Heterozygous E1506K substitution in the SUR1 gene causes congenital hyperinsulinism in infancy, loss of insulin secretory capacity in early adulthood, and diabetes in middle-age.
Diabetes results from a newly discovered mechanism whereby the basal magnesium-nucleotide-dependent stimulatory action of SUR1 on the Kir pore is elevated and blockade by sulfonylureas is preserved.
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.
The possibility of a significant discordance in the correlation between genotype and phenotype needs to be taken into account when ABCC8 mutation dependent diabetes occurs within the same family.
The KCNJ11 E23K and ABCC8 exon 31 variants contribute to susceptibility to T2D diabetes, glucose intolerance and altered insulin secretion in a Russian population.
In the patients with either a hetero-type mutation or no mutation of the SUR1 gene, a focal type is suspected, whereas a homo-type mutation is considered to be associated with a diffuse type and also is a predictor of poor blood sugar control and a tendency toward diabetes.
The results of these studies thus revealed that mutations in the coding region of Kir6.2 1) were not responsible for the previously noted association of the SUR1 variants with NIDDM (Inoue H et al., Diabetes 45:825-831, 1996) and 2) did not contribute to the impaired insulin secretion characteristic of NIDDM in Caucasian patients.
Glucose intolerance and diabetes are observed in the long-term follow-up of nonpancreatectomized patients with persistent hyperinsulinemic hypoglycemia of infancy due to mutations in the ABCC8 gene.
STZ treatment also suppressed expression of a wide range of genes linked with key β-cell functions or diabetes development, such as G6pc2, Slc2a2 (Glut2), Slc30a8, Neurod1, Ucn3, Gad1, Isl1, Foxa2, Vdr, Pdx1, Fkbp1b and Abcc8, suggesting global β-cell defects in STZ-treated islets.
Loss of function mutations in the KCNJ11 and ABCC8 genes that encode for Kir6.2 and SUR1 can cause over-secretion of insulin and result in hyperinsulinism of infancy, while gain of function mutations in KCNJ11 and ABCC8 have recently been described that result in the opposite phenotype of diabetes.Genetic testing is important for patients with hyperinsulinism or neonatal diabetes, as identification of a K(ATP) channel mutation confirms a diagnosis of their disorder.
The meta-analysis of East Asian populations also showed a strong significant association of the K allele with diabetes (OR=1.15, P=3 x 10(-9)), whereas the exon16-3t/c variant (rs1799854) in ABCC8 showed no significant association.
A total of 40 individuals with diabetes (1.8% of early onset sub-group and 0.6% of adult onset sub-group) were carriers of known pathogenic missense variants in the GCK, HNF1A, HNF4A, ABCC8, and INS genes.
Type 2 diabetes-associated missense polymorphisms KCNJ11 E23K and ABCC8A1369S influence progression to diabetes and response to interventions in the Diabetes Prevention Program.
The diabetes associated exon 16 -3t variant of the SUR1 gene associates with a functional change of the beta cell as reflected by reduced second-phase insulin secretion in response to a standardized hyperglycaemia in normal and impaired glucose tolerant subjects.
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.
The diminished glucose responsiveness suggests that SUR1 mutations and lack of KATP channel activity may contribute to the late development of diabetes in patients with hyperinsulinism independently of subtotal pancreatectomy.
Here, we report a family carrying the dominant heterozygous germ line E1506K mutation in ABCC8 associated with persistent hypoglycemia in the newborn period and diabetes in adulthood.
It has resulted in great challenges for researchers elucidating the aetiology of diabetes and related features in other organ systems, for clinicians specifying a diagnosis that leads to improved genetic counselling, predicting of clinical course and changes in treatment, and for patients to altered treatment that has lead to coming off insulin and injections with no alternative (Glucokinase mutations), insulin injections being replaced by tablets (e.g. low dose in HNFalpha or high dose in potassium channel defects -Kir6.2 and SUR1) or with tablets in addition to insulin (e.g. metformin in insulin resistant syndromes).
The SUR1 polymorphism was genotyped in 68 type 2 diabetic patients who required insulin treatment and had known diabetes duration L 5 years, compared to 99 patients receiving oral agents (sulfonylurea alone or in combination with metformin or acarbose) with known diabetes duration of at least 15 years.
The KCNJ11 and ABCC8 genes were sequenced in 115 infants with permanent diabetes diagnosed between 6 and 12 months and in 405 patients presenting before 6 months.
Mutations in KCNJ11, ABCC8, or INS are the cause of permanent neonatal diabetes mellitus in about 50% of patients diagnosed with diabetes before 6 months of age and in a small fraction of those diagnosed between 6 and 12 months.