HLA class II alleles specify phenotypes of ketosis-prone diabetes

Atypical Diabetes: What Have We Learned and What Does the Future Hold?

As our understanding of the pathophysiology of diabetes evolves, we increasingly recognize that many patients may have a form of diabetes that does not neatly fit with a diagnosis of either type 1 or type 2 diabetes. The discovery and description of these forms of "atypical diabetes" have led to major contributions to our collective understanding of the basic biology that drives insulin secretion, insulin resistance, and islet autoimmunity. These discoveries now pave the way to a better classification of diabetes based on distinct endotypes. In this review, we highlight the key biological and clinical insights that can be gained from studying known forms of atypical diabetes. Additionally, we provide a framework for identification of patients with atypical diabetes based on their clinical, metabolic, and molecular features. Helpful clinical and genetic resources for evaluating patients suspected of having atypical diabetes are provided. Therefore, appreciating the various endotypes associated with atypical diabetes will enhance diagnostic accuracy and facilitate targeted treatment decisions.

Type 1 Diabetes Genetic Risk Score Differentiates Subgroups of Ketosis-Prone Diabetes

OBJECTIVE

To determine whether genetic risk for type 1 diabetes (T1D) differentiates the four Aβ subgroups of ketosis-prone diabetes (KPD), where A+ and A- define the presence or absence of islet autoantibodies and β+ and β- define the presence or absence of β-cell function.

RESEARCH DESIGN AND METHODS

We compared T1D genetic risk scores (GRS) of patients with KPD across subgroups, race/ethnicity, β-cell function, and glycemia.

RESULTS

Among 426 patients with KPD (54% Hispanic, 31% African American, 11% White), rank order of GRS was A+β- > A+β+ = A-β- > A-β+. GRS of A+β- KPD was lower than that of a T1D cohort, and GRS of A-β+ KPD was higher than that of a type 2 diabetes cohort. GRS was lowest among African American patients, with a similar distribution across KPD subgroups.

CONCLUSIONS

T1D genetic risk delineates etiologic differences among KPD subgroups. Patients with A+β- KPD have the highest and those with A-β+ KPD the lowest GRS.

Remission in Ketosis-Prone Diabetes

Heterogeneous forms of Ketosis-prone diabetes (KPD) are characterized by patients who present with diabetic ketoacidosis (DKA) but lack the typical features and biomarkers of autoimmune T1D. The A-β+ subgroup of KPD provides unique insight into the concept of "remission" since these patients have substantial preservation of beta-cell function permitting the discontinuation of insulin therapy, despite initial presentation with DKA. Measurements of C-peptide levels are essential to predict remission and guide potential insulin withdrawal. Further studies into predictors of remission and relapse can help us guide patients with A-β+ KPD toward remission and develop targeted treatments for this form of atypical diabetes.

The first series of cases of ketosis-prone type 2 diabetes (flatbush diabetes) in Brazilian adults

Ketosis-prone type 2 diabetes (KPD) is an emerging form of diabetes mellitus characterized by unprovoked ketoacidosis, absence of autoimmunity and beta-cell dysfunction. The KPD may improve after initial glycemic compensation and evolve to exogenous insulin independence, most cases were observed in populations with African or Hispanic backgrounds. We reviewed the literature on KPD and, to date, only one case of KPD has been described in Brazil's multi-ethnic population. A group of adult Brazilian KPD patients without autoimmunity and insulinopenia was identified for this study. We report a retrospective study of four KPD cases (3 males) evaluated in southeast Brazil, the patients were overweight or obese, age between the third and fifth decades of life, had a family history of type 2 diabetes, hyperglycemia (809.5 ± 344.2 mg/dL), acidosis (pH 7.21 ± 0.07; normal range (nr): 7.35-7.45 and bicarbonate 9.1 ± 6.2; nr: 22-26 mEq/mL), ketonuria (142.5 ± 114.4 mg/dL; nr: absence), absence of glutamic acid decarboxylase antibodies (GAD-65), and beta-cell function reserve (C-peptide 1.19 ± 0.53 ng/mL - nr: 1.1-4.4 ng/mL) on diagnosis. After glycemic compensation, there was increase of C-peptide (2.21 ± 0.41) indicating the recovery of beta-cell function and the time to insulin independence was 7.7 ± 3.5 months. They evolved after the period of glucotoxicity with insulin withdrawal and could be treated with oral antidiabetic therapy. This is the first case series of KPD described in Brazil being characterized by ketoacidosis at diagnosis, absence of autoimmunity, recovery of beta-cell function and insulin independence.

