Relative contribution of type 1 and type 2 diabetes loci to the genetic etiology of adult-onset, non-insulin-requiring autoimmune diabetes

Prognosis and outcome of latent autoimmune diabetes in adults: T1DM or T2DM?

Latent Autoimmune Diabetes in Adults (LADA) is a type of diabetes mellitus often overlooked in clinical practice for its dual resemblance to Type 1 Diabetes Mellitus (T1DM) in pathogenesis and to Type 2 Diabetes Mellitus (T2DM) in clinical presentation. To better understand LADA's distinctiveness from T1DM and T2DM, we conducted a comprehensive review encompassing etiology, pathology, clinical features, treatment modalities, and prognostic outcomes. With this comparative lens, we propose that LADA defies simple classification as either T1DM or T2DM. The specific treatments for the disease are limited and should be based on the therapies of T1DM or T2DM that address specific clinical issues at different stages of the disease. It is crucial to identify LADA cases potentially misdiagnosed as T2DM, warranting prompt screening for poor blood sugar control, short-term blood sugar deterioration, and other conditions. If the prognosis for LADA is similar to T2DM, it can be managed as T2DM. However, if the prognosis fundamentally differs, early LADA screening is crucial to optimize patient outcomes and enhance research on tailored treatments. The pathogenesis of LADA is clear, so the prognosis may be the key to determining whether it can be classified as T2DM, which is also the direction of future research. On the one hand, this paper aims to provide suggestions for the clinical screening and treatment of LADA based on the latest progress and provide worthy directions for future research on LADA.

Untangling the genetics of beta cell dysfunction and death in type 1 diabetes

BACKGROUND

Type 1 diabetes (T1D) is a complex multi-system disease which arises from both environmental and genetic factors, resulting in the destruction of insulin-producing pancreatic beta cells. Over the past two decades, human genetic studies have provided new insight into the etiology of T1D, including an appreciation for the role of beta cells in their own demise.

SCOPE OF REVIEW

Here, we outline models supported by human genetic data for the role of beta cell dysfunction and death in T1D. We highlight the importance of strong evidence linking T1D genetic associations to bona fide candidate genes for mechanistic and therapeutic consideration. To guide rigorous interpretation of genetic associations, we describe molecular profiling approaches, genomic resources, and disease models that may be used to construct variant-to-gene links and to investigate candidate genes and their role in T1D.

MAJOR CONCLUSIONS

We profile advances in understanding the genetic causes of beta cell dysfunction and death at individual T1D risk loci. We discuss how genetic risk prediction models can be used to address disease heterogeneity. Further, we present areas where investment will be critical for the future use of genetics to address open questions in the development of new treatment and prevention strategies for T1D.

Prediction of progression to type 1 diabetes with dynamic biomarkers and risk scores

Identifying biomarkers of functional β-cell loss is an important step in the risk stratification of type 1 diabetes. Genetic risk scores (GRS), generated by profiling an array of single nucleotide polymorphisms, are a widely used type 1 diabetes risk-prediction tool. Type 1 diabetes screening studies have relied on a combination of biochemical (autoantibody) and GRS screening methodologies for identifying individuals at high-risk of type 1 diabetes. A limitation of these screening tools is that the presence of autoantibodies marks the initiation of β-cell loss, and is therefore not the best biomarker of progression to early-stage type 1 diabetes. GRS, on the other hand, represents a static biomarker offering a single risk score over an individual's lifetime. In this Personal View, we explore the challenges and opportunities of static and dynamic biomarkers in the prediction of progression to type 1 diabetes. We discuss future directions wherein newer dynamic risk scores could be used to predict type 1 diabetes risk, assess the efficacy of new and emerging drugs to retard, or prevent type 1 diabetes, and possibly replace or further enhance the predictive ability offered by static biomarkers, such as GRS.

Characterization of the gut bacterial and viral microbiota in latent autoimmune diabetes in adults

Latent autoimmune diabetes in adults (LADA) is a heterogeneous disease characterized by autoantibodies against insulin producing pancreatic beta cells and initial lack of need for insulin treatment. The aim of the present study was to investigate if individuals with LADA have an altered gut microbiota relative to non-diabetic control subjects, individuals with type 1 diabetes (T1D), and individuals with type 2 diabetes (T2D). Bacterial community profiling was performed with primers targeting the variable region 4 of the 16S rRNA gene and sequenced. Amplicon sequence variants (ASVs) were generated with DADA2 and annotated to the SILVA database. The gut virome was sequenced, using a viral particle enrichment and metagenomics approach, assembled, and quantified to describe the composition of the viral community. Comparison of the bacterial alpha- and beta-diversity measures revealed that the gut bacteriome of individuals with LADA resembled that of individuals with T2D. Yet, specific genera were found to differ in abundance in individuals with LADA compared with T1D and T2D, indicating that LADA has unique taxonomical features. The virome composition reflected the stability of the most dominant order Caudovirales and the families Siphoviridae, Podoviridae, and Inoviridae, and the dominant family Microviridae. Further studies are needed to confirm these findings.

Association of human leukocyte antigen (HLA) footprints with the comorbidity of latent autoimmune diabetes in adults (LADA) and hepatitis C virus (HCV) infection: A multicenter cross-sectional study

AIMS

This study aims to investigate the interplay between hepatitis C virus (HCV) infection and major forms of diabetes: type 1 diabetes (T1D), type 2 diabetes (T2D), and latent autoimmune diabetes in adults (LADA).

METHODS

This multicenter study analyzed a cohort of 2699 diabetic and 7344 non-diabetic subjects who visited medical centers in China from 2014 to 2021. T1D, T2D, LADA, and HCV were diagnosed using standard procedures. High-throughput sequencing was conducted to identify genetic footprints of human leukocyte antigen (HLA) alleles and haplotypes at the DRB1, DQA1, and DQB1 loci.

RESULTS

HCV infection was detected in 3 % (23/766) of LADA patients, followed by 1.5 % (15/977) of T2D patients, 1.4 % (13/926) of T1D patients, and 0.5 % (38/7344) of non-diabetic individuals. HCV prevalence was significantly higher in people with diabetes than in non-diabetic individuals (p < 0.01). HLA alleles (DQB1*060101, DQB1*040101) and haplotypes (DRB1*080302-DQA1*010301-DQB1*060101) in LADA patients with HCV revealed higher frequencies than in LADA patients without HCV (adjusted p < 0.03). Furthermore, a higher risk of diabetes complications was found among LADA patients with HCV infection (p < 0.001).

CONCLUSIONS

LADA patients are susceptible to HCV infection, potentially associated with certain HLA alleles/haplotypes. Early diagnosis and treatment of HCV infection among people with diabetes are important for the management of severe complications.

Utility of genetic risk scores in type 1 diabetes

Iterative advances in understanding of the genetics of type 1 diabetes have identified >70 genetic regions associated with risk of the disease, including strong associations across the HLA class II region that account for >50% of heritability. The increased availability of genetic data combined with the decreased costs of generating these data, have facilitated the development of polygenic scores that aggregate risk variants from associated loci into a single number: either a genetic risk score (GRS) or a polygenic risk score (PRS). PRSs incorporate the risk of many possibly correlated variants from across the genome, even if they do not reach genome-wide significance, whereas GRSs estimate the cumulative contribution of a smaller subset of genetic variants that reach genome-wide significance. Type 1 diabetes GRSs have utility in diabetes classification, aiding discrimination between type 1 diabetes, type 2 diabetes and MODY. Type 1 diabetes GRSs are also being used in newborn screening studies to identify infants at risk of future presentation of the disease. Most early studies of type 1 diabetes genetics have been conducted in European ancestry populations, but, to develop accurate GRSs across diverse ancestries, large case-control cohorts from non-European populations are still needed. The current barriers to GRS implementation within healthcare are mainly related to a lack of guidance and knowledge on integration with other biomarkers and clinical variables. Once these limitations are addressed, there is huge potential for 'test and treat' approaches to be used to tailor care for individuals with type 1 diabetes.

Heterogeneity and endotypes in type 1 diabetes mellitus

Despite major advances over the past decade, prevention and treatment of type 1 diabetes mellitus (T1DM) remain suboptimal, with large and unexplained variations in individual responses to interventions. The current classification schema for diabetes mellitus does not capture the complexity of this disease or guide clinical management effectively. One of the approaches to achieve the goal of applying precision medicine in diabetes mellitus is to identify endotypes (that is, well-defined subtypes) of the disease each of which has a distinct aetiopathogenesis that might be amenable to specific interventions. Here, we describe epidemiological, clinical, genetic, immunological, histological and metabolic differences within T1DM that, together, suggest heterogeneity in its aetiology and pathogenesis. We then present the emerging endotypes and their impact on T1DM prediction, prevention and treatment.

