What are the genetic changes related to permanent neonatal diabetes mellitus ?
Permanent neonatal diabetes mellitus may be caused by mutations in several genes.  About 30 percent of individuals with permanent neonatal diabetes mellitus have mutations in the KCNJ11 gene. An additional 20 percent of people with permanent neonatal diabetes mellitus have mutations in the ABCC8 gene. These genes provide instructions for making parts (subunits) of the ATP-sensitive potassium (K-ATP) channel. Each K-ATP channel consists of eight subunits, four produced from the KCNJ11 gene and four from the ABCC8 gene.  K-ATP channels are found across cell membranes in the insulin-secreting beta cells of the pancreas. These channels open and close in response to the amount of glucose in the bloodstream. Closure of the channels in response to increased glucose triggers the release of insulin out of beta cells and into the bloodstream, which helps control blood sugar levels.  Mutations in the KCNJ11 or ABCC8 gene that cause permanent neonatal diabetes mellitus result in K-ATP channels that do not close, leading to reduced insulin secretion from beta cells and impaired blood sugar control.  Mutations in the INS gene, which provides instructions for making insulin, have been identified in about 20 percent of individuals with permanent neonatal diabetes mellitus. Insulin is produced in a precursor form called proinsulin, which consists of a single chain of protein building blocks (amino acids). The proinsulin chain is cut (cleaved) to form individual pieces called the A and B chains, which are joined together by connections called disulfide bonds to form insulin. Mutations in the INS gene are believed to disrupt the cleavage of the proinsulin chain or the binding of the A and B chains to form insulin, leading to impaired blood sugar control.  Permanent neonatal diabetes mellitus can also be caused by mutations in other genes, some of which have not been identified.