Beta cell function and insulin sensitivity in obese youth with maturity onset diabetes of youth mutations vs type 2 diabetes in TODAY: Longitudinal observations and glycemic failure

Abstract

Objective:

In treatment options for type 2 diabetes in adolescents and youth (TODAY), 4.5% of obese youth clinically diagnosed with type 2 diabetes (T2D) had genetic variants consistent with maturity onset diabetes of youth (MODY) diagnosis. The course of IS and β-cell function in obese youth with MODY remains unknown. In this secondary analysis, we examined IS and β-cell function in MODY vs. non-MODY obese youth at randomization and over time.

Methods:

Genetic data in TODAY included 426 non-MODY (T2D) and 22 MODY youth (7 glucokinase MODY mutation positive [GCK-MODY], 12 hepatocyte nuclear factor MODY mutation positive [HNF-MODY], 2 Insulin gene mutation [insulin (INS)-MODY], and 1 Kruppel-like factor 11 [KLF11-MODY]). Oral glucose tolerance test (OGTT)-derived IS, C-peptide index, and β-cell function relative to IS oral disposition index (oDI) was measured at randomization, and over 24 months in addition to total and high-molecular-weight adiponectin (HMWA).

Results:

At randomization, IS, total adiponectin, and HMWA were significantly higher in the two MODY groups than in non-MODY. β-cell function measured by C-peptide oDI was 3-fold higher in GCK-MODY than in HNF-MODY and 1.5-fold higher than non-MODY (P for both <.05) Glycemic failure rate was 75.0% in HNF-MODY, 46.9% in non-MODY, and zero in GCK-MODY youth. While the changes in IS and oDI were not different among the three groups in the first 6 months, IS improved from 6 to 24 months in HNF-MODY vs GCK-MODY youth.

Conclusions:

In TODAY, β-cell function at randomization was worse in obese HNF-MODY youth compared with GCK-MODY youth, while insulin sensitivity was worse in non-MODY compared with the other two MODY groups. Over time, IS showed the greatest improvement in HNF-MODY youth. This raises the possibility that TODAY therapeutic modalities of insulin sensitization in these obese HNF-MODY youth may have played a beneficial role.

1 |. INTRODUCTION

The term “MODY” (Maturity Onset Diabetes of the Young), currently referred to as monogenic diabetes, was coined almost 4 decades ago to describe patients with a noninsulin-dependent form of diabetes occurring at a young age.¹ The most common subtypes of MODY are hepatocyte nuclear factor 1 (HNF1A) (MODY3), HNF4A (MODY1), and glucokinase (GCK) (MODY2).² The reported prevalence of MODY is wide ranging from 1.1%−6.5% depending on the population studied, biomarkers used to categorize diabetes type, and the fasting plasma glucose set as thresholds for genetic analysis.^3–8 For example, when individuals with impaired fasting glucose instead of diabetes are included in genetic screening, the number of people identified as carriers of GCK mutations almost quintuplicates at 4.8%, as shown by Delvecchio et al⁸ vs 1% reported by Shepherd et al.⁵ The SEARCH for diabetes in youth study sequenced for mutations of the three most common genes and found a prevalence of 8% (47/586) (7 HNF4A-MODY, 26 HNF1A-MODY, and 14 GCK-MODY).⁹ The treatment options for type 2 diabetes in adolescents and youth (TODAY) trial showed that 4.5% (22/488) of overweight/obese youth clinically diagnosed with type 2 diabetes (T2D) had genetic variants consistent with a diagnosis of MODY (7 hepatocyte nuclear factor 4 [HNF4A-MODY], 5 HNF1A-MODY, 7 glucokinase [GCK-MODY], 1 Kruppel-like factor 11 [KLF11-MODY], and 2 insulin (INS)-MODY).¹⁰ MODY patients were found across all racial/ethnic categories and across all treatment arms of TODAY.¹⁰ While T2D in youth is characterized by hepatic and peripheral insulin resistance, and low adiponectin concentration together with β-cell dysfunction,^11,12 a primary β-cell failure, is the pathophysiological element in MODY diabetes.² In the last 3 decades, β-cell function has been studied extensively in adults with MODY mutations using oral glucose tolerance test (OGTT), test meals, intravenous glucose tolerance test (IVGTT), and hyperglycemic clamps,^2,13–19 but almost none in pediatrics, especially in obese adolescents with a clinical diagnosis of T2D. In a study comparing insulin sensitivity and β-cell function in adults >40 years old with T2D, HNF4A-MODY, and HNF1A-MODY, it was stated “it is not known whether T2D and MODY patients differ with regard to mean progression rate of diabetes.”²⁰ In TODAY, MODY genetic mutations were discovered after participants who were clinically diagnosed to have T2D were randomized to protocol-assigned treatments. Six of seven patients with HNF4A-MODY failed treatment over the first 2 years, across all three treatments, with a hazard ratio of 5.03 (P = .0002).¹⁰ There was no difference in glycemic failure rates between youth with HNF1A-MODY and youth without MODY (non-MODY, i.e., T2D).¹⁰ Among the GCK-MODY patients, who typically do not need pharmacotherapy, none had glycemic failure. Their HbA1c at prerandomization and at 2 years was 5.7% and 5.9% for the metformin group, 6.3% and 6.4% for the metformin plus rosiglitazone group and 6.0% and 6.1% for the metformin plus intensive lifestyle group, respectively. Here we build upon these findings by exploring the physiological underpinnings of these observations and investigating if differences in insulin sensitivity and β-cell function at randomization and the change in them over time explain these results. Our specific objectives in this secondary analysis of the TODAY cohort were (a) to examine insulin sensitivity and adiponectin, a biomarker of insulin sensitivity, and β-cell function at randomization in non-MODY obese youth with T2D compared with MODY youth and (b) to investigate temporal changes in insulin sensitivity and β-cell function (at 6 and 24 months) in non-MODY compared with MODY youth.

