Targeted next-generation sequencing reveals MODY in up to 6.5% of antibody-negative diabetes cases listed in the Norwegian Childhood Diabetes Registry

Clinical and genetic analysis in a Chinese cohort of children and adolescents with diabetes/persistent hyperglycemia

Aims/Introduction

To investigate the genetic etiology and evaluate the diagnostic application of next‐generation sequencing for diabetes/persistent hyperglycemia in children and adolescents.

Materials and Methods

Patients with diabetes/persistent hyperglycemia, presenting with at least one other clinical manifestation (other than diabetes) or with a family history of diabetes, were recruited. The clinical and laboratory characteristics of the patients were recorded. Next‐generation sequencing was carried out, and candidate variants were verified by Sanger sequencing. Variant pathogenicity was further evaluated according to the American College of Medical Genetics and Genomics guidelines.

Results

This study included 101 potential probands, 36 of whom were identified as positive by genetic testing. A further 51.2 and 20.9% of variants were determined to be pathogenic or likely pathogenic, respectively. Variants associated with the disease were primarily identified in 21 genes and three regions of copy number variants. Among the 39 variants in 21 genes, 61.5% (24/39) were novel. The genetic diagnosis of 23 patients was confirmed based on genetic evidence and associated clinical manifestations. We reported GCK variants (21.7%, 5/23) as the most common etiology in our cohort. Different clinical manifestations were observed in one family with WFS1 variants.

Conclusions

Our findings support the use of next‐generation sequencing as a standard method in patients with diabetes/persistent hyperglycemia and provide insights into the etiologies of these conditions.

EARLY ONSET OF MODY5 DUE TO HAPLOINSUFFICIENCY OF HNF1B

Objective

To report 2 patients with haploinsufficiency of hepatic nuclear factor 1 homeobox B (HNF1B) that results in the onset of maturity onset diabetes of the young type 5 (MODY5) before 3 years of age.

Methods

We present 2 unusual patients with MODY5 that was diagnosed at 33 and 22 months of age, respectively. We describe the presentations, clinical course, and genetic tests of both patients, and lastly, we review the literature on the prevalence and the age of presentation of MODY5 both in children and in adult patients.

Results

The first patient had severe congenital renal dysplasia, and deoxyribonucleic acid microarray indicated the deletion of 17q12. Hemoglobin A1c (HbA1c) was obtained due to the concern of MODY5, and the initial level (6.6%, 49 mmol/mol) was abnormally elevated. The second patient had mild renal dysplasia and 17q12 deletion encompassing the HNF1B gene. Hyperglycemia was identified during an episode of respiratory illness. HbA1c (6.2%, 44 mmol/mol) level was abnormally elevated. Pancreatic autoantibodies were absent in both patients. Diet modification resulted in an improvement of HbA1c in both patients.

Conclusion

Our report highlights the importance of considering MODY5 in patients with congenital anomalies of kidney. Identification of children with MODY5 permits early management of hyperglycemia.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Systematic Genetic Study of Youth With Diabetes in a Single Country Reveals the Prevalence of Diabetes Subtypes, Novel Candidate Genes, and Response to Precision Therapy

Identifying gene variants causing monogenic diabetes (MD) increases understanding of disease etiology and allows for implementation of precision therapy to improve metabolic control and quality of life. Here, we aimed to assess the prevalence of MD in youth with diabetes in Lithuania, uncover potential diabetes-related gene variants, and prospectively introduce precision treatment. First, we assessed all pediatric and most young-adult patients with diabetes in Lithuania (n = 1,209) for diabetes-related autoimmune antibodies. We then screened all antibody-negative patients (n = 153) using targeted high-throughput sequencing of >300 potential candidate genes. In this group, 40.7% had MD, with the highest percentage (100%) in infants (diagnosis at ages 0-12 months), followed by those diagnosed at ages >1-18 years (40.3%) and >18-25 years (22.2%). The overall prevalence of MD in youth with diabetes in Lithuania was 3.5% (1.9% for GCK diabetes, 0.7% for HNF1A, 0.2% for HNF4A and ABCC8, 0.3% for KCNJ11, and 0.1% for INS). Furthermore, we identified likely pathogenic variants in 11 additional genes. Microvascular complications were present in 26% of those with MD. Prospective treatment change was successful in >50% of eligible candidates, with C-peptide >252 pmol/L emerging as the best prognostic factor.

