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Monogenetic diabetes mellitus (DM) describes a collection of single-gene diseases marked by hyperglycemia presenting in childhood or adulthood and the absence of immunological markers of type 1 DM. Mutations in the human insulin gene INS give rise to two separate clinical syndromes: permanent neonatal DM, type 4 (PNDM4), and maturity-onset diabetes of youth, type 10 (MODY10); the former presents shortly after birth and the latter presents in childhood and adulthood. We describe a 40-year-old man in a kindred with high prevalence of DM who presented with severe hyperglycemia but not ketoacidosis or hypertriglyceridemia. Twelve years after initial presentation, the patient had elevated proinsulin and normal plasma C-peptide when nearly euglycemic on treatment with insulin glargine. A novel INS mutation, Gln65Arg, within the C-peptide region was identified. The INS (p.Gln65Arg) mutation may cause MODY10 by disrupting proinsulin maturation. [ABSTRACT FROM AUTHOR]

Autophagy is a lysosomal catabolic process by which cells degrade or recycle their contents to maintain cellular homeostasis, adapt to stress, and respond to disease. Impairment of autophagy in endothelial cells studied under static conditions results in oxidant stress and impaired nitric oxide (NO) bioavailability. We tested the hypothesis that vascular autophagy is also important for induction of NO production caused by exposure of endothelial cells to shear stress (i.e., 3 h x ≅ 20 dyn/[cm.sup.2]). Atg3 is a requisite autophagy pathway mediator. Control cells treated with non-targeting control siRNA showed increased autophagy, reactive oxygen species (ROS) production, endothelial NO synthase (eNOS) phosphorylation, and NO production upon exposure to shear stress (p < 0.05 for all). In contrast, cells with >85% knockdown of Atg3 protein expression (via Atg3 siRNA) exhibited a profound impairment of eNOS phosphorylation, and were incapable of increasing NO in response to shear stress. Moreover, ROS accumulation and inflammatory cytokine production (MCP-1 and IL-8) were exaggerated (all p < 0.05) in response to shear stress. These findings reveal that autophagy not only plays a critical role in maintaining NO bioavailability, but may also be a key regulator of oxidant-antioxidant balance and inflammatory-anti-inflammatory balance that ultimately regulate endothelial cell responses to shear stress. Key words: blood flow, exercise, mitochondrial turnover, mitophagy, nutrient deprivation, oxidant stress, vascular. L'autophagie est un processus catabolique lysosomal par lequel les cellules degradent ou recyclent leur contenu afin de maintenir l'homeostasie cellulaire, s'adapter au stress et repondre a une maladie. La defaillance de l'autophagie chez les cellules endotheliales etudiees en conditions statiques provoque un stress oxydant et une diminution de la biodisponibilite d'oxyde nitrique (NO). Les auteurs ont teste l'hypothese que l'autophagie vasculaire est aussi importante a l'induction de la production de NO provoquee par l'exposition des cellules endotheliales a un stress de cisaillement (par example, 3 h x ≅ 20 dyn/[cm.sup.2]). Atg3 est un mediateur necessaire de la voie de l'autophagie. L'autophagie, la production d'especes reactives d'oxygene (ERO), la phosphorylation de la NO synthase endotheliale (eNOS) et la production de NO etaient accrues chez des cellules controles traitees avec un pARNi controle non-ciblant, exposees a un stress de cisaillement (p < 0,05 pour tous les parametres). En revanche, la phosphorylation de eNOS etait diminuee de facon marquee chez les cellules dont Atg3 avait ete inactive de > 85 % par << knockdown >> (au moyen du pARNi Atg3), et ces cellules etaient incapables d'accroitre le niveau de NO en reponse a un stress de cisaillement. De plus, l'accumulation d'ERO et la production de cytokines inflammatoires (MCP-1 et IL-8) etaient accrues (p < 0,05) en reponse a un stress de cisaillement. Ces donnees revelent que l'autophagie joue non seulement un role dans le maintien de la biodisponibilite de NO, mais qu'elle agit aussi comme regulateur cle de la balance oxydante--anti-oxydante et inflammatoire--antiinflammatoire, qui regule ultimement les reponses des cellules endotheliales au stress de cisaillement. [Traduit par la Redaction] Mots-cles : flux sanguin, exercice, << turnover >> mitochondrial, mitophagie, privation nutritionnelle, stress oxydant, vasculaire., Introduction Autophagy (i.e., 'self-eating') is a highly conserved, ubiquitous lysosomal trafficking pathway of eukaryotic cells that preserves cell health by degrading nonessential or damaged intracellular constituents that accumulate during the [...]

