Diabetes develops when the beta cell is stressed because of increased demand for insulin, as observed in individuals with other insulin mutations that affect the processing of proinsulin to insulin or mutations that reduce the affinity for the insulin receptor.
Proinsulin and PI:C were graded according to risk of diabetes as expressed by positivity for (multiple) antibodies or IA-2 antibodies, especially in persons carrying the high-risk HLA DQ2/DQ8 genotype and in prediabetic relatives.
Proinsulin folding within the endoplasmic reticulum (ER) remains incompletely understood, but it is clear that in mutant INS gene-induced diabetes of youth (MIDY), progression of the (three) native disulfide bonds of proinsulin becomes derailed, causing insulin deficiency, β-cell ER stress, and onset of diabetes.
INS mutations have a broad spectrum of clinical presentations, ranging from severe neonatal onset to mild adult onset, which suggests that the products of different mutant INS alleles behave differently and utilize distinct mechanisms to induce diabetes.
Proinsulin misfolding is a phenotype that is very much linked to deficient insulin production and diabetes, as is seen in a variety of contexts: rodent models bearing proinsulin-misfolding mutants, human patients with Mutant INS-gene-induced Diabetes of Youth (MIDY), animal models and human patients bearing mutations in critical ER resident proteins, and, quite possibly, in more common variety type 2 diabetes.
Proinsulin processing is quite sensitive to nutrient flux, and β-cell-specific deletion of the nutrient-sensing protein modifier OGlcNAc transferase (βOGTKO) causes β-cell failure and diabetes, including early development of hyperproinsulinemia.
A plasmid DNA vaccine encoding mouse proinsulin II reduced the incidence of diabetes in a mouse model of type I diabetes when administered to hyperglycemic (therapeutic mode) or normoglycemic (prophylactic mode) NOD mice.
A total of 1440 patients (IDDM and NIDDM) of North European extraction attending two hospital diabetes services were initially screened by questionnaire.
A total of 218 sets of matched case-control questionnaire data established that paternal IDDM (odds ratio (OR) = 16.11, 95% confidence interval (CI) 1.94-133.7, p < = 0.001) is independently associated with increased risk, and higher birth order (OR = 0.64, CI 0.44-0.94, p = 0.021) and paternal age greater than 25 years (age 25-39 OR = 0.52, CI 0.30-0.89; age 40 + OR = 0.23, CI 0.08-0.67, p = 0.009) with decreased risk of diabetes.
A total of 40 individuals with diabetes (1.8% of early onset sub-group and 0.6% of adult onset sub-group) were carriers of known pathogenic missense variants in the GCK, HNF1A, HNF4A, ABCC8, and INS genes.
Accumulated evidence indicates that, in the molecular pathogenesis of the disease, misfolded proinsulin exerts dominant effects that initially inhibit insulin production, progressing to beta cell demise with diabetes.
Although more than 18 diabetes-predisposing genes have been reported to date, only the major histocompatibility complex (HLA) region on chromosome 6p21 (IDDM1) and the insulin gene on chromosome 11p15 (IDDM 2) have been conclusively associated with susceptibility to type 1 diabetes.
Autoantibody-negative patients were retested at median diabetes duration of 3.2 yr (range 0.9-16.2) for autoantibodies (GAD, IA2, ZnT8), human leukocyte antigen (HLA) typing, non-fasting C-peptide, and sequencing of HNF4A, HNF1A, KCNJ11, and INS.
Beyond neonatal diabetes mellitus (NDM), KCNJ11 is also a MODY gene ('MODY13'), confirming the wide spectrum of diabetes related phenotypes due to mutations in NDM genes (i.e.KCNJ11, ABCC8 and INS).
C-peptide and proinsulin were measured in fasting and stimulated sera from 319 subjects with long-standing type 1 diabetes (≥3 years) and 12 control subjects without diabetes.