Neonatal diabetes caused by a homozygous KCNJ11 mutation demonstrates that tiny changes in ATP sensitivity markedly affect diabetes risk.
The pancreatic ATP-sensitive potassium (KATP) channel plays a pivotal role in linking beta cell metabolism to insulin secretion. Mutations in KATP channel genes can result in hypo- or hypersecretion of insulin, as in neonatal diabetes mellitus and congenital hyperinsulinism, respectively. To date, all patients affected by neonatal diabetes due to a mutation in the pore-forming subunit of the channel (Kir6.2, KCNJ11) are heterozygous for the mutation. Here, we report the first clinical case of neonatal diabetes caused by a homozygous KCNJ11 mutation.



A male patient was diagnosed with diabetes shortly after birth. At 5 months of age, genetic testing revealed he carried a homozygous KCNJ11 mutation, G324R, (Kir6.2-G324R) and he was successfully transferred to sulfonylurea therapy (0.2 mg kg(-1) day(-1)). Neither heterozygous parent was affected. Functional properties of wild-type, heterozygous and homozygous mutant KATP channels were examined after heterologous expression in Xenopus oocytes.



Functional studies indicated that the Kir6.2-G324R mutation reduces the channel ATP sensitivity but that the difference in ATP inhibition between homozygous and heterozygous channels is remarkably small. Nevertheless, the homozygous patient developed neonatal diabetes, whereas the heterozygous parents were, and remain, unaffected. Kir6.2-G324R channels were fully shut by the sulfonylurea tolbutamide, which explains why the patient's diabetes was well controlled by sulfonylurea therapy.



The data demonstrate that tiny changes in KATP channel activity can alter beta cell electrical activity and insulin secretion sufficiently to cause diabetes. They also aid our understanding of how the Kir6.2-E23K variant predisposes to type 2 diabetes.
Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.
Natascia
N
Vedovato
Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.|Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, VIC, Australia.
Edward
E
Cliff
Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.
Peter
P
Proks
Chengalpattu Medical College, Chengalpattu, Tamil Nadu, India.
Varadarajan
V
Poovazhagi
Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, UK.
Sarah E
SE
Flanagan
Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, UK.
Sian
S
Ellard
Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, UK.
Andrew T
AT
Hattersley
Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK. frances.ashcroft@dpag.ox.ac.uk.
Frances M
FM
Ashcroft
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000328:Adult; D000818:Animals; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D004594:Electrophysiology; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D007223:Infant; D007328:Insulin / Q000378:metabolism; D008297:Male; D009154:Mutation / Q000235:genetics; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism*; D013453:Sulfonylurea Compounds / Q000627:therapeutic use; D014981:Xenopus; D000099161:Kcnj11 Channel
D000255:Adenosine Triphosphate; D007328:Insulin; D024661:Potassium Channels, Inwardly Rectifying; D013453:Sulfonylurea Compounds; D000099161:Kcnj11 Channel
ATP sensitivity; ATP-sensitive potassium channel; KCNJ11; Neonatal diabetes; Type 2 diabetes