Mutations in the ABCC8 (SUR1 subunit of the K(ATP) channel) gene are associated with a variable clinical phenotype.
OBJECTIVE
Mutations in the ABCC8 gene encoding the SUR1 subunits of the beta-cell K-ATP channel cause neonatal diabetes (ND) mellitus. We aimed to determine the contribution of ABCC8 gene to ND in Poland, to describe the clinical phenotype associated with its mutations and to examine potential modifying factors.


METHODS
The Nationwide Registry of ND in Poland includes patients diagnosed before 6 months of age. In total 16 Kir6.2 negative patients with ND, 14 permanent and 2 relapsed transient, were examined.


METHODS
ABCC8 gene mutations were detected by direct sequencing. Mutation carriers' characteristics included clinical data and biochemical parameters. In addition, we performed the hyperinsulinaemic euglycaemic clamp and tested for islet-specific antibodies in diabetic subjects.


RESULTS
We identified two probands with permanent ND (one heterozygous F132V mutation carrier and one compound heterozygote with N23H and R826W mutations) and two others with relapsed transient ND (heterozygotes for R826W and V86A substitutions, respectively). One subject, a heterozygous relative with the R826W mutation, had adult onset diabetes. There were striking differences in the clinical picture of the mutation carriers as the carrier of two mutations, N23H and R826W, was controlled on diet alone with HbA(1c) of 7.3%, whereas the F132V mutation carrier was on 0.66 IU/kg/day of insulin with HbA(1c) of 11.7%. The C-peptide level varied from 0.1 ng/ml (F132V) to 0.75 ng/ml (V86A). We also observed a variable insulin resistance, from moderate (M = 5.5 and 5.6 mg/kg/min, respectively, in the two R826W mutation carriers) to severe (M = 2.6 mg/kg/min in the F132V mutation carrier). We were able to transfer two patients off insulin to sulphonylurea (SU) and to reduce insulin dose in one other patient. Interestingly, there was no response to SU in the most insulin resistant F132V mutation carrier despite high dose of glibenclamide. All examined auto-antibodies were present in one of the subjects, the V86A mutation carrier, although this did not seem to influence the clinical picture, as we were able to transfer this girl off insulin.


CONCLUSIONS
Mutations in SUR1 are the cause of about 15% of Kir6.2 negative permanent ND in Poland. The clinical phenotype of SUR1 diabetic mutation carriers is heterogeneous and it appears to be modified by variable sensitivity to insulin.
Klupa
Tomasz
T
Department of Metabolic Diseases, Jagiellonian University, Medical College, Krakow, Poland.
Kowalska
Irina
I
Wyka
Krystyna
K
Skupien
Jan
J
Patch
Ann-Marie
AM
Flanagan
Sarah E
SE
Noczynska
Anna
A
Arciszewska
Malgorzata
M
Ellard
Sian
S
Hattersley
Andrew T
AT
Sieradzki
Jacek
J
Mlynarski
Wojciech
W
Malecki
Maciej T
MT
D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000293:Adolescent; D002648:Child; D003920:Diabetes Mellitus / Q000235:genetics*; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009154:Mutation; D010375:Pedigree; D010641:Phenotype; D011044:Poland; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics*; D011955:Receptors, Drug / Q000235:genetics*; D064233:Sulfonylurea Receptors
C577507:ABCC8 protein, human; D018528:ATP-Binding Cassette Transporters; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors