As of September 30, 2008, a total of 411 Medalists had participated in this study; 47% were male (). The average age was 67.2 ± 7.4 years, mean age at diagnosis of diabetes was 11.0 ± 6.5 years, and mean duration of diabetes was 56.2 ± 5.8 years. Medalists had a favorable lipid profile (calculated HDL 1.6 ± 0.58 mmol/l, LDL 2.2 ± 0.6 mmol/l, total cholesterol 4.2 ± 0·9 mmol/l, triglycerides 0.9 ± 0.5 mmol/l). Average insulin dose per kilogram was 0.46 ± 0.2 u/kg. The frequency of HLA risk alleles DR3 and DR4 (0602 excluded) was greater than 93% (). The prevalence of participants who were autoantibody positive was 29.7% (111) for either antigen; 14.9% (55) and 18.4% (69) for IA2 only or GAD only, respectively ().
Characteristics of Medalist study participants
In addition to characterizing basic clinical traits, we examined family history and the presence of MODY polymorphisms. The family histories of both type 1 diabetes and type 2 diabetes of all patients were reviewed. We determined that 12.9% of Medalists had at least one first-degree relative with type 1 diabetes, and 29.7% had a first-degree relative with any type of diabetes (). No significant differences were observed in the frequency of first degree relatives with type 1 diabetes or any type of diabetes mellitus when random C-peptide levels were compared (). Additionally, 50 individuals with random C-peptide levels in excess of 0.1 nmol/l were genotyped for risk polymorphisms in MODY genes 1–5 ( HNF4A,  GCK,  TCF1,  IPF1,  TCF2). Of those typed, only 4 were found to have risk polymorphisms (HNF4A, IPF1 and 2 had TCF1). Only 1 of the 4 identified with MODY polymorphisms had a C-peptide level greater than 0.2 nmol/l. Analyses were done excluding these individuals and there was no difference in statistical results.
Characteristics of Medalist study participants by DCCT categories of residual insulin production
To further examine the role of residual C-peptide, Medalists were categorized based on their serum random C-peptide measures. These categories were derived from the Diabetes Control and Complications Trial (DCCT) criteria for examining residual C-peptide production based on response to MMTT. These categories were as follows: undetectable, ≤0.03 nmol/l; minimal, 0.03–0.2 nmol/l; and sustained, ≥0.2 nmol/l (17
). Our categorization was done using the patient's random C-peptide measure. We hypothesize that our means of categorization may underestimate the degree of insulin production, as random C-peptide levels are not necessarily at their maximum since production was likely not stimulated in most cases. There were 33.0% in the undetectable category, 64.4% with minimal, and 2.6% with sustained random serum C-peptide levels, resulting in 67.4% (n
= 256) with at least detectable C-peptide levels (). Analyses indicated a significant difference in glycemic control as measured by glycated hemoglobin across the DCCT-defined groups of random serum C-peptide levels, however, did not increase linearly with C-peptide levels (7.5 ± 1.0%, 7.1 ± 1.1%, and 7.3 ± 0.7%, respectively, P
= 0.005). The group with sustained levels of random C-peptide had a much higher mean of age at diagnosis (16.2 ± 8.6 years) compared with each of the other groups (mean of 10.9 years in each of the other groups, ANOVA P
= 0.02). MHC HLA risk alleles were also differentially distributed across these three groups of random C-peptide (). The sustained group had the highest frequency of DR3 risk alleles, whereas the minimal group (0.03–0.2 nmol/l) had the highest frequency of DR4 risk alleles. Of interest is the higher frequency of the DR3 risk allele among those with sustained random C-peptide production compared with those with undetectable random levels (57.1% vs. 33.6% DR3). The presence of islet cell antibodies, either IA2 or GAD, was not different across the three groups; however, the frequency of IA2 autoantibodies was lower than that of GAD in all groups, with none present in the sustained group (). As shown in , there was no difference across the three groups in terms of sex, age, duration of disease, A1C, family history of diabetes, BMI, insulin dose, lipid profile, or prevalence of microvascular or macrovascular complications.
There were 14 individuals who had significantly higher random C-peptide levels than the majority (in excess of 0.17 nmol/l, representing the top 3.5%) (). On average these individuals had an older age at diagnosis versus the rest of the cohort (17.4 ± 7.4 vs. 10.8 ± 6.3 years, P = 0.0008, respectively). Trends that did not reach statistical significance comparing this group with the rest of the cohort were higher frequency of DR3 or DR4 risk alleles (100% vs. 93.2%) and lower prevalence of autoantibodies (20.0% vs. 28.7%).
