ABCC8 (SUR1) and KCNJ11 (KIR6.2) Mutations in Persistent Hyperinsulinemic Hypoglycemia of Infancy and Evaluation of Different Therapeutic Measures
Persistent hyperinsulinemic hypoglycemia of infancy (PHHI) can occur as a result of mutations in the subunits that form the ATP-sensitive potassium channel (K+ATP) in pancreatic beta-cells which play a major role in modulating insulin secretion from the beta-cells. Mutations have been shown in the genes for these subunits, namely for the plasma membrane sulfonylurea receptor (SUR1), ABCC8, and its associated inwardly rectifying potassium channel (KIR6.2) KCNJ11. Drugs which act on K+ATP channels, such as diazoxide, seem to need intact ABCC8 to be able to show their effects. Thus, it would be desirable to know the exact locus of the abnormality in the beta-cell to be able to choose the right therapeutic agent or to perform early pancreatectomy. The aim of this study was to search for the correlation between the mutations of the K+ATP channel and the outcome of therapeutic measures in patients with PHHI followed for a duration of 4 months to 7.3 years. Thirteen patients (5 F, 8 M) with PHHI with a median age of 2.5 months (8 days-12.1 years) were included in the study. Therapy for PHHI was initiated either with diazoxide (n = 9) or with calcium channel blocker (n = 4) as the agent of first choice. Three patients unresponsive to drugs underwent 95% pancreatectomy. Mutation analysis was performed by polymerase chain reaction (PCR) and single strand conformation polymorphism (SSCP) in DNA samples extracted from patients' peripheral leukocytes. The PCR products were directly sequenced. Screening of ABCC8 and KCNJ11 for mutations revealed abnormalities in the ABCC8 gene in three patients out of 13: homozygosity for the 155del1 mutation, compound heterozygosity for T267-->G/A4612-2-->G, and compound heterozygosity for G4310-->A/ R1494Q. No mutations in the KCNJ11 gene were identified. Of the three patients who underwent pancreatectomy, two had identified mutations and one did not have any known mutation. In two patients in whom hyperinsulinism recurred after surgery and in the rest of the children, therapy with either diazoxide or calcium channel blocker proved to be effective in controlling hypoglycemia over the follow-up period. Thus it may be concluded that mutations in the ABCC8 gene were not predictive of the response to drugs. Unidentified mutations in the K+ATP channels other than those screened or other functional abnormalities in these channels may account for the different therapeutic responses.