Alternative titles; symbols
HGNC Approved Gene Symbol: KCNJ13
Cytogenetic location: 2q37.1 Genomic coordinates (GRCh38): 2:232,765,802-232,776,565 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 2q37.1 | Leber congenital amaurosis 16 | 614186 | Autosomal recessive | 3 |
| Snowflake vitreoretinal degeneration | 193230 | Autosomal dominant | 3 |
Inwardly rectifying potassium (Kir) channels are expressed in a wide variety of cells and have been implicated in many different physiologic processes with the common role of maintaining resting membrane potential near the potassium equilibrium potential. By searching EST databases for new members of the Kir family, Partiseti et al. (1998) and Krapivinsky et al. (1998) identified Kir7.1 cDNAs. The predicted 360-amino acid protein contains the 2 transmembrane segments characteristic of Kir channel subunits. Both groups of authors assigned Kir7.1 to a new Kir subfamily because of its low degree of structural homology to other Kir channels.
Using Northern blot analysis of human tissues, Partiseti et al. (1998) determined that Kir7.1 is expressed as a 3.4-kb mRNA predominantly in small intestine. Expression was also detected in stomach, kidney, and all central nervous system regions tested with the exception of spinal cord. By immunolocalization, Krapivinsky et al. (1998) found that Kir7.1 is widely expressed in rat brain and is especially abundant in the Purkinje cell layer in the cerebellum and the pyramidal cell layer in the hippocampus. The antibody specifically labeled neurons but not glial cells. Kir7.1 migrates as a 45-kD protein on Western blots of human brain membrane preparations.
Using confocal microscopy and immunohistochemical analysis, Zhang et al. (2013) found that human Kir7.1 was expressed primarily on basolateral membranes of transfected polarized Madin-Darby canine kidney (MDCK) cells, with lower expression at apical and basal surfaces. In normal human retina, Kir7.1 was expressed on apical microvilli of retinal pigment epithelia, but not in neural retina or in choroid.
Derst et al. (1998) reported the partial genomic structure of KCNJ13 and identified a 2,088-bp intron in its coding region. Sergouniotis et al. (2011) noted that the KCNJ13 gene contains 3 exons spanning 10.11 kb.
By PCR analysis of monochromosomal and radiation hybrid panels, Derst et al. (1998) assigned the KCNJ13 gene to chromosome 2q37.
Hejtmancik et al. (2008) identified the KCNJ13 gene on chromosome 2q36 through direct DNA sequencing.
Sergouniotis et al. (2011) noted that the KCNJ13 gene maps to chromosome 2q37.1.
By expressing Kir7.1 in mammalian cells, Krapivinsky et al. (1998) found that it has several unique features, including very low single channel conductance, low sensitivity to block by external barium and cesium, and no dependence of its inward rectification properties on the internal blocking particle magnesium. They attributed these unusual pore properties to amino acid differences in the conserved pore region. Krapivinsky et al. (1998) hypothesized that the role of Kir7.1 is to set reliably the resting membrane potential, since its low conductance allows for significant precision in regulating membrane potential.
Zhang et al. (2013) found that Xenopus oocytes injected with wildtype human Kir7.1 cRNA developed a large negative membrane potential and exhibited inwardly rectifying currents. Application of the K+ channel blocker Ba(2+) eliminated most of the inward current.
In mice, Ghamari-Langroudi et al. (2015) showed that regulation of firing activity of neurons from the paraventricular nucleus of the hypothalamus (PVN) by alpha-melanocyte-stimulating hormone (alpha-MSH; see 176830) and Agouti-related protein (AGRP; 602311) can be mediated independently of G-alpha-s (see 139320) signaling by ligand-induced coupling of Mc4r (155541) to closure of inwardly rectifying potassium channel Kir7.1. Furthermore, Agrp is a biased agonist that hyperpolarizes neurons by binding to Mc4r and opening Kir7.1, independently of its inhibition of alpha-Msh binding. Consequently, Kir7.1 signaling appears to be central to melanocortin-mediated regulation of energy homeostasis within the PVN. Coupling of Mc4r to Kir7.1 may explain unusual aspects of the control of energy homeostasis by melanocortin signaling, including the gene dosage effect of Mc4r and the sustained effects of Agrp on food intake.
Snowflake Vitreoretinal Degeneration
Snowflake vitreoretinal degeneration (SVD; 193230) is a developmental and progressive hereditary eye disorder that affects multiple tissues within the eye. Diagnostic features include fibrillar degeneration of the vitreous humor, early-onset cataract, minute crystalline deposits in the neurosensory retina, and retinal detachment. Hejtmancik et al. (2008) sequenced 20 of 59 genes within the SVD critical region and identified a heterozygous missense mutation in KCNJ13 (R162W; 603208.0001).