The relationship between islet autoantibody status and the genetic risk of type 1 diabetes in adult-onset type 1 diabetes

AIMS/HYPOTHESIS

The reason for the observed lower rate of islet autoantibody positivity in clinician-diagnosed adult-onset vs childhood-onset type 1 diabetes is not known. We aimed to explore this by assessing the genetic risk of type 1 diabetes in autoantibody-negative and -positive children and adults.

METHODS

We analysed GAD autoantibodies, insulinoma-2 antigen autoantibodies and zinc transporter-8 autoantibodies (ZnT8A) and measured type 1 diabetes genetic risk by genotyping 30 type 1 diabetes-associated variants at diagnosis in 1814 individuals with clinician-diagnosed type 1 diabetes (1112 adult-onset, 702 childhood-onset). We compared the overall type 1 diabetes genetic risk score (T1DGRS) and non-HLA and HLA (DR3-DQ2, DR4-DQ8 and DR15-DQ6) components with autoantibody status in those with adult-onset and childhood-onset diabetes. We also measured the T1DGRS in 1924 individuals with type 2 diabetes from the Wellcome Trust Case Control Consortium to represent non-autoimmune diabetes control participants.

RESULTS

The T1DGRS was similar in autoantibody-negative and autoantibody-positive clinician-diagnosed childhood-onset type 1 diabetes (mean [SD] 0.274 [0.034] vs 0.277 [0.026], p=0.4). In contrast, the T1DGRS in autoantibody-negative adult-onset type 1 diabetes was lower than that in autoantibody-positive adult-onset type 1 diabetes (mean [SD] 0.243 [0.036] vs 0.271 [0.026], p<0.0001) but higher than that in type 2 diabetes (mean [SD] 0.229 [0.034], p<0.0001). Autoantibody-negative adults were more likely to have the more protective HLA DR15-DQ6 genotype (15% vs 3%, p<0.0001), were less likely to have the high-risk HLA DR3-DQ2/DR4-DQ8 genotype (6% vs 19%, p<0.0001) and had a lower non-HLA T1DGRS (p<0.0001) than autoantibody-positive adults. In contrast to children, autoantibody-negative adults were more likely to be male (75% vs 59%), had a higher BMI (27 vs 24 kg/m²) and were less likely to have other autoimmune conditions (2% vs 10%) than autoantibody-positive adults (all p<0.0001). In both adults and children, type 1 diabetes genetic risk was unaffected by the number of autoantibodies (p>0.3). These findings, along with the identification of seven misclassified adults with monogenic diabetes among autoantibody-negative adults and the results of a sensitivity analysis with and without measurement of ZnT8A, suggest that the intermediate type 1 diabetes genetic risk in autoantibody-negative adults is more likely to be explained by the inclusion of misclassified non-autoimmune diabetes (estimated to represent 67% of all antibody-negative adults, 95% CI 61%, 73%) than by the presence of unmeasured autoantibodies or by a discrete form of diabetes. When these estimated individuals with non-autoimmune diabetes were adjusted for, the prevalence of autoantibody positivity in adult-onset type 1 diabetes was similar to that in children (93% vs 91%, p=0.4).

CONCLUSIONS/INTERPRETATION

The inclusion of non-autoimmune diabetes is the most likely explanation for the observed lower rate of autoantibody positivity in clinician-diagnosed adult-onset type 1 diabetes. Our data support the utility of islet autoantibody measurement in clinician-suspected adult-onset type 1 diabetes in routine clinical practice.

Identifying type 1 and 2 diabetes in research datasets where classification biomarkers are unavailable: assessing the accuracy of published approaches

OBJECTIVES

We aimed to compare the performance of approaches for classifying insulin-treated diabetes within research datasets without measured classification biomarkers, evaluated against two independent biological definitions of diabetes type.

STUDY DESIGN AND SETTING

We compared accuracy of ten reported approaches for classifying insulin-treated diabetes into type 1 (T1D) and type 2 (T2D) diabetes in two cohorts: UK Biobank (UKBB) n = 26,399 and Diabetes Alliance for Research in England (DARE) n = 1,296. The overall performance for classifying T1D and T2D was assessed using: a T1D genetic risk score and genetic stratification method (UKBB); C-peptide measured at >3 years diabetes duration (DARE).

RESULTS

Approaches' accuracy ranged from 71% to 88% (UKBB) and 68% to 88% (DARE). When classifying all participants, combining early insulin requirement with a T1D probability model (incorporating diagnosis age and body image issue [BMI]), and interview-reported diabetes type (UKBB available in only 15%) consistently achieved high accuracy (UKBB 87% and 87% and DARE 85% and 88%, respectively). For identifying T1D with minimal misclassification, models with high thresholds or young diagnosis age (<20 years) had highest performance. Findings were incorporated into an online tool identifying optimum approaches based on variable availability.

CONCLUSION

Models combining continuous features with early insulin requirement are the most accurate methods for classifying insulin-treated diabetes in research datasets without measured classification biomarkers.

Phenotypic and genetic classification of diabetes

The historical subclassification of diabetes into predominantly types 1 and 2 is well appreciated to inadequately capture the heterogeneity seen in patient presentations, disease course, response to therapy and disease complications. This review summarises proposed data-driven approaches to further refine diabetes subtypes using clinical phenotypes and/or genetic information. We highlight the benefits as well as the limitations of these subclassification schemas, including practical barriers to their implementation that would need to be overcome before incorporation into clinical practice.

Adult-onset autoimmune diabetes

Adult-onset autoimmune (AOA) diabetes pathophysiology starts with immune changes, followed by dysglycaemia and overt disease. AOA diabetes can occur as classic type 1 diabetes when associated with severe loss of insulin secretion. More frequently, it is diagnosed as latent autoimmune diabetes in adults, a slowly progressing form with late onset, a long period not requiring insulin, and it is often misdiagnosed as type 2 diabetes. As its clinical presentation varies remarkably and immune markers often lack specificity, it is challenging to classify each case ad hoc, especially when insulin treatment is not required at diagnosis. Proper care of AOA diabetes aims to prevent complications and to improve quality of life and life expectancy. To achieve these goals, attention should be paid to lifestyle factors, with the aid of pharmacological therapies properly tailored to each individual clinical setting. Given the heterogeneity of the disease, choosing the right therapy for AOA diabetes is challenging. Most of the trials testing disease-modifying therapies for autoimmune diabetes are conducted in people with childhood onset, whereas non-insulin diabetes therapies have mostly been studied in the larger population with type 2 diabetes. More randomized controlled trials of therapeutic agents in AOA diabetes are needed.

Latent autoimmune diabetes in adults in China

Latent autoimmune diabetes in adults (LADA) is a type of diabetes caused by slow progression of autoimmune damage to pancreatic beta cells. According to the etiological classification, LADA should belong to the autoimmune subtype of type 1 diabetes (T1D). Previous studies have found general immune genetic effects associated with LADA, but there are also some racial differences. Multicenter studies have been conducted in different countries worldwide, but it is still unclear how the Chinese and Caucasian populations differ. The epidemiology and phenotypic characteristics of LADA may vary between Caucasian and Chinese diabetic patients as lifestyle, food habits, and body mass index differ between these two populations. The prevalence of LADA in China has reached a high level compared to other countries. The prevalence of LADA in China has reached a high level compared to other countries, and the number of patients with LADA ranks first in the world. Previous studies have found general immune genetic effects associated with LADA, but some racial differences also exist. The prevalence of LADA among newly diagnosed type 2 diabetes patients over the age of 30 years in China is 5.9%, and LADA patients account for 65% of the newly diagnosed T1D patients in the country. As a country with a large population, China has many people with LADA. A summary and analysis of these studies will enhance further understanding of LADA in China. In addition, comparing the similarities and differences between the Chinese and the Caucasian population from the perspectives of epidemiology, clinical, immunology and genetics will help to improve the understanding of LADA, and then promote LADA studies in individual populations.

Type 1 diabetes in diverse ancestries and the use of genetic risk scores

Over 75 genetic loci within and outside of the HLA region influence type 1 diabetes risk. Genetic risk scores (GRS), which facilitate the integration of complex genetic information, have been developed in type 1 diabetes and incorporated into models and algorithms for classification, prognosis, and prediction of disease and response to preventive and therapeutic interventions. However, the development and validation of GRS across different ancestries is still emerging, as is knowledge on type 1 diabetes genetics in populations of diverse genetic ancestries. In this Review, we provide a summary of the current evidence on the evolutionary genetic variation in type 1 diabetes and the racial and ethnic differences in type 1 diabetes epidemiology, clinical characteristics, and preclinical course. We also discuss the influence of genetics on type 1 diabetes with differences across ancestries and the development and validation of GRS in various populations.