Preitner F, Mody N, Graham TE, Peroni OD, Kahn BB. Long-term Fenretinide treatment prevents high-fat diet-induced obesity, insulin resistance, and hepatic steatosis. Am J Physiol Endocrinol Metab 297: E1420-E1429, 2009. First published October 13, 2009; doi: 10.1152/ajpendo.00362.2009.--The synthetic retinoid Fenretinide (FEN) increases insulin sensitivity in obese rodents and is in early clinical trials for treatment of insulin resistance in obese humans with hepatic steatosis (46). We aimed to determine the physiological mechanisms for the insulin-sensitizing effects of FEN. Wild-type mice were fed a high-fat diet (HFD) with or without FEN from 4-5 wk to 36-37 wk of age (preventive study) or following 22 wk of HF diet-induced obesity (12 wk intervention study). Retinol-binding protein-4 (RBP4) knockout mice were also fed the HFD with or without FEN in a preventive study. FEN had minimal effects on HFD-induced body weight gain but markedly reduced HFD-induced adiposity and hyperleptinemia in both studies. FEN-HFD mice gained epididymal fat but not subcutaneous or visceral fat mass in contrast to HFD mice without FEN. FEN did not have a measurable effect on energy expenditure, food intake, physical activity, or stool lipid content. Glucose infusion rate during hyperinsulinemic-euglycemic clamp was reduced 86% in HFD mice compared with controls and was improved 3.6-fold in FEN-HFD compared with HFD mice. FEN improved insulin action on glucose uptake and glycogen levels in muscle, insulin-stimulated suppression of hepatic glucose production, and suppression of serum FFA levels in HFD mice. Remarkably, FEN also reduced hepatic steatosis. In RBP4 knockout mice, FEN reduced the HFD-induced increase in adiposity and hyperleptinemia. In conclusion, long-term therapy with FEN partially prevents or reverses obesity, insulin resistance, and hepatic steatosis in mice on HFD. The anti-adiposity effects are independent of the RBP4 lowering effect. retinol-binding protein-4; type 2 diabetes; hyperleptinemia; retinoids doi: 10.1152/ajpendo.00362.2009

Serum retinol-binding protein (RBP4) is secreted by liver and adipocytes and is implicated in systemic insulin resistance in rodents and humans. RBP4 normally binds to the larger transthyretin (TTR) homotetramer, forming a protein complex that reduces renal clearance of RBP4. To determine whether alterations in RBP4-TTR binding contribute to elevated plasma RBP4 levels in insulin-resistant states, we investigated RBP4TTR interactions in leptin-deficient ob/ob mice and high-fat-fed obese mice (HFD). Gel filtration chromatography of plasma showed that 88-94% of RBP4 is contained within the RBP4-TTR complex in ob/ob and lean mice. Coimmunoprecipitation with an RBP4 antibody brought down stoichiometrically equal amounts of TTR and RBP4, indicating that TTR was not more saturated with RBP4 in ob/ob mice than in controls. However, plasma TTR levels were elevated approximately four-fold in ob/ob mice vs. controls. RBP4 injected intravenously in lean mice cleared rapidly, whereas the [t.sub.1/2] for disappearance was approximately two-fold longer in ob/ob plasma. Urinary fractional excretion of RBP4 was reduced in ob/ob mice, consistent with increased retention. In HFD mice, plasma TTR levels and clearance of injected RBP4 were similar to chow-fed controls. Hepatic TTR mRNA levels were elevated approximately twofold in ob/ob but not in HFD mice. Since elevated circulating RBP4 causes insulin resistance and glucose intolerance in mice, these findings suggest that increased TTR or alterations in RBP4-TTR binding may contribute to insulin resistance by stabilizing RBP4 at higher steady-state concentrations in circulation. Lowering TTR levels or interfering with RBP4-TTR binding may enhance insulin sensitivity in obesity and type 2 diabetes. obesity; adipose; high-fat diet

A study was conducted to determine the serum levels of retinol-binding protein 4, a molecule secreted by adipocytes, correlated with the magnitude of insulin resistance in subjects with obesity, impaired glucose tolerance, or type 2 diabetes and in nonobese, nondiabetic subjects with a strong family history of type 2 diabetes. Levels of adipocytes secreted molecule appear to be elevated in serum before the development of frank diabetes and might be used to identify insulin resistance and associated cardiovascular risk factors.

