PHHI is a consequence of a loss of normal regulated insulin secretion by the pancreatic , (-cell. In some children this is a result of a mutation in one of two genes encoding one of the protein components (SUR1 or KIR6.2) of a (-cell potassium channel (K+ATP ), yet in others, hyperinsulinism is not linked to this genetic locus (1lpl5.1). (-cells from these infants exhibit abnormalities of other ionic channels or ion channel independent abnormalities to account for the unregulated insulin secretion. These differences in cellular pathology in PHHI may account for differences in responsiveness to pharmacological therapies. This programme will isolate genomic DNA from infants with PHHI from a variety of ethnic backgrounds (and their families) to perform detailed studies of genetic linkage to sites within and without 1lpl5.1. Acutely isolated pancreatic tissue will be used to search for somatic mutations which will not be detected in genomic DNA derived from whole blood and to construct a cDNA library. Acutely isolated (-cells will be studied using patch clamp, capacitance and microfluorimetric methods to define ion channel dependent and independent causes for the loss of regulated insulin secretion and the pharmacological manipulation of these processes studied in vitro. Detailed descriptions of genotype / clinical phenotype / cell biological phenotype (in vitro) will be constructed and on the basis of this detailed clinical management guidelines published.
Hyperinsulinism, PHHI, 1lpl5.1 Linkage analysis, K+ATP channel, SUR1, KIR6.2 (-Cell, LOH, Insulin secretion, Patch clamp, Capacitance, Genotype-Phenotype relationship, Clinical management guidelines.
Persistent hyperinsulinaemic hypoglycaemia of infancy (PPHI) is a rare disease in which severe and intractable hypoglycaemia frequently results in death or severe disability of newborn babies and infants. Current treatment protocols are far from adequate necessitating the use of dnugs with frequent and undesirable side effects or in more severe cases a sub-total pancreatectomy. The latter approach poses all the risks of a major operation in a sick infant, and commonly results in the long-term sequelae of pancreatic exocrine deficiency and diabetes mellitus. Recent advances have demonstrated that the final common pathway of the disease involves an absence of functional ATP dependent potassium channels (K+ATP channels) in the b-cells of the endocrine pancreas. These K'ATP channels are composed of two protein subunits (SUR1 and KIR6.2) the genes for which are found on the short arm of chromosome 11 (11p15.1) and function as the on / off switch for insulin secretion by the pancreatic +-cell. It is now known that mutations in either of the genes for these proteins in familial PHHI may result in an absence of KATP channel currents with the clinical manifestation of PHHI. Most European cases of PHHI are however not familial yet still exhibit and absence of KATP channel currents. The finding of a loss of maternal alleles at a gene locus containing several imprinted and non imprinted alleles several megabases (at 11p15.5) from the gene locus focalled focal PHHI poses an unresolved question of the interrelationship between these findings. Both these observations have important implications for the clinical management of PHHI. This proposal aims to correlate the clinical phenotype of PHHI with the gene defect (SUR! / KIR6.2 mutation / deletion of imprinted domain / other novel gene mutation) and will result not only in a better understanding of the pathophysiology of PHHI but also in rationalisation of current treatment protocols avoiding the long term consequences of inappropriate treatment. The cell biological observations will open the way for the development of new pharmacological treatments and the establishment of clonal cell lines with known genetic defect will pave the way for gene therapeutic strategies and Beta-cell autotransplantation in affected individuals.KEY WORDS Nesidioblastosis; Hyperinsulinaemic hypoglycaemia; Beta-cell;Imprinting; sulphonylurea receptor; K'ATP channel. 01 01