2 |. RESEARCH DESIGN AND METHODS

Detailed description of the TODAY protocol (www.ClinicalTrial.gov: NCT00081328) and the primary outcome results were published.^21–23 Briefly, eligible participants in TODAY were 10 to <18 years old, had diabetes by ADA 2005 criteria for <2 years, were overweight or obese [body mass index (BMI) ≥85th and ≥95th percentile, respectively], islet cell antibody negative and C-peptide positive. After screening, eligible participants entered a 2- to 6-month run-in period to wean from nonstudy diabetes medications, tolerate metformin up to a dose of 1000 mg twice daily but no less than 1000 mg/day, attain HbA1c <8.0% [<64 mmol/mol] for at least 2 months on metformin alone, and demonstrate adherence to study medications and visit attendance.^22,23 Following the run-in phase, 699 youth were randomly assigned to receive metformin monotherapy, or metformin plus rosiglitazone, or metformin plus lifestyle intervention.^21,23 Demographic, anthropometric, and metabolic data were collected at randomization.²² HbA1c was obtained at screening, randomization, and at every study visit thereafter. Glycemic failure was defined as sustained elevation in HbA1c ≥8% [≥64 mmol/mol] over a 6-month period or inability to wean from temporary insulin therapy within 3 months of acute metabolic decompensation.²¹ OGTTs were performed after 10 to 14 hours of overnight fasting at randomization, 6 months, 24 months, and annually thereafter. OGTT blood samples were obtained at 0, 30, 60, 90, and 120 minutes for glucose, insulin, and C-peptide.²⁴

A subset of 488 TODAY youth with T2D provided genetic data.¹⁰ Of the 699 TODAY randomized participants, 563 (80.5%) signed consent to have their DNA samples collected; 43 did not have enough DNA samples collected to be used for sequencing; 17 had DNA samples that did not pass quality control; and 15 samples were excluded from the current analysis to keep a more homogeneous sample of non-MODY, consistent with Kleinberger¹⁰ approach because none had MODY gene variants and they were from undefined race/ethnicity with small sample sizes. Comparison of the genetic analysis sample (n = 488) with the 211 other TODAY participants showed they were comparable for sex, race/ethnicity, baseline age, BMI, and HbA1c.¹⁰ Participants with previously cited monogenic diabetes variants that were not classified as pathogenic or likely pathogenic (40/488) were not included in the analysis due to uncertainty over their monogenic diabetes status.¹⁰ MODY pathogenic variants were identified in 22/488 participants (4.5%), and included (7 HNF4A-MODY, 5 HNF1A-MODY, 7 GCK-MODY, 1 KLF11-MODY, and 2 INS-MODY).¹⁰ To include the most common MODY types, MODY youth were categorized into two groups, those with GCK mutations (GCK-MODY), and those with HNF MODY mutations (HNF1A-MODY and HNF4A-MODY). The rational is that the defect in GCK is a stable defect of glucose sensing, whereas the transcription factor mutations cause a progressive defect that alters β-cell insulin secretion directly rather than the sensing of glucose.^2,17 Furthermore, the HNF4A and HNF1A MODY have a similar clinical phenotype associated with beta cell dysfunction.¹⁹ KLF11 and INS are extremely rare forms of MODY associated with beta cell dysfunction with a phenotype that is less well defined.²⁵ They were eliminated from the current analyses due to small numbers, INS-MODY (n = 2) and KLF11-MODY (n = 1).

2.1 |. Assays and calculations

All assays, including HbA1c, fasting lipids, C-peptide, insulin, total and high-molecular-weight adiponectin (HMWA) were performed at the TODAY central laboratory (Northwest Lipid Research Laboratory, University of Washington, Seattle, Washington) as previously described.²⁶

Surrogate estimates of insulin sensitivity (1/fasting insulin [1/I_F]), C-peptide index, the ratio of the incremental C-peptide and glucose responses over the first 30 minutes (ΔC₃₀/ΔG₃₀) of the OGTT, and the oral disposition index (oDI), the product of insulin sensitivity and C-peptide index (1/I_F × ΔC₃₀/ΔG₃₀), a measure of β-cell function relative to insulin sensitivity, were calculated as before.^26–28 As before,²⁶ we utilized the C-peptide-index as a measure of insulin secretion because some participants had received insulin prior to screening/enrollment in TODAY, which could potentially result in circulating insulin antibodies interfering with the insulin assay. In addition, differences in insulin clearance in different racial groups could confound the insulinogenic index data.²⁶ OGTT Area under the curve (AUC) for glucose, C-peptide, and insulin were calculated according to the trapezoidal rule.