Author(s): Qin Yang [1, 4]; Timothy E. Graham [1, 4]; Nimesh Mody [1]; Frederic Preitner [1]; Odile D. Peroni [1]; Janice M. Zabolotny [1]; Ko Kotani [1]; Loredana Quadro [2, [...]

Abstract Background Obesity contributes to Type 2 diabetes by promoting systemic insulin resistance. Obesity causes features of metabolic dysfunction in the adipose tissue that may contribute to later impairments of insulin action in skeletal muscle and liver; these include reduced insulin-stimulated glucose transport, reduced expression of GLUT4, altered expression of adipokines, and adipocyte hypertrophy. Animal studies have shown that expansion of adipose tissue alone is not sufficient to cause systemic insulin resistance in the absence of adipose tissue metabolic dysfunction. To determine if this holds true for humans, we studied the relationship between insulin resistance and markers of adipose tissue dysfunction in non-obese individuals. Method 32 non-obese first-degree relatives of Type 2 diabetic patients were recruited. Glucose tolerance was determined by an oral glucose tolerance test and insulin sensitivity was measured with the hyperinsulinaemic-euglycaemic clamp. Blood samples were collected and subcutaneous abdominal adipose tissue biopsies obtained for gene/protein expression and adipocyte cell size measurements. Results Our findings show that also in non-obese individuals low insulin sensitivity is associated with signs of adipose tissue metabolic dysfunction characterized by low expression of GLUT4, altered adipokine profile and enlarged adipocyte cell size. In this group, insulin sensitivity is positively correlated to GLUT4 mRNA (R = 0.49, p = 0.011) and protein (R = 0.51, p = 0.004) expression, as well as with circulating adiponectin levels (R = 0.46, 0 = 0.009). In addition, insulin sensitivity is inversely correlated to circulating RBP4 (R = −0.61, 0 = 0.003) and adipocyte cell size (R = −0.40, p = 0.022). Furthermore, these features are inter-correlated and also associated with other clinical features of the metabolic syndrome in the absence of obesity. No association could be found between the hypertrophy-associated adipocyte dysregulation and HIF-1alpha in this group of non-obese individuals. Conclusions In conclusion, these findings support the concept that it is not obesity per se, but rather metabolic dysfunction of adipose tissue that is associated with systemic insulin resistance and the metabolic syndrome.

RBP4 is produced mainly by hepatocytes. In type 2 diabetes and obesity, circulating RBP4 is increased and may act systemically to cause insulin resistance and glucose intolerance. Observations that adipocyte RBP4 mRNA increases in parallel with circulating RBP4 in these conditions, whereas liver RBP4 mRNA does not, led to a widely held hypothesis that elevated circulating RBP4 is a direct result of increased production by adipocytes. To test this, we generated mice with hepatocyte-specific deletion of RBP4 (liver RBP4 knockout or LRKO mice). Adipose tissue RBP4 expression and secretion remained intact in LRKO mice and increased as expected in the setting of diet-induced insulin resistance. However, circulating RBP4 was undetectable in LRKO mice. We conclude that adipocyte RBP4 is not a significant source of circulating RBP4, even in the setting of insulin resistance. Adipocyte RBP4, therefore, may have a more important autocrine or paracrine function that is confined within the adipose tissue compartment. [ABSTRACT FROM AUTHOR]

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OBJECTIVE--We identified lipocalin 2 (Lcn2) as a gene induced by dexamethasone and tumor necrosis factor-α in cultured adipocytes. The purpose of this study was to determine how expression of Lcn2 is regulated in fat cells and to ascertain whether Lcn2 could be involved in metabolic dysregulation associated with obesity. RESEARCH DESIGN AND METHODS--We examined Lcn2 expression in murine tissues and in 3T3-L1 adipocytes in the presence and absence of various stimuli. We used quantitative Western blotting to observe Lcn2 serum levels in lean and obese mouse models. To assess effects on insulin action, we used retroviral delivery of short hairpin RNA to reduce Lcn2 levels in 3T3-L1 adipocytes. RESULTS--Lcn2 is highly expressed by fat cells in vivo and in vitro. Expression of Lcn2 is elevated by agents that promote insulin resistance and is reduced by thiazolidinediones. The expression of Lcn2 is induced during 3T3-L1 adipogenesis in a CCAAT/enhancer-binding protein-dependent manner. Lcn2 serum levels are elevated in multiple rodent models of obesity, and forced reduction of Lcn2 in 3T3-L1 adipocytes improves insulin action. Exogenous Lcn2 promotes insulin resistance in cultured hepatocytes. CONCLUSIONS--Lcn2 is an adipokine with potential importance in insulin resistance associated with obesity. Diabetes 56:2533-2540, 2007 [ABSTRACT FROM AUTHOR]

