Mutations in the genes encoding the pancreatic beta-cell KATP channel subunits Kir6.2 (KCNJ11) and SUR1 (ABCC8) in diabetes mellitus and hyperinsulinism

The beta-cell ATP-sensitive potassium channel is a key component of stimulus-secretion coupling in the pancreatic beta-cell. The channel couples metabolism to membrane electrical events, bringing about insulin secretion. Given the critical role of this channel in glucose homeostasis, it is not surprising that mutations in the genes encoding for the two essential subunits of the channel can result in both hypo- and hyperglycemia. The channel consists of four subunits of the inwardly rectifying potassium channel Kir6.2 and four subunits of the sulfonylurea receptor 1. It has been known for some time that loss of function mutations in KCNJ11, which encodes for Kir6.2, and ABCC8, which encodes for SUR1, can cause oversecretion of insulin and result in hyperinsulinemia (HI) of infancy; however, heterozygous activating mutations in KCNJ11 that result in the opposite phenotype of diabetes have recently been described. This review focuses on reported mutations in both genes, the spectrum of phenotypes, and the implications for treatment when patients are diagnosed with mutations in these genes.     

ABCC8 and ABCC9: ABC transporters that regulate K+ channels

The sulfonylurea receptors (SURs) ABCC8/SUR1 and ABCC9/SUR2 are members of the C-branch of the transport adenosine triphosphatase superfamily. Unlike their brethren, the SURs have no identified transport function; instead, evolution has matched these molecules with K⁺ selective pores, either K_IR6.1/KCNJ8 or K_IR6.2/KCNJ11, to assemble adenosine triphosphate (ATP)-sensitive K⁺ channels found in endocrine cells, neurons, and both smooth and striated muscle. Adenine nucleotides, the major regulators of ATP-sensitive K⁺ (K_ATP) channel activity, exert a dual action. Nucleotide binding to the pore reduces the activity or channel open probability, whereas Mg-nucleotide binding and/or hydrolysis in the nucleotide-binding domains of SUR antagonize this inhibitory action to stimulate channel openings. Mutations in either subunit can alter this balance and, in the case of the SUR1/KIR6.2 channels found in neurons and insulin-secreting pancreatic β cells, are the cause of monogenic forms of hyperinsulinemic hypoglycemia and neonatal diabetes. Additionally, the subtle dysregulation of K_ATP channel activity by a K_IR6.2 polymorphism has been suggested as a predisposing factor in type 2 diabetes mellitus. Studies on K_ATP channel null mice are clarifying the roles of these metabolically sensitive channels in a variety of tissues.     

Update of mutations in the genes encoding the pancreatic beta-cell K(ATP) channel subunits Kir6.2 (KCNJ11) and sulfonylurea receptor 1 (ABCC8) in diabetes mellitus and hyperinsulinism

The beta-cell ATP-sensitive potassium (K(ATP)) channel is a key component of stimulus-secretion coupling in the pancreatic beta-cell. The channel couples metabolism to membrane electrical events bringing about insulin secretion. Given the critical role of this channel in glucose homeostasis it is therefore not surprising that mutations in the genes encoding for the two essential subunits of the channel can result in both hypo- and hyperglycemia. The channel consists of four subunits of the inwardly rectifying potassium channel Kir6.2 and four subunits of the sulfonylurea receptor 1 (SUR1). It has been known for some time that loss of function mutations in KCNJ11, which encodes for Kir6.2, and ABCC8, which encodes for SUR1, can cause oversecretion of insulin and result in hyperinsulinism of infancy, while activating mutations in KCNJ11 and ABCC8 have recently been described that result in the opposite phenotype of diabetes. This review focuses on reported mutations in both genes, the spectrum of phenotypes, and the implications for treatment on diagnosing patients with mutations in these genes.     