Lifestyle or Environmental Influences and Their Interaction With Genetic Susceptibility on the Risk of LADA

Background

LADA is a common form of diabetes described as a mix between type 1 and type 2 diabetes. Understanding of how genes and environmental factors interact in the development of LADA is central for future efforts to prevent the disease. This review aims to synthesize the literature on lifestyle factors linked to LADA risk and discuss their potential interaction with genetic susceptibility.

Findings

Current knowledge on environmental risk factors for LADA is primarily based on observational data from Scandinavian populations. Increasing evidence suggest that lifestyle factors promoting type 2 diabetes such as obesity, sedentariness, low birth weight and smoking, is implicated in the risk of LADA. Data from mendelian randomization studies support that the link between LADA and obesity, low birth weight and smoking is causal. Limited evidence indicates that dietary factors including consumption of red meat, coffee and sweetened beverages may increase the risk while consumption of alcohol and omega-3 fatty acids may reduce the risk. Several lifestyle factors, including smoking and obesity, seem to interact with human leukocyte antigen genes associated with autoimmunity, conferring much stronger effects on disease risk among those exposed to both factors.

Summary

Available studies suggest that lifestyle modification has the potential for prevention of LADA, particularly for individuals with high risk of disease such as those with genetic susceptibility. Research into risk factors of LADA is however limited, confirmations are warranted, many factors remain to be explored, and there is a need for intervention studies to assess causality.

Association of Polymorphisms within HOX Transcript Antisense RNA (HOTAIR) with Type 2 Diabetes Mellitus and Laboratory Characteristics: A Preliminary Case-Control Study

Type 2 diabetes mellitus (T2DM) is a complex heterogeneous disease resulting from the environment and genetic interactions. Lately, genetic association studies have shown that polymorphisms in long noncoding RNAs (lncRNAs) are associated with T2DM susceptibility. This preliminary study is aimed at investigating if HOX transcript antisense RNA (HOTAIR) polymorphisms contribute to T2DM development. Five hundred clinically diagnosed T2DM cases and 500 healthy controls were recruited from the southeast Iranian population. Genomic DNA was isolated from nucleated blood cells and genotyped for MspI (C/T) (rs920778) and AluI (A/G) (rs4759314) polymorphisms using the PCR-RFLP technique. For genotyping rs12826786 C/T and rs1899663 G/T variants, ARMS-PCR method was applied. Our findings indicated that HOTAIR rs920778 C/T, rs12826786 C/T, and rs4759314 A/G polymorphisms have a significant positive association with T2DM, while a negative association was observed between rs1899663 G/T T2DM susceptibility. Significant associations were also observed between rs920778 C/T and HDL-C as well as s4759314 A/G and both FBS and LDL-C in T2DM patients. Haplotype analysis indicated that the CGCG, CTTG, TGTA, and TTTG haplotypes of rs920778/rs1899663/rs12826786/rs4759314 significantly enhanced T2DM risk by 1.47, 1.96, 2.81, and 4.80 folds, respectively. No strong linkage disequilibrium was found between the four HOTAIR SNPs. We firstly reported that HOTAIR rs1899663 G/T, rs12826786 C/T, rs4759314 A/G, and rs920778 C/T polymorphisms might influence T2DM susceptibility by modulating different signaling pathways and could be regarded as potential prognostic markers in T2DM patients.

Prevalence of Latent Autoimmune Diabetes in Adult Based on the Presence of GAD 65 Antibodies in North-Eastern Uttar Pradesh, India

Objective The objective of this paper was (1) to study the prevalence of latent autoimmune diabetes in adult (LADA) in the region of north-eastern Uttar Pradesh, India, based on the positivity for glutamic acid decarboxylase 65 (GAD65) antibodies and (2) to compare the glycemic profile between GAD65-positive and GAD65-negative subjects.

Materials and Methods The subjects were of more than 30 years of age, with either recently diagnosed pre-diabetes/diabetes presenting with the hemoglobin A1c (HbA1c) level of ≥5.7% or already diagnosed cases of type 2 diabetes mellitus (T2DM) who had no requirement of insulin therapy for at least 6 months from the time of their diagnosis. All the patients were natives of north-eastern Uttar Pradesh. The GAD65 test was done by the enzyme-linked immunosorbent assay. Further, the glycemic status of GAD-positive and GAD-negative subjects were compared on the basis of fasting blood sugar (FBS), fasting insulin (FI), and homeostatic model assessment for insulin resistance (HOMA-IR).

Statistical Analysis The “unpaired t-test” was used to compare and assess the significance of differences between the glycemic profile of GAD65-positive and GAD65-negative subjects using the GraphPad Prism Scientific Software, San Diego, CA, United States. The p-value of <0.05 was considered to be significant.

Results A total of 77 patients were included in the study, with the age group ranging from 30 to 75 years (47.81 ± 12.9 years) with the male–female ratio of 1:2.6. The prevalence of LADA was found to be 51.95%. On comparing GAD65-positive and GAD65-negative groups, a higher value of HbA1c levels and FBS were found in the former, whereas FI and HOMA-IR were found to be higher in the latter. On testing for significance of difference, only FI and HbA1c values were significant (p-value <0.0001).

Conclusion LADA can no longer be considered a rare type of diabetes mellitus, with the present study showing a high prevalence of LADA in this north eastern region of Uttar Pradesh. Identification of adult-onset diabetics accurately as LADA or true T2DM is very crucial for the appropriate treatment, as LADA patients require insulin inevitably and much earlier than true T2DM patients, who can be managed mostly on oral hypoglycemic agents with seldom requirement of insulin.

Stem Cell-Derived β Cells: A Versatile Research Platform to Interrogate the Genetic Basis of β Cell Dysfunction

Pancreatic β cell dysfunction is a central component of diabetes progression. During the last decades, the genetic basis of several monogenic forms of diabetes has been recognized. Genome-wide association studies (GWAS) have also facilitated the identification of common genetic variants associated with an increased risk of diabetes. These studies highlight the importance of impaired β cell function in all forms of diabetes. However, how most of these risk variants confer disease risk, remains unanswered. Understanding the specific contribution of genetic variants and the precise role of their molecular effectors is the next step toward developing treatments that target β cell dysfunction in the era of personalized medicine. Protocols that allow derivation of β cells from pluripotent stem cells, represent a powerful research tool that allows modeling of human development and versatile experimental designs that can be used to shed some light on diabetes pathophysiology. This article reviews different models to study the genetic basis of β cell dysfunction, focusing on the recent advances made possible by stem cell applications in the field of diabetes research.

Characteristics of the Gut Microbiota and Metabolism in Patients With Latent Autoimmune Diabetes in Adults: A Case-Control Study

OBJECTIVE

Type 1 and type 2 diabetes are associated with gut dysbiosis. However, the relationship between the gut microbiota and latent autoimmune diabetes in adults (LADA), sharing clinical and metabolic features with classic type 1 and type 2 diabetes, remains unclear. Here, we used a multiomics approach to identify the characteristics of the gut microbiota and metabolic profiles in patients with LADA.

RESEARCH DESIGN AND METHODS

This age- and sex-matched case-control study included 30 patients with LADA, 31 patients with classic type 1 diabetes, 30 patients with type 2 diabetes, and 29 healthy individuals. The gut microbiota profiles were identified through the 16S rRNA gene, and fecal and serum metabolites were measured through untargeted liquid chromatography-mass spectrometry.

RESULTS

Patients with LADA had a significantly different structure and composition of the gut microbiota and their metabolites as well as a severe deficiency of short-chain fatty acid-producing bacteria. The gut microbiota structure of the patients with LADA was more similar to that of patients with type 1 diabetes who were positive for GAD antibody. We identified seven serum metabolite modules and eight fecal metabolite modules that differed between the LADA group and the other groups.

CONCLUSIONS

The characteristic gut microbiota and related metabolites of patients with LADA are associated with autoantibodies, glucose metabolism, islet function, and inflammatory factors, which may contribute to the pathogenesis of LADA. Future longitudinal studies should explore whether modulating the gut microbiota and related metabolites can alter the natural course of autoimmune diabetes in the quest for new therapeutics.

Genome Editing Human Pluripotent Stem Cells to Model β-Cell Disease and Unmask Novel Genetic Modifiers

A mechanistic understanding of the genetic basis of complex diseases such as diabetes mellitus remain elusive due in large part to the activity of genetic disease modifiers that impact the penetrance and/or presentation of disease phenotypes. In the face of such complexity, rare forms of diabetes that result from single-gene mutations (monogenic diabetes) can be used to model the contribution of individual genetic factors to pancreatic β-cell dysfunction and the breakdown of glucose homeostasis. Here we review the contribution of protein coding and non-protein coding genetic disease modifiers to the pathogenesis of diabetes subtypes, as well as how recent technological advances in the generation, differentiation, and genome editing of human pluripotent stem cells (hPSC) enable the development of cell-based disease models. Finally, we describe a disease modifier discovery platform that utilizes these technologies to identify novel genetic modifiers using induced pluripotent stem cells (iPSC) derived from patients with monogenic diabetes caused by heterozygous mutations.