Leber Congenital Amaurosis 16
In a consanguineous Middle Eastern family with Leber congenital amaurosis mapping to chromosome 2q (LCA16; 614186), Sergouniotis et al. (2011) performed targeted exome sequencing and identified homozygosity for a nonsense mutation in the KCNJ13 gene (R166X; 603208.0002) that segregated with disease in the family. The authors then analyzed the KCNJ13 gene in 132 additional unrelated patients with recessive LCA or childhood-onset retinal dystrophy who were negative for mutation in known LCA genes as well as 201 patients diagnosed with autosomal recessive adult-onset rod/cone dystrophy (see 120970), and in a 33-year-old man of European descent with a phenotype 'remarkably similar' to that of the Middle Eastern family, they identified homozygosity for a missense mutation (L241P; 603208.0003).
In 2 unrelated Saudi Arabian probands with vitreoretinal dystrophy and early-onset cataract, Khan et al. (2015) identified homozygosity for a missense mutation in the KCNJ13 gene (I120T; 603208.0004).
In a 10-year-old boy of Jordanian descent with Leber congenital amaurosis, Pattnaik et al. (2015) identified homozygosity for a nonsense mutation in the KCNJ13 gene (W53X; 603208.0005). Functional analysis showed alteration of protein localization and disruption of potassium currents.
Using the CRISPR-Cas9 gene editing system, Zhong et al. (2015) generated mouse Kcnj13 null alleles. After germline transmission, all F1 and F2 mice possessing 2 Kcnj13 null alleles died at postnatal day 1. However, 8 of 10 (80%) surviving F0 mutant mice displayed mosaic Kcnj13 expression in tail DNA and retinal sections. Mosaic Kcnj13 expression correlated with decreased response to light and photoreceptor degeneration. In large patches of retina where Kcnj13 was absent, severe photoreceptor loss was detected, whereas retinal pigment epithelial (RPE) cell layer survived. At the same time, wildtype RPE cells appeared to rescue overlying Kcnj13-null photoreceptors.
Pattnaik et al. (2015) performed electroretinography (ERG) on mice before and 48 hours after intravitreal injection with shRNA lentiviral particles that inhibit KIr7.1 channel expression, and observed a substantial reduction in both the photoreceptor a- and postsynaptic bipolar cell b-wave response amplitudes. The c-wave was also severely attenuated in mice treated with Kir7.1 shRNA inhibition. Pattnaik et al. (2015) stated that this suppression of Kir7.1 function in mice reproduced the characteristic severe ERG phenotype seen in Leber congenital amaurosis patients (see 614186).
In the American family of European extraction in which snowflake vitreoretinal degeneration (SVD; 193230) was first described, Hejtmancik et al. (2008) found that affected members were heterozygous for a missense mutation in the KCNJ13 gene, an arg162-to-trp substitution (R162W) that arose from a 484C-T transition. Thirteen members of the family diagnosed with SVD ranged from 12 to 85 years of age at the time of diagnosis. No other families with confirmed SVD were available to test further the association between the KCNJ13 mutation and SVD.
R162 of KCNJ13 belongs to a cluster of positively charged residues on the surface of the channel's cytoplasmic domain that interacts with phosphatidylinositol 4,5-bisphosphate in the plasma membrane to gate the channel open. Using immunohistochemical analysis, Zhang et al. (2013) found that both wildtype KCNJ13 and KCNJ13 with the R162W mutation were normally targeted to the plasma membrane in Xenopus oocytes and polarized MDCK cells. However, unlike wildtype KCNJ13, KCNJ13 with the R162W mutation did not develop whole cell currents when expressed in Xenopus oocytes. Coinjection experiments revealed a dominant-negative effect of mutant KCNJ13 on currents produced by wildtype KCNJ13.
In affected brothers from a consanguineous Middle Eastern family with Leber congenital amaurosis (LCA16; 614186), Sergouniotis et al. (2011) identified homozygosity for a 496C-T transition in exon 3 of the KCNJ13 gene, resulting in an arg166-to-ter (R166X) substitution predicted to produce a peptide lacking almost the entire C-terminal intracellular segment of 204 amino acids. Their asymptomatic 39-year-old sister, who was heterozygous for the mutation, had normal fundus examination, 55-degree fundus autofluorescence imaging, and spectral domain OCT. The mutation was not found in 382 European control chromosomes.
In a 33-year-old man of European descent with Leber congenital amaurosis (LCA16; 614186), Sergouniotis et al. (2011) identified homozygosity for a 722T-C transition in exon 3 of the KCNJ13 gene, resulting in a leu241-to-pro (L241P) substitution at a highly conserved residue in the C-terminal intracellular region. His unaffected 62-year-old mother and 64-year-old father, who were heterozygous for the mutation, had normal funduscopy, 55-degree fundus autofluorescence imaging, and spectral domain OCT. The mutation was not found in 382 ethnically matched control chromosomes.
In a 12-year-old Saudi Arabian girl and an unrelated 33-year-old Saudi man, who both exhibited vitreoretinal dystrophy and early-onset cataract (LCA16; 614186), Khan et al. (2015) identified homozygosity for a c.359T-C transition (c.359T-C, NM_002242.4) in the KCNJ13 gene, resulting in an ile120-to-thr (I120T) substitution at a highly conserved residue. The girl's affected younger sister was also homozygous for the mutation, whereas their first-cousin unaffected parents were heterozygous. Reexamination of the parents confirmed that both had 20/20 uncorrected visual acuity, with no evidence of corneal guttae or retinal degeneration.
