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Published on: August 15, 2019
GRID2 mutations span from congenital to mild adult-onset cerebellar ataxia
Marie Coutelier1, Lydie Burglen1, Emeline Mundwiller1
1From Institut du Cerveau et de la Moelle épinière (M.C., A.B., G.S., A.D.), ICM, Paris; CNRS (M.C., A.B., G.S., A.D.), UMR 7225, Paris; Sorbonne Universités (M.C., A.B., G.S., A.D.), UPMC Univ Paris 06, UMRS_1127, Paris; INSERM (M.C., E.M., A.B., G.S., A.D.), U 1127, Paris, France; Laboratory of Human Molecular Genetics (M.C.), de Duve Institute, Université catholique de Louvain, Brussels, Belgium; Laboratoire de Neurogénétique (M.C., G.S.), Ecole Pratique des Hautes Etudes, ICM, GHU Pitié-Salpêtrière, Paris; Centre de Référence Malformations et Maladies Congénitales du Cervelet (L.B., D.R., S.C.-B., C.R., A.A.), Paris-Lyon-Lille; INSERM U1141 (L.B., D.R.), Paris; APHP (L.B., S.C.-B.), Armand-Trousseau Hospital, Department of Genetics, Paris, France; Service de Neurologie (M.A.-B.), CHU Bab el Oued, Alger, Algeria; APHP (D.R., A.A.), Armand-Trousseau Hospital, Department of Neuropediatrics, UPMC Univ Paris 06; Hospices Civils de Lyon (C.R.), HFME, Service de Neuropédiatrie, Bron; Centre Hospitalier du Pays d'Aix (M.-A.C.), Service de Pédiatrie, Aix en Provence; APHM (M.M.), Service de neurologie pédiatrique, Hôpital de la Timone, Marseille; Service de Génétique (A.T.), Hôpital Bretonneau, Centre Hospitalier Universitaire, Tours; Centre National de Génotypage (D.B., V.M., J.-F.D.), Institut de Génomique, CEA, Evry; APHP (A.B., D.H., A.D.), Department of Genetics and Cytogenetics, Groupe Hospitalier Pitié-Salpêtrière, Paris; Centre de Référence Déficiences Intellectuelles de causes rares (D.H.), Paris; and Groupe de Recherche Clinique déficiences intellectuelles (D.H.), UPMC Univ Paris 06, France.
Objectives:
In a large family of Algerian origin, we aimed to identify the genetic mutation segregating with simultaneous presence of adult-onset, paucisymptomatic, slowly progressive, cerebellar ataxia in 7 adults and congenital ataxia in 1 child, and then to assess the involvement of GRID2 mutations in 144 patients with congenital cerebellar ataxia.
Methods:
We used a combined approach of linkage analysis and whole-exome sequencing in one family, and a targeted gene panel sequencing approach in 144 congenital ataxias.
Results:
In the large family with spinocerebellar ataxia, we identified a missense mutation (c.1966C>G/p.Leu656Val) in the GRID2 gene, in a heterozygous state in adults, and in a homozygous state in one child with congenital ataxia, compatible with a semidominant transmission pattern. In 144 patients affected with congenital ataxia, we identified 2 missense de novo GRID2 mutations in 2 children (c.1960G>A/p.Ala654Thr, c.1961C>A/p.Ala654Asp). They affect the same amino acid as the previously described Lurcher mutation in mice; the variant in the large family concerns a nearby amino acid.
Conclusions:
In humans, GRID2 had only been involved in ataxia through complete loss-of-function mutations due to exon deletions. We report the first point mutations in this gene, with putative gain-of-function mechanisms, and a semidominant transmission as was observed in the Lurcher mice model. Of note, cerebellar ataxia is the core phenotype, but with variable severity ranging from very mild adult-onset to congenital-onset ataxias linked to both the heterozygous and homozygous state of the variant, and the position of the mutation.
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