2.2 |. Statistical methods

As before, outliers, suspected nonfasting values, and values for C-peptide index of ≤0 were set to missing for analysis purposes.²⁴ Of the 1848 C-peptide index values obtained over the 24 months’ visits, 41 (2.2%) were ≤0. Although mathematically possible, such values were judged biologically implausible and were treated as missing values similar to our approach in prior TODAY publications.^24,26

Data are presented in mean and SD or percentage. Variables with a skewed distribution were log transformed as appropriate. At baseline, quantitative and categorical characteristics were compared by MODY status using F tests and χ² test, respectively. The nonparametric Mann-Whitney U test was used for months since diagnosis due to skewness. Baseline differences in metabolic parameters by MODY status were assessed before and after adjustment for race/ethnicity, baseline BMI z-score, pubertal stage, and duration of diabetes. Baseline data were also presented by MODY gene subtype.

Glycemic failure rates by MODY status were compared. Longitudinal analyses were performed on data collected at baseline (n = 448), month 6 (n = 397), and month 24 (n = 292). Data collected after month 24 were not considered because the numbers were too small for meaningful statistical analysis. Metabolic assessments performed after participants reached treatment failure are not reported because accurate assessment of β-cell function is hindered by the impact of exogenous insulin therapy on parameters of insulin secretion. Thus, MODY status group differences in the above measures over time may be influenced by the successive removal of subjects who reached treatment failure.

Longitudinal data for insulin sensitivity, insulin secretion, and β-cell function were analyzed using linear mixed models to account for the multiple observations per participant (SAS PROC MIXED), and estimate mean levels of the parameters over time by MODY status. Models examining differences in insulin sensitivity, insulin secretion, and β-cell function by MODY status over time were adjusted for time, randomized treatment group, sex, race/ethnicity, baseline pubertal stage, age, and BMI, and included a term of the interaction of time with MODY group. The models assumed an unstructured covariance structure. Due to skewness of the data, longitudinal analyses were performed on log-transformed values. Data shown in the figures are model-adjusted geometric means ± SE asymmetric limits (obtained as exp [mean ± SE] of the log values). Longitudinal analyses performed on the log values allowed model-derived estimates to be presented in terms of percentage change over time. Mean percent change from baseline to 6 months and from 6 to 24 months was computed and compared across the MODY groups. Temporal patterns by MODY gene subtype were also explored. Analyses were performed using SAS for Windows (version 9.4; SAS Institute Inc., Cary, North Carolina). All analyses were considered exploratory with statistical significance defined as P-values of <.05 and no adjustment for multiple testing.

3 |. RESULTS

3.1 |. Baseline demographic and metabolic characteristics by MODY status

Table 1 depicts the physical and metabolic characteristics of non-MODY vs HNF-MODY and GCK-MODY youth at randomization in TODAY. Age and sex distribution was not different between the three groups. There were no non-Hispanic black participants among GCK-MODY youth and this was different from non-MODY and HNF-MODY groups. Non-MODY youth had higher BMI, BMI z-scores, and waist circumference compared with the two MODY groups. Fasting and OGTT-AUC for C-peptide and insulin were higher in non-MODY youth compared with the two MODY groups, with no significant differences in glucose and HbA1c. Insulin sensitivity, total adiponectin, and HMWA were significantly lower in non-MODY than the two MODY groups. After adjusting for age, sex, race/ethnicity, and BMI z-score, insulin sensitivity remained significantly lower in non-MODY vs HNF-MODY and vs GCK-MODY youth, but the significant differences in adiponectin disappeared. C-peptide index was higher in non-MODY compared with HNF-MODY youth (Table 1), and this persisted after adjusting for age, sex, race/ethnicity and BMI z-score (P = .03), while the difference between HNF-MODY and GCK-MODY became significant after adjustment (P = .02). Fasting proinsulin was higher in non-MODY youth compared with the other two MODY groups (Table 1), and these differences remained significant after adjustment for age, sex, race/ethnicity, and BMI z-score. C-peptide oDI was significantly higher in GCK-MODY youth compared with HNF-MODY and non-MODY youth (Table 1), and the significant differences stayed after adjustment for age, sex, race/ethnicity, and BMI z-score. Supplemental Table S1 depicts demographic and metabolic characteristics of TODAY participants by MODY gene subtypes at randomization. Among the various MODY gene subtypes, GCK-MODY had the highest C-peptide-AUC and the highest oDI.

TABLE 1.