In obesity and type 2 diabetes, expression of the GLUT4 glucose transporter is decreased selectively in adipocytes. Adipose-specific Glut4 (also known as Slc2a4) knockout (adipose-Glut4-/-) mice show insulin resistance secondarily in muscle and liver. Here we show, using DNA arrays, that expression of retinol binding protein-4 (RBP4) is elevated in adipose tissue of adipose-Glut4-/- mice. We show that serum RBP4 levels are elevated in insulin-resistant mice and humans with obesity and type 2 diabetes. RBP4 levels are normalized by rosiglitazone, an insulin-sensitizing drug. Transgenic overexpression of human RBP4 or injection of recombinant RBP4 in normal mice causes insulin resistance. Conversely, genetic deletion of Rbp4 enhances insulin sensitivity. Fenretinide, a synthetic retinoid that increases urinary excretion of RBP4, normalizes serum RBP4 levels and improves insulin resistance and glucose intolerance in mice with obesity induced by a high-fat diet. Increasing serum RBP4 induces hepatic expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) and impairs insulin signalling in muscle. Thus, RBP4 is an adipocyte-derived ‘signal’ that may contribute to the pathogenesis of type 2 diabetes. Lowering RBP4 could be a new strategy for treating type 2 diabetes. [ABSTRACT FROM AUTHOR]

Serum levels of retinol binding protein 4 (RBP4) are increased in insulin resistant states. We measured RBP4 levels in 240 non-diabetic offspring of type 2 diabetic subjects. Offspring had the following measurements: oral glucose tolerance test (OGTT), intravenous glucose tolerance test (IVGTT), euglycemic hyperinsulinemic clamp, and CT scan to evaluate subcutaneous and intra-abdominal fat. Mean age was 36.5±6.4 years, mean BM126±5 kg/m². No statistically significant differences in serum RBP4 levels were found between subjects with normoglycemia (n=170, mean RBP4 25.6 µg/ml), impaired fasting glucose (n=47, RBP4 27.4 µg/ml) and impaired glucose tolerance (n=23, RBP4 26.7 µg/ml). RBP4 levels correlated positively with BMI (p=0.007), systolic (p=0.022) and diastolic (p=0.02 l) blood pressure, fasting glucose (p=0.004) and insulin (p=0.029), 1st phase insulin response in an IVGTT (p=0.009), plasma glucose (p<0.001) and insulin (p=0.005) area under the curve during OGTT, total and LDL cholesterol (p<0.001), total triglycerides (p<0.001), and intra-abdominal fat area (13<0.001). RBP4 levels correlated inversely with whole body glucose uptake (WBGU) (p=0.003) and HDL cholesterol (p=0.027). In multivariate linear regression analysis including RBP4 levels, age, BMI, WBGU, and 1st phase insulin response as independent variables and glucose AUC in OGTT as the dependent variable, RBP4 levels were associated with glucose AUC in OGTT (p=0.006) independently of other variables. Genetic analysis of 900 Caucasian nondiabetic offspring of type 2 diabetic subjects revealed that several SNPs in the RBP4 gene are associated with circulating glucose levels from 10 to 60 min during an IVGTT. In sum, high serum RBP4 levels are associated with components of the metabolic syndrome in nonobese, nondiabetic subjects. High RBP4 is also associated with hyperglycemia, evaluated by glucose AUC in OGTT, independently of age, BMI, insulin sensitivity and insulin secretion in offspring of type 2 diabetic patients. In conclusion, genetic and metabolic data suggest that RBP4 may regulate insulin action on hepatic glucose output. Furthermore, RBP4 is a convenient marker to assess risk of diabetes and cardiovascular disease in subjects in whom the risk might otherwise be overlooked. [ABSTRACT FROM AUTHOR]