Elevated β-cell stress levels promote severe diabetes development in mice with MODY4

Maturity-onset diabetes of the young (MODY) is a group of monogenetic forms of diabetes mellitus caused by mutations in genes regulating β-cell development and function. MODY represents a heterogeneous group of non-insulin-dependent diabetes arising in childhood or adult life. Interestingly, clinical heterogeneity in MODY patients like variable disease onset and severity is observed even among individual family members sharing the same mutation, an issue that is not well understood. As high blood glucose levels are a well-known factor promoting β-cell stress and ultimately leading to cell death, we asked whether additional β-cell stress might account for the occurrence of disease heterogeneity in mice carrying a MODY4 mutation. In order to challenge β-cells, we established a MODY4 animal model based on Pdx1 (pancreatic and duodenal homeobox 1) haploinsufficiency, which allows conditional modulation of cell stress by genetic inhibition of the stress-responsive IKK/NF-κB signalling pathway. While Pdx1+/- mice were found glucose intolerant without progressing to diabetes, additional challenge of β-cell function by IKK/NF-κB inhibition promoted rapid diabetes development showing hyperglycaemia, hypoinsulinemia and loss of β-cell mass. Disease pathogenesis was characterized by deregulation of genes controlling β-cell homeostasis and function. Importantly, restoration of normal IKK/NF-κB signalling reverted the diabetic phenotype including normalization of glycaemia and β-cell mass. Our findings implicate that the avoidance of additional β-cell stress can delay a detrimental disease progression in MODY4 diabetes. Remarkably, an already present diabetic phenotype can be reversed when β-cell stress is normalized.

High Prevalence of a Monogenic Cause in Han Chinese Diagnosed With Type 1 Diabetes, Partly Driven by Nonsyndromic Recessive WFS1 Mutations

It is estimated that ∼1% of European ancestry patients clinically diagnosed with type 1 diabetes (T1D) actually have monogenic forms of the disease. Because of the much lower incidence of true T1D in East Asians, we hypothesized that the percentage would be much higher. To test this, we sequenced the exome of 82 Chinese Han patients clinically diagnosed with T1D but negative for three autoantibodies. Analysis focused on established or proposed monogenic diabetes genes. We found credible mutations in 18 of the 82 autoantibody-negative patients (22%). All mutations had consensus pathogenicity support by five algorithms. As in Europeans, the most common gene was HNF1A (MODY3), in 6 of 18 cases. Surprisingly, almost as frequent were diallelic mutations in WFS1, known to cause Wolfram syndrome but also described in nonsyndromic cases. Fasting C-peptide varied widely and was not predictive. Given the 27.4% autoantibody negativity in Chinese and 22% mutation rate, we estimate that ∼6% of Chinese with a clinical T1D diagnosis have monogenic diabetes. Our findings support universal sequencing of autoantibody-negative cases as standard of care in East Asian patients with a clinical T1D diagnosis. Nonsyndromic diabetes with WSF1 mutations is not rare in Chinese. Its response to alternative treatments should be investigated.

Absence of Islet Autoantibodies and Modestly Raised Glucose Values at Diabetes Diagnosis Should Lead to Testing for MODY: Lessons From a 5-Year Pediatric Swedish National Cohort Study

OBJECTIVE

Identifying maturity-onset diabetes of the young (MODY) in pediatric populations close to diabetes diagnosis is difficult. Misdiagnosis and unnecessary insulin treatment are common. We aimed to identify the discriminatory clinical features at diabetes diagnosis of patients with glucokinase (GCK), hepatocyte nuclear factor-1A (HNF1A), and HNF4A MODY in the pediatric population.

RESEARCH DESIGN AND METHODS

Swedish patients (n = 3,933) aged 1-18 years, diagnosed with diabetes May 2005 to December 2010, were recruited from the national consecutive prospective cohort Better Diabetes Diagnosis. Clinical data, islet autoantibodies (GAD insulinoma antigen-2, zinc transporter 8, and insulin autoantibodies), HLA type, and C-peptide were collected at diagnosis. MODY was identified by sequencing GCK, HNF1A, and HNF4A, through either routine clinical or research testing.