Demographic and metabolic characteristics of TODAY participants (n = 445) by MODY status (non-MODY vs HNF-MODY vs GCK-MODY) at baseline

	Non-MODY (n = 426)	HNF-MODY (n = 12)	GCK-MODY (n = 7)	Non-MODY vs HNF-MODY P-valuea	Non-MODY vs GCK-MODY P-valuea	HNF-MODY vs GCK-MODY P-valuea
	Demographic characteristics
Age at randomization (y)	13.9 ± 2.0	12.6 ± 1.8	13.0 ± 2.1	.06	.44	.90
Female (%)	65.0%	58.3%	57.1%	.64	.67	.96
Race/ethnicity (%)
Black non-Hispanic	32.6%	16.7%	0.0%	.38	.0007	.05
Hispanic	46.9%	50.0%	14.3%
White non-Hispanic	20.4%	33.3%	85.7%
Tanner pubertal stage (%)
1–3	9.4%	16.7%	42.9%	.44	.02	.22
4–5	90.6%	83.3%	57.1%
Months since diagnosis	7.6 ± 5.7	9.1 ± 3.8	10.0 ± 8.5	.03	.69	.83
Family history of diabetes (%)	58.0%	75.0%	42.9%	.22	.42	.16
Birth weight (g)	3322 ± 805	3584 ± 648	2920 ± 749	.53	.39	.20
Anthropometric characteristics
BMI (kg/m2)	35.3 ± 7.6	28.9 ± 5.8	27.6 ± 5.4	.01	.02	.93
BMI Z-score	2.3 ± 0.5	1.9 ± 0.4	1.7 ± 0.5	.04	.006	.57
Waist circumference (cm)	109.9 ± 16.2	90.9 ± 13.1	88.2 ± 7.8	.0003	.0012	.93
Metabolic characteristics
HbA1c (%)	6.0 ± 0.7	6.4 ± 1.0	6.1 ± 0.4	.19	.96	.67
(mmol/mol)	42 ± 7.7	46 ± 10.9	43 ± 4.4
Total cholesterol (mg/dL)	145.4 ± 29.2	125.4 ± 25.4	144.9 ± 21.0	.06	.99	.34
LDL-C (mg/dL)	83.7 ± 24.3	69.5 ± 24.0	83.6 ± 14.8	.13	.98	.45
HDL-C (mg/dL)	38.5 ± 8.5	40.3 ± 7.9	43.4 ± 9.3	.76	.28	.72
Triglycerides (mg/dL)b	118.3 ± 80.4	80.7 ± 53.9	88.9 ± 64.4	.07	.40	.94
Adiponectin (ng/mL)b	5456 ± 2358	7167 ± 2885	7183 ± 1256	.02	.03	.76
HMWA (ng/mL)b	2822 ± 1687	4109 ± 1888	3979 ± 1455	.02	.05	.93
Fasting glucose (mg/dL)b	109.3 ± 23.4	114.8 ± 25.0	121.7 ± 5.3	.70	.21	.66
Fasting C-peptide (ng/mL)b	3.9 ± 1.5	2.5 ± 0.8	2.1 ± 0.7	.001	.0003	.61
Fasting insulin (μU/mL)b	30.9 ± 22.0	16.5 ± 9.1	11.1 ± 4.2	.009	.001	.57
AUC glucose (mg/dL)b	377.7 ± 89.1	428.3 ± 84.4	356.9 ± 39.1	.14	.92	.29
AUC C-peptide (ng/mL)b	18.7 ± 8.2	10.6 ± 3.6	13.3 ± 3.8	<.0001	.05	.47
AUC insulin (μU/mL)b	243.7 ± 215.6	106.3 ± 54.4	116.3 ± 46.1	.0007	.03	.92
Proinsulin (pM)b	34.2 ± 28.8	17.3 ± 12.0	9.1 ± 3.7	.008	.0002	.37
Insulin sensitivity (1/IF, mL/μU)b	0.048 ± 0.040	0.077 ± 0.045	0.090 ± 0.035	.009	.004	.72
C-peptide index (ΔC30/ΔG30, ng/mL per mg/dL)b	0.087 ± 0.139	0.034 ± 0.014	0.071 ± 0.032	.02	.76	.08
C-peptide oDI(1/IF × ΔC30/ΔG30)b	0.004 ± 0.007	0.002 ± 0.001	0.006 ± 0.003	.83	.02	.04

Notes: Continuous data are presented as mean ± SD and categorical data as indicated. HNF-MODY includes HNF4A and HNF1A variants.

Abbreviations: AUC, area under the curve; GCK, glucokinase; HDL-C, high-density lipoprotein-C; HMWA, high molecular weight adiponectin; HNF, hepatocyte nuclear facto; LDL-C, low-density lipoprotein-C; MODY, monogenic diabetes pathogenic or likely pathogenic mutation; oDI, oral disposition index; TODAY, type 2 diabetes in adolescents and youth.

^aP-values were calculated from F-tests and/or Kruskal Wallis tests for continuous variables; and from chi-square tests for categorical variables. The nonparametric Mann-Whitney U test was used for months since diagnosis.

^bVariables were log-transformed prior to testing.

