Functional confirmation that the R1488* variant in SCN9A results in complete loss-of-function of Nav1.7

Abstract

BackgroundIndividuals with an extremely rare inherited condition, termed Congenital Insensitivity to Pain (CIP), do not feel pain in response to noxious stimuli. Variants in SCN9A, encoding the transmembrane voltage-gated sodium channel Nav1.7, have previously been reported in subjects with CIP accompanied by anosmia, which are typically transmitted in a recessive pattern. Functional characterisations of some of these SCN9A mutations show that they result in complete loss-of-function of Nav1.7.MethodsIn a consanguineous family we performed whole exome sequencing of three members who have a diagnosis of CIP and one unaffected family member. The functional effects of the segregating variant in SCN9A were determined using patch clamp electrophysiology in human embryonic kidney (HEK) 293 cells transfected with the variant.ResultsWe found that each CIP subject was homozygous for a putatively nonsense variant, R1488*, in SCN9A. This variant was reported elsewhere in a subject with CIP, though the functional effect was not determined. Using electrophysiology, we confirm that this variant results in a complete loss-of-function of Nav1.7.ConclusionsWe confirm through electrophysiological analysis that this R1488* variant in SCN9A results in complete loss-of-function of Nav1.7, which is consistent with reports on other variants in this gene in subjects with CIP.

Response to letter regarding “SCN9A variant in a family of mixed breed dogs with congenital insensitivity to pain”

“…Unfortunately, we were unable to demonstrate its impact on the direct function of the Nav1.7 sodium channel, because we could not perform in vitro electrophysiological studies as previously reported. 2 , 3 We agree with Drs. Taisuke Ichikawa and Hiroshi Aoki that the presented data in our study is insufficient to conclusively prove the pathogenicity of the reported variant.…”

“…Unfortunately, we were unable to demonstrate its impact on the direct function of the Nav1.7 sodium channel, because we could not perform in vitro electrophysiological studies as previously reported. 2,3 We agree with Drs. Taisuke Ichikawa and Hiroshi Aoki that the presented data in our study is insufficient to conclusively prove the pathogenicity of the reported variant.For this reason, we reported the genetic variant as "likely" pathogenic or as "candidate" causative variant.We completely agree that we should try to move toward functional annotation of mutated proteins in veterinary medicine and follow genetic guidelines used in humans, but doing so can sometimes be challenging.We believe there is still interest in reporting likely pathogenic variants of rare diseases promptly, to inform the veterinary community and avoid further breeding of potentially affected animals.…”

Upregulation of Nav1.7 by endogenous hydrogen sulfide contributes to maintenance of neuropathic pain

“…Those changes are inhibited when rats are pretreated with ScN9A-RNA interference lentivirus delivered via an intrathecal tube (4). He et al (25) confirmed that R1488 * , a variant of ScN9A, results in a complete loss-of-function of Na v 1.7, which is consistent with variants in this gene in subjects with congenital insensitivity to pain. Geha et al (27) demonstrated that pharmacotherapy guided by genomic analysis, molecular modeling and functional profiling attenuated neuropathic pain in patients carrying an S241T Na v 1.7 mutant channel.…”

Novel SCN9A variant associated with congenital insensitivity to pain

“…Nav1.7 is composed of 1988 amino acids organized into 4 domains each with 6 transmembrane segments [3]. Both gain and loss of function variants have been reported in SCN9A gene [5]. In 2006, Cox et al initially reported that loss of function variants in SCN9A gene leads to a defective Nav1.7 channel resulting in the inability to experience pain [6].…”