys H
authors.initials: RH
authors.lastname: Thomas
authors.forename: Charlotte
authors.initials: C
authors.lastname: Hunt
authors.forename: Sian-Elin
authors.initials: SE
authors.lastname: Wood
authors.forename: William O
authors.initials: WO
authors.lastname: Pickrell
authors.forename: Cheney J G
authors.initials: CJ
authors.lastname: Drew
authors.forename: Sumimasa
authors.initials: S
authors.lastname: Yamashita
authors.forename: Rita
authors.initials: R
authors.lastname: Shiang
authors.forename: Steffen
authors.initials: S
authors.lastname: Leiz
authors.forename: Ann-Carolyn
authors.initials: AC
authors.lastname: Longardt
authors.forename: Ann-Carolyn
authors.initials: AC
authors.lastname: Longhardt
authors.forename: Vera
authors.initials: V
authors.lastname: Raile
authors.forename: Bernhard
authors.initials: B
authors.lastname: Weschke
authors.forename: Ratna D
authors.initials: RD
authors.lastname: Puri
authors.forename: Ishwar C
authors.initials: IC
authors.lastname: Verma
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Harvey
authors.forename: Didi D
authors.initials: DD
authors.lastname: Ratnasinghe
authors.forename: Michael
authors.initials: M
authors.lastname: Parker
authors.forename: Chris
authors.initials: C
authors.lastname: Rittey
authors.forename: Amira
authors.initials: A
authors.lastname: Masri
authors.forename: Lokesh
authors.initials: L
authors.lastname: Lingappa
authors.forename: Owain W
authors.initials: OW
authors.lastname: Howell
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Vanbellinghen
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Mullins
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Lynch
authors.forename: Mark I
authors.initials: MI
authors.lastname: Rees
mesh_terms: D000293:Adolescent; D000328:Adult; D000595:Amino Acid Sequence; D002648:Child; D002675:Child, Preschool; D004827:Epilepsy / Q000235:genetics* / Q000503:physiopathology; D005260:Female; D040181:Genetic Diseases, X-Linked / Q000235:genetics* / Q000503:physiopathology; D020022:Genetic Predisposition to Disease; D050487:Glycine Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D006720:Homozygote; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009122:Muscle Hypertonia / Q000235:genetics* / Q000503:physiopathology; D009154:Mutation; D010375:Pedigree; D011487:Protein Conformation; D022821:RNA Splice Sites / Q000235:genetics; D018009:Receptors, Glycine / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012021:Reflex, Abnormal / Q000235:genetics*; D013329:Structure-Activity Relationship
chemical_list: C000657604:GLRA1 protein, human; C114561:GLRB protein, human; D050487:Glycine Plasma Membrane Transport Proteins; D022821:RNA Splice Sites; D018009:Receptors, Glycine; C493271:SLC6A5 protein, human