3.2 |. Glycemic failure rates in TODAY by MODY status

Glycemic failure rates differed significantly (P = .002) among the three groups. While none of the GCK-MODY youth failed (0%) in the first 2 years after randomization, 9 of the 12 HNF-MODY group failed (75.0%) (P = .0003 vs GCK-MODY), and 200/426 non-MODY failed (46.9%) (P = .05 vs HNF-MODY). HNF-MODY youth who had glycemic failure (n = 9) compared with those who did not (n = 3), had higher HbA1c at randomization (6.7 ± 0.9 vs 5.5 ± 0.4%, P = .05), and 50% lower C-peptide index (0.030 ± 0.010 vs 0.052 ± 0.017 ng/mL per mg/dL, P = .03), but the difference in randomization fasting glucose concentrations, though higher in the former group (118.9 ± 26.1 vs 102.7 ± 20.3 mg/dL, P = .35), and the 30% lower C-peptide oDI (0.002 ± 0.001 vs 0.003 ± 0.001, P = .16) did not reach significance due to the small numbers. Non-MODY youth who failed had significantly higher HbA1c, higher fasting glucose concentrations, lower C-peptide index and lower C-peptide oDI at randomization (all P < .0001) compared with non-MODY who did not fail (data not shown).

3.3 |. OGTT glucose, C-peptide, and insulin AUC by MODY status

Figure 1 depicts OGTT plasma glucose, C-peptide and insulin concentrations in non-MODY, HNF-MODY, and GCK-MODY groups at randomization, and 6 and 24 months after. There were no statistically significant differences in OGTT glucose concentrations among the three groups at randomization, though the pattern was highest in HNF-MODY and lowest in GCK-MODY (Figure 1A), and at 6 and 24 months (Figure 1B,C). However, OGTT C-peptide and insulin concentrations were significantly different among the three groups at randomization (Figure 1D,G), highest in non-MODY vs HNF-MODY youth (for C-peptide P < .0001, and for insulin P = .001) and vs GCK-MODY youth (for C-peptide P = 0.01, and for insulin P = .006). Similarly, at 6 and 24 months, the OGTT plasma C-peptide (Figure 1E,F) and insulin concentrations (Figure 1 H,I) were significantly different among the three groups highest in non-MODY with post hoc significance between non-MODY and HNF-MODY groups. Supplemental Figure S1 depicts OGTT plasma glucose, C-peptide, and insulin concentrations by the three most common MODY gene subtypes at randomization, 6 and 24 months. Overall HNF4A-MODY and HNF1A-MODY appear to have higher glucose concentrations than GCK-MODY.

FIGURE 1.

OGTT plasma glucose (A-C), C-peptide (D-F), and insulin concentrations (G-I) at randomization, and 6 and 24 months of follow-up, in non-MODY, HNF-MODY and GCK-MODY youth.*Data are mean ± SE (upper or lower bars only to minimize crowding by error bars and enhance figure clarity). P values refer to an overall difference between the three MODY groups at each time point (ie, testing whether the three curves overlap), in unadjusted generalized linear mixed models using log transformed values. Sample sizes (based on complete non-missing records) for the three groups at each time point (randomization, month 6, and month 24) were as follows: non-MODY (n = 406, n = 359, n = 264), HNF-MODY (n = 12, n = 8, n = 5) and GCK-MODY (n = 7, n = 7, n = 7). OGTT, oral glucose tolerance test; GCK, glucokinase; HNF, hepatocyte nuclear factor; MODY, maturity onset diabetes of youth

Supplemental Table S2 depicts the OGTT AUC for glucose, C-peptide, and insulin at randomization, 6 and 24 months. Reflective of Figure 1, glucose-AUC at randomization, 6 and 24 months were not different among the three groups. However, C-peptide-AUC and insulin-AUC at randomization were significantly different among the three groups and highest in non-MODY. The three group difference in C-peptide-AUC at 6 months was (P = .006), and at 24 months (P = .01).

3.4 |. Temporal patterns of insulin sensitivity, C-peptide index, and oDI by MODY status

Figure 2 depicts temporal patterns of insulin sensitivity (Figure 2A), C-peptide index (Figure 2B) and C-peptide oDI (Figure 2C) by MODY status over 24 months of follow-up in TODAY. These longitudinal models present data adjusted for randomized treatment group, sex, race/ethnicity, and BMI z-scores. Over the 24-month period, insulin sensitivity (Figure 2A) and C-peptide oDI (Figure 2C) were significantly different among the three groups, and C-peptide index approached significance. GCK-MODY started with higher C-peptide oDI and C-peptide index at randomization and maintained it throughout the 24 months, while non-MODY started with the lowest insulin sensitivity and remained so throughout. Supplemental Figure S2 depicts temporal patterns of insulin sensitivity, C-peptide index and C-peptide oDI by MODY gene subtypes over 24 months. Overall, C-peptide oDI appears to be lowest in HNF4A-MODY and highest in GCK-MODY at randomization and throughout the 24 months.

FIGURE 2.