Latent Autoimmune Diabetes of Adults (LADA) Is Likely to Represent a Mixed Population of Autoimmune (Type 1) and Nonautoimmune (Type 2) Diabetes

Latent autoimmune diabetes of adults (LADA) is typically defined as a new diabetes diagnosis after 35 years of age, presenting with clinical features of type 2 diabetes, in whom a type 1 diabetes-associated islet autoantibody is detected. Identifying autoimmune diabetes is important since the prognosis and optimal therapy differ. However, the existing LADA definition identifies a group with clinical and genetic features intermediate between typical type 1 and type 2 diabetes. It is unclear whether this is due to 1) true autoimmune diabetes with a milder phenotype at older onset ages that initially appears similar to type 2 diabetes but later requires insulin, 2) a disease syndrome where the pathophysiologies of type 1 and type 2 diabetes are both present in each patient, or 3) a heterogeneous group resulting from difficulties in classification. Herein, we suggest that difficulties in classification are a major component resulting from defining LADA using a diagnostic test-islet autoantibody measurement-with imperfect specificity applied in low-prevalence populations. This yields a heterogeneous group of true positives (autoimmune type 1 diabetes) and false positives (nonautoimmune type 2 diabetes). For clinicians, this means that islet autoantibody testing should not be undertaken in patients who do not have clinical features suggestive of autoimmune diabetes: in an adult without clinical features of type 1 diabetes, it is likely that a single positive antibody will represent a false-positive result. This is in contrast to patients with features suggestive of type 1 diabetes, where false-positive results will be rare. For researchers, this means that current definitions of LADA are not appropriate for the study of autoimmune diabetes in later life. Approaches that increase test specificity, or prior likelihood of autoimmune diabetes, are needed to avoid inclusion of participants who have nonautoimmune (type 2) diabetes. Improved classification will allow improved assignment of prognosis and therapy as well as an improved cohort in which to analyze and better understand the detailed pathophysiological components acting at onset and during disease progression in late-onset autoimmune diabetes.

The role of transcription factor 7-like 2 in metabolic disorders

Transcription factor 7-like 2 (TCF7L2), a member of the T cell factor/lymphoid enhancer factor family, generally forms a complex with β-catenin to regulate the downstream target genes as an effector of the canonical Wnt signalling pathway. TCF7L2 plays a vital role in various biological processes and functions in many organs and tissues, including the liver, islet and adipose tissues. Further, TCF7L2 down-regulates hepatic gluconeogenesis and promotes lipid accumulation. In islets, TCF7L2 not only affects the insulin secretion of the β-cells but also has an impact on other cells. In addition, TCF7L2 influences adipogenesis in adipose tissues. Thus, an out-of-control TCF7L2 expression can result in metabolic disorders. The TCF7L2 gene is composed of 17 exons, generating 13 different transcripts, and has many single-nucleotide polymorphisms (SNPs). The discovery that these SNPs have an impact on the risk of type 2 diabetes (T2D) has attracted thorough investigations in the study of TCF7L2. Apart from T2D, TCF7L2 SNPs are also associated with type 1, posttransplant and other types of diabetes. Furthermore, TCF7L2 variants affect the progression of other disorders, such as obesity, cancers, metabolic syndrome and heart diseases. Finally, the interaction between TCF7L2 variants and diet also needs to be investigated.

Familial autoimmunity in neurological patients with GAD65 antibodies: an interview-based study

The common co-occurrence of autoimmune systemic diseases in patients with neurological disorders and antibodies against glutamic acid decarboxylase 65 (GAD65) suggests a shared genetic predisposition to these disorders. However, the nature and frequency of familial aggregation of autoimmune diseases, which might also support this hypothesis, have been poorly investigated. Herein, an exploratory, interview-based study was conducted with the aim of describing the autoimmune diseases displayed by the relatives of GAD65 neurological patients, their frequency, kinship, and potential patterns of inheritance. Patients were enrolled only if they had GAD65 antibodies in the cerebrospinal fluid and typical clinical phenotypes associated with such antibodies (stiff-person syndrome, cerebellar ataxia, limbic encephalitis, or temporal lobe epilepsy). A total of 65 patients were included in the study, and 44/65 (67.7%) reported family history of autoimmunity, including first-degree relatives in 36/65 (55.4%); the sibling recurrence risk (λ_S) was 5.5, reinforcing the hypothesis of an underlying strong genetic predisposition. Most pedigrees with familial autoimmunity (38/44, 86.4%) showed multiple autoimmune diseases, all but 2 of them with diabetes mellitus or autoimmune thyroid disease, therefore resembling autoimmune polyendocrine syndromes. Inheritance patterns were diverse, possibly autosomal dominant in 17/44 (38.6%) pedigrees or autosomal recessive in 5/44 (11.4%), and un-defined or complex in 24/44 (54.5%). However, a total of 21/65 (32.3%) patients had no identified family history of autoimmunity. In conclusion, these results suggest a variable and heterogeneous genetic predisposition to GAD65 neurological disorders, possibly involving multiple loci and modes of inheritance with different contribution in each family.

Adult-onset autoimmune diabetes: comparative analysis of classical and latent presentation

INTRODUCTION

Adult-onset autoimmune diabetes (AID) has two different phenotypes: classic type 1 diabetes mellitus (T1DM), with insulin requirement just after diagnosis, and latent autoimmune diabetes in adults (LADA). The purpose of this study is to characterize patients with AID followed on a tertiary centre, comparing classic T1DM and LADA.

METHODS

We collected data from patients with diabetes and positive islet autoantibodies, aged 30 years old and over at diagnosis. Patients who started insulin in the first 6 months were classified as T1DM and patients with no insulin requirements in the first 6 months were classified as LADA. Data regarding clinical presentation, autoantibodies, A1C and C-peptide at diagnosis, pharmacologic treatment and complications were analysed.

RESULTS

We included 92 patients, 46 with classic T1DM and 46 with LADA. The percentage of females was 50% in T1DM group and 52.1% in LADA group. The median age at diagnosis was 38 years (IQR-15) for T1DM and 42 years (IQR-15) for LADA (p = 0.057). The median time between diagnosis of diabetes and diagnosis of autoimmune aetiology was 0 months in T1DM group and 60 months in LADA group (p < 0.001). The mean BMI at diagnosis was 24.1 kg/m² in T1DM group and 26.1 kg/m² in LADA group (p = 0.042). In T1DM group, 67.4% of the patients had more than one positive autoantibody, comparing to 41.3% of LADA patients (p = 0.012). There was no statistical difference in what concerns to title of GAD autoantibodies, A1C and C-peptide at diagnosis of autoimmune aetiology. The presence of symptoms at diagnosis was associated with T1DM group (p < 0.001). The median daily insulin dose was 40 IU for T1DM (0.58 IU/kg) and 33.5 IU for LADA (0.57 IU/kg), with no statistical difference. LADA patients were more often under non-insulin antidiabetic drugs (p = 0.001). At 10 years follow up, 21.1% of T1DM patients and 63.3% of LADA patients had microvascular complications (p = 0.004). Diabetic nephropathy was present in 23.5% of T1DM patients and 53.3% of LADA patients (p = 0.047). At the last evaluation, 55.6% of T1DM and 82.6% of LADA patients had metabolic syndrome and this difference was independent of diabetes duration.

CONCLUSION

Patients with classic T1DM presented more often with symptoms, lower BMI and higher number of autoantibodies, which may be related to a more aggressive autoimmune process. Patients with LADA developed more frequently microvascular complications for the same disease duration, namely diabetic nephropathy, and had more often metabolic syndrome.

Physical Activity, Genetic Susceptibility, and the Risk of Latent Autoimmune Diabetes in Adults and Type 2 Diabetes

PURPOSE

Physical activity (PA) has been linked to a reduced risk of type 2 diabetes by reducing weight and improving insulin sensitivity. We investigated whether PA is associated with a lower incidence of latent autoimmune diabetes in adults (LADA) and whether the association is modified by genotypes of human leukocyte antigen (HLA), transcription factor 7-like 2 (TCF7L2)-rs7903146, or the fat mass and obesity-associated gene, FTO-rs9939609.

METHODS

We combined data from a Swedish case-control study and a Norwegian prospective study including 621 incident cases of LADA and 3596 cases of type 2 diabetes. We estimated adjusted pooled relative risks (RRs) and 95% CI of diabetes in relation to high (≥ 30 minutes of moderate activity 3 times/week) self-reported leisure time PA, compared to sedentariness.

