A novel pathogenic SLC12A5 missense variant in epilepsy of infancy with migrating focal seizures causes impaired KCC2 chloride extrusion

Viivi Järvelä; Mira Hamze; Jonna Komulainen-Ebrahim; Elisa Rahikkala; Johanna Piispala; Mika Kallio; Salla M Kangas; Tereza Nickl; Marko Huttula; Reetta Hinttala; Johanna Uusimaa; Igor Medina; Esa-Ville Immonen

doi:10.3389/fnmol.2024.1372662

A novel pathogenic SLC12A5 missense variant in epilepsy of infancy with migrating focal seizures causes impaired KCC2 chloride extrusion

Front Mol Neurosci. 2024 Apr 10:17:1372662. doi: 10.3389/fnmol.2024.1372662. eCollection 2024.

Authors

Viivi Järvelä^{1

2

3}, Mira Hamze⁴, Jonna Komulainen-Ebrahim^{2

3

5}, Elisa Rahikkala^{2

3

6}, Johanna Piispala⁷, Mika Kallio⁷, Salla M Kangas^{2

3}, Tereza Nickl^{2

3

8}, Marko Huttula¹, Reetta Hinttala^{2

3

9}, Johanna Uusimaa^{2

3

5}, Igor Medina⁴, Esa-Ville Immonen^{1

2

3}

Affiliations

¹ Nano and Molecular Systems Research Unit, University of Oulu, Oulu, Finland.
² Research Unit of Clinical Medicine, University of Oulu, Oulu, Finland.
³ Medical Research Center Oulu, University of Oulu and Oulu University Hospital, Oulu, Finland.
⁴ INMED, INSERM, Aix-Marseille University, Marseille, France.
⁵ Department of Children and Adolescents, Division of Pediatric Neurology, Oulu University Hospital, Oulu, Finland.
⁶ Department of Clinical Genetics, Oulu University Hospital, Oulu, Finland.
⁷ Department of Clinical Neurophysiology, Oulu University Hospital, Oulu, Finland.
⁸ Laboratory of Transgenic Models of Diseases, Institute of Molecular Genetics of the Czech Academy of Sciences, Prague, Czechia.
⁹ Biocenter Oulu, University of Oulu, Oulu, Finland.

Abstract

The potassium-chloride co-transporter 2, KCC2, is a neuron-specific ion transporter that plays a multifunctional role in neuronal development. In mature neurons, KCC2 maintains a low enough intracellular chloride concentration essential for inhibitory neurotransmission. During recent years, pathogenic variants in the KCC2 encoding gene SLC12A5 affecting the functionality or expression of the transporter protein have been described in several patients with epilepsy of infancy with migrating focal seizures (EIMFS), a devastating early-onset developmental and epileptic encephalopathy. In this study, we identified a novel recessively inherited SLC12A5 c.692G>A, p. (R231H) variant in a patient diagnosed with severe and drug-resistant EIMFS and profound intellectual disability. The functionality of the variant was assessed in vitro by means of gramicidin-perforated patch-clamp experiments and ammonium flux assay, both of which indicated a significant reduction in chloride extrusion. Based on surface immunolabeling, the variant showed a reduction in membrane expression. These findings implicate pathogenicity of the SLC12A5 variant that leads to impaired inhibitory neurotransmission, increasing probability for hyperexcitability and epileptogenesis.

Keywords: Cl−; GABA; SLC12A5; chloride; epilepsy; neurodevelopmental disorder; potassium-chloride co-transporter.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. The work of VJ was funded by the University of Oulu Graduate School UniOGS. Arvo ja Lea Ylppö Säätiö granted a travel grant for VJ for a research visit to Igor Medina's lab to conduct part of the experimental work. MHa was funded by French Ministry of Education (MRT) and a grant from MarMaRa, a Marseille Institute of Rare Diseases. ER has received research grant support from the Research Council of Finland (decision no 338446). JK-E has received research grant support from the Alma and K.A. Snellman Foundation, Oulu, Finland; the Arvo ja Lea Ylppö Säätiö, Helsinki, Finland; and the Finnish Cultural Foundation, North Ostrobothnia Regional Fund, Oulu, Finland (grant number 60152194, 2015). The work of TN was funded by an EDUFI fellowship (TM-19-11311), Finnish National Agency for Education. RH has received research grant support from the Research Council of Finland (decisions no: 317711 and 311934). JU has received research grant support from the Research Council of Finland (decision no: 331436), and jointly with RH from the Foundation for Pediatric Research, Finland. JU has received Special State Grants for Health Research in the Clinic for Children and Adolescents (grant number K56772), Oulu University Hospital. The work of IM was supported by grant from French National Research Agency (ANR-22-CE16-0032 AuDy).