The adipocyte-derived peptide retinol-binding protein 4 (RBP4) is associated with insulin resistance. Genetic deletion enhances insulin sensitivity and overexpression causes insulin resistance in mice. RBP4 is elevated in insulin resistant subjects. Metabolic syndrome markers (obesity, dyslipidemia, insulin resistance) improve with dietary carbohydrate restriction. Here, we test whether in RBP4 levels are also reduced by carbohydrate restriction. Overweight/obese nondiabetic subjects with atherogenic dyslipidemia were randomized to a very low carbohydrate ketogenic diet (n=20, VLCKD) (1504 kcal: %CHO:fat:protein = 12:59:28) or a low fat diet (n=19, LFD) (1478 kcal: %CHO:fat:protein = 56:24:20) for 12 wk. Compared to subjects consuming LFD, subjects on VLCKD reduced body weight and adiposity, and improved glycemic control, insulin sensitivity and atherogenic dyslipidemia (decreased triglyceride, increased HDL-C, and increased LDL particle size). Serum RBP4 levels were reduced more in subjects on VLCKD (-20.2%) compared to LFD (+5.1%) (p = 0.02). For all subjects, the change in amount of dietary carbohydrate intake correlated with the change in RBP4; the correlation was stronger in subjects on VLCKD (r=0.54). The absolute and percent changes in RBP4 correlated with weight loss, fat loss, and improvement in glucose, insulin, triglycerides, and the quantity of small LDL particles. These findings link the role of RBP4 in insulin resistance with studies showing a tight connection between carbohydrate restriction and features of metabolic syndrome. In addition to improvement in markers of metabolic syndrome, restriction of dietary carbohydrate is more effective than a low fat diet for reducing RBP4. [ABSTRACT FROM AUTHOR]

Increased intraabdominal fat is associated with insulin resistance and increased cardiovascular risk. Adipose tissue secretes proteins (adipokines) that regulate systemic insulin action. Adipokine production varies among fat depots. The adipokine, RBP4, is increased in obesity, impaired glucose tolerance, and type 2 diabetes and serum concentrations correlate highly with insulin resistance (measured by clamp), dyslipidemia, hypertension, and intraabdominal fat mass. We aimed to determine whether (1) RBP4 expression differs in visceral and subcutaneous fat depots, (2) is associated with increased intraabdominal fat mass, and (3) correlates with adipose GLUT4 expression. Serum RBP4 and RBP4 mRNA in paired visceral and subcutaneous adipose biopsies were measured in 196 subjects with a wide range of metabolic characteristics. RBP4 mRNA in visceral fat was increased ∼60-fold in subjects with visceral, and 12-fold with subcutaneous, obesity versus lean subjects, and ∼2-fold with Type 2 diabetes versus nondiabetic subjects. Serum RBP4 levels were increased 3-fold with visceral obesity and 2-fold with subcutaneous obesity. Serum RBP4 correlated with RBP4 mRNA in visceral (Fig A) and subcutaneous adipose tissue (R=0.80 and R=0.50, respectively, p<0.001), with intra-abdominal fat area measured by CT (R=0.42,p=0.004, Fig B), and inversely with insulin sensitivity (R=0.50, p<0.001), independently of age, gender and BMI. RBP4 mRNA correlated inversely with GLUT4 mRNA in visceral fat (R=0.47, p=0.001). Among many adipokines, RBP4 was the strongest predictor of insulin resistance (glucose disposal rate during clamp) and intraabdominal fat mass. In summary, RBP4 concentrations are linked to visceral adiposity. In conclusion, visceral fat with reduced expression of GLUT4 may be a major source of RBP4 in insulin-resistant states. RBP4 can be used as a marker for intraabdominal fat mass and associated abnormalities. [ABSTRACT FROM AUTHOR]