RESULTS

The minimal prevalence of MODY was 1.2%. Discriminatory factors for MODY at diagnosis included four islet autoantibody negativity (100% vs. 11% not-known MODY; P = 2 × 10^-44), HbA_1c (7.0% vs. 10.7% [53 vs. 93 mmol/mol]; P = 1 × 10^-20), plasma glucose (11.7 vs. 26.7 mmol/L; P = 3 × 10^-19), parental diabetes (63% vs. 12%; P = 1 × 10^-15), and diabetic ketoacidosis (0% vs. 15%; P = 0.001). Testing 303 autoantibody-negative patients identified 46 patients with MODY (detection rate 15%). Limiting testing to the 73 islet autoantibody-negative patients with HbA_1c <7.5% (58 mmol/mol) at diagnosis identified 36 out of 46 (78%) patients with MODY (detection rate 49%). On follow-up, the 46 patients with MODY had excellent glycemic control, with an HbA_1c of 6.4% (47 mmol/mol), with 42 out of 46 (91%) patients not on insulin treatment.

CONCLUSIONS

At diagnosis of pediatric diabetes, absence of all islet autoantibodies and modest hyperglycemia (HbA_1c <7.5% [58 mmol/mol]) should result in testing for GCK, HNF1A, and HNF4A MODY. Testing all 12% patients negative for four islet autoantibodies is an effective strategy for not missing MODY but will result in a lower detection rate. Identifying MODY results in excellent long-term glycemic control without insulin.

Update on clinical screening of maturity-onset diabetes of the young (MODY)

BACKGROUND

Maturity-onset diabetes of the young (MODY) is the most common type of monogenic diabetes, being characterized by beta-cell disfunction, early onset, and autosomal dominant inheritance. Despite the rapid evolution of molecular diagnosis methods, many MODY cases are misdiagnosed as type 1 or type 2 diabetes. High costs of genetic testing and limited knowledge of MODY as a relevant clinical entity are some of the obstacles that hinder correct MODY diagnosis and treatment. We present a broad review of clinical syndromes related to most common MODY subtypes, emphasizing the role of biomarkers that can help improving the accuracy of clinical selection of candidates for molecular diagnosis.

MAIN BODY

To date, MODY-related mutations have been reported in at least 14 different genes. Mutations in glucokinase (GCK), hepatocyte nuclear factor-1 homeobox A (HNF1A), and hepatocyte nuclear factor-4 homeobox A (HNF4A) are the most common causes of MODY. Accurate etiological diagnosis can be challenging. Many biomarkers such as apolipoprotein-M (ApoM), aminoaciduria, complement components, and glycosuria have been tested, but have not translated into helpful diagnostic tools. High-sensitivity C-reactive protein (hs-CRP) levels are lower in HNF1A-MODY and have been tested in some studies to discriminate HNF1A-MODY from other types of diabetes, although more data are needed. Overall, presence of pancreatic residual function and absence of islet autoimmunity seem the most promising clinical instruments to select patients for further investigation.

CONCLUSIONS

The selection of diabetic patients for genetic testing is an ongoing challenge. Metabolic profiling, diabetes onset age, pancreatic antibodies, and C-peptide seem to be useful tools to better select patients for genetic testing. Further studies are needed to define cut-off values in different populations.

Maturity-Onset Diabetes of the Young Identified Among Algerian Probands with Early-Onset Diabetes

AIM

To investigate the prevalence of variants within selected maturity-onset diabetes of the young (MODY)-genes among Algerian patients initially diagnosed with type 1 diabetes (T1D) or type 2 diabetes (T2D), yet presenting with a MODY-like phenotype.

METHODS

Eight unrelated patients with early-onset diabetes (before 30 years) and six relatives with diabetes were examined by targeted re-sequencing for variants in genes known to be involved in MODY (HNF1A, GCK, HNF4A, HNF1B, INS, ABCC8, KCNJ1). Clinical data for probands were retrieved from hospital records.

RESULTS

A total of 12 variants were identified, of which three were classified as pathogenic and one as a variant of uncertain clinical significance (VUS). Two of the pathogenic variants were found in GCK (p.Gly261Arg and p.Met210Lys, respectively) in one proband each and the remaining pathogenic variant was found in HNF1B (p.Gly76Cys) in a proband also carrying the VUS in HNF1A (p.Thr156Met).

CONCLUSION

Variants in known MODY-genes can be the cause of early-onset diabetes in Algerians diagnosed with T1D or T2D among patients presenting with a MODY-like phenotype; thus, genetic screening should be considered.

Screening of monogenic autoimmune diabetes among children with type 1 diabetes and multiple autoimmune diseases: is it worth doing?