Prevalence and clinical characteristics of hypertension and metabolic syndrome in newly diagnosed patients with ketosis-onset diabetes: a cross-sectional study

BACKGROUND

To investigate the prevalence and clinical characteristics of hypertension (HTN) and metabolic syndrome (MetS) in newly diagnosed diabetes with ketosis-onset.

METHODS

A cross-sectional study was adopted in 734 newly diagnosed diabetics including 83 type 1 diabetics with positive islet-associated autoantibodies, 279 ketosis-onset diabetics without islet-associated autoantibodies and 372 non-ketotic type 2 diabetics. The clinical characteristics of HTN and MetS were compared across the three groups, and the risk factors of them were appraised in each group.

RESULTS

The prevalence of HTN and MetS were substantially higher in the ketosis-onset diabetics (34.4% for HTN and 58.8% for MetS) than in the type 1 diabetics (15.7% for HTN, P = 0.004; 25.3% for MetS, P < 0.001), but showed no remarkable difference compared with the type 2 diabetics (42.7% for HTN, P = 0.496; 72.3% for MetS, P = 0.079). Furthermore, the risk factors for both HTN and MetS in the ketosis-onset diabetics resembled those in the type 2 diabetics, but significantly different from those in the type 1 diabetics.

CONCLUSIONS

The prevalence of HTN and MetS in the ketosis-onset diabetics were magnificently higher than in the type 1 diabetics but showed no difference in comparison to the type 2 diabetics. Likewise, the clinical features and risk factors of HTN and MetS in the ketosis-onset diabetes resembled those in the type 2 diabetes but differed from those in the type 1 diabetes. Our findings indicate that ketosis-onset diabetes should be classified into type 2 diabetes rather than idiopathic type 1 diabetes.

Factors associated with early relapse to insulin dependence in unprovoked A-β+ ketosis-prone diabetes

OBJECTIVE

Unprovoked "A-β+" Ketosis-Prone Diabetes (KPD), a unique diabetic syndrome of adult-onset, obesity and proneness to ketoacidosis, is associated with rapid recovery of β cell function and insulin-independence. Whereas most patients experience prolonged remission, a subset relapses early to insulin dependence. We sought to define factors associated with early relapse.

METHODS

We utilized a prospective, longitudinal database to analyze 50 unprovoked A-β+ KPD patients with >2 measurements of β cell function and glycemia following baseline assessment.

RESULTS

19 patients (38%) relapsed to insulin dependence <1 year after the index DKA episode, while 31 (62%) remained insulin-independent for >1 year (median 4.2 years). Younger age at baseline (OR=0.947, P=0.033), and lower HOMA2-%β (OR=0.982, P=0.001), lower HOMA2-IR (OR=0.582, P=0.046) and higher HbA1c at 1 year (OR=1.71, P=0.002) were associated with early relapse. A multivariate model with these variables and the interaction of HOMA2-%β and HbA1c at 1 year provided a good fit (P<0.05).

CONCLUSIONS

Relapse to insulin dependence in unprovoked A-β+ KPD patients is associated with younger age and, after 1 year, lack of robust increase in β cell functional reserve, and suboptimal glycemic control. Measurements of these parameters 1 year after the index DKA episode can be used to assess the need for insulin therapy.

Association of HLA class II markers with autoantibody-negative ketosis-prone atypical diabetes compared to type 2 diabetes in a population of sub-Saharan African patients

AIM

We investigated the association of HLA DRB1 and DQB1 alleles, haplotypes and genotypes with unprovoked antibody-negative ketosis-prone atypical diabetes (A(-) KPD) in comparison to type 2 diabetes (T2D).