Serum RBP4 levels correlate highly with insulin resistance and associated metabolic abnormalities. RBP4 overexpression in mice causes insulin resistance. Chronic exercise training that improves insulin sensitivity in insulin resistant human subjects lowers serum RBP4. Liver is considered the primary source of circulating RBP4 but adipose tissue may also produce RBP4 in insulin resistance. RBP4 mRNA is detected in cardiac and skeletal muscle, but it is not known whether muscle contributes to circulating RBP4 levels. Our aims were to determine: (1) whether RBP4 expression is altered in muscle in subjects with impaired glucose tolerance (IGT) or type 2 diabetes (T2D) and (2) whether RBP4 is regulated by chronic or acute exercise. RBP4 mRNA in quadriceps biopsies from IGT or T2D subjects was increased ∼250-fold (p<0.0001) at baseline relative to normal glucose tolerant control subjects. Exercise training for 1 month improved insulin sensitivity (measured by clamp) and lowered muscle RBP4 mRNA in the majority of IGT/T2D subjects. These decreases in muscle RBP4 mRNA correlated highly with decreases in serum RBP4 (R=0.86, p<0.0001) and inversely with changes in insulin sensitivity (R= -0.65, p<0.0001). In contrast, 1 mo of exercise training in lean, normoglycemic control subjects increased serum RBP4 and muscle RBP4 mRNA∼2-fold and ∼30-fold, respectively (p<0.0001), although mRNA was still only ∼8% of IGT/T2D levels. After 6 mo of training, serum RBP4 levels returned to baseline in controls. Studies of acute exercise in untrained control subjects demonstrated that exercise for 180 min at ∼70% VO[sub 2]max increased muscle RBP4 mRNA 9-fold (p=0.001) and serum RBP4 levels by 70% (p<0.05). Similarly, acute treadmill exercise in rats increased muscle RBP4 mRNA ∼5-fold and serum RBP4 40% with no change in liver or adipose tissue RBP4 mRNA. The amount of RBP4 secreted from soleus muscle ex vivo was greater than from the same amount of fat. These results show: (1) In IGT/T2D subjects, exercise training-induced decreases in muscle RBP4 mRNA correlate inversely with changes in insulin sensitivity; (2) in normal subjects, exercise training increases muscle RBP4; and (3) acute exercise-induced increases of RBP4 in serum correspond to increased RBP4 mRNA in muscle but not in other tissues. These findings suggest that RBP4 may be a novel muscle-secreted signal regulating fuel homeostasis in exercise. [ABSTRACT FROM AUTHOR]

Autophagy is a lysosomal catabolic process by which cells degrade or recycle their contents to maintain cellular homeostasis, adapt to stress, and respond to disease. Impairment of autophagy in endothelial cells studied under static conditions results in oxidant stress and impaired nitric oxide (NO) bioavailability. We tested the hypothesis that vascular autophagy is also important for induction of NO production caused by exposure of endothelial cells to shear stress (i.e., 3 h × ≈20 dyn/cm2). Atg3 is a requisite autophagy pathway mediator. Control cells treated with non-targeting control siRNA showed increased autophagy, reactive oxygen species (ROS) production, endothelial NO synthase (eNOS) phosphorylation, and NO production upon exposure to shear stress ( p < 0.05 for all). In contrast, cells with >85% knockdown of Atg3 protein expression (via Atg3 siRNA) exhibited a profound impairment of eNOS phosphorylation, and were incapable of increasing NO in response to shear stress. Moreover, ROS accumulation and inflammatory cytokine production (MCP-1 and IL-8) were exaggerated (all p < 0.05) in response to shear stress. These findings reveal that autophagy not only plays a critical role in maintaining NO bioavailability, but may also be a key regulator of oxidant-antioxidant balance and inflammatory-anti-inflammatory balance that ultimately regulate endothelial cell responses to shear stress. [ABSTRACT FROM AUTHOR]

Monogenetic diabetes mellitus (DM) describes a collection of single-gene diseases marked by hyperglycemia presenting in childhood or adulthood and the absence of immunological markers of type 1 DM. Mutations in the human insulin gene INS give rise to two separate clinical syndromes: permanent neonatal DM, type 4 (PNDM4), and maturity-onset diabetes of youth, type 10 (MODY10); the former presents shortly after birth and the latter presents in childhood and adulthood. We describe a 40-year-old man in a kindred with high prevalence of DM who presented with severe hyperglycemia but not ketoacidosis or hypertriglyceridemia. Twelve years after initial presentation, the patient had elevated proinsulin and normal plasma C-peptide when nearly euglycemic on treatment with insulin glargine. A novel INS mutation, Gln65Arg, within the C-peptide region was identified. The INS (p.Gln65Arg) mutation may cause MODY10 by disrupting proinsulin maturation., (© The Author(s) 2022. Published by Oxford University Press on behalf of American Society for Clinical Pathology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)