Background Paediatric type 1 diabetes (T1D) and rare syndromes of monogenic multi-organ autoimmunity share basic features such as full insulin dependency and the presence of circulating beta-cell autoantibodies. However, the aetiopathogenesis, natural course and treatment of these conditions differ; therefore, monogenic multi-organ autoimmunity requires early recognition. We aimed to search for these monogenic conditions among a large cohort of children with T1D. Methods Of 519 children with T1D followed-up in a single centre, 18 had multiple additional autoimmune conditions - either autoimmune thyroid disease (AITD) and coeliac disease (CD) or at least one additional organ-specific autoimmune condition in addition to AITD or CD. These 18 children were tested by direct Sanger sequencing (four patients with a suggestive phenotype of immune dysregulation, polyendocrinopathy, enteropathy, X-linked [IPEX] or signal transducer and activator of transcription 3 [STAT3]- and cytotoxic T-lymphocyte protein 4 [CTLA4]-associated syndromes) or by whole-exome sequencing (WES) focused on autoimmune regulator (AIRE), forkhead box protein 3 (FOXP3), CTLA4, STAT3, signal transducer and activator of transcription 1 (STAT1), lipopolysaccharide-responsive and beige-like anchor protein (LRBA) and interleukin-2 receptor subunit α (IL2RA) genes. In addition, we assessed their T1D genetic risk score (T1D-GRS). Results We identified novel variants in FOXP3, STAT3 and CTLA4 in four cases. All patients had a severe phenotype suggestive of a single gene defect. No variants were identified in the remaining 14 patients. T1D-GRS varied among the entire cohort; four patients had scores below the 25th centile including two genetically confirmed cases. Conclusions A monogenic cause of autoimmune diabetes was confirmed only in four patients. Genetic screening for monogenic autoimmunity in children with a milder phenotype and a combination of AITD and CD is unlikely to identify a monogenic cause. In addition, the T1D-GRS varied among individual T1D patients.

Whole‑exome sequencing in Russian children with non‑type 1 diabetes mellitus reveals a wide spectrum of genetic variants in MODY‑related and unrelated genes

The present study reports on the frequency and the spectrum of genetic variants causative of monogenic diabetes in Russian children with non-type 1 diabetes mellitus. The present study included 60 unrelated Russian children with non-type 1 diabetes mellitus diagnosed before the age of 18 years. Genetic variants were screened using whole-exome sequencing (WES) in a panel of 35 genes causative of maturity onset diabetes of the young (MODY) and transient or permanent neonatal diabetes. Verification of the WES results was performed using PCR-direct sequencing. A total of 38 genetic variants were identified in 33 out of 60 patients (55%). The majority of patients (27/33, 81.8%) had variants in MODY-related genes: GCK (n=19), HNF1A (n=2), PAX4 (n=1), ABCC8 (n=1), KCNJ11 (n=1), GCK+HNF1A (n=1), GCK+BLK (n=1) and GCK+BLK+WFS1 (n=1). A total of 6 patients (6/33, 18.2%) had variants in MODY-unrelated genes: GATA6 (n=1), WFS1 (n=3), EIF2AK3 (n=1) and SLC19A2 (n=1). A total of 15 out of 38 variants were novel, including GCK, HNF1A, BLK, WFS1, EIF2AK3 and SLC19A2. To summarize, the present study demonstrates a high frequency and a wide spectrum of genetic variants causative of monogenic diabetes in Russian children with non-type 1 diabetes mellitus. The spectrum includes previously known and novel variants in MODY-related and unrelated genes, with multiple variants in a number of patients. The prevalence of GCK variants indicates that diagnostics of monogenic diabetes in Russian children may begin with testing for MODY2. However, the remaining variants are present at low frequencies in 9 different genes, altogether amounting to ~50% of the cases and highlighting the efficiency of using WES in non-GCK-MODY cases.

How Recent Advances in Genomics Improve Precision Diagnosis and Personalized Care of Maturity-Onset Diabetes of the Young

PURPOSE OF REVIEW

Non-autoimmune monogenic diabetes (MD) in young people shows a broad spectrum of clinical presentations, which is largely explained by multiple genetic etiologies. This review discusses how the application of state-of-the-art genomics research to precision diagnosis of MD, particularly the various subtypes of maturity-onset diabetes of the young (MODY), has increasingly informed diabetes precision medicine and patient care throughout life.

