Residual β cell function and monogenic variants in long-duration type 1 diabetes patients

Abstract

BACKGROUNDIn the Joslin Medalist Study (Medalists), we determined whether significant associations exist between β cell function and pathology and clinical characteristics.METHODSIndividuals with type 1 diabetes (T1D) for 50 or more years underwent evaluation including HLA analysis, basal and longitudinal autoantibody (AAb) status, and β cell function by a mixed-meal tolerance test (MMTT) and a hyperglycemia/arginine clamp procedure. Postmortem analysis of pancreases from 68 Medalists was performed. Monogenic diabetes genes were screened for the entire cohort.RESULTSOf the 1019 Medalists, 32.4% retained detectable C-peptide levels (>0.05 ng/mL, median: 0.21 ng/mL). In those who underwent a MMTT (n = 516), 5.8% responded with a doubling of baseline C-peptide levels. Longitudinally (n = 181, median: 4 years), C-peptide levels increased in 12.2% (n = 22) and decreased in 37% (n = 67) of the Medalists. Among those with repeated MMTTs, 5.4% (3 of 56) and 16.1% (9 of 56) had waxing and waning responses, respectively. Thirty Medalists with baseline C-peptide levels of 0.1 ng/mL or higher underwent the clamp procedure, with HLA-/AAb- and HLA+/AAb- Medalists being most responsive. Postmortem examination of pancreases from 68 Medalists showed that all had scattered insulin-positive cells; 59 additionally had few insulin-positive cells within a few islets; and 14 additionally had lobes with multiple islets with numerous insulin-positive cells. Genetic analysis revealed that 280 Medalists (27.5%) had monogenic diabetes variants; in 80 (7.9%) of these Medalists, the variants were classified as "likely pathogenic" (rare exome variant ensemble learner [REVEL] >0.75).CONCLUSIONAll Medalists retained insulin-positive β cells, with many responding to metabolic stimuli even after 50 years of T1D. The Medalists were heterogeneous with respect to β cell function, and many with HLA+ diabetes risk alleles also had monogenic diabetes variants, indicating the importance of genetic testing for clinically diagnosed T1D.FUNDINGFunding for this work was provided by the Dianne Nunnally Hoppes Fund; the Beatson Pledge Fund; the NIH, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK); and the American Diabetes Association (ADA).

Keywords: Beta cells; Diabetes; Endocrinology; Metabolism; Monogenic diseases.

Figure 1. Postmortem pancreases from 68 Medalists.

(A) All pancreases showed the presence of scattered insulin-positive cells, with some additionally having a few insulin-positive cells within islets and others additionally having lobes with islets with numerous insulin-positive cells. The pancreases were categorized on the basis of distribution of the insulin-positive cells. Insulin (red), glucagon (green). Scale bars: 50 μm and 63 μm (image on far right). (B) C-peptide levels and AAb presence and monogenic variant within the categories based on distribution of insulin-positive cells in postmortem pancreases (n = 68).

Figure 2. Medalist responses to a hyperglycemic/arginine clamp.

(A) Individual responses of the Joslin Medalists to a hyperglycemic clamp with arginine infusion. Blood glucose was clamped at 300 mg/dL within 45 minutes of beginning the infusion, at which point the subjects received a 5-g arginine bolus. Gray denotes previous MMTT responders; black indicates nonresponders. The graphs of nonresponders may overlap. C-peptide concentration, ng/mL; duration of clamp, min (n = 22). (B) Comparison of the clamp response with MMTT response. Shaded cells represent the cases in which the MMTT and arginine clamp responses were not the same for both tests. The response to the arginine clamp was defined as a doubling of C-peptide levels 5 minutes after the arginine bolus infusion; the response to the MMTT was defined as a doubling of baseline C-peptide levels (n = 22).

Figure 3. Medalist responses to a hyperglycemic/arginine clamp by risk allele and AAb status.

(A) Risk allele (+), AAb (–) (n = 14). (B) Risk-allele and AAb (+) (n = 11). (C) Risk-allele and AAb (–) (n = 5). The graphs of nonresponders may overlap. Monogenic variants are indicated on the right. A subset of the data from Figure 2A is reshown (n = 22). C-peptide concentration, ng/mL; duration of clamp, min.

Figure 4. Flowchart comparing the median random C-peptide levels of different subsets in the entire cohort.

The REVEL cutoff value was greater than 0.75 (n = 1007). Median (Q1, Q3). A Kruskal-Wallis test was used to determine statistical significance.