Severe congenital hyperinsulinism caused by a mutation in the Kir6.2 subunit of the adenosine triphosphate-sensitive potassium channel impairing trafficking and function.
BACKGROUND
The ATP-sensitive potassium (K(ATP)) channel, assembled from the inwardly rectifying potassium channel Kir6.2 and the sulfonylurea receptor 1, regulates insulin secretion in beta-cells. A loss of function of K(ATP) channels causes depolarization of beta-cells and congenital hyperinsulinism (CHI), a disease presenting with severe hypoglycemia in the newborn period.


OBJECTIVE
Our objective was identification of a novel mutation in Kir6.2 in a patient with CHI and molecular and cell-biological analysis of the impact of this mutation.


METHODS
We combined immunohistochemistry, advanced life fluorescence imaging, and electrophysiology in HEK293T cells transiently transfected with mutant Kir6.2.


METHODS
The patient presented with macrosomia at birth and severe hyperinsulinemic hypoglycemia. Despite medical treatment, the newborn continued to suffer from severe hypoglycemic episodes, and at 4 months of age subtotal pancreatectomy was performed.


METHODS
We assessed patch-clamp recordings and confocal microscopy in HEK293T cells.


RESULTS
We have identified a homozygous missense mutation, H259R, in the Kir6.2 subunit of a patient with severe CHI. Coexpression of Kir6.2(H259R) with sulfonylurea receptor 1 in HEK293T cells completely abolished K(ATP) currents in electrophysiological recordings. Double immunofluorescence staining revealed that mutant Kir6.2 was partly retained in the endoplasmic reticulum (ER) causing decreased surface expression as observed with total internal reflection fluorescence. Mutation of an ER-retention signal partially rescued the trafficking defect without restoring whole-cell currents.


CONCLUSIONS
The H259R mutation of the Kir6.2 subunit results in a channel that is partially retained in the ER and nonfunctional upon arrival at the plasma membrane.
Marthinet
Eric
E
Pediatric Endocrinology and Diabetology, Children's Hospital, 6, rue Willy Donzé, CH-1211 Geneva, Switzerland.
Bloc
Alain
A
Oka
Yoshimoto
Y
Tanizawa
Yukio
Y
Wehrle-Haller
Bernhard
B
Bancila
Victor
V
Dubuis
Jean-Michel
JM
Philippe
Jacques
J
Schwitzgebel
Valerie M
VM
D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D002460:Cell Line; D005455:Fluorescent Antibody Technique; D006720:Homozygote; D006801:Humans; D006946:Hyperinsulinism / Q000151:congenital* / Q000235:genetics*; D007150:Immunohistochemistry; D007231:Infant, Newborn; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D021381:Protein Transport; D011955:Receptors, Drug / Q000235:genetics / Q000378:metabolism; D013194:Staining and Labeling; D064233:Sulfonylurea Receptors; D014162:Transfection; D000099161:Kcnj11 Channel
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D000099161:Kcnj11 Channel