FIG. 1. Distribution of the first 97% of C-peptide levels among 50-year Medalists. Inset shows C-peptide values from all values. These pictures demonstrate the outlying 3% in excess of 0.17 nmol/l. (A high-quality color representation of this figure is available (more ...)
The physiologic characterization of the C-peptide production in the Medalists was studied through MMTT. A total of 31 individuals were invited to the Joslin Diabetes Center for MMTT based on their random C-peptide levels being greater than 0.1 nmol/l. In addition, 6 nondiabetic age-matched controls were also studied. Thirteen of the 31 Medalist participants who returned for the MMTT responded with doubling of C-peptide levels over their level at time 0 min (). As shown in , the nondiabetic age-matched controls had fasting levels (mean ± SD) of 0.73 ± 0.5 nmol/l and stimulated levels at 60 min of 3.74 ± 1.1 nmol/l, (P < 0.004). The 13 Medalist responders had fasting C-peptide levels of 0.14 ± 0.2 nmol/l and reached a maximum of 0.45 ± 0.54 nmol/l at 90 min (P = 0.03). In contrast, the 18 nonresponders had fasting C-peptide level of 0.11 ± 0.1 nmol/l and a maximum level of 0.15 ± 0.2 nmol/l at 90 min (P = 0.33) (). Analysis demonstrated a higher proportion of responders were in the sustained C-peptide group. It is clear that those diabetic patients with sustained random levels of C-peptides (57.1%) were significantly more responsive to MMTT, defined as at least a doubling of baseline fasting measure of C-peptide, than the minimal group (14.2%). Additionally, the sustained C-peptide group showed a significantly greater response to MMTT at 36.4% compared with the minimal group as established by random C-peptide level 15.0%, (P < 0.001).
MMTT average response curves for responders and nonresponders. (A high-quality color representation of this figure is available in the online issue.)
Mean C-peptide levels from MMTT at baseline and peak value of control subjects, responders, and nonresponders. *P value is from a paired t-test. Error bars represent standard deviation.
Pancreases from 9 Medalists representing all three DCCT categories of C-peptide production were recovered after death for pathologic analysis (). All were DR3, DR4, or DR3/DR4 positive; and 3 (33%) were antibody positive to GAD or IA2 autoantibodies. None of the pancreases studied came from patients who had a MODY risk polymorphism, and none of these have been reported before.
Summary of findings in nine Medalist's pancreases, including insulin, Ki67, and TUNEL staining in cells
Insulin+ cells were observed in all the pancreases as scattered single extrainsular cells or small clusters in some lobes (). In the seven Medalists who had onset of diabetes at age 8 or younger, most islets were atrophic with no insulin staining (A and C), although there were often also small islets with a few central cells that did not stain for glucagon. Although these unstained central cells are hypothesized to be degranulated β-cells, as yet no specific β-cell markers have stained positive. However, in two of these Medalists, insulin-positive cells were found within occasional islets.
FIG. 4. Histologic findings in pancreases from nine Medalists. In seven of nine pancreases, there were mainly atrophic islets (A) in which all or almost all cells were immunostained for glucagon, with occasional small islets that had peripheral glucagon+ cells (more ...)
In the pancreases from the two Medalists (Medalists 8 and 9, ) who had later onset diabetes (23 and 30 years) and responded by doubling their C-peptide during MMTT, considerably more insulin+ cells were found, and these were clearly within islets (D–I). In both, there were islets depleted of insulin+ cells, as well as islets with considerable proportion of insulin+ cells. Intriguingly, in Medalist 8 (onset at 23 years), half of the pancreases had only atrophic islets (C), but in a lobular pattern there were islets with significant insulin+ cells (D–F) and even some with amyloid deposits (F). Clinical evaluations of Medalist 8 showed her to be positive for DR3 and DR4 and well controlled with an A1C of 6.7%. Two MMTTs in Medalist 8 confirmed a 360% rise in C-peptide at 90 min.
Turnover of β-cells was supported by a few TUNEL+ insulin+ cells in islets or clusters in two of four (50%) TUNEL-stained pancreases (B) and by Ki67+ islet cells in two other pancreases; only one of which had insulin+ Ki67+ cells (H).
In three (33%) antibody-negative Medalists, a few CD3+ cells were found in insulin+ islets (I), and in one, antibody-positive without noticeable insulin+ cells within islets, a few islets had a CD3+ cell. There were no other CD3 cells in the low magnification fields of these pancreases.