RESULTS

High PA was associated with a reduced risk of LADA (RR 0.61; CI, 0.43-0.86), which was attenuated after adjustment for body mass index (BMI) (RR 0.90; CI, 0.63-1.29). The reduced risk applied only to noncarriers of HLA-DQB1 and -DRB1 (RR 0.49; CI, 0.33-0.72), TCF7L2 (RR 0.62; CI, 0.45-0.87), and FTO (RR 0.51; CI, 0.32-0.79) risk genotypes. Adjustment for BMI attenuated but did not eliminate these associations. For type 2 diabetes, there was an inverse association with PA (RR 0.49; CI, 0.42-0.56), irrespective of genotype.

MAIN CONCLUSIONS

Our findings indicate that high PA is associated with a reduced risk of LADA in individuals without genetic susceptibility.

Diabetes and Psoriasis: Different Sides of the Same Prism

Diabetes and psoriasis are prevalent conditions with a spectrum of serious adverse outcomes. Both diseases are common comorbidities for each other, and diabetes is considered as a risk factor for psoriasis and vice versa. However, it is our contention that these diseases are not merely comorbidities of each other but rather share common underlying pathophysiologies (ie, genes and epigenetic changes, inflammation, abnormal environment, and insulin resistance) that drive disease. As such, they can be viewed as facets of the same prism. Genes can cause or permit susceptibility to damage from abnormal external and internal environmental factors, inflammation, and insulin resistance which can also drive epigenetic changes. These co-existing mechanisms act in a vicious cycle over time to potentiate cell and tissue damage to ultimately drive disease. Viewing diabetes and psoriasis through the same prism suggests potential for therapies that could be used to treat both conditions. Although additional controlled trials and research are warranted, we believe that our understanding of the overlapping pathophysiologies continues to grow, so too will our therapeutic options.

Type 1 diabetes in Africa: an immunogenetic study in the Amhara of North-West Ethiopia

AIMS/HYPOTHESIS

We aimed to characterise the immunogenic background of insulin-dependent diabetes in a resource-poor rural African community. The study was initiated because reports of low autoantibody prevalence and phenotypic differences from European-origin cases with type 1 diabetes have raised doubts as to the role of autoimmunity in this and similar populations.

METHODS

A study of consecutive, unselected cases of recently diagnosed, insulin-dependent diabetes (n = 236, ≤35 years) and control participants (n = 200) was carried out in the ethnic Amhara of rural North-West Ethiopia. We assessed their demographic and socioeconomic characteristics, and measured non-fasting C-peptide, diabetes-associated autoantibodies and HLA-DRB1 alleles. Leveraging genome-wide genotyping, we performed both a principal component analysis and, given the relatively modest sample size, a provisional genome-wide association study. Type 1 diabetes genetic risk scores were calculated to compare their genetic background with known European type 1 diabetes determinants.

RESULTS

Patients presented with stunted growth and low BMI, and were insulin sensitive; only 15.3% had diabetes onset at ≤15 years. C-peptide levels were low but not absent. With clinical diabetes onset at ≤15, 16-25 and 26-35 years, 86.1%, 59.7% and 50.0% were autoantibody positive, respectively. Most had autoantibodies to GAD (GADA) as a single antibody; the prevalence of positivity for autoantibodies to IA-2 (IA-2A) and ZnT8 (ZnT8A) was low in all age groups. Principal component analysis showed that the Amhara genomes were distinct from modern European and other African genomes. HLA-DRB1*03:01 (p = 0.0014) and HLA-DRB1*04 (p = 0.0001) were positively associated with this form of diabetes, while HLA-DRB1*15 was protective (p < 0.0001). The mean type 1 diabetes genetic risk score (derived from European data) was higher in patients than control participants (p = 1.60 × 10-7). Interestingly, despite the modest sample size, autoantibody-positive patients revealed evidence of association with SNPs in the well-characterised MHC region, already known to explain half of type 1 diabetes heritability in Europeans.

CONCLUSIONS/INTERPRETATION

The majority of patients with insulin-dependent diabetes in rural North-West Ethiopia have the immunogenetic characteristics of autoimmune type 1 diabetes. Phenotypic differences between type 1 diabetes in rural North-West Ethiopia and the industrialised world remain unexplained.

An Exploratory Association Analysis of the Insulin Gene Region With Diabetes Mellitus in Two Dog Breeds

Samoyeds and Australian Terriers are the 2 dog breeds at highest risk (>10-fold) for diabetes mellitus in the United States. It is unknown if the insulin (INS) gene is involved in the pathophysiology of diabetes in Samoyeds and Australian Terriers. It was hypothesized that the INS gene region provides a common genetic causality for diabetes in Samoyeds and Australian Terriers. We conducted a 2-stage genetic association study involving both breeds. In the discovery stage (Stage 1), Samoyeds with and without diabetes were compared in the frequencies of 447 tagging single-nucleotide polymorphisms (SNPs) within 2.5 megabases (Mb) up- and downstream of the INS gene on the Illumina CanineHD BeadChip. SNPs yielding a P-value < 0.005 were selected for further follow-up. In the validation stage (Stage 2), Australian Terriers with and without diabetes were compared in the SNPs genotyped by the Affymetrix GeneChip Canine Genome 2.0 Array and within 1 Mb up- and downstream of the selected SNPs from Stage 1. Two SNPs that were in high linkage disequilibrium (LD, r2 = 0.7) were selected from Stage 1. In Stage 2, among the 76 SNPs examined, 5 were significantly associated with diabetes after Bonferroni's correction for multiple comparisons. Three of these 5 SNPs were in complete LD (r2 = 1 for all associations) and the 2 remaining SNPs were in moderate LD (r2 = 0.4). In conclusion, an association between the INS gene region and diabetes was suggested in 2 dog breeds of different clades. This region could have importance in diabetes in other breeds or in canine diabetes at large.

New Insights into the Genetics of Latent Autoimmune Diabetes in Adults

PURPOSE OF REVIEW

Diabetes is a spectrum of clinical manifestations, including latent autoimmune diabetes in adults (LADA). However, it has been questioned whether LADA exists or simply is a group of misclassified type 1 diabetes (T1D) and type 2 diabetes (T2D) patients. This review will provide an updated overview of the genetics of LADA, highlight what genetics tell us about LADA as a diabetes subtype, and point to future directions in the study of LADA.

RECENT FINDINGS

Recent studies have verified the genetic overlap between LADA and both T1D and T2D and have contributed identification of a novel LADA-specific locus, namely, PFKFB3, and subtype-specific signatures in the HLA region. Genetic risk scores comprising T1D-risk variants have been shown to be a promising tool for discriminating diabetes subtypes and identifying patients rapidly progressing to insulin dependence. Genetic data support the existence of LADA, but further studies are needed to fully determine the place of LADA in the diabetes spectrum.

Consumption of red meat, genetic susceptibility, and risk of LADA and type 2 diabetes

Purpose

Red meat consumption is positively associated with type 1 (T1D) and type 2 (T2D) diabetes. We investigated if red meat consumption increases the risk of latent autoimmune diabetes in adults (LADA) and T2D, and potential interaction with family history of diabetes (FHD), HLA and TCF7L2 genotypes.

Methods

Analyses were based on Swedish case–control data comprising incident cases of LADA (n = 465) and T2D (n = 1528) with matched, population-based controls (n = 1789; n = 1553 in genetic analyses). Multivariable-adjusted ORs in relation to self-reported processed and unprocessed red meat intake were estimated by conditional logistic regression models. Attributable proportion (AP) due to interaction was used to assess departure from additivity of effects.

Results

Consumption of processed red meat was associated with increased risk of LADA (per one servings/day OR 1.27, 95% CI 1.07–1.52), whereas no association was observed for unprocessed red meat. For T2D, there was no association with red meat intake once BMI was taken into account. The combination of high (> 0.3 servings/day vs. less) processed red meat intake and high-risk HLA-DQB1 and -DRB1 genotypes yielded OR 8.05 (95% CI 4.86–13.34) for LADA, with indications of significant interaction (AP 0.53, 95% CI 0.32–0.73). Results were similar for the combination of FHD-T1D and processed red meat. No interaction between processed red meat intake and FHD-T2D or risk variants of TCF7L2 was seen in relation to LADA or T2D.

Conclusion

Consumption of processed but not unprocessed red meat may increase the risk of LADA, especially in individuals with FHD-T1D or high-risk HLA genotypes.

Electronic supplementary material

The online version of this article (10.1007/s00394-020-02285-2) contains supplementary material, which is available to authorized users.