Update of variants identified in the pancreatic β‐cell KATP channel genes KCNJ11 and ABCC8 in individuals with congenital hyperinsulinism and diabetes

The most common genetic cause of neonatal diabetes and hyperinsulinism is pathogenic variants in ABCC8 and KCNJ11. These genes encode the subunits of the β‐cell ATP‐sensitive potassium channel, a key component of the glucose‐stimulated insulin secretion pathway. Mutations in the two genes cause dysregulated insulin secretion; inactivating mutations cause an oversecretion of insulin, leading to congenital hyperinsulinism, whereas activating mutations cause the opposing phenotype, diabetes. This review focuses on variants identified in ABCC8 and KCNJ11, the phenotypic spectrum and the treatment implications for individuals with pathogenic variants.     

Dominantly acting ABCC8 mutations in patients with medically unresponsive hyperinsulinaemic hypoglycaemia

Flanagan SE, Kapoor RR, Banerjee I, Hall C, Smith VV, Hussain K, Ellard S. Dominantly acting ABCC8 mutations in patients with medically unresponsive hyperinsulinaemic hypoglycaemia. Recessive inactivating mutations in the ABCC8 and KCNJ11 genes encoding the adenosine triphosphate‐sensitive potassium (K_ATP) channel subunit sulphonylurea receptor 1 (SUR1) and inwardly rectifying potassium channel subunit (Kir6.2) are the most common cause of hyperinsulinaemic hypoglycaemia (HH). Most of these patients do not respond to treatment with the K_ATP channel agonist diazoxide. Dominant inactivating ABCC8 and KCNJ11 mutations are less frequent, but are usually associated with a milder form of hypoglycaemia that is responsive to diazoxide therapy. We studied five patients from four families with HH who were unresponsive to diazoxide and required a near total pancreatectomy. Mutations in KCNJ11 and ABCC8 were sought by sequencing and dosage analysis. Three novel heterozygous ABCC8 mis‐sense mutations (G1485E, D1506E and M1514K) were identified in four probands. All the mutations affect residues located within the Nucleotide Binding Domain 2 of the SUR1 subunit. Testing of family members showed that the mutations had arisen de novo with dominant inheritance in one pedigree. This study extends the clinical phenotype associated with dominant K_ATP channel mutations to include severe congenital HH requiring near total pancreatectomy in addition to a milder form of diazoxide responsive hypoglycaemia. The identification of dominant vs recessive mutations does not predict clinical course but it is important for estimating the risk of HH in future siblings and offspring.     

Clinical features and genetic analysis of seven patients with congenital hyperinsulinismCSCD

Objective: To analyze clinical characteristics, genetic mutation and therapeutic effect of seven patients diagnosed with congenital hyperinsulinism(CHI). Methods: Clinical data for the patients was retrospectively analyzed. Results: All patients presented with hyperinsulinism(serum insulin:2. 0-58. 4 mU/L),even after hypoglycemia (blood glucose: 0. 7-2. 39 mmol/L)has developed. Mutations were identified in 4 patients (57. 1%), which included a heterozygous c. 262C>T(p. R88C) mutation in exon 4 of the UCP2 gene, a heterozygous c. 1495C>A(p. G499C) mutation in exon 12 of the GLUD1 gene, a heterozygous c. 1493C>T(p. S498L) mutation in exon 1 of the GLUD1 gene, and a heterozygous c. 4432G > A (p. G1478R) mutation in exon 37 of the ABCC8 gene. The patient carrying a maternally inherited ABCC8 mutation was treated with cornstarch and had his blood glucose kept normal. All other patients responded well to diazoxide. Conclusion: A genetic diagnosis was attained for 51. 7% of patients in this study. Mild CHI patients can have their blood glucose controlled by giving cornstarch. Diazoxide is safe and effective for most CHI patients. © 2018 MeDitorial Ltd. All rights reserved.     

Clinical and molecular characterization of neonatal diabetes and monogenic syndromic diabetes in Asian Indian children