METHODS

A(-) KPD and T2D sub-Saharan African patients aged 19-63 years were consecutively recruited. Patients positive for cytoplasmic islet cell, insulin, glutamic acid decarboxylase or islet antigen-2 autoantibodies were excluded. Odds ratios were obtained via logistic regression after considering alleles with a minimum frequency of 5% in the study population. Bonferroni correction was used in the case of multiple comparisons.

RESULTS

Among the 130 participants, 35 (27%) were women and 57 (44%) were A(-) KPD. DRB1 and DQB1 allele frequencies were similar for both A(-) KPD and T2D patients; they did not confer any substantial risk even after considering type 1 diabetes susceptibility and resistance alleles. We found no association between A(-) KPD and the derived DRB1*07-DQB1*02:02 (OR: 0.55 [95%CI: 0.17-1.85], P=0.336); DRB1*11-DQB1*03:01 (OR: 2.42 [95%CI: 0.79-7.42], P=0.123); DRB1*15-DQB1*06:02 (OR: 0.87 [95%CI: 0.39-1.95], P=0.731) and DRB1*03:01-DQB1*02:01 (OR: 1.48 [95%CI: 0.55-3.96], P=0.437) haplotypes. Overall, we did not find any evidence of susceptibility to ketosis associated with DRB1 and DQB1 genotypes (all P>0.05) in A(-) KPD compared to T2D. Similar results were obtained after adjusting the analysis for age and sex.

CONCLUSION

Factors other than DRB1 and DQB1 genotype could explain the propensity to ketosis in A(-) KPD. These results need to be confirmed in a larger population with the perspective of improving the classification and understanding of the pathophysiology of A(-) KPD.

Masked and overt autoantibodies specific to the DPD epitope of 65-kDa glutamate decarboxylase (GAD65-DPD) are associated with preserved β-cell functional reserve in ketosis-prone diabetes

CONTEXT

Ketosis-prone diabetes (KPD), defined by presentation with diabetic ketoacidosis (DKA), comprises 4 subgroups based on the presence or absence of islet cell autoantibodies (A(-) or A(+)) and β-cell functional reserve (β(-) or β(+)). Among A(+) KPD, autoantibody epitope reactivity to 65-kDa glutamate decarboxylase (GAD65), defined by monoclonal GAD65Ab(DPD), was associated with greater β-cell functional reserve. In a majority of healthy individuals, GAD65Ab are present in the sera but are masked by anti-idiotypic antibodies; in contrast, overtly GAD65Ab-positive patients with autoimmune type 1 diabetes patients lack these anti-idiotypic antibodies.

OBJECTIVE

Our objective was to determine the presence of masked and overt GAD65Ab(DPD) in relation to β-cell function and genetic risk factors in KPD patients.

DESIGN

We investigated the associations of masked and overt GAD65Ab(DPD) with β-cell functional reserve, and their relationship with human leukocyte antigen (HLA) class II haplotypes linked to autoimmune diabetes susceptibility or resistance, in a large KPD cohort.

PATIENTS

Adult KPD patients (n = 384) were followed longitudinally in a research clinic.

MAIN OUTCOME MEASURES

β-Cell function, autoantibody status, GAD65Ab epitopes, and HLA class II haplotypes were evaluated.

RESULTS

Overall, KPD patients with β-cell functional reserve (β(+) subgroups) showed significantly higher frequency of masked GAD65Ab(DPD) than patients without β-cell functional reserve (β(-) subgroups): 112 of 144 (79%) compared with 59 of 100 (59%), respectively (P = .002). Masked or overt GAD65Ab(DPD) were also more frequent among autoantibody-positive patients with preserved β-cell functional reserve (A(+)β(+) KPD) than those lacking β-cell function (A(+)β(-) KPD): 77% compared with 55% (P = .01). The susceptibility HLA haplotypes DQA1*0301/DQB1*0302 and DQA1*0301/DQB1*0201 were associated with absence of overt or masked GAD65Ab(DPD) (odds Ratios 2.3 and 2.2, respectively).

CONCLUSIONS

Masked GAD65Ab(DPD) are strongly associated with preserved β-cell functional reserve among patients with KPD. Absence of GAD65Ab(DPD) reactivity is associated with 2 HLA class II susceptibility haplotypes for autoimmune type 1 diabetes.