Temporal patterns of insulin sensitivity A, C-peptide index B, and C-peptide oDI C, in non-MODY, HNF-MODY, and GCK-MODY youth. *Data are reported as model-adjusted geometric mean ± SE asymmetric limits, obtained as exp(mean ± SE of log values) over 24 months of follow-up in TODAY, analyzed using log-transformed values. P-values refer to an overall difference over time between the three MODY groups, in generalized linear mixed models adjusted for randomized treatment group, sex, race/ethnicity, and BMIz. GCK, glucokinase; HNF, hepatocyte nuclear factor; MODY, maturity onset diabetes of youth; oDI, oral disposition index; TODAY, type 2 diabetes in adolescents and youth

Table 2 shows the short-term change, as the mean percent change from baseline to 6 months, and the longer-term change, mean percent change from 6 to 24 months, for insulin sensitivity, C-peptide index, and oDI by MODY status in the three groups. There was no difference among the three groups with respect to the short-term change in insulin sensitivity, C-peptide index, and C-peptide oDI. However, from 6 to 24 months, the mean percent change in insulin sensitivity was significantly different between HNF-MODY (47.0%) and GCK-MODY (−31.5%) but not non-MODY (−0.5%).The mean percent change in C-peptide index from 6 to 24 months was different between non-MODY (−25.9%) and GCK-MODY (24.6%). There was no significant differences among the three groups in mean percent change from 6 to 24 months in oDI. Figure S3 demonstrates HbA1c values over the 24 months in the three groups.

TABLE 2.

Changes in measures of insulin sensitivity, C-peptide index, and C-peptide oDI by MODY status over 24 months of follow-up in TODAY, in adjusted models

Factor	Non-MODY (n = 426)	HNF-MODY (n = 12)	GCK-MODY (n = 7)	Non-MODY vs HNF-MODY P-value	Non-MODY vs GCK-MODY P-value	HNF-MODY vs GCK-MODY P-value
Insulin sensitivity [1/IF] (mL/μU)
Mean % change from 0 to 6 months	1.4 [−3.6, 6.7]	−6.8 [−33.3, 30.2]	−2.2 [−32.6, 41.9]	NS	NS	NS
Mean % change from 6 to 24 months	−0.5 [−6.7, 6.1]	47.0 [−6.9, 132.1]	−31.5 [−54.8, 3.8]	NS	NS	0.04
C-peptide Index [ΔC30/ΔG30](ng/mL per mg/dL)
Mean % change from 0 to 6 months	−11.9 [−17.1, −6.5]	4.1 [−31.1, 57.3]	1.5 [−34.1, 56.3]	NS	NS	NS
Mean % change from 6 to 24 months	−25.9 [−32.0, −19.3]	−25.2 [−62.4, 48.5]	24.6 [−27.7, 114.5]	NS	0.04	NS
oDI (1/IF × ΔC30/ΔG30)
Mean % change from 0 to 6 months	−9.4 [−16.7, −1.4]	−0.8 [−44.0, 75.7]	−0.7 [−45.8, 81.6]	NS	NS	NS
Mean % change from 6 to 24 months	−22.4 [−31.0, −12.6]	22.8 [−51.5, 211.0]	−14.7 [−59.9, 81.5]	NS	NS	NS

Notes: HNF-MODY includes HNF4A and HNF1A variants. Data are reported as the 0–6 or 6–24 month mean percentage change, and 95% confidence interval from generalized linear mixed models based on the log-transformed value adjusted for randomized treatment group, sex, race/ethnicity, and BMI z-scores. NS, not significant (P > .05).

Abbreviations: GCK, glucokinase; HNF, hepatocyte nuclear factor; MODY, monogenic diabetes pathogenic or likely pathogenic mutation; oDI, oral disposition index; TODAY, type 2 diabetes in adolescents and youth.

4 |. DISCUSSION

The present investigation of obese youth with clinically diagnosed T2D in TODAY who were found to have MODY mutations vs those who did not reveal that at randomization: (a) insulin sensitivity in obese non-MODY youth was ~38% lower compared with obese HNF-MODY, and 47% lower than obese GCK-MODY; (b) β-cell function was most impaired in obese HNF-MODY youth, ~50% lower than non-MODY and ~67% lower than GCK-MODY; (c) During the first 24 months, glycemic failure rates were zero in obese GCK-MODY youth, and highest in HNF-MODY youth (75%); and (d) over time, the short-term change in insulin sensitivity and β-cell function did not differ among the three groups, but from 6 to 24 months insulin sensitivity appeared to improve in obese HNF-MODY youth.