Mutations in the pancreatic ATP sensitive K⁺ channel proteins [sulfonyluea receptor 1 (SUR1) and inward rectifier K⁺ channel Kir6.2 (Kir6.2), encoded by ATP‐binding cassette transporter subfamily C member 8 (ABCC8) and potassium channel J11 (KCNJ11), respectively], are the most common cause of neonatal diabetes. We describe the clinical presentation and molecular characterization of Asian Indian children with neonatal diabetes mellitus and monogenic syndromes of diabetes. We sequenced KCNJ11, ABCC8 and insulin (INS) genes in 33 unrelated Indian probands with onset of diabetes below one year of age. A total of 12 mutations were identified which included ABCC8 mutations in seven, KCNJ11 mutations in three and INS mutations in two children. The Asp212Tyr mutation in ABCC8 was novel. We also detected two novel mutations (Val67Met and Leu19Arg) in children with syndromic forms of diabetes like Berardinelli Seip syndrome [1‐acyl‐sn‐glycerol‐3‐phosphate acyltransferase beta (AGPAT2)] and Fanconi Bickel syndrome [solute carrier family 2A2 (SLC2A2)]. Children carrying the KCNJ11 (Cys42Arg, Arg201Cys) and ABCC8 (Val86Ala, Asp212Tyr) mutations have been successfully switched over from insulin therapy to oral sulfonylurea. Our study is the first large genetic screening study of neonatal diabetes in India.     

Pseudoxanthoma elasticum: Point mutations in the ABCC6 gene and a large deletion including also ABCC1 and MYH11

Pseudoxanthoma elasticum (PXE) is a mendelian disorder characterized by calcification of elastic fibers in skin, arteries, and retina. It results in dermal lesions, arterial insufficiency and retinal hemorrhages, leading to macular degeneration. PXE is transmitted either as an autosomal dominant or recessive trait and several sporadic cases have been observed. Mutations in the ABCC6 gene have been identified very recently in patients. Here, we report on a large Italian family affected by pseudoxanthoma elasticum for which linkage analysis had pointed to a region encompassing markers D16S3069‐D16S405‐D16S3103; hemizygosity of marker D16S405 allowed us to detect a submicroscopic deletion of at least 900 kb involving ABCC6, ABCC1, and MYH11. Mutation analysis on the other allele of the family, as well as on two additional sporadic cases, revealed nonsense (Y227X, R518X, R1164X) and frame‐shift (c.960delC) mutations in ABCC6 (MRP6) further confirming the role of this multi‐drug resistance gene in the etiology of pseudoxanthoma elasticum. Furthermore, clinical re‐examination of members of the family harboring the deletion led to the detection of additional features, potentially caused by the deletion of the MYH11 gene. In the course of the analysis five nonpathogenic variants were found in ABCC6: 1233T>C, 1245G>A, 1838 T>G (V614A), 1890C>G, and 3506+83C>A. Hum Mutat 18:85, 2001. © 2001 Wiley‐Liss, Inc.     

ABCB1 (P-glycoprotein) but not ABCC1 (MRP1) is downregulated in peripheral blood mononuclear cells of spontaneously hypertensive rats

Although the kidney is a major target in hypertension, several studies have correlated important immune alterations with the development of hypertension in spontaneously hypertensive rats (SHR), like increased secretion of pro-inflammatory cytokines, inflammatory infiltration in kidneys and thymic atrophy. Because adenosine-triphosphate-binding cassette sub-family B member 1 (ABCB1; P-glycoprotein) and adenosine-triphosphate-binding cassette sub-family C member 1 (ABCC1; multidrug resistance protein 1), two proteins first described in multidrug resistant tumors, physiologically transport several immune mediators and are required for the adequate functioning of the immune system, we aimed to measure the expression and activity of these proteins in peripheral blood mononuclear cells (PBMC), thymocytes, and also kidneys of normotensive Wistar Kyoto rats and SHR. Our results showed that ABCB1, but not ABCC1, activity was diminished (nearly 50%) in PBMC. Moreover, Abcb1b gene was downregulated in PBMC and kidney of SHR and this was not counterbalanced by an upregulation of its homolog Abcb1a, suggesting that the diminished activity is due to downregulation of the gene. No alteration was detected in ABCB1 activity in SHR thymocytes, indicating that this downregulation occurs after lymphocytes leave the primary lymphoid organs. Even though it is not known at present which parameter(s) is(are) responsible for this downregulation, it may contribute for the altered immune response observed in hypertension and to possible altered drug disposition in hypertensive individuals, resulting in greater drug interaction and increased drug toxicity. Raphael C. Valente and Márcia A. M. Capella contributed equally to this work.     

