Mutations in genes encoding the ATP-regulated potassium (K(ATP)) channels of the pancreatic beta-cell (SUR1 and Kir6.2) are the major known cause of persistent hyperinsulinemic hypoglycemia of infancy (PHHI). We collected all cases of PHHI diagnosed in Finland between 1983 and 1997 (n = 24). The overall incidence was 1:40,400, but in one area of Central Finland it was as high as 1:3,200. Haplotype analysis using polymorphic markers spanning the SUR1/Kir6.2 gene cluster confirmed linkage to the 11p region. Sequence analysis revealed a novel point mutation in exon 4 of SUR1, predicting a valine to aspartic acid change at amino acid 187 (V187D). Of the total cases, 15 affected individuals harbored this mutation in heterozygous or homozygous form, and all of these had severe hyperinsulinemia that responded poorly to medical treatment and required subtotal pancreatectomy. No K(ATP) channel activity was observed in beta-cells isolated from a homozygous patient or after coexpression of recombinant Kir6.2 and SUR1 carrying the V187D mutation. Thus, the mutation produces a nonfunctional channel and, thereby, continuous insulin secretion. This unique SUR1 mutation explains the majority of PHHI cases in Finland and is strongly associated with a severe form of the disease. These findings provide diagnostic and prognostic utility for suspected PHHI patients.

Persistent hyperinsulinemic hypoglycemia of infancy (PHHI) is a neonatal disease characterized by dysregulation of insulin secretion accompanied by profound hypoglycemia. We have discovered that islet cells, isolated from the pancreas of a PHHI patient, proliferate in culture while maintaining a beta celllike phenotype. The PHHI-derived cell line (NES2Y) exhibits insulin secretory characteristics typical of islet cells derived from these patients, i.e. they have no K ATP channel activity and as a consequence secrete insulin at constitutively high levels in the absence of glucose. In addition, they exhibit impaired expression of the homeodomain transcription factor PDX1, which is a key component of the signaling pathway linking nutrient metabolism to the regulation of insulin gene expression. To repair these defects NES2Y cells were triple-transfected with cDNAs encoding the two components of the K ATP channel (SUR1 and Kir6.2) and PDX1. One selected clonal cell line (NISK9) had normal K ATP channel activity, and as a result of changes in intracellular Ca 2؉ homeostasis ([Ca 2؉ ] i ) secreted insulin within the physiological range of glucose concentrations. This approach to engineering PHHI-derived islet cells may be of use in gene therapy for PHHI and in cell engineering techniques for administering insulin for the treatment of diabetes mellitus. Persistent hyperinsulinemic hypoglycemia of infancy (PHHI)1 is a potentially lethal disease of the newborn. It is characterized by inappropriate insulin release in relation to the corresponding levels of glycemia (1, 2). Affected children run the risk of severe neurological damage unless immediate and adequate steps are taken to avoid profound hypoglycemia. Treatment involves administration of glucose along with drugs such as diazoxide and somatostatin that inhibit insulin secretion. However, in many cases this is not effective, and within the first few weeks of birth a near total (ϳ95%) pancreatectomy is required to control blood glucose levels.Recently, it has been shown that PHHI arises from defects in the regulation of insulin secretion. This is due principally to the loss of function of ATP-regulated potassium (K ATP ) channels. Genetic linkage has identified a susceptibility locus for PHHI within a region of chromosome 11 that encodes subunits of these channels (3, 4), while direct recordings of beta cells isolated from PHHI patients (following pancreatectomy) have documented the absence of K ATP channels (5). In beta cells these channels are composed of at least two subunits as follows: a K ϩ channel pore, Kir6.2, and an ATP-binding cassette protein, SUR1 (6, 7). Open K ATP channels set the resting membrane potential for the beta cell and a change in the intracellular ATP/ADP ratio following glucose metabolism results in their closure and the initiation of a depolarization of the cell membrane. This in turn activates voltage-dependent calcium channels and the ensuing influx of calcium stimulates membrane docking and fusion of preformed insulin granules resulting ...

Hyperinsulinism of infancy (HI) is a congenital defect in the regulated release of insulin from pancreaticH yperinsulinism of infancy (HI) (congenital hyperinsulinism) is a consequence of unregulated insulin release. The disease is clinically heterogeneous, with highly variable age of onset, severity, and responsiveness to medical treatments (1). Mutations in four different genes have been identified: the ATP-sensitive K + channel (K ATP channel) genes SUR1 and Kir6.2, glucokinase (GK), and glutamate dehydrogenase (GLUD1). Despite this, in as many as 60% of patients, the genetic basis of the condition has not been elucidated (2). The most common and most severe forms of HI arise from SUR1 and/or Kir6.2 gene defects (HI-SUR1 and HI-Kir6.2, respectively, also termed persistent hyperinsulinemic hypoglycemia of infancy [PHHI]) (2). These patients commonly exhibit symptomatic hypoglycemia soon after birth, are largely unresponsive to inhibitors of insulin release such as diazoxide and somatostatin, and require subtotal (95%) resection of the pancreas to alleviate hypoglycemia (1). For individuals with the rarer forms (HI-GK or HI-GLUD1), surgical resection of the pancreas is not usually necessary because hyperinsulinism is avoided by managing nutrition or by inhibiting insulin secretion with the K ATP channel activator diazoxide (3,4).The genetic basis of HI-K ATP is heterogeneous; more than 40 mutations in SUR1 have been identified, and 3 mutations in Kir6.2 have been described (2). Using both recombinant expression systems (5-8) and ␤-cells isolated from patients after surgery (6-10), investigators have shown these mutations to lead to impaired trafficking or assembly of K ATP channels or to cause defects in the ADP-dependent regulation of channel activity. Functional studies on ␤-cells isolated from patients with HI have further demonstrated that loss of operational channels results in depolarized ␤-cells with unregulated Ca 2+ channel activity (9). However, whereas these studies have provided a means of correlating the genetics of HI

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