RECENT FINDINGS

Due to extended genetic and clinical heterogeneity of MODY, diagnosis approaches based on next-generation sequencing have been worthwhile to better ascribe a specific subtype to each patient with young-onset diabetes. This guides the best appropriate treatment and clinical follow-up. Early etiological diagnosis of MD and individualized treatment are essential for achieving metabolic targets and avoiding long-term diabetes complications, as well as for drastically decreasing the financial and societal burden of diabetes-related healthcare. Genomic medicine-based practices help to optimize long-term clinical follow-up and patient care management.

Copy Number Variation in GCK in Patients With Maturity-Onset Diabetes of the Young

PURPOSE

Next generation sequencing (NGS) methods to diagnose maturity-onset diabetes of the young (MODY), a monogenic autosomal dominant cause of diabetes, do not typically detect large-scale copy number variations (CNVs). New techniques may allow assessment for CNVs using output data from targeted NGS, without requiring additional sequencing. Using this technique, two kindreds of patients presenting with features of MODY were found to bear the same heterozygous large-scale deletion in GCK.

METHODS

Patients suspected of having MODY but with negative targeted NGS pathogenic variant calling were reanalyzed using the CNV caller tool (VarSeq v1.4.3). Two patients were identified as having a possible heterozygous whole exon deletion affecting exon 1 of GCK. For confirmation and determination of the exact breakpoints, whole exome sequencing followed by Sanger sequencing were used. Familial samples from both affected and nonaffected first-degree relatives were then analyzed for each proband.

RESULTS

A heterozygous whole-exon deletion spanning 4763 bp affecting the entire exon 1 of GCK was detected in two apparently unrelated patients with clinical features of MODY. This deletion showed segregation concordance across generations in affected and nonaffected family members.

CONCLUSIONS

Our findings confirm the utility of applying the CNV caller tool to screen for CNVs in GCK from NGS data. In so doing, we identified a deletion of exon 1 of GCK as likely causal for MODY. Our data indicate that incorporating CNV analysis routinely when assessing for MODY via targeted NGS may increase diagnostic yield and reduce false negative genetic testing rates.

Pediatric Monogenic Diabetes: A Unique Challenge and Opportunity

Monogenic diabetes affects approximately 120,000 people in the United States but continues to be misdiagnosed. Within the pediatric population, 1% to 3% of diabetes is monogenic, and early diagnosis and genetically targeted management of congenital diabetes and maturity onset diabetes of the young (MODY) can have a tremendous impact on future health outcomes and quality of life. In some of the more common monogenic diabetes types, patients can switch from insulin therapy to sulfonylureas or even discontinue glucose-lowering therapy with stable glycemic control. Advancements in the field have identified tools and resources to aid in distinguishing patients likely to have monogenic diabetes from the more common forms of type 1 and type 2 diabetes. However, genetic testing with accurate interpretation of results is necessary to confirm a diagnosis and direct treatment selection and disease management. This article discusses challenges and opportunities in monogenic diabetes in the pediatric population. [Pediatr Ann. 2019;48(8):e319-e325.].

Maturity Onset Diabetes of the Young is Not Necessarily Associated with Autosomal Inheritance: Case Description of a De Novo HFN1A Mutation

Maturity onset diabetes of the young (MODY) accounts for up to 4% of all cases of diabetes in pediatric patients. MODY is usually characterized by autosomal dominant inheritance, impaired insulin secretion, and an average age at diagnosis of 18-26 years. Mutations in the hepatocyte nuclear factor 1-alpha (HNF1A), glucokinase, hepatocyte nuclear factor 4-alpha, and hepatocyte nuclear factor 1-beta genes are the mutations most frequently observed in cases of MODY. We herein report a case of HNF1A-MODY characterized by an early onset of diabetes. Genetic investigations revealed a de novo heterozygous substitution, N237D (HNF1A c.709A>G), in exon 3 of the HNF1A gene. Our case supports the hypothesis that de novo mutations are more frequent than expected. This recent evidence may suggest that conventional clinical diagnostic criteria for MODY should be revised and personalized according to the individual patient.

Negative autoimmunity in a Spanish pediatric cohort suspected of type 1 diabetes, could it be monogenic diabetes?

Objective

Monogenic diabetes can be misdiagnosed as type 1 or type 2 diabetes in children. The right diagnosis is crucial for both therapeutic choice and prognosis and influences genetic counseling. The main objective of this study was to search for monogenic diabetes in Spanish pediatric patients suspected of type 1 diabetes with lack of autoimmunity at the onset of the disease. We also evaluated the extra value of ZnT8A in addition to the classical IAA, GADA and IA2A autoantibodies to improve the accuracy of type 1 diabetes diagnosis.