CYP1B1 Gene Mutations Causing Primary Congenital Glaucoma in Tunisia

Primary congenital glaucoma (PCG) is responsible for a significant proportion of childhood blindness in Tunisia. Early prevention based on genetic diagnosis is therefore required. This study sought to determine the frequency of CYP1B1 (cytochrome P450, family 1, subfamily B, polypeptide 1) mutations in 18 PCG patients, recruited from Central and Southern of Tunisia. Genomic DNA was extracted and the coding regions of CYP1B1 were analysed by direct sequencing. A phylogenetic network of CYP1B1 haplotypes was drawn using the median‐joining algorithm. Sequence analysis revealed a “tetra‐allelic mutation” (two novel mutations, p.F231I and p.P437A in the homozygous state) in one patient. The healthy members of his family carried those variations on the same allele. Two previously described mutations p.G61E and c.535delG were also identified in the homozygous state in seven and two probands, respectively. Seven single‐nucleotide polymorphisms were identified and used to generate haplotypes. Our results showed that the CYP1B1 mutations were present in 55% of Tunisian PCG patients’ alleles. Haplotype analysis allowed us to define the proto‐haplotype and to confirm historical migratory flows. Establishment of PCG genetic aetiology in Tunisia will improve genetic diagnosis and counselling.     

The spectrum of ABCC8 mutations in Norwegian patients with congenital hyperinsulinism of infancy

Potassium channels in the plasma membrane of the pancreatic beta cells are critical in maintaining glucose homeostasis by responding to ATP and coupling metabolic changes to insulin secretion. These channels consist of subunits denoted the sulfonylurea receptor SUR1 and the inwardly rectifying ion channel KIR6.2, which are encoded by the genes ABCC8 and KCNJ11 , respectively. Activating mutations in the subunit genes can result in monogenic diabetes, whereas inactivating mutations are the most common cause of congenital hyperinsulinism of infancy (CHI). Twenty-six Norwegian probands with CHI were analyzed for alterations in ABCC8 and KCNJ11 . Fifteen probands (58%) had mutations in the ABCC8 gene. Nine patients were homozygous or compound heterozygous for the mutations, indicating diffuse pancreatic disease. In five patients, heterozygous and paternally inherited mutations were found, suggesting focal disease. One patient had a de novo mutation likely to cause a milder, dominant form of CHI. Altogether, 16 different ABCC8 mutations (including the novel alterations W231R, C267X, IVS6-3C>G, I462V, Q917X and T1531A) were identified. The mutations IVS10+1G>T, R1493W and V21D occurred in five, three and two families, respectively. KCNJ11 mutations were not found in any patients. Based on our mutation screening, we estimate the minimum birth prevalence of ABCC8 -CHI in Norway to 1:70,000 during the past decade. Our results considerably extend the knowledge of the molecular genetics behind CHI in Scandinavia.     

A heterozygous activating mutation in the sulphonylurea receptor SUR1 (ABCC8) causes neonatal diabetes

Neonatal diabetes is a genetically heterogeneous disorder with nine different genetic aetiologies reported to date. Heterozygous activating mutations in the KCNJ11 gene encoding Kir6.2, the pore-forming subunit of the ATP-sensitive potassium (K(ATP)) channel, are the most common cause of permanent neonatal diabetes. The sulphonylurea receptor (SUR) SUR1 serves as the regulatory subunit of the K(ATP) channel in pancreatic beta cells. We therefore hypothesized that activating mutations in the ABCC8 gene, which encodes SUR1, might cause neonatal diabetes. We identified a novel heterozygous mutation, F132L, in the ABCC8 gene of a patient with severe developmental delay, epilepsy and neonatal diabetes (DEND syndrome). This mutation had arisen de novo and was not present in 150 control chromosomes. Residue F132 shows evolutionary conservation across species and is located in the first set of transmembrane helices (TMD0) of SUR1, which is proposed to interact with Kir6.2. Functional studies of recombinant K(ATP) channels demonstrated that F132L markedly reduces the sensitivity of the K(ATP) channel to inhibition by MgATP and this increases the whole-cell K(ATP) current. The functional consequence of this ABCC8 mutation mirrors that of KCNJ11 mutations causing neonatal diabetes and provides new insights into the interaction of Kir6.2 and SUR1. As SUR1 is expressed in neurones as well as in beta cells, this mutation can account for both neonatal diabetes and the neurological phenotype. Our results demonstrate that SUR1 mutations constitute a new genetic aetiology for neonatal diabetes and that they act by reducing the K(ATP) channel's ATP sensitivity.     