Islet-specific T-cell responses and proinflammatory monocytes define subtypes of autoantibody-negative ketosis-prone diabetes

OBJECTIVE

Ketosis-prone diabetes (KPD) is characterized by diabetic ketoacidosis (DKA) in patients lacking typical features of type 1 diabetes. A validated classification scheme for KPD includes two autoantibody-negative ("A-") phenotypic forms: "A-β-" (lean, early onset, lacking β-cell functional reserve) and "A-β+" (obese, late onset, with substantial β-cell functional reserve after the index episode of DKA). Recent longitudinal analysis of a large KPD cohort revealed that the A-β+ phenotype includes two distinct subtypes distinguished by the index DKA episode having a defined precipitant ("provoked," with progressive β-cell function loss over time) or no precipitant ("unprovoked," with sustained β-cell functional reserve). These three A- KPD subtypes are characterized by absence of humoral islet autoimmune markers, but a role for cellular islet autoimmunity is unknown.

RESEARCH DESIGN AND METHODS

Islet-specific T-cell responses and the percentage of proinflammatory (CD14+CD16+) blood monocytes were measured in A-β- (n = 7), provoked A-β+ (n = 15), and unprovoked A-β+ (n = 13) KPD patients. Genotyping was performed for type 1 diabetes-associated HLA class II alleles.

RESULTS

Provoked A-β+ and A-β- KPD patients manifested stronger islet-specific T-cell responses (P < 0.03) and higher percentages of proinflammatory CD14+CD16+ monocytes (P < 0.01) than unprovoked A-β+ KPD patients. A significant relationship between type 1 diabetes HLA class II protective alleles and negative T-cell responses was observed.

CONCLUSIONS

Provoked A-β+ KPD and A-β- KPD are associated with a high frequency of cellular islet autoimmunity and proinflammatory monocyte populations. In contrast, unprovoked A-β+ KPD lacks both humoral and cellular islet autoimmunity.

Types of pediatric diabetes mellitus defined by anti-islet autoimmunity and random C-peptide at diagnosis

OBJECTIVE

To test the hypothesis that anti-islet autoantibody expression and random serum C-peptide obtained at diagnosis define phenotypes of pediatric diabetes with distinct clinical features.

SUBJECTS

We analyzed 607 children aged <19 yr consecutively diagnosed with diabetes after exclusion of 13% of cases with secondary diabetes (e.g., cystic fibrosis related, steroid induced) and 7.3% of cases lacking measurement of C-peptide and/or autoantibodies.

METHODS

Autoantibody positivity (A+) was defined as ≥ 1 positive out of GAD65, insulin, and ICA512 antibodies. Preserved beta-cell function (β+) was defined as random serum C-peptide at diagnosis ≥ 0.6 ng/mL. Body mass index (BMI) was measured at median 1.2 months after diagnosis. Characteristics at diagnosis and 2 yr (range 18-30 months) after diagnosis were compared among groups.

RESULTS

Autoantibody expression and C-peptide at diagnosis defined the following groups: A+β- (52.1% of the children), A+β+ (32.8%), A-β+ (12.5%), and A-β- (2.6%). These four groups differed in gender, race/ethnicity, and clinical characteristics at diagnosis [i.e., age, pubertal development, obesity/overweight, diabetic ketoacidosis, glycemia, and hemoglobin A1c (HbA1c)] and at 2 yr (i.e., clinical diagnosis, treatment, and HbA1c) (all p < 0.0001). Among all β+ children, C-peptide >2 ng/mL was associated with lower HbA1c at onset (p = 0.0001) and, in the A+β+ subgroup, with higher frequency of achieving HbA1c < 7% at 2 yr (p = 0.03). All three patients (0.7% of total) with monogenic diabetes (maturity onset diabetes of the young, MODY) were A-β+ with C-peptide between 0.6 and 2 ng/mL.

CONCLUSIONS

Anti-islet autoantibodies status and serum random C-peptide at diagnosis define four distinct phenotypes of pediatric diabetes with prognostic value.

Personalizing guidelines for diabetes management: twilight or dawn of the expert?