In a 10-year-old boy of Jordanian descent with Leber congenital amaurosis (LCA16; 614186), Pattnaik et al. (2015) identified homozygosity for a c.158G-A transition (SCV000212649) in exon 2 of the KCNJ13 gene, resulting in a trp53-to-ter (W53X) substitution within a highly conserved WRW sequence in the N-terminal cytoplasmic domain. His unaffected parents were heterozygous for the mutation. Patch-clamp recordings in transfected CHO-K1 cells demonstrated a 30-mV depolarization and an 85% reduction in the inward current amplitude with the mutant channel compared to wildtype. In addition, the authors noted that wildtype Kir7.1 protein localizes to the cell membrane, whereas the W53X mutant showed distribution throughout transfected CHO-K1 cells, with the exception of membrane structures.
Derst, C., Doring, F., Preisig-Muller, R., Daut, J., Karschin, A., Jeck, N., Weber, S., Engel, H., Grzeschik, K.-H. Partial gene structure and assignment to chromosome 2q37 of the human inwardly rectifying K+ channel (Kir7.1) gene (KCNJ13). Genomics 54: 560-563, 1998. [PubMed: 9878260] [Full Text: https://doi.org/10.1006/geno.1998.5598]
Ghamari-Langroudi, M., Digby, G. J., Sebag, J. A., Millhauser, G. L., Palomino, R., Matthews, R., Gillyard, T., Panaro, B. L., Tough, I. R., Cox, H. M., Denton, J. S., Cone, R. D. G-protein-independent coupling of MC4R to Kir7.1 in hypothalamic neurons. Nature 520: 94-98, 2015. [PubMed: 25600267] [Full Text: https://doi.org/10.1038/nature14051]
Hejtmancik, J. F., Jiao, X., Li, A., Sergeev, Y. V., Ding, X., Sharma, A. K., Chan, C.-C., Medina, I., Edwards, A. O. Mutations in KCNJ13 cause autosomal-dominant snowflake vitreoretinal degeneration. Am. J. Hum. Genet. 82: 174-180, 2008. [PubMed: 18179896] [Full Text: https://doi.org/10.1016/j.ajhg.2007.08.002]
Khan, A. O., Bergmann, C., Neuhaus, C., Bolz, H. J. A distinct vitreo-retinal dystrophy with early-onset cataract from recessive KCNJ13 mutations. Ophthal. Genet. 36: 79-84, 2015. [PubMed: 25475713] [Full Text: https://doi.org/10.3109/13816810.2014.985846]
Krapivinsky, G., Medina, I., Eng, L., Krapivinsky, L., Yang, Y., Clapham, D. E. A novel inward rectifier K+ channel with unique pore properties. Neuron 20: 995-1005, 1998. [PubMed: 9620703] [Full Text: https://doi.org/10.1016/s0896-6273(00)80480-8]
Partiseti, M., Collura, V., Agnel, M., Culouscou, J.-M., Graham, D. Cloning and characterization of a novel human inwardly rectifying potassium channel predominantly expressed in small intestine. FEBS Lett. 434: 171-176, 1998. [PubMed: 9738472] [Full Text: https://doi.org/10.1016/s0014-5793(98)00972-7]
Pattnaik, B. R., Shahi, P. K., Marino, M. J., Liu, X., York, N., Brar, S., Chiang, J., Pillers, D.-A. M., Traboulsi, E. I. A novel KCNJ13 nonsense mutation and loss of Kir7.1 channel function causes Leber congenital amaurosis (LCA16). Hum. Mutat. 36: 720-727, 2015. [PubMed: 25921210] [Full Text: https://doi.org/10.1002/humu.22807]
Sergouniotis, P. I., Davidson, A. E., Mackay, D. S., Li, Z., Yang, X., Plagnol, V., Moore, A. T., Webster, A. R. Recessive mutations in KCNJ13, encoding an inwardly rectifying potassium channel subunit, cause Leber congenital amaurosis. Am. J. Hum. Genet. 89: 183-190, 2011. [PubMed: 21763485] [Full Text: https://doi.org/10.1016/j.ajhg.2011.06.002]
Zhang, W., Zhang, X., Wang, H., Sharma, A. K., Edwards, A. O., Hughes, B. A. Characterization of the R162W Kir7.1 mutation associated with snowflake vitreoretinopathy. Am. J. Physiol. Cell Physiol. 304: C440-C449, 2013. [PubMed: 23255580] [Full Text: https://doi.org/10.1152/ajpcell.00363.2012]
Zhong, H., Chen, Y., Li, Y., Chen, R., Mardon, G. CRISPR-engineered mosaicism rapidly reveals that loss of Kcnj13 function in mice mimics human disease phenotypes. Sci. Rep. 5: 8366, 2015. Note: Electronic Article. Erratum: Sci Rep. 5: 9731, 2015. [PubMed: 25666713] [Full Text: https://doi.org/10.1038/srep08366]