c-peptide and Polycystic-Kidney-Diseases

Maturity-onset diabetes of the young type 5 (MODY5) is caused by mutation of hepatocyte nuclear factor 1beta (HNF1 beta) (TCF2) gene, resulting in a wide range of phenotypes including diabetes and renal abnormalities, but little is known about the pathogenesis of the clinical spectrum. We describe a 27-year-old Japanese male with the MODY phenotype including an atrophic kidney and multiple renal cysts. Genetic analysis revealed the patient to be heterozygous for a nonsense mutation in codon 276 of the HNF1beta gene (CGA or Arginine to TGA or stop codon; R276X). To clarify the pathophysiological relevance of this mutation, we conducted an in vitro study monitoring human C-peptide secretion after transfecting both the HNF1beta mutant cDNA and preproinsulin cDNA into a murine beta cell line, MIN6. Functional studies of the transformed MIN6 cells indicated that expression of the R276X caused a significant decrease in glucose-stimulated insulin secretion but no change in either KCl-stimulated or basal insulin secretion. These results suggest that the R276X functions in a negative manner in regard to metabolic responses of insulin secretion in beta cells. Analysis with light and electron microscopy on biopsied kidney specimens suggested that the origin of the cysts might be glomeruli but the primary lesion could be tubules.

Topics: Adult; Age of Onset; Arginine; C-Peptide; Cells, Cultured; Codon, Nonsense; Diabetes Mellitus, Type 2; Hepatocyte Nuclear Factor 1-beta; Humans; Insulin-Secreting Cells; Male; Pedigree; Polycystic Kidney Diseases; Transfection

A young woman given a renal allograft for polycystic kidney disease developed insulin dependent diabetes mellitus 25 days after transplantation. There was no family history of diabetes, plasma glucose concentrations had been normal at presentation and on five subsequent occasions, and at no time were islet cell antibodies detectable. Plasma C peptide concentrations, however, were greatly suppressed after transplantation and remained so for up to six months. The immunosuppressive regimen had included cyclosporin A, which had been difficult to regulate and caused definite signs of toxicity in the patient. By virtue of its reported toxicity for beta cells and the reversal of the diabetes several months after the dose was reduced cyclosporin was incriminated as the probable causative agent. Dose related beta cell toxicity of cyclosporin A may be a risk in recipients of this drug and warrants careful monitoring of drug and glucose concentrations.

Topics: Adolescent; C-Peptide; Cyclosporins; Diabetes Mellitus, Type 1; Female; Humans; Kidney Transplantation; Polycystic Kidney Diseases