Studies of insulin sensitivity and β-cell function in individuals with MODY mutations have been on middle-age adults who were not obese, including a mix of individuals with established diabetes, IGT, and normal glucose tolerance (NGT).^2,13–19 These studies have focused on the most common forms of MODY, which are GCK-MODY and HNF1A-MODY.² β-cell dysfunction has been studied in adults with GCK-MODY.^{13,17,18,29,30} GCK mutations are fully penetrant in utero and consequently at birth impacting birth weight,³¹ and occasionally presenting as neonatal diabetes.³² However, most individuals with GCK mutations present with mild, incidental hyperglycemia in early childhood (ie, they are fortuitously identified). This mild fasting hyperglycemia remains quite stable throughout life, slightly deteriorating with increasing age¹⁸ likely consequent to the normal aging process. In normal-weight adults with GCK-MODY, homeostasis model assessment showed similar insulin sensitivity to control subjects who were the nonmutation carriers within the families, but reduced β-cell function, with no increase in proinsulin/insulin ratio.^18,33 However, GCK mutation carriers with established diabetes were more insulin resistant than those with NGT or with mild fasting hyperglycemia consistent with insulin resistance being secondary to chronic hyperglycemia.³⁴ Individuals with HNF1A-MODY mutations have normal glucose tolerance in early childhood, and typically present in their teens or early adult life with symptomatic diabetes, and frequently require treatment with oral agents or insulin. ^{14,15,17,18,30,35–38} Unlike GCK-MODY, their insulin sensitivity is higher than control non-mutation carries within the families,^18,39 but their β-cell function is severely impaired,^14,15,18,20 with increased proinsulin/insulin ratio compared with controls,¹⁸ and steep deterioration in β-cell function and elevations in fasting plasma glucose with age.^15,18,37 The increased insulin sensitivity and β-cell deficiency in these individuals is present before the development of hyperglycemia, compared with control individuals without mutations.³⁷ With progressive β-cell failure, hyperglycemia develops and diabetes ensues. However, there is controversy as to whether there is altered insulin sensitivity in individuals with diabetes due to HNF1A mutations because insulin sensitivity has been reported to be increased,^18,39 similar,¹⁵ and reduced.¹⁷ But these comparisons are confounded by the control groups, who sometimes are mutation carriers but not affected with diabetes, at other times they are family members without mutations, and occasionally individuals with T2D. Nondiabetic and diabetic subjects with HNF4A-MODY mutations also have β-cell dysfunction, manifested by decreased insulin secretion in response to glucose,^40,41 arginine⁴² and a test meal.²⁰

To our knowledge, no studies have assessed insulin sensitivity and β-cell function in obese adolescents with MODY mutations and established diabetes. In TODAY, obese youth with clinically diagnosed T2D who were mutation negative, had higher BMI, BMI z-score, and waist circumference compared with MODY youth. Insulin sensitivity was significantly lower in non-MODY youth (~30%−50%) compared with the two groups of MODY even after adjusting for adiposity differences. This is consistent with the inherent insulin resistance typical of the pathophysiology of youth-onset-T2D.^11,12 Total adiponectin and HMWA were significantly lower in non-MODY youth but the significance disappeared after adjusting for age, sex, race/ethnicity and adiposity. This is most likely due to the small numbers of MODY across the different ethnicities and inadequate power after adjustment, since black youth are known to have low adiponectin concentrations.²⁶ Whereas insulin sensitivity was lowest in non-MODY youth, β-cell function was lowest in HNF-MODY youth (~50%−67%) compared with non-MODY and compared with GCK-MODY. Consistent with a failing β-cell, proinsulin, a feature of β-cell stress was significantly higher in non-MODY compared with HNF-MODY and GCK-MODY (Table 1). This is consistent with a study in adults with much lower BMI values, where proinsulin was lower in HNF4A (n = 5) and HNF1A (n = 12) compared with T2D (n = 8).²⁰ In TODAY, the metabolic outcome of worse insulin sensitivity in non-MODY youth and worse β-cell function in HNF-MODY youth was reflected in higher fasting and OGTT C-peptide-AUC in non-MODY youth. However, HbA1c and fasting glucose concentrations were comparable among the three groups.

Most pediatric studies of MODY have focused on prevalence, identification of cases with genetic testing, clinical features and management strategies, and all uniformly show that MODY in childhood is rare ranging from 1.1% to 6.5% in different countries and different childhood diabetes registries.^3–8,43,44 Polish youth (1.9–20 years old) with GCK mutation, had HbA1c, mean fasting glucose, and C-peptide concentrations similar to our GCK-MODY youth, despite the fact that they were not obese, and only 32% fulfilled criteria for diabetes.⁴⁵ In Italian youth with GCK-MODY, first-phase insulin release during an IVGTT was impaired in about half of the cases, but there was no correlation between first phase insulin values and the metabolic status of the patients.⁴⁶ Insulin sensitivity, measured by HOMA or an oral insulin sensitivity index, was found to be lower in those with diabetes than those with normal glucose tolerance, despite the fact that 5 of 11 children in the latter group were overweight.⁴⁶ This is similar to the aforementioned adult study³⁴ and suggestive that chronic hyperglycemia might play a role in the insulin resistance in these youth with GCK-MODY. In a study of individuals with HNF1A-MODY, with a very wide age range of 7.5–47.5 years, fasting insulin and C-peptide concentrations were lower than adults with T2D, together with lower insulinogenic index, lower HOMA-IR and higher Matsuda index in HNF1A-MODY, consistent with the differences in our HNF-MODY and non-MODY youth despite the difference in ages between the two studies.³⁸ Results with respect to AUC after a test meal were coherent with our OGTT AUC data, showing higher glucose AUC and lower C-peptide AUC in HNF1A-MODY compared with T2D.³⁸ A study comparing OGTT between GCK-MODY and HNF1A-MODY in individuals with a wide age range (2–79 years) and with IFG, IGT, and diabetes showed that individuals with HNF1A-MODY had lower fasting glucose, but higher 2-hour glucose and higher OGTT increment with lower insulin concentrations throughout the OGTT.³⁰ Our findings in HNF-MODY vs GCK-MODY youth contrast with theirs demonstrating no significant differences in fasting and OGTT-AUC in glucose, insulin, and C-peptide. This is likely due to all of our participants having diabetes, the tight adolescent age range, and their excess adiposity, all of which are important modulators of glycaemia and insulinemia.

