NPRL3 mutations

Inspired by a patient

Baldassari S, Picard F, Verbeek NE, van Kempen M, Brilstra EH, Lesca G, Conti V, Guerrini R, Bisulli F, Licchetta L, Pippucci T, Tinuper P, Hirsch E, de Saint Martin A, Chelly J, Rudolf G, Chipaux M, Ferrand-Sorbets S, Dorfmüller G, Sisodiya S, Balestrini S, Schoeler N, Hernandez-Hernandez L, Krithika S, Oegema R, Hagebeuk E, Gunning B, Deckers C, Berghuis B, Wegner I, Niks E, Jansen FE, Braun K, de Jong D, Rubboli G, Talvik I, Sander V, Uldall P, Jacquemont ML, Nava C, Leguern E, Julia S, Gambardella A, d'Orsi G, Crichiutti G, Faivre L, Darmency V, Benova B, Krsek P, Biraben A, Lebre AS, Jennesson M, Sattar S, Marchal C, Nordli DR Jr, Lindstrom K, Striano P, Lomax LB, Kiss C, Bartolomei F, Lepine AF, Schoonjans AS, Stouffs K, Jansen A, Panagiotakaki E, Ricard-Mousnier B, Thevenon J, de Bellescize J, Catenoix H, Dorn T, Zenker M, Müller-Schlüter K, Brandt C, Krey I, Polster T, Wolff M, Balci M, Rostasy K, Achaz G, Zacher P, Becher T, Cloppenborg T, Yuskaitis CJ, Weckhuysen S, Poduri A, Lemke JR, Møller RS, Baulac S. The landscape of epilepsy-related GATOR1 variants. Genet Med. 2019 Feb;21(2):398-408. doi: 10.1038/s41436-018-0060-2. Epub 2018 Aug 10. Erratum in: Genet Med. 2018 Aug 29;: Erratum in: Genet Med. 2018 Sep 27;: PMID: 30093711; PMCID: PMC6292495.

Abstract

Purpose: To define the phenotypic and mutational spectrum of epilepsies related to DEPDC5, NPRL2 and NPRL3 genes encoding the GATOR1 complex, a negative regulator of the mTORC1 pathway METHODS: We analyzed clinical and genetic data of 73 novel probands (familial and sporadic) with epilepsy-related variants in GATOR1-encoding genes and proposed new guidelines for clinical interpretation of GATOR1 variants.

Results: The GATOR1 seizure phenotype consisted mostly in focal seizures (e.g., hypermotor or frontal lobe seizures in 50%), with a mean age at onset of 4.4 years, often sleep-related and drug-resistant (54%), and associated with focal cortical dysplasia (20%). Infantile spasms were reported in 10% of the probands. Sudden unexpected death in epilepsy (SUDEP) occurred in 10% of the families. Novel classification framework of all 140 epilepsy-related GATOR1 variants (including the variants of this study) revealed that 68% are loss-of-function pathogenic, 14% are likely pathogenic, 15% are variants of uncertain significance and 3% are likely benign.

Conclusion: Our data emphasize the increasingly important role of GATOR1 genes in the pathogenesis of focal epilepsies (>180 probands to date). The GATOR1 phenotypic spectrum ranges from sporadic early-onset epilepsies with cognitive impairment comorbidities to familial focal epilepsies, and SUDEP.

Iffland PH 2nd, Carson V, Bordey A, Crino PB. GATORopathies: The role of amino acid regulatory gene mutations in epilepsy and cortical malformations. Epilepsia. 2019 Nov;60(11):2163-2173. doi: 10.1111/epi.16370. Epub 2019 Oct 17. PMID: 31625153; PMCID: PMC7155771.

Abstract

The mechanistic target of rapamycin (mTOR) pathway has been implicated in a growing number of malformations of cortical development (MCD) associated with intractable epilepsy. Mutations in single genes encoding mTOR pathway regulatory proteins have been linked to MCD such as focal cortical dysplasia (FCD) types IIa and IIb, hemimegalencephaly (HME), and megalencephaly. Recent studies have demonstrated that the GATOR1 protein complex, comprised of DEPDC5, NPRL3, and NPRL2, plays a pivotal role in regulating mTOR signaling in response to cellular amino acid levels and that mutations in DEPDC5, NPRL3, or NPRL2 are linked to FCD, HME, and seizures. Histopathological analysis of FCD and HME tissue specimens resected from individuals harboring DEPDC5, NPRL3, or NPRL2 gene mutations reveals hyperactivation of mTOR pathway signaling. Family pedigrees carrying mutations in either DEPDC5 or NPRL3 share clinical phenotypes of epilepsy and MCD, as well as intellectual and neuropsychiatric disabilities. Interestingly, some individuals with seizures associated with DEPDC5, NPRL3, or NPRL2 variants exhibit normal brain imaging suggesting either occult MCD or a role for these genes in non-lesional neocortical epilepsy. Mouse models resulting from knockdown or knockout of either Depdc5 or Nprl3 exhibit altered cortical lamination, neuronal dysmorphogenesis, and enhanced neuronal excitability as reported in models resulting from direct mTOR activation through expression of its canonical activator RHEB. The role of the GATOR1 proteins in regulating mTOR signaling suggest plausible options for mTOR inhibition in the treatment of epilepsy associated with mutations in DEPDC5, NPRL3, or NPRL2.

Li Y, Zhao X, Wang S, Xu K, Zhao X, Huang S, Zhu S. A Novel Loss-of-Function Mutation in the NPRL3 Gene Identified in Chinese Familial Focal Epilepsy with Variable Foci. Front Genet. 2021 Nov 12;12:766354. doi: 10.3389/fgene.2021.766354. PMID: 34868250; PMCID: PMC8633433.

Abstract

Familial focal epilepsy with variable foci is an autosomal dominant disorder characterized by partial epilepsy with variable foci. In this study, we report a six-generation with segregation of the mutation present in four generations Chinese family presenting with focal epilepsy with variable foci. Whole exome sequencing confirms a novel pathogenic mutation in the NPRL3 gene (c316C>T; p. Q106*). PCR, Western blotting, and immunohistochemistry were conducted to analyze the gene transcription, protein expression, and subcellular localization of NPRL3 and related signaling molecules in peripheral blood cells from family members. As compared with healthy family members, both mRNA level and protein expression of NPRL3 are decreased in peripheral blood cells of the mutation carrier. In addition, the expression of downstream molecular Phospho-p70 S6 kinase (P-s6k) are increased consequently. Our findings expand the genotypic and phenotypic spectrum of the NPRL3-associated epilepsy and reveal the mechanisms of mTOR pathway signaling and GATOR1 pathogenesis in focal epilepsies, providing exciting potential for future diagnostic and therapeutic interventions. However, further in vitro and animal experiments are still needed to evaluate the role of NPRL3 loss-of-function mutation in epileptogensis.