Methods

Four hundred Spanish pediatric patients with recent-onset diabetes (mean age 8.9 ± 3.9 years) were analyzed for IAA, GADA, IA2A and ZnT8A pancreatic-autoantibodies and HLA-DRB1 alleles. Patients without autoimmunity and those with only ZnT8A positive were screened for 12 monogenic diabetes genes by next generation sequencing.

Results

ZnT8A testing increased the number of autoantibody-positive patients from 373 (93.3%) to 377 (94.3%). An isolated positivity for ZnT8A allowed diagnosing autoimmune diabetes in 14.8% (4/27) of pediatric patients negative for the rest of the antibodies tested. At least 2 of the 23 patients with no detectable autoimmunity (8%) carried heterozygous pathogenic variants: one previously reported missense variant in the INS gene (p.Gly32Ser) and one novel frameshift variant (p.Val264fs) in the HNF1A gene. One variant of uncertain significance was also found. Carriers of pathogenic variants had HLA-DRB1 risk alleles for autoimmune diabetes and clinical characteristics compatible with type 1 diabetes except for the absence of autoimmunity.

Conclusion

ZnT8A determination improves the diagnosis of autoimmune diabetes in pediatrics. At least 8% of pediatric patients suspected of type 1 diabetes and with undetectable autoimmunity have monogenic diabetes and can benefit from the correct diagnosis of the disease by genetic study.

Maturity onset diabetes of the young (MODY) in Chinese children: genes and clinical phenotypes

Background To investigate the clinical and molecular characteristics of Chinese children with maturity onset diabetes of the young (MODY). Methods A total of 42 Chinese patients suspected MODY referred to our unit from 2014 to 2018 were enrolled. Mutational analysis of monogenic diabetes mellitus genes was performed by next-generation sequencing and confirmed by Sanger sequencing. Results There were 28 males (66.7%) and 14 females (33.3%) with a mean age of 9.49 ± 3.46 years (range, 1.4-15.3 years) and a mean birth weight of 3.38 ± 0.49 kg (range, 2.55-4.90 kg). Among these patients, 15 patients had polyuria, polydipsia or weight loss. Two patients (4.8%) were obese and six (14.3%) were overweight. Moreover, 13 patients (30.9%) had a family history of diabetes. Thirty variants were identified in 28 patients. Twenty-six variants in 25 patients were pathogenic or likely pathogenic genes (59.5%, 25/42), including 15 patients (60.0%, 15/25) with GCK mutation, four (16.0%, 4/25) with PAX4 mutation, three (12.0%, 3/25) with HNF4A mutation, one (4.0%, 1/25) with INS mutation, one (4.0%, 1/25) with NEUROD1 mutation and one (4.0%, 1/25) with HNF1A mutation. Nine mutations (36.0%, 9/25) were novel. There was no difference between mutation-suspected patients and MODY-confirmed patients except for a 2-h glucose increment in an oral glucose tolerance test (OGTT), while the GCK-MODY had lower glycated hemoglobin (HbA1c) and a significantly smaller 2-h glucose increment in an OGTT compared with transcription factor MODYs. The GCK-MODY was identified by incidental hyperglycemia without glycosuria. GCK-MODY without drug management and hepatocyte nuclear factor-1 alpha (HNF4A) or HNF1A-MODY with sulfonylurea therapy obtained good glucose controlling. Conclusions Mutation of the GCK gene is the most common in MODY patients in China followed by PAX4. The screening criteria can improve the cost-effectiveness of disease diagnosis and treatment. A precise molecular diagnosis would lead to optimal treatment of the patients.

Next-generation sequencing identifies monogenic diabetes in 16% of patients with late adolescence/adult-onset diabetes selected on a clinical basis: a cross-sectional analysis

BACKGROUND

Monogenic diabetes (MgD) accounts for 1-2% of all diabetes cases. In adults, MgD is difficult to distinguish from common diabetes causes. We assessed the diagnosis rate and genetic spectrum of MgD using next-generation sequencing in patients with late adolescence/adult-onset diabetes referred for a clinical suspicion of MgD.

METHODS

This cross-sectional study was performed in 1564 probands recruited in 116 Endocrinology departments. Inclusion criteria were the absence of diabetes autoantibodies, and at least two of the three following criteria: an age ≤ 40 years and a body mass index (BMI) < 30 kg/m² at diagnosis in the proband or in at least two relatives with diabetes, and a family history of diabetes in ≥ 2 generations. Seven genes (GCK, HNF1A, HNF4A, HNF1B, ABCC8, KCNJ11, and INS) were analyzed. Variant pathogenicity was assessed using current guidelines.