Pancreas Pathology of Latent Autoimmune Diabetes in Adults (LADA) in Patients and in a LADA Rat Model Compared With Type 1 Diabetes

Approximately 10% of patients with type 2 diabetes suffer from latent autoimmune diabetes in adults (LADA). This study provides a systematic assessment of the pathology of the endocrine pancreas of patients with LADA and for comparison in a first rat model mimicking the characteristics of patients with LADA. Islets in human and rat pancreases were analyzed by immunohistochemistry for immune cell infiltrate composition, by in situ RT-PCR and quantitative real-time PCR of laser microdissected islets for gene expression of proinflammatory cytokines, the proliferation marker proliferating cell nuclear antigen (PCNA), the anti-inflammatory cytokine interleukin (IL) 10, and the apoptosis markers caspase 3 and TUNEL as well as insulin. Human and rat LADA pancreases showed differences in areas of the pancreas with respect to immune cell infiltration and a changed ratio between the number of macrophages and CD8 T cells toward macrophages in the islet infiltrate. Gene expression analyses revealed a changed ratio due to an increase of IL-1β and a decrease of tumor necrosis factor-α. IL-10, PCNA, and insulin expression were increased in the LADA situation, whereas caspase 3 gene expression was reduced. The analyses into the underlying pathology in human as well as rat LADA pancreases provided identical results, allowing the conclusion that LADA is a milder form of autoimmune diabetes in patients of an advanced age.

Altered peripheral nerve structure and function in latent autoimmune diabetes in adults

AIM

The present study was undertaken to investigate mechanisms of peripheral nerve dysfunction in latent autoimmune diabetes in adults (LADA).

MATERIALS AND METHODS

Participants with LADA (n = 15) underwent median nerve ultrasonography and nerve excitability to examine axonal structure and function, in comparison to cohorts of type 1 diabetes (n = 15), type 2 diabetes (n = 23) and healthy controls (n = 26). The LADA group was matched for diabetes duration, glycaemic control, and neuropathy severity with the type 1 and type 2 diabetes groups. A validated mathematical model of the human axon was utilized to investigate the pathophysiological basis of nerve dysfunction.

RESULTS

The most severe changes in nerve structure and function were noted in the LADA group. The LADA cohort demonstrated a significant increase in nerve cross-sectional area compared to type 1 participants and controls. Compared to type 1 and 2 diabetes, measures of threshold electrotonus, which assesses nodal and internodal conductances, were significantly worse in LADA in response to both depolarising currents and hyperpolarising currents. In the recovery cycle, participants with LADA had a significant increase in the relative refractory period. Mathematical modelling of excitability recordings indicated the basis of nerve dysfunction in LADA was different to type 1 and 2 diabetes.

CONCLUSIONS

Participants with LADA exhibited more severe changes in nerve function and different underlying pathophysiological mechanisms compared to participants with type 1 or 2 diabetes. Intensive management of risk factors to delay the progression of neuropathy in LADA may be required.

Autoimmunity plays a role in the onset of diabetes after 40 years of age

AIMS/HYPOTHESIS

Type 1 and type 2 diabetes differ with respect to pathophysiological factors such as beta cell function, insulin resistance and phenotypic appearance, but there may be overlap between the two forms of diabetes. However, there are relatively few prospective studies that have characterised the relationship between autoimmunity and incident diabetes. We investigated associations of antibodies against the 65 kDa isoform of GAD (GAD65) with type 1 diabetes and type 2 diabetes genetic risk scores and incident diabetes in adults in European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct, a case-cohort study nested in the EPIC cohort.

METHODS

GAD65 antibodies were analysed in EPIC participants (over 40 years of age and free of known diabetes at baseline) by radioligand binding assay in a random subcohort (n = 15,802) and in incident diabetes cases (n = 11,981). Type 1 diabetes and type 2 diabetes genetic risk scores were calculated. Associations between GAD65 antibodies and incident diabetes were estimated using Prentice-weighted Cox regression.

RESULTS

GAD65 antibody positivity at baseline was associated with development of diabetes during a median follow-up time of 10.9 years (HR for GAD65 antibody positive vs negative 1.78; 95% CI 1.43, 2.20) after adjustment for sex, centre, physical activity, smoking status and education. The genetic risk score for type 1 diabetes but not type 2 diabetes was associated with GAD65 antibody positivity in both the subcohort (OR per SD genetic risk 1.24; 95% CI 1.03, 1.50) and incident cases (OR 1.97; 95% CI 1.72, 2.26) after adjusting for age and sex. The risk of incident diabetes in those in the top tertile of the type 1 diabetes genetic risk score who were also GAD65 antibody positive was 3.23 (95% CI 2.10, 4.97) compared with all other individuals, suggesting that 1.8% of incident diabetes in adults was attributable to this combination of risk factors.

CONCLUSIONS/INTERPRETATION

Our study indicates that incident diabetes in adults has an element of autoimmune aetiology. Thus, there might be a reason to re-evaluate the present subclassification of diabetes in adulthood.

Genetic Discrimination Between LADA and Childhood-Onset Type 1 Diabetes Within the MHC

OBJECTIVE

The MHC region harbors the strongest loci for latent autoimmune diabetes in adults (LADA); however, the strength of association is likely attenuated compared with that for childhood-onset type 1 diabetes. In this study, we recapitulate independent effects in the MHC class I region in a population with type 1 diabetes and then determine whether such conditioning in LADA yields potential genetic discriminators between the two subtypes within this region.

RESEARCH DESIGN AND METHODS

Chromosome 6 was imputed using SNP2HLA, with conditional analysis performed in type 1 diabetes case subjects (n = 1,985) and control subjects (n = 2,219). The same approach was applied to a LADA cohort (n = 1,428) using population-based control subjects (n = 2,850) and in a separate replication cohort (656 type 1 diabetes case, 823 LADA case, and 3,218 control subjects).

RESULTS

The strongest associations in the MHC class II region (rs3957146, β [SE] = 1.44 [0.05]), as well as the independent effect of MHC class I genes, on type 1 diabetes risk, particularly HLA-B*39 (β [SE] = 1.36 [0.17]), were confirmed. The conditional analysis in LADA versus control subjects showed significant association in the MHC class II region (rs3957146, β [SE] = 1.14 [0.06]); however, we did not observe significant independent effects of MHC class I alleles in LADA.

CONCLUSIONS

In LADA, the independent effects of MHC class I observed in type 1 diabetes were not observed after conditioning on the leading MHC class II associations, suggesting that the MHC class I association may be a genetic discriminator between LADA and childhood-onset type 1 diabetes.

Monogenic Diabetes: Genetics and Relevance on Diabetes Mellitus Personalized Medicine

BACKGROUND

Diabetes mellitus (DM) is a complex disease with significant impression in today's world. Aside from the most common types recognized over the years, such as type 1 diabetes (T1DM) and type 2 diabetes (T2DM), recent studies have emphasized the crucial role of genetics in DM, allowing the distinction of monogenic diabetes.

METHODS

Authors did a literature search with the purpose of highlighting and clarifying the subtypes of monogenic diabetes, as well as the accredited genetic entities responsible for such phenotypes.

RESULTS

The following subtypes were included in this literature review: maturity-onset diabetes of the young (MODY), neonatal diabetes mellitus (NDM) and maternally inherited diabetes and deafness (MIDD). So far, 14 subtypes of MODY have been identified, while three subtypes have been identified in NDM - transient, permanent, and syndromic.

DISCUSSION

Despite being estimated to affect approximately 2% of all the T2DM patients in Europe, the exact prevalence of MODY is still unknown, accentuating the need for research focused on biomarkers. Consequently, due to its impact in the course of treatment, follow-up of associated complications, and genetic implications for siblings and offspring of affected individuals, it is imperative to diagnose the monogenic forms of DM accurately.

CONCLUSION

Currently, advances in the genetics field allowed the recognition of new DM subtypes, which until now, were considered slight variations of the typical forms. Thus, it is imperative to act in the close interaction between genetics and clinical manifestations, to facilitate diagnosis and individualize treatment.

Latent Autoimmune Diabetes in Adults: A Review of Clinically Relevant Issues

Latent autoimmune diabetes in adults (LADA) is still a poorly characterized entity. However, its prevalence may be higher than that of classical type 1 diabetes. Patients with LADA are often misclassified as type 2 diabetes. The underlying autoimmune process against β-cell has important consequences for the prognosis, comorbidities, treatment choices and even patient-reported outcomes with this diabetes subtype. However, there is still an important gap of knowledge in many areas of clinical relevance. We are herein focusing on the state of knowledge of relevant clinical issues than may help in the diagnosis and management of subjects with LADA.

Past, present and future of latent autoimmune diabetes in adults

Latent autoimmune diabetes in adults (LADA) is the most common form of autoimmune diabetes diagnosed in adults. Similar to type 1 diabetes, the prevalence of LADA is impacted by ethnicity and geography. LADA is characterized by β cell loss due to autoimmunity and insulin resistance and has highly heterogeneous clinical features, autoimmunity, and genetics in a glutamic acid decarboxylase antibody (GADA) titre-dependent manner, suggesting LADA is part of a continuum spectrum between type 1 and type 2 diabetes. Although LADA is the most frequent form of autoimmune diabetes diagnosed in adults, clinical trials involving LADA are scarce. Here we review the recent advancements in LADA epidemiology, clinical features, pathogenesis, and interventions. We also highlight the environmental factors that are thought to play an important role in addition to genetics in the pathogenesis of LADA. In the future, high-throughput molecular profiles might shed light on the nature of LADA among the wide spectrum of diabetes and offer new opportunities to identify novel LADA-specific biomarkers.

