Mutations in the insulin gene can cause MODY and autoantibody-negative type 1 diabetes.
OBJECTIVE
Mutations in the insulin (INS) gene can cause neonatal diabetes. We hypothesized that mutations in INS could also cause maturity-onset diabetes of the young (MODY) and autoantibody-negative type 1 diabetes.


METHODS
We screened INS in 62 probands with MODY, 30 probands with suspected MODY, and 223 subjects from the Norwegian Childhood Diabetes Registry selected on the basis of autoantibody negativity or family history of diabetes.


RESULTS
Among the MODY patients, we identified the INS mutation c.137G>A (R46Q) in a proband, his diabetic father, and a paternal aunt. They were diagnosed with diabetes at 20, 18, and 17 years of age, respectively, and are treated with small doses of insulin or diet only. In type 1 diabetic patients, we found the INS mutation c.163C>T (R55C) in a girl who at 10 years of age presented with ketoacidosis and insulin-dependent, GAD, and insulinoma-associated antigen-2 (IA-2) antibody-negative diabetes. Her mother had a de novo R55C mutation and was diagnosed with ketoacidosis and insulin-dependent diabetes at 13 years of age. Both had residual beta-cell function. The R46Q substitution changes an invariant arginine residue in position B22, which forms a hydrogen bond with the glutamate at A17, stabilizing the insulin molecule. The R55C substitution involves the first of the two arginine residues localized at the site of proteolytic processing between the B-chain and the C-peptide.


CONCLUSIONS
Our findings extend the phenotype of INS mutation carriers and suggest that INS screening is warranted not only in neonatal diabetes, but also in MODY and in selected cases of type 1 diabetes.
Molven
Anders
A
Gade Institute, University of Bergen, Norway.
Ringdal
Monika
M
Nordbø
Anita M
AM
Raeder
Helge
H
Støy
Julie
J
Lipkind
Gregory M
GM
Steiner
Donald F
DF
Philipson
Louis H
LH
Bergmann
Ines
I
Aarskog
Dagfinn
D
Undlien
Dag E
DE
Joner
Geir
G
Søvik
Oddmund
O
Bell
Graeme I
GI
Njølstad
Pål R
PR
D000328:Adult; D001323:Autoantibodies / Q000097:blood*; D002648:Child; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology / Q000235:genetics*; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology / Q000235:genetics* / Q000276:immunology*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007328:Insulin / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009154:Mutation; D009664:Norway / Q000453:epidemiology; D010375:Pedigree; D010641:Phenotype; D012042:Registries
D001323:Autoantibodies; D007328:Insulin