ABCC9/SUR2 in the brain: Implications for hippocampal sclerosis of aging and a potential therapeutic target

The ABCC9 gene and its polypeptide product, SUR2, are increasingly implicated in human neurologic disease, including prevalent diseases of the aged brain. SUR2 proteins are a component of the ATP-sensitive potassium (“K_ATP”) channel, a metabolic sensor for stress and/or hypoxia that has been shown to change in aging. The K_ATP channel also helps regulate the neurovascular unit. Most brain cell types express SUR2, including neurons, astrocytes, oligodendrocytes, microglia, vascular smooth muscle, pericytes, and endothelial cells. Thus it is not surprising that ABCC9 gene variants are associated with risk for human brain diseases. For example, Cantu syndrome is a result of ABCC9 mutations; we discuss neurologic manifestations of this genetic syndrome. More common brain disorders linked to ABCC9 gene variants include hippocampal sclerosis of aging (HS-Aging), sleep disorders, and depression. HS-Aging is a prevalent neurological disease with pathologic features of both neurodegenerative (aberrant TDP-43) and cerebrovascular (arteriolosclerosis) disease. As to potential therapeutic intervention, the human pharmacopeia features both SUR2 agonists and antagonists, so ABCC9/SUR2 may provide a “druggable target”, relevant perhaps to both HS-Aging and Alzheimer's disease. We conclude that more work is required to better understand the roles of ABCC9/SUR2 in the human brain during health and disease conditions.     

三例谷氨酸脱氢酶型先天性高胰岛素血症患儿的GLUD1基因突变分析

目的 对3例临床诊断为谷氨酸脱氢酶型先天性高胰岛素血症的患儿家系进行遗传学分析并对中国儿童谷氨酸脱氢酶型先天性高胰岛素血症的遗传发病机制进行初步探讨.方法 选取3例临床诊断为谷氨酸脱氢酶型先天性高胰岛素血症患儿的家系,应用PCR-DNA直接测序技术对3例患儿家系谷氨酸脱氢酶1基因(glutamate dehydrogenase 1,GLUD1)第6,7,10,11,12外显子区进行测序分析.结果 第1例患儿及其父亲GLUD1基因第7外显子区发现了1个R269H杂合突变,遗传方式为常染色体显性遗传.第2例患者GLUD1基因的第11外显子区发现了1个S445L杂合突变,为新生突变.第3例患儿家系GLUD1基因第6,7,10,11,12外显子均未发现突变.结论 在某些中国人中,谷氨酸脱氢酶基因R269H,S445L杂合突变可以导致谷氨酸脱氢酶型先天性高胰岛素血症的发生.     

Glucose metabolism and insulin secretion in a patient with ABCC8 mutation and Fanconi-Bickel syndrome caused by maternal isodisomy of chromosome 3

Fanconi-Bickel syndrome (FBS) is a rare disorder of glucose transport caused by autosomal recessive mutations in GLUT2. Clinically, FBS results in growth failure, hepatomegaly, renal Fanconi syndrome, and abnormal glucose homeostasis. We report a 23 month old female with FBS characterized by more severe and refractory hypoglycemia than typically seen in this disorder. Although previous reports indicate that FBS patients have diminished insulin secretion, our patient showed evidence of hyperinsulinism (HI). Sequence analysis showed that the patient was homozygous for a known null mutation in GLUT2, confirming the clinical diagnosis of FBS. Parental genotyping showed that the mother was heterozygous for the GLUT2 mutation, while the father was wild type. Tandem repeat marker analysis showed that the patient inherited the GLUT2 mutation via maternal isodisomy of chromosome 3. Further molecular testing showed that the patient was heterozygous for a mutation in ABCC8, a known cause of congenital HI. We discuss the patient's biochemical responses in light of the molecular findings.     