The Genetic Contribution to Type 1 Diabetes

PURPOSE OF REVIEW

To provide an updated summary of discoveries made to date resulting from genome-wide association study (GWAS) and sequencing studies, and to discuss the latest loci added to the growing repertoire of genetic signals predisposing to type 1 diabetes (T1D).

RECENT FINDINGS

Genetic studies have identified over 60 loci associated with T1D susceptibility. GWAS alone does not specifically inform on underlying mechanisms, but in combination with other sequencing and omics-data, advances are being made in our understanding of T1D genetic etiology and pathogenesis. Current knowledge indicates that genetic variation operating in both pancreatic β cells and in immune cells is central in mediating T1D risk. One of the main challenges is to determine how these recently discovered GWAS-implicated variants affect the expression and function of gene products. Once we understand the mechanism of action for disease-causing variants, we will be well placed to apply targeted genomic approaches to impede the premature activation of the immune system in an effort to ultimately prevent the onset of T1D.

Interaction Between Overweight and Genotypes of HLA, TCF7L2, and FTO in Relation to the Risk of Latent Autoimmune Diabetes in Adults and Type 2 Diabetes

OBJECTIVE

We investigated potential interactions between body mass index (BMI) and genotypes of human leukocyte antigen (HLA), TCF7L2-rs7903146, and FTO-rs9939609 in relation to the risk of latent autoimmune diabetes in adults (LADA) and type 2 diabetes.

METHODS

We pooled data from two population-based studies: (i) a Swedish study with incident cases of LADA [positive for glutamic acid decarboxylase autoantibodies (GADA); n = 394) and type 2 diabetes (negative for GADA; n = 1290) and matched controls without diabetes (n = 2656) and (ii) a prospective Norwegian study that included incident cases of LADA (n = 131) and type 2 diabetes (n = 1901) and 886,120 person-years of follow-up. Analyses were adjusted for age, sex, physical activity, and smoking. Interaction between overweight (BMI ≥ 25 kg/m2) and HLA/TCF7L2/FTO high-risk genotypes was assessed by attributable proportion due to interaction (AP).

RESULTS

The combination of overweight and high-risk genotypes of HLA, TCF7L2, and FTO was associated with pooled relative risk (RRpooled) of 7.59 (95% CI, 5.27 to 10.93), 2.65 (95% CI, 1.97 to 3.56), and 2.21 (95% CI, 1.60 to 3.07), respectively, for LADA, compared with normal-weight individuals with low/intermediate genetic risk. There was a significant interaction between overweight and HLA (AP, 0.29; 95% CI, 0.10 to 0.47), TCF7L2 (AP, 0.31; 95% CI, 0.09 to 0.52), and FTO (AP, 0.38; 95% CI, 0.15 to 0.61). The highest risk of LADA was seen in overweight individuals homozygous for the DR4 genotype [RR, 26.76 (95% CI, 15.42 to 46.43); AP, 0.58 (95% CI, 0.32 to 0.83) (Swedish data)]. Overweight and TCF7L2 also significantly interacted in relation to type 2 diabetes (AP, 0.26; 95% CI, 0.19 to 0.33), but no interaction was observed with high-risk genotypes of HLA or FTO.

CONCLUSIONS

Overweight interacts with HLA high-risk genotypes but also with genes associated with type 2 diabetes in the promotion of LADA.

HLA-DQB1 and HLA-DRB1 Variants Confer Susceptibility to Latent Autoimmune Diabetes in Adults: Relative Predispositional Effects among Allele Groups

Latent autoimmune diabetes in adults (LADA) was recently demonstrated to be the most frequent form of adult-onset autoimmune diabetes mellitus. Case–control studies have investigated the relationship between human leukocyte antigen (HLA)-DQB1 and HLA-DRB1 polymorphisms and LADA risk, but their conclusions are inconsistent. This study aimed to more precisely explore the correlation between these HLA gene variants and LADA development. Eight databases, including PubMed, Embase, and Medline, were systematically searched for relevant studies up to September 15, 2018. We performed this retrospective study using meta-analysis and relative predispositional effect (RPE) methods. The meta-analysis results indicated that DQB1*02 (odds ratio (OR) = 1.685, p_c < 0.005) and DQB1*06 (OR = 0.604, p_c = 0.010) have opposite effects on susceptibility to LADA, while a significant decrease in LADA risk caused by DQB1*05 (OR = 0.764, p_c = 0.100) disappeared upon Bonferroni correction. The RPE method confirmed the roles of DQB1*02 (χ² = 46.475, p < 0.001) and DQB1*06 (χ² = 17.883, p < 0.001) and further suggested protective effects of DQB1*05 (χ² = 16.496, p < 0.001). Additionally, the meta-analysis results showed that DRB1*03 (OR = 2.685, p_c < 0.013), DRB1*04 (OR = 1.954, p_c < 0.013), and DRB1*09 (OR = 1.346, p_c < 0.013) are associated with increased LADA risk, while DRB1*12 (OR = 0.600, p_c < 0.013) and DRB1*13 (OR = 0.583, p_c < 0.013) carriers have a decreased risk of developing LADA. Furthermore, the RPE method revealed that DRB1*03 (χ² = 98.754, p < 0.001), DRB1*04 (χ² = 94.685, p < 0.001), DRB1*09 (χ² = 40.489, p < 0.001), DRB1*01 (χ² = 12.181, p < 0.001), DRB1*07 (χ² = 10.882, p = 0.001), and DRB1*08 (χ² = 5.000, p = 0.025) play protective roles against LADA. LADA showed a close relationship with genetic polymorphisms of HLA-DQB1 and WHLA-DRB1, which could contribute to a better understanding of disease pathogenesis and the identification of predisposing loci in the diagnosis and treatment of LADA.

Persistent C-peptide secretion in Type 1 diabetes and its relationship to the genetic architecture of diabetes

BACKGROUND

The objective of this cross-sectional study was to explore the relationship of detectable C-peptide secretion in type 1 diabetes to clinical features and to the genetic architecture of diabetes.

METHODS

C-peptide was measured in an untimed serum sample in the SDRNT1BIO cohort of 6076 Scottish people with clinically diagnosed type 1 diabetes or latent autoimmune diabetes of adulthood. Risk scores at loci previously associated with type 1 and type 2 diabetes were calculated from publicly available summary statistics.

RESULTS

Prevalence of detectable C-peptide varied from 19% in those with onset before age 15 and duration greater than 15 years to 92% in those with onset after age 35 and duration less than 5 years. Twenty-nine percent of variance in C-peptide levels was accounted for by associations with male gender, late age at onset and short duration. The SNP heritability of residual C-peptide secretion adjusted for gender, age at onset and duration was estimated as 26%. Genotypic risk score for type 1 diabetes was inversely associated with detectable C-peptide secretion: the most strongly associated loci were the HLA and INS gene regions. A risk score for type 1 diabetes based on the HLA DR3 and DQ8-DR4 serotypes was strongly associated with early age at onset and inversely associated with C-peptide persistence. For C-peptide but not age at onset, there were strong associations with risk scores for type 1 and type 2 diabetes that were based on SNPs in the HLA region but not accounted for by HLA serotype.

CONCLUSIONS

Persistence of C-peptide secretion varies widely in people clinically diagnosed as type 1 diabetes. C-peptide persistence is influenced by variants in the HLA region that are different from those determining risk of early-onset type 1 diabetes. Known risk loci for diabetes account for only a small proportion of the genetic effects on C-peptide persistence.

Modeling Monogenic Diabetes using Human ESCs Reveals Developmental and Metabolic Deficiencies Caused by Mutations in HNF1A

Human monogenic diabetes, caused by mutations in genes involved in beta cell development and function, has been a challenge to study because multiple mouse models have not fully recapitulated the human disease. Here, we use genome edited human embryonic stem cells to understand the most common form of monogenic diabetes, MODY3, caused by mutations in the transcription factor HNF1A. We found that HNF1A is necessary to repress an alpha cell gene expression signature, maintain endocrine cell function, and regulate cellular metabolism. In addition, we identified the human-specific long non-coding RNA, LINKA, as an HNF1A target necessary for normal mitochondrial respiration. These findings provide a possible explanation for the species difference in disease phenotypes observed with HNF1A mutations and offer mechanistic insights into how the HNF1A gene may also influence type 2 diabetes.