RESULTS

Pathogenic variants were identified in 254 patients (16.2%) and in 23.2% of EuroCaucasian patients. Using more stringent selection criteria (family history of diabetes in ≥ 3 generations, age at diabetes ≤ 40 years and BMI < 30 kg/m² in the proband, EuroCaucasian origin) increased the diagnosis rate to 43%, but with 70% of the identified cases being missed. GCK (44%), HNF1A (33%), and HNF4A (10%) accounted for the majority of the cases. HNF1B (6%), ABCC8/KCNJ11 (4.4%), and INS (2.8%) variants accounted for 13% of the cases. As compared to non-monogenic cases, a younger age, a lower BMI and the absence of diabetes symptoms at diagnosis, a EuroCaucasian origin, and a family history of diabetes in ≥ 3 generations were associated with MgD, but with wide phenotype overlaps between the two groups. In the total population, two clusters were identified, that mainly differed by the severity of diabetes at onset. MgDs were more prevalent in the milder phenotypic cluster. The phenotypes of the 59 patients (3.8%) with variants of uncertain significance were different from that of patients with pathogenic variants, but not from that of non-monogenic patients.

CONCLUSION

Variants of HNF1B and the K-ATP channel genes were more frequently involved in MgD than previously reported. Phenotype overlapping makes the diagnosis of MgD difficult in adolescents/adults and underlies the benefit of NGS in clinically selected patients.

Insulin: still a miracle after all these years

The discovery of insulin almost 100 years ago has resulted in a remarkable increase in lifespan and quality of life for patients with type 1 diabetes. The Joslin Medalist Study has allowed researchers to access and study patients (Medalists) with type 1 diabetes who have been insulin dependent for 50 years or more. In this issue of the JCI, Yu et al. evaluated HLA variants, autoantibody status, β cell function, C-peptide release, and monogenetic diabetes genes in a cohort of Medalists. Postmortem analysis of pancreata from Medalists revealed the presence of insulin-positive β cells in these patients. Moreover, some patients were still able to respond to metabolic stimuli despite long-term insulin dependence. Overall, the Medalist cohort was highly heterogenous, and genetic testing suggested that several patients would fall into categories other than type 1 diabetes on the basis of REVEL (rare exome variant ensemble learner) classification and may be able to transfer to other therapy options.

HNF1B nephropathy has a slow-progressive phenotype in childhood-with the exception of very early onset cases: results of the German Multicenter HNF1B Childhood Registry

BACKGROUND

HNF1B gene mutations are an important cause of bilateral (cystic) dysplasia in children, complicated by chronic renal insufficiency. The clinical variability, the absence of genotype-phenotype correlations, and limited long-term data render counseling of affected families difficult.

METHODS

Longitudinal data of 62 children probands with genetically proven HNF1B nephropathy was obtained in a multicenter approach. Genetic family cascade screening was performed in 30/62 cases.

RESULTS

Eighty-seven percent of patients had bilateral dysplasia, 74% visible bilateral, and 16% unilateral renal cysts at the end of observation. Cyst development was non-progressive in 72% with a mean glomerular filtration rate (GFR) loss of - 0.33 ml/min/1.73m² per year (± 8.9). In patients with an increase in cyst number, the annual GFR reduction was - 2.8 ml/min/1.73m² (± 13.2), in the total cohort - 1.0 ml/min/1.73m² (±10.3). A subset of HNF1B patients differs from this group and develops end stage renal disease (ESRD) at very early ages < 2 years. Hyperuricemia (37%) was a frequent finding at young age (median 1 year), whereas hypomagnesemia (24%), elevated liver enzymes (21%), and hyperglycemia (8%) showed an increased incidence in the teenaged child. Genetic analysis revealed no genotype-phenotype correlations but a significant parent-of-origin effect with a preponderance of 81% of maternal inheritance in dominant cases.

CONCLUSIONS

In most children, HNF1B nephropathy has a non-progressive course of cyst development and a slow-progressive course of kidney function. A subgroup of patients developed ESRD at very young age < 2 years requiring special medical attention. The parent-of-origin effect suggests an influence of epigenetic modifiers in HNF1B disease.

