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KCNE1 encodes a regulatory subunit of the KCNQ1 potassium channel-complex. Both KCNE1 and KCNQ1 are necessary for normal hearing and cardiac ventricular repolarization. Recessive variants in these genes are associated with Jervell and Lange-Nielson syndrome (JLNS1 and JLNS2), a cardio-auditory syndrome characterized by congenital profound sensorineural deafness and a prolonged QT interval that can cause ventricular arrhythmias and sudden cardiac death. Some normal-hearing carriers of heterozygous missense variants of KCNE1 and KCNQ1 have prolonged QT intervals, a dominantly inherited phenotype designated Romano-Ward syndrome (RWS), which is also associated with arrhythmias and elevated risk of sudden death. Co-assembly of certain mutant KCNE1 monomers with wild-type KCNQ1 subunits results in RWS by a dominant negative mechanism. This Mutation Update reviews variants of KCNE1 and their associated phenotypes, including biallelic truncating null variants of KCNE1 that have not been previously reported. We describe three homozygous nonsense mutations of KCNE1 segregating in families ascertained ostensibly for nonsyndromic deafness: c.50G>A (p.Trp17*), c.51G>A (p.Trp17*), and c.138C>A (p.Tyr46*). Some individuals carrying missense variants of KCNE1 have RWS. However, heterozygotes for loss of function variants of KCNE1 may have normal QT intervals while biallelic null alleles are associated with JLNS2, indicating a complex genotype-phenotype spectrum for KCNE1 variants.

Melanoma is the most deadly form of skin cancer and DiGeorge syndrome (DGS) is the most frequent interstitial deletion syndrome. We characterized a novel balanced t(9;22)(p21;q11.2) translocation in a patient with melanoma, DNA repair deficiency, and features of DGS including deafness and malformed inner ears. Using chromosome sorting, we located the 9p21 breakpoint in CDKN2A intron 1. This resulted in underexpression of the tumor suppressor p14 alternate reading frame (p14ARF); the reduced DNA repair was corrected by transfection with p14ARF. Ultraviolet radiation-type p14ARF mutations in his melanoma implicated p14ARF in its pathogenesis. The 22q11.2 breakpoint was located in a palindromic AT-rich repeat (PATRR22). We identified a new gene, FAM230A, that contains PATRR22 within an intron. The 22q11.2 breakpoint was located 800 kb centromeric to TBX1, which is required for inner ear development. TBX1 expression was greatly reduced. The translocation resulted in a chimeric transcript encoding portions of p14ARF and FAM230A. Inhibition of chimeric p14ARF-FAM230A expression increased p14ARF and TBX1 expression and improved DNA repair. Expression of the chimera in normal cells produced dominant negative inhibition of p14ARF. Similar chimeric mRNAs may mediate haploinsufficiency in DGS or dominant negative inhibition of other genes such as those involved in melanoma.

Hearing loss with enlargement of the vestibular aqueduct (EVA) can be associated with mutations of the SLC26A4 gene encoding pendrin, a transmembrane Cl(-)/I(-)/HCO(3)(-) exchanger. Pendrin's critical transport substrates are thought to be I(-) in the thyroid gland and HCO(3)(-) in the inner ear. We previously reported that bi-allelic SLC26A4 mutations are associated with Pendred syndromic EVA whereas one or zero mutant alleles are associated with nonsyndromic EVA. One study proposed a correlation of nonsyndromic EVA with SLC26A4 alleles encoding pendrin with residual transport activity. Here we describe the phenotypes and SLC26A4 genotypes of 47 EVA patients ascertained since our first report of 39 patients. We sought to determine the pathogenic potential of each variant in our full cohort of 86 patients. We evaluated the trafficking of 11 missense pendrin products expressed in COS-7 cells. Products that targeted to the plasma membrane were expressed in Xenopus oocytes for measurement of anion exchange activity. p.F335L, p.C565Y, p.L597S, p.M775T, and p.R776C had Cl(-)/I(-) and Cl(-)/HCO(3)(-) exchange rate constants that ranged from 13 to 93% of wild type values. p.F335L, p.L597S, p.M775T and p.R776C are typically found as mono-allelic variants in nonsyndromic EVA. The high normal control carrier rate for p.L597S indicates it is a coincidentally detected nonpathogenic variant in this context. We observed moderate differential effects of hypo-functional variants upon exchange of HCO(3)(-) versus I(-) but their magnitude does not support a causal association with nonsyndromic EVA. However, these alleles could be pathogenic in trans configuration with a mutant allele in Pendred syndrome.