1. Missense variants in the N-terminal domain of the A isoform of FHF2/FGF13 cause an X-linked developmental and epileptic encephalopathy.
- Author
-
Fry AE, Marra C, Derrick AV, Pickrell WO, Higgins AT, Te Water Naude J, McClatchey MA, Davies SJ, Metcalfe KA, Tan HJ, Mohanraj R, Avula S, Williams D, Brady LI, Mesterman R, Tarnopolsky MA, Zhang Y, Yang Y, Wang X, Rees MI, Goldfarb M, and Chung SK
- Subjects
- Adolescent, Amino Acid Sequence, Child, Exons genetics, Female, Gain of Function Mutation genetics, Genes, X-Linked genetics, Heterozygote, Humans, Male, NAV1.6 Voltage-Gated Sodium Channel genetics, Neurons physiology, Seizures genetics, Brain Diseases genetics, Epilepsy genetics, Fibroblast Growth Factors genetics, Mutation, Missense genetics, Protein Isoforms genetics
- Abstract
Fibroblast growth factor homologous factors (FHFs) are intracellular proteins which regulate voltage-gated sodium (Na
v ) channels in the brain and other tissues. FHF dysfunction has been linked to neurological disorders including epilepsy. Here, we describe two sibling pairs and three unrelated males who presented in infancy with intractable focal seizures and severe developmental delay. Whole-exome sequencing identified hemi- and heterozygous variants in the N-terminal domain of the A isoform of FHF2 (FHF2A). The X-linked FHF2 gene (also known as FGF13) has alternative first exons which produce multiple protein isoforms that differ in their N-terminal sequence. The variants were located at highly conserved residues in the FHF2A inactivation particle that competes with the intrinsic fast inactivation mechanism of Nav channels. Functional characterization of mutant FHF2A co-expressed with wild-type Nav 1.6 (SCN8A) revealed that mutant FHF2A proteins lost the ability to induce rapid-onset, long-term blockade of the channel while retaining pro-excitatory properties. These gain-of-function effects are likely to increase neuronal excitability consistent with the epileptic potential of FHF2 variants. Our findings demonstrate that FHF2 variants are a cause of infantile-onset developmental and epileptic encephalopathy and underline the critical role of the FHF2A isoform in regulating Nav channel function., (Copyright © 2020 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)- Published
- 2021
- Full Text
- View/download PDF