title: Recessive loss-of-function mutation in the pacemaker HCN2 channel causing increased neuronal excitability in a patient with idiopathic generalized epilepsy.
abstract: The hyperpolarization-activated I(h) current, coded for by hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, controls synaptic integration and intrinsic excitability in many brain areas. Because of their role in pacemaker function, defective HCN channels are natural candidates for contributing to epileptogenesis. Indeed, I(h) is pathologically altered after experimentally induced seizures, and several independent data indicate a link between dysfunctional HCN channels and different forms of epilepsy. However, direct evidence for functional changes of defective HCN channels correlating with the disease in human patients is still elusive. By screening families with epilepsy for mutations in Hcn1 and Hcn2 genes, we found a recessive loss-of-function point mutation in the gene coding for the HCN2 channel in a patient with sporadic idiopathic generalized epilepsy. Of 17 screened members of the same family, the proband was the only one affected and homozygous for the mutation. The mutation (E515K) is located in the C-linker, a region known to affect channel gating. Functional analysis revealed that homomeric mutant, but not heteromeric wild-type/mutant channels, have a strongly inhibited function caused by a large negative shift of activation range and slowed activation kinetics, effectively abolishing the HCN2 contribution to activity. After transfection into acutely isolated newborn rat cortical neurons, homomeric mutant, but not heteromeric wild type/mutant channels, lowered the threshold of action potential firing and strongly increased cell excitability and firing frequency when compared with wild-type channels. This is the first evidence in humans for a single-point, homozygous loss-of-function mutation in HCN2 potentially associated with generalized epilepsy with recessive inheritance.
authors: Dipartimento di Neuroscienze e Tecnologie Biomediche, Ospedale S. Gerardo, Università di Milano-Bicocca, 20052 Monza, Italy.
authors: Jacopo C
authors: JC
authors: DiFrancesco
authors: Andrea
authors: A
authors: Barbuti
authors: Raffaella
authors: R
authors: Milanesi
authors: Stefania
authors: S
authors: Coco
authors: Annalisa
authors: A
authors: Bucchi
authors: Georgia
authors: G
authors: Bottelli
authors: Carlo
authors: C
authors: Ferrarese
authors: Silvana
authors: S
authors: Franceschetti
authors: Benedetta
authors: B
authors: Terragni
authors: Mirko
authors: M
authors: Baruscotti
authors: Dario
authors: D
authors: DiFrancesco
mesh_terms: D000200:Action Potentials / Q000235:genetics; D000328:Adult; D000483:Alleles; D000818:Animals; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000502:physiology; D002648:Child; D004827:Epilepsy / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D006801:Humans; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D015640:Ion Channel Gating / Q000235:genetics; D007473:Ion Channels / Q000235:genetics* / Q000378:metabolism; D008297:Male; D009154:Mutation; D009474:Neurons / Q000502:physiology*; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide; D015221:Potassium Channels; D051381:Rats; D014162:Transfection
chemical_list: C578710:HCN2 protein, human; C578712:Hcn2 protein, rat; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D015221:Potassium Channels