BACKGROUND

This opinion article on the management of type 2 diabetes considers the old and new format of guidelines and critical changes in the character of such guidelines. We highlight limitations of the guidelines and make recommendations for how treatment can be more personalised.

DISCUSSION

Published guidelines for the management of adult-onset non-insulin requiring diabetes have adopted a formulaic approach to patient management that can be overseen centrally and delivered by personnel with limited training. Recently, guidelines have taken a patient-centered, multiple risk-factor approach. Importantly, local funding issues are considered, but drive the final action and not the decision-making process. The nature of the disease can be determined by laboratory tests, including screening for diabetes-associated autoantibodies. The strategy remains step-up, with intensification of drug or insulin dose. As with past guidelines, there is an assumption that in each patient with type 2 diabetes, metformin is used initially, but targets and therapies then veer in different directions to create a matrix of options based on the features and responses of each individual. Factors to consider include: (A)ge, (B)ody weight, (C)omplications and co-morbidities, Diabetes (D)uration and (E)xpense, but also patient preference and patient response.

SUMMARY

Guidelines for the management of type 2 diabetes have important limitations and a patient-centered, multiple target, multiple therapy approach is proposed.

Pathogenesis of A⁻β⁺ ketosis-prone diabetes

A⁻β⁺ ketosis-prone diabetes (KPD) is an emerging syndrome of obesity, unprovoked ketoacidosis, reversible β-cell dysfunction, and near-normoglycemic remission. We combined metabolomics with targeted kinetic measurements to investigate its pathophysiology. Fasting plasma fatty acids, acylcarnitines, and amino acids were quantified in 20 KPD patients compared with 19 nondiabetic control subjects. Unique signatures in KPD--higher glutamate but lower glutamine and citrulline concentrations, increased β-hydroxybutyryl-carnitine, decreased isovaleryl-carnitine (a leucine catabolite), and decreased tricarboxylic acid (TCA) cycle intermediates--generated hypotheses that were tested through stable isotope/mass spectrometry protocols in nine new-onset, stable KPD patients compared with seven nondiabetic control subjects. Free fatty acid flux and acetyl CoA flux and oxidation were similar, but KPD had slower acetyl CoA conversion to β-hydroxybutyrate; higher fasting β-hydroxybutyrate concentration; slower β-hydroxybutyrate oxidation; faster leucine oxidative decarboxylation; accelerated glutamine conversion to glutamate without increase in glutamate carbon oxidation; and slower citrulline flux, with diminished glutamine amide-nitrogen transfer to citrulline. The confluence of metabolomic and kinetic data indicate a distinctive pathogenic sequence: impaired ketone oxidation and fatty acid utilization for energy, leading to accelerated leucine catabolism and transamination of α-ketoglutarate to glutamate, with impaired TCA anaplerosis of glutamate carbon. They highlight a novel process of defective energy production and ketosis in A⁻β⁺ KPD.

Ketosis-onset diabetes and ketosis-prone diabetes: same or not?

Objective. To compare clinical characteristics, immunological markers, and β -cell functions of 4 subgroups ("A β " classification system) of ketosis-onset diabetes and ketosis prone diabetes patients without known diabetes, presenting with ketosis or diabetic ketoacidosis (DKA) and admitted to our department from March 2011 to December 2011 in China, with 50 healthy persons as control group. Results. β -cell functional reserve was preserved in 63.52% of patients. In almost each subgroup (except A-   β - subgroup of ketosis prone group), male patients were more than female ones. The age of the majority of patients in ketosis prone group was older than that of ketosis-onset group, except A-   β - subgroup of ketosis prone group. The durations from the patient first time ketosis or DKA onset to admitting to the hospital have significant difference, which were much longer for the ketosis prone group except the A+ β + subgroup. BMI has no significant difference among subgroups. FPG of ketosis prone group was lower than that of A-   β + subgroup and A+ β + subgroup in ketosis-onset group. A-   β - subgroup and A+ β + subgroup of ketosis prone group have lower HbA1c than ketosis-onset group. Conclusions. Ketosis-onset diabetes and ketosis prone diabetes do not absolutely have the same clinical characteristics. Each subgroup shows different specialty.