Association of eNOS (G894T,rs1799983) and KCNJ11 (E23K,rs5219) gene polymorphism with coronary artery disease in North Indian population

BackgroundEndothelial nitric oxide synthase (eNOS) and potassium voltage-gated channel subfamily J member 11 (KCNJ11) could be the candidate genes for coronary artery disease (CAD). This study investigated the relationship of the eNOS (rs1799983) and KCNJ11 (rs5219) polymorphisms with the presence and severity of CAD in the North Indian population.MethodsThis study included 300 subjects, 150 CAD cases and 150 healthy controls. Single nucleotide polymorphism was evaluated by Polymerase chain reaction and Restriction fragment length polymorphism (PCR-RFLP). Analysis was performed by SPSS (version 21.0).ResultsWe observed that KK genotype of KCNJ11E23K (rs5219) polymorphism (P=0.0001) genotypes and K allele (P=0.0001) was found to be a positive risk factor and strongly associated with CAD. In the case of eNOSG894T (rs1799983) there was no association found with CAD.ConclusionThese results illustrate the probability of associations between SNPs and CAD although specific genetic polymorphisms affecting ion channel function and expression have still to be clarified by further investigations involving larger cohorts.     

Distinct Clinical Phenotype and Immunoreactivity in Japanese Siblings with Autoimmune Polyglandular Syndrome Type 1 (APS-1) Associated with Compound Heterozygous Novel AIRE Gene Mutations

We herein report on two Japanese siblings with autoimmune polyglandular syndrome type 1 (APS-1). The brother, who expressed a characteristic phenotype of APS-1, had developed severe mucocutaneous candidiasis in early infancy and thereafter developed hypoparathyroidism and Addison's disease, along with a severe deterioration of his immunologic function. In contrast, the 44-year-old sister, who showed a noncharacteristic phenotype of APS-1, developed insulin-dependent diabetes with high anti-glutamic acid decarboxylase antibody, mild nail candidiasis, and autoimmune hepatitis with intact immunoreactivity. She had three susceptible human leukocyte antigen (HLA) loci for type 1 autoimmune diabetes. The expression of T cell receptor (TCR)Vβ5.1 increased in both patients, while the brother showed a widely suppressed expression of many TCRVβ families. Both individuals possessed compound heterozygous novel autoimmune regulator (AIRE) gene mutations (L29P and IVS9–1G>C). The same AIRE gene mutations can thus be associated with characteristic and noncharacteristic phenotypes of APS-1, and HLA may possibly influence the phenotype of APS-1.     

ABCB1和ABCC2基因多态性与中国汉族儿童抗结核药物致肝毒性易感性的相关性研究

目的 探讨ABCB1和ABCC2基因多态性与中国汉族儿童抗结核药物致肝毒性(anti-tuberculosis drug-induced hepatotoxicity,ATDH)易感性的相关性.方法 在中国汉族结核病患儿中,采用病例对照研究,利用高通量的MassARRAY平台,对于ABCB1和ABCC2基因的16个标签单核苷酸多态性(single nucleotide polymorphisms,SNPs)位点展开基因分型,并采用logistic回归分析以上SNP位点等位基因和基因型频率在ATDH病例组和ATDH对照组中的分布差异.结果 本研究共纳入41例ATDH病例以及189例对照.ABCB1和ABCC2基因SNP位点的等位基因以及基因型在两组间频率分布差异均无统计学意义(P＞0.05).SNP位点分别按照显性遗传模型和隐性遗传模型分析,各位点基因型在两组间频率分布差异均无统计学意义(P＞0.05).结论 ABCB1和ABCC2基因多态性可能与中国汉族儿童ATDH的发生并无相关性.     

Identification of a novel single base-pair polymorphism in the glutamate dehydrogenase (GLUD1) gene

A novel single base-pair polymorphism, G/A at ntd 955, was identified within the coding region of the glutamate dehydrogenase gene (GLUD1). This polymorphism should prove useful for the study of human disorders with altered ammonia and/or blood glucose levels. Received: February 15, 1999 / Accepted: February 18, 1999