Association of common type 1 and type 2 diabetes gene variants with latent autoimmune diabetes in adults: A meta-analysis

BACKGROUND

The aim of this meta-analysis was to determine the association of common type 1 diabetes (T1D) and type 2 diabetes (T2D) gene variants (protein tyrosine phosphatase non-receptor 22 [PTPN22] rs2476601C/T, insulin [INS] rs689A/T and transcription factor 7-like 2 [TCF7L2] rs7903146C/T) with latent autoimmune diabetes in adults (LADA).

METHODS

A systematic search of electronic databases was conducted up to 2017 and data from 16 independent case-control studies for three gene variants were pooled. The pooled allele and genotype frequencies for each T1D and T2D gene variant were used to calculate odds ratios (ORs) with 95% confidence intervals (CIs) to assess the strength of the association. Heterogeneity tests and evaluation of publication bias were performed for all studies.

RESULTS

In all, 8869 cases and 20 829 controls pooled from 16 case-control studies were included in the analysis. For rs2476601, a significant association was found for homozygote TT (OR 2.67; 95% CI 1.92-3.70; P < 0.0001), heterozygote CT (OR 1.61; 95% CI 1.44-1.79; P < 0.0001), and the T allele (OR 1.62; 95% CI 1.48-1.78; P < 0.0001). Overall, a significant inverse association was observed for rs689 in the TT genotype (OR 0.43; 95% CI 0.30-0.64; P < 0.0001), AT genotype (OR 0.53; 95% CI 0.45-0.62; P < 0.0001), and T allele (OR 0.61; 95% CI 0.52-0.71; P < 0.0001). For the rs7903146 polymorphism, the T allele (OR 1.19; 95% CI 1.00-1.40; P = 0.04) may be associated with the risk of LADA.

CONCLUSION

The rs2476601C/T, rs689A/T, and rs7903146C/T polymorphisms were found to be associated with the risk of LADA, thereby indicating that, genetically, LADA could be an admixture of both T1D and T2D.

Identification of autoimmune type 1 diabetes and multiple organ-specific autoantibodies in adult-onset non-insulin-requiring diabetes in China: A population-based multicentre nationwide survey

AIMS

To investigate the prevalence of adult-onset autoimmune diabetes (ADM) and predisposition to autoimmune diseases by quantifying serum organ-specific autoantibodies in people with phenotype of type 2 diabetes (T2D).

MATERIALS AND METHODS

We included a nationally representative sample of 46 239 adults aged ≥20 years from 14 provinces, of whom 4671 had diabetes, plus 1000 control subjects with normal glucose tolerance (NGT). Participants were screened centrally for autoantibodies to glutamic acid decarboxylase (GAD), islet antigen 2 (IA2) and zinc transporter isoform-8 (Znt8) and were defined as having ADM where positive for these antibodies. We then assayed thyroid peroxidase (TPO), tissue transglutaminase (tTG) and 21-hydroxylase (21-OH) autoantibodies in randomly selected participants with ADM and in age-matched, sex-matched and non-ADM controls with T2D plus controls with NGT.

RESULTS

Post-normalization, the standardized prevalence rate of ADM was 6.0% (95% confidence interval [CI] 5.3-6.8) in initially non-insulin-requiring participants with ADM, corresponding to six million adults in China, in whom adjusted antibody positivity was: TPO autoantibodies 16.3% (95% CI 10.8-21.8), tTG autoantibodies 2.1% (95% CI 0.0-4.2), and 21-OH autoantibodies 1.8% (95% CI -0.2 to 3.8). Those participants with ADM who were GAD autoantibody-positive had high risk of TPO autoantibody positivity (odds ratio [OR] 2.39, P = 0.0031) and tTG autoantibody positivity (OR 6.98, P = 0.027), while those positive for IA2 autoantibodies had a high risk of tTG autoantibody positivity (OR 19.05, P = 0.001).

CONCLUSIONS

A proportion of people with phenotype of T2D in China have ADM, with diabetes-associated autoantibodies, and may be at risk of developing other organ-specific autoimmune diseases; therefore, it may be clinically relevant to consider screening such Chinese populations.

Etiology and Pathogenesis of Latent Autoimmune Diabetes in Adults (LADA) Compared to Type 2 Diabetes

As the heterogeneity of diabetes is becoming increasingly clear, opportunities arise for more accurate assessment of factors influencing disease onset, which may lead to more efficient primary prevention. LADA - latent autoimmune diabetes in adults - is a common, hybrid form of diabetes with features of both type 1 and type 2 diabetes. This review aims to summarize current knowledge on the pathophysiological and etiological overlap and differences between LADA and type 2 diabetes, discuss similarities between LADA and type 1 diabetes and point at future research needs. Studies conducted to date show a clear genetic overlap between LADA and type 1 diabetes with a high risk conferred by variants in the human leukocyte antigen (HLA) region. In contrast, data from the limited number of studies on lifestyle factors available indicate that LADA may share several environmental risk factors with type 2 diabetes including overweight, physical inactivity, alcohol consumption (protective) and smoking. These factors are known to influence insulin sensitivity, suggesting that insulin resistance, in addition to insulin deficiency due to autoimmune destruction of the beta cells, may play a key role in the pathogenesis of LADA. Moreover, this implies that onset of LADA, similar to type 2 diabetes, to some extent could be prevented or postponed by lifestyle modification such as weight reduction and increased physical activity. The preventive potential of LADA is an important topic to elucidate in future studies, preferably intervention studies.

Tetraspanin 7 autoantibodies predict progressive decline of beta cell function in individuals with LADA

AIMS/HYPOTHESIS

The aim of this work was to investigate whether tetraspanin 7 autoantibodies (TSPAN7A) are valuable in predicting poor beta cell function in individuals with latent autoimmune diabetes in adults (LADA).

METHODS

The cross-sectional study involved participants with LADA (n = 173), type 1 diabetes (n = 158), type 2 diabetes (n = 204) and healthy control participants (n = 170). The longitudinal study involved 53 participants with LADA, with a 3-year follow-up. In both cohorts, TSPAN7A in the sera were measured by a luciferase immunoprecipitation system assay, and physical and clinical characteristics were recorded.

RESULTS

The prevalence of TSPAN7A in LADA, type 1 diabetes, type 2 diabetes and healthy control participants was 21.4% (37/173), 26% (41/158), 0.5% (1/204) and 1.2% (2/170), respectively. Importantly, measurement of TSPAN7A significantly increased the number of individuals with LADA found to be positive for multiple antibodies (32.4% vs 22%; p < 0.001). Further logistic regression analysis demonstrated that positivity for TSPAN7A (OR 2.87, p = 0.034), disease duration (OR 1.83, p = 0.019) and GAD antibody titre (OR 2.67, p = 0.009) were risk factors for beta cell function in LADA, while BMI (OR 0.34, p = 0.001) was a protective factor. In the prospective study in individuals with LADA, the median annual decrease in rates of fasting C-peptide and 2 h postprandial C-peptide in individuals who were positive for TSPAN7A was significantly higher when compared with the decrease in those who were negative for TSPAN7A (34.6% vs 7.9%, p = 0.043 and 33.2% vs 11%, p = 0.041, respectively).

CONCLUSIONS/INTERPRETATION

TSPAN7A are valid islet autoantibodies for use in East Asian populations with autoimmune diabetes and can discriminate individuals with LADA who have lower beta cell function after disease progression.

Slowly Progressive Type 1 Diabetes Mellitus: Current Knowledge And Future Perspectives

Slowly progressive type 1 insulin-dependent diabetes mellitus (SPIDDM), sometimes referred to as latent autoimmune diabetes in adults (LADA), is a heterogeneous disease that is often confused with type 1 and type 2 diabetes. As a result, there were few diagnostic criteria for this disorder until 2012, when the Japan Diabetes Society established criteria that could be used in clinical practice. A primary question is whether pathologic markers for type 1 or type 2 diabetes are present in the pancreas of patients with SPIDDM, because the phenotype of SPIDDM is similar to both type 1 and type 2 diabetes. Recent studies clarified pathologic findings in the pancreas of patients with SPIDDM, which included T-cell-mediated insulitis, a marker of type 1 diabetes; pseudoatrophic islets (islets specifically devoid of beta cells), another hallmark of type 1 diabetes; and a lack of amylin (ie, islet amyloid polypeptide) deposition to the islet cells, a pathologic marker of type 2 diabetes. In terms of preventing the loss of beta-cell function in patients with SPIDDM, several studies have shown that some drugs, including dipeptidyl peptidase-4 inhibitors, are effective. There is an increased need for early diagnosis of SPIDDM to preserve beta-cell function. This review presents updated findings on the pathogenesis and immunologic findings of the affected pancreas, diagnostic markers, risk factors for progression of beta-cell dysfunction, epidemiology, clinical features, diagnostic strategies, prevention strategies, and clinical options for patients with SPIDDM.