Challenges in diagnosing type 1 diabetes in different populations

Diabetes affects today an estimated 366 million people world-wide, including 20 million to 40 million of patients with type 1 diabetes (T1D). While T1D accounts for 5% to 20% of those with diabetes, it is associated with higher morbidity, mortality and health care cost than the more prevalent type 2 diabetes. Patients with T1D require exogenous insulin for survival and should be identified as soon as possible after diagnosis to avoid high morbidity due to a delay in insulin treatment. It is also important to present to the patient correct prognosis that differs by the type of diabetes. From the research point of view, correct classification should help to identify the etiologies and to develop specific prevention for T1D. This review summarizes evidence that may be helpful in diagnosing T1D in various ethnic groups. Challenges in interpretation of results commonly used to determine the type of diabetes are highlighted.

Update on diagnosis, pathogenesis and management of ketosis-prone Type 2 diabetes mellitus

Diabetic ketoacidosis (DKA) has been considered a key clinical feature of Type 1 diabetes mellitus; however, increasing evidence indicates that DKA is also a common feature of Type 2 diabetes (T2DM). Many cases of DKA develop under stressful conditions such as trauma or infection but an increasing number of cases without precipitating cause have been reported in children and adults with T2DM. Such patients present with severe hyperglycemia and ketosis as in Type 1 diabetes mellitus but can discontinue insulin after a few months and maintain acceptable glycemic control on diet or oral agents. This subtype of diabetes has been referred to as ketosis-prone T2DM. In this article, we reviewed the literature on ketosis-prone T2DM and summarized the epidemiology, putative pathophysiology and approaches to management.

HLA class II alleles susceptibility markers of type 1 diabetes fail to specify phenotypes of ketosis-prone diabetes in adult Tunisian patients

We aimed to characterize the different subgroups of ketosis-prone diabetes (KPD) in a sample of Tunisian patients using the Aβ scheme based on the presence or absence of β-cell autoantibodies (A+ or A-) and β-cell functional reserve (β+ or β-) and we investigated whether HLA class II alleles could contribute to distinct KPD phenotypes. We enrolled 43 adult patients with a first episode of ketosis. For all patients we evaluated clinical parameters, β-cell autoimmunity, β-cell function and HLA class II alleles. Frequency distribution of the 4 subgroups was 23.3% A+β-, 23.3% A-β-, 11.6% A+β+ and 41.9% A-β+. Patients from the group A+β- were significantly younger than those from the group A-β- (P = .002). HLA susceptibility markers were significantly more frequent in patients with autoantibodies (P = .003). These patients also had resistance alleles but they were more frequent in A+β+ than A+β- patients (P = .04). Insulin requirement was not associated to the presence or the absence of HLA susceptibility markers. HLA class II alleles associated with susceptibility to autoimmune diabetes have not allowed us to further define Tunisian KPD groups. However, high prevalence of HLA resistance alleles in our patients may reflect a particular genetic background of Tunisian KPD population.

Presence or absence of a known diabetic ketoacidosis precipitant defines distinct syndromes of "A-β+" ketosis-prone diabetes based on long-term β-cell function, human leukocyte antigen class II alleles, and sex predilection

