Indeed, MMR deficiency does not invariably, at the cellular level, lead to MSI or cancer development, as evidenced by experimental studies showing that acute MMR dysfunction does not cause MSI or WRN dependence, the subset of Lynch syndrome patients that do not develop cancer in their lifetimes, and the presence of MMR deficient cancers that are not MSI55–58. This evidence concerns the gene MRC1 and hyperinsulinemic hypoglycemia, familial, 4.