KCNJ10 Mutations Display Differential Sensitivity to Heteromerisation with KCNJ16

Abstract

Background/Aims: Mutations in the inwardly-rectifying K⁺-channel KCNJ10/Kir4.1 cause autosomal recessive EAST syndrome (epilepsy, ataxia, sensorineural deafness and tubulopathy). KCNJ10 is expressed in the distal convoluted tubule of the kidney, stria vascularis of the inner ear and brain glial cells. Patients diagnosed clinically with EAST syndrome were genotyped and mutations in KCNJ10 were studied functionally. Methods: Patient DNA was amplified and sequenced, and new mutations were identified. Mutant and wild-type KCNJ10 constructs were cloned and heterologously expressed in Xenopus oocytes. Whole-cell K⁺ currents were measured by 2-electrode voltage clamping and channel expression was analysed by Western blotting. Results: We identified 3 homozygous mutations in KCNJ10 (p.F75C, p.A167V and p.V91fs197X), with mutation p.A167V previously reported in a compound heterozygous state. Oocytes expressing wild-type human KCNJ10 showed inwardly rectified currents, which were significantly reduced in all of the mutants (p < 0.001). Specific inhibition of KCNJ10 currents by Ba²⁺ demonstrated a large residual function in p.A167V only, which was not compatible with causing disease. However, co-expression with KCNJ16 abolished function in these heteromeric channels almost completely. Conclusion: This study provides an explanation for the pathophysiology of the p.A167V KCNJ10 mutation, which had previously not been considered pathogenic on its own. These findings provide evidence for the functional cooperation of KCNJ10 and KCNJ16. Thus, in vitro ascertainment of KCNJ10 function may necessitate co-expression with KCNJ16.

The novel homozygous KCNJ10 c.986T>C (p.(Leu329Pro)) variant is pathogenic for the SeSAME/EAST homologue in Malinois dogs

“…Results of motor nerve conduction velocity studies and repetitive nerve stimulation in dogs 1 and 2 did not differ from two age-matched Malinois control dogs. MRI of the brain/cervical spine and , showing described SeSAME/EAST syndrome causing variants in humans (in grey) 4 and dogs (in black). 6 The KCNJ10 c.986T4C (p.(Leu329Pro)) variant described here is indicated with an asterisk.…”

“…Until now, 14 variants have been described causing SeSAME/EAST, all in the KCNJ10 coding sequence (Figure 1). 4 A similar disease (OMIA 001820-9615) has also been described in a number of dog breeds (Border collie, Dachshund and Terrier breeds; reviewed in Vanhaesebrouck et al 5 ). Until now, only the KCNJ10 c.627C4G (p.(Ile209Met)) variant has been reported to be associated with spinocerebellar ataxia and myokymia, seizures or both (SAMS) in certain Terrier breeds.…”

Screen-based identification and validation of four new ion channels as regulators of renal ciliogenesis

“…A previous study performed patch clamp assays on a series of KCNJ10 mutant alleles to quantify the effect of the missense mutation on ion channel function, showing many of them to be hypomorphic (Parrock et al, 2013). The alleles we tested were: KCNJ10-c.194G>C/p.R65P (20% retained function) and KCNJ10-c.418T>C/p.C140R (total loss of function), normalized to KCNJ10-WT (100% function).…”

Contribution of KCNJ10 Gene Polymorphisms in Childhood Epilepsy

“…Some mutations have residual function (p.A167V>p.R65P>p.R175Q>p.G77R), but others display complete loss of function. 23 In conclusion, our study showed that allele frequency and the genotypes of the rs2486253 polymorphism were associated with patients with idiopathic generalized and tonic-clonic epilepsies. Therefore, the results of the present study suggest that rs2486253 polymorphism in KCNJ10 gene is likely to contribute to the risk for idiopathic generalized epilepsy in a pediatric group of Turkish population.…”

“…15 All functionally characterized mutations in KCNJ10 published so far include p.T57I, p.R65C, p.R65P, p.F75 L, p.G77R, p.C140R, p.T164I, p.A167 V, p.R175Q, p.R199X, p.V259X, and p.R297C. 23 Recently, 2 new homozygous mutations, p.F75C and p.V91fs197X (frameshift mutation due to a c.272delT mutation at cDNA level) have been identified. Some mutations have residual function (p.A167V>p.R65P>p.R175Q>p.G77R), but others display complete loss of function.…”