Ketosis-prone diabetes (KPD) is heterogeneous. Longitudinal follow-up revealed that patients with "A-β+" KPD (absent autoantibodies and preserved β-cell function) segregated into 2 subgroups with distinct evolution of β-cell function and glycemic control. Generalized linear analysis demonstrated that the variable that most significantly differentiated them was presence of a clinically evident precipitating event for the index diabetic ketoacidosis (DKA). Hence, we performed a comprehensive analysis of A-β+ KPD patients presenting with "provoked" compared with "unprovoked" DKA. Clinical, biochemical, and β-cell functional characteristics were compared between provoked and unprovoked A-β+ KPD patients followed prospectively for 1 to 8 years. Human leukocyte antigen class II allele frequencies were compared between these 2 groups and population controls. Unprovoked A-β+ KPD patients (n = 83) had greater body mass index, male preponderance, higher frequency of women with oligo-/anovulation, more frequent African American ethnicity, and less frequent family history of diabetes than provoked A-β+ KPD patients (n = 64). The provoked group had higher frequencies of the human leukocyte antigen class II type 1 diabetes mellitus susceptibility alleles DQB1*0302 (than the unprovoked group or population controls) and DRB1*04 (than the unprovoked group), whereas the unprovoked group had a higher frequency of the protective allele DQB1*0602. β-Cell secretory reserve and glycemic control improved progressively in the unprovoked group but declined in the provoked group. The differences persisted in comparisons restricted to patients with new-onset diabetes. "Unprovoked" A-β+ KPD is a distinct syndrome characterized by reversible β-cell dysfunction with male predominance and increased frequency of DQB1*0602, whereas "provoked" A-β+ KPD is characterized by progressive loss of β-cell reserve and increased frequency of DQB1*0302 and DRB1*04. Unprovoked DKA predicts long-term β-cell functional reserve, insulin independence, and glycemic control in KPD.

A-beta-subtype of ketosis-prone diabetes is not predominantly a monogenic diabetic syndrome

OBJECTIVE

Ketosis-prone diabetes (KPD) is an emerging syndrome that encompasses several distinct phenotypic subgroups that share a predisposition to diabetic ketoacidosis. We investigated whether the A-beta- subgroup of KPD, characterized by complete insulin dependence, absent beta-cell functional reserve, lack of islet cell autoantibodies, and strong family history of type 2 diabetes, represents a monogenic form of diabetes.

RESEARCH DESIGN AND METHODS

Over 8 years, 37 patients with an A-beta- phenotype were identified in our longitudinally followed cohort of KPD patients. Seven genes, including hepatocyte nuclear factor 4A (HNF4A), glucokinase (GCK), HNF1A, pancreas duodenal homeobox 1 (PDX1), HNF1B, neurogenic differentiation 1 (NEUROD1), and PAX4, were directly sequenced in all patients. Selected gene regions were also sequenced in healthy, unrelated ethnically matched control subjects, consisting of 84 African American, 96 Caucasian, and 95 Hispanic subjects.

RESULTS

The majority (70%) of the A-beta- KPD patients had no significant causal polymorphisms in either the proximal promoter or coding regions of the seven genes. The combination of six potentially significant low-frequency, heterozygous sequence variants in HNF-1 alpha (A174V or G574S), PDX1 (putative 5'-untranslated region CCAAT box, P33T, or P239Q), or PAX4 (R133W) were found in 27% (10/37) of patients, with one additional patient revealing two variants, PDX1 P33T and PAX4 R133W. The A174V variant has not been previously reported.

CONCLUSIONS

Despite its well-circumscribed, robust, and distinctive phenotype of severe, nonautoimmune-mediated beta-cell dysfunction, A-beta- KPD is most likely not a predominantly monogenic diabetic syndrome. Several A-beta- KPD patients have low-frequency variants in HNF1A, PDX1, or PAX4 genes, which may be of functional significance in their pathophysiology.

Syndromes of ketosis-prone diabetes mellitus

Ketosis-prone diabetes (KPD) is a widespread, emerging, heterogeneous syndrome characterized by patients who present with diabetic ketoacidosis or unprovoked ketosis but do not necessarily have the typical phenotype of autoimmune type 1 diabetes. Multiple, severe forms of beta-cell dysfunction appear to underlie the pathophysiology of KPD. Until recently, the syndrome has lacked an accurate, clinically relevant and etiologically useful classification scheme. We have utilized a large, longitudinally followed, heterogeneous, multiethnic cohort of KPD patients to identify four clinically and pathophysiologically distinct subgroups that are separable by the presence or absence of beta-cell autoimmunity and the presence or absence of beta-cell functional reserve. The resulting "Abeta" classification system of KPD has proven to be highly accurate and predictive of such clinically important outcomes as glycemic control and insulin dependence, as well as an aid to biochemical and molecular investigations into novel causes of beta-cell dysfunction. In this review, we describe the current state of knowledge in regard to the natural history, pathophysiology, and treatment of the subgroups of KPD, with an emphasis on recent advances in understanding their immunological and genetic bases.