With respect to glycemic failure rates, none of the GCK-MODY youth had glycemic failure during the first 24 months. This is not surprising considering that most GCK-MODY patients can be managed without antidiabetic pharmacotherapy. In adults with GCK-MODY, there was no difference in HbA1c between patients on pharmacological treatment compared with those receiving no treatment,⁴⁷ and HbA1c did not change following discontinuation of oral hypoglycemic agents or insulin therapy.⁴⁷ However, in obese youth with GCK-MODY diabetes, it is possible that insulin sensitization with pharmacotherapy, or lifestyle modification with weight loss, and/or prevention of continued weight gain may have the benefit of lessening obesity-associated insulin resistance thus diminishing the burden on the already compromised β-cell. Glycemic failure rate in HNF-MODY youth was 75% while in non-MODY it was 46.9%. The high glycemic failure rate in HNF-MODY youth is not surprising since initial β-cell reserve at randomization, an independent predictor of glycemic durability,²⁴ was the most deficient in these youth compared with the other two groups, and especially that in nonobese adults with HNF1A-MODY the glycemic response to metformin is much less (5.2-fold) than to sulfonylurea.³⁵ In TODAY, metformin was the shared pharmacotherapy among the three treatment arms, combined with rosiglitazone and lifestyle intervention in the other two arms. Insulin sensitization could lessen the obesity-associated insulin resistance and consequently reduce the β-cell overload that results in progressive worsening of β-cell dysfunction, which seems to be typical for such patients. Our current data demonstrate that in HNF-MODY youth insulin sensitivity seemed to have improved from 6 to 24 months, but this was not translated to improvement in oDI (Table 2) and no improvement in HbA1c (Figure S3) possibly due to our limited numbers. The Diabetes Prevention Program in adults showed that genetic variation in MODY genes is associated with a differential response to insulin-sensitizing interventions. After 1 year of randomization to metformin, intensive lifestyle or placebo, a minor allele of HNF4A was associated with improved β-cell function in the metformin and lifestyle groups but not the placebo group.⁴⁸ Whether or not obese youth with HNF-MODY could benefit from insulin sensitizing therapy with improvement in β-cell function and HbA1c needs to be investigated in future studies.

The unique aspects of our study are (a) obese adolescents with established diabetes; (b) a tight age range of 10 to <18 years old; (c) longitudinal assessment of β-cell function, insulin sensitivity, and OGTT glucose, insulin and C-peptide-AUCs; and (d) evaluation of glycemic failure rates in each MODY category. Potential limitations are the small numbers with MODY mutations, but this has always hampered previous publications due to the rarity of MODY mutations,^{3–5,25,43,44} with a prevalence of 0.17 per 100 000 children in the UK⁴⁹ and an incidence rate of 0.2 cases per 100 000 children in Canada.⁴³ Additional potential drawbacks are that youth at enrollment in TODAY were on a variety of treatments, and the standardized run-in period with metformin therapy, both of which may have altered OGTT responses and insulin sensitivity and β-cell function. However, the response to metformin in obese youth with MODY mutations is not known. Lastly, we could only use surrogate estimates of insulin sensitivity and β-cell function in such a large cohort.

In summary, the present study is the first to examine β-cell function and insulin sensitivity in obese adolescents with MODY mutations and diabetes compared with non-MODY youth with T2D, not only cross sectionally, but longitudinally. Our findings demonstrate that β-cell function at randomization was poorest in obese HNF-MODY youth compared with non-MODY and GCK-MODY youth, whereas insulin sensitivity was worse in non-MODY youth. While none of the GCK-MODY youth had glycemic failure over the first 2 years, failure rates were highest in HNF-MODY youth. Over time insulin sensitivity seemed to improve in HNF-MODY youth, raising the possibility that TODAY therapeutic modalities of insulin sensitization in these obese HNF-MODY youth may have played a beneficial role. Larger studies are needed to confirm or negate this.

Abbreviations:

AUC

area under the curve

GCK

glucokinase

GCK-MODY

glucokinase MODY mutation positive

HMWA

high-molecular-weight adiponectin

HNF1A

hepatocyte nuclear factor 1

HNF4A

hepatocyte nuclear factor 4

HNF-MODY

hepatocyte nuclear factor MODY mutation positive

INS

insulin gene mutation

KLF11

Kruppel-like factor 11

MODY

maturity onset diabetes of youth

Non-MODY

MODY mutation negative, that is, type 2 diabetes

oDI

oral disposition index

OGTT

oral glucose tolerance test

TODAY

treatment options for type 2 diabetes in adolescents and youth