Phenotypic variability in two siblings with monogenic diabetes due to the same ABCC8 gene mutation

ABCC8 gene mutations with different inheritance patterns have been well described to cause transient and permanent forms of neonatal diabetes with onset of hyperglycemia commonly before the age of 6 months, and rare cases between 6 and 12 months. However, recent analyses have also demonstrated ABCC8 gene mutations in patients with monogenic diabetes (maturity onset diabetes of the young, MODY), with milder clinical phenotypes and later onset of hyperglycemia. We report two siblings with diabetes mellitus due to a novel homozygous p.(Phe1068Ile) (c.3202T>A) missense mutation of the ABCC8 gene, but significantly different phenotypes. The index case was diagnosed with diabetes due to an incidental finding of hyperglycemia at the age of 3 years, while her younger sibling presented with severe hyperglycemia and hyperosmolar dehydration at the age of 10 weeks. The possibility of a significant discordance in the correlation between genotype and phenotype needs to be taken into account when ABCC8 mutation dependent diabetes occurs within the same family. Genetic screening in children with diabetes from consanguineous family needs consideration, especially in case of negative autoantibodies and early onset of hyperglycemia.

GCK-MODY in the US Monogenic Diabetes Registry: Description of 27 unpublished variants

We report on 134 unique GCK variants in 217 families, including 27 unpublished variants, identified in the US Monogenic Diabetes Registry in the last decade. Using ACMG guidelines, 26% were pathogenic, 56% likely pathogenic and 18% were of uncertain significance. Those with pathogenic variants had clinical features consistent with GCK-MODY.

HDAC4 mutations cause diabetes and induce β-cell FoxO1 nuclear exclusion

Background

Studying patients with rare Mendelian diabetes has uncovered molecular mechanisms regulating β‐cell pathophysiology. Previous studies have shown that Class IIa histone deacetylases (HDAC4, 5, 7, and 9) modulate mammalian pancreatic endocrine cell function and glucose homeostasis.

Methods

We performed exome sequencing in one adolescent nonautoimmune diabetic patient and detected one de novo predicted disease‐causing HDAC4 variant (p.His227Arg). We screened our pediatric diabetes cohort with unknown etiology using Sanger sequencing. In mouse pancreatic β‐cell lines (Min6 and SJ cells), we performed insulin secretion assay and quantitative RT‐PCR to measure the β‐cell function transfected with the detected HDAC4 variants and wild type. We carried out immunostaining and Western blot to investigate if the detected HDAC4 variants affect the cellular translocation and acetylation status of Forkhead box protein O1 (FoxO1) in the pancreatic β‐cells.

Results

We discovered three HDAC4 mutations (p.His227Arg, p.Asp234Asn, and p.Glu374Lys) in unrelated individuals who had nonautoimmune diabetes with various degrees of β‐cell loss. In mouse pancreatic β‐cell lines, we found that these three HDAC4 mutations decrease insulin secretion, down‐regulate β‐cell‐specific transcriptional factors, and cause nuclear exclusion of acetylated FoxO1.

Conclusion

Mutations in HDAC4 disrupt the deacetylation of FoxO1, subsequently decrease the β‐cell function including insulin secretion, resulting in diabetes.

Comprehensive genetic screening: The prevalence of maturity-onset diabetes of the young gene variants in a population-based childhood diabetes cohort

BACKGROUND

Maturity-onset diabetes of the young (MODY) is caused by autosomal dominant mutations in one of 13 confirmed genes. Estimates of MODY prevalence vary widely, as genetic screening is usually restricted based on clinical features, even in population studies. We aimed to determine prevalence of MODY variants in a large and unselected pediatric diabetes cohort.

METHODS

MODY variants were assessed using massively parallel sequencing in the population-based diabetes cohort (n = 1363) of the sole tertiary pediatric diabetes service for Western Australia (population 2.6 million). All individuals were screened, irrespective of clinical features. MODY variants were also assessed in a control cohort (n = 993).

RESULTS

DNA and signed consent were available for 821 children. Seventeen children had pathogenic/likely pathogenic variants in MODY genes, two diagnosed with type 2 diabetes, four diagnosed with antibody-negative type 1 diabetes (T1DM), three diagnosed with antibody-positive T1DM, and eight previously diagnosed with MODY. Prevalence of MODY variants in the sequenced cohort was 2.1%, compared to 0.3% of controls.

CONCLUSIONS

This is the first comprehensive study of MODY variants in an unselected population-based pediatric diabetes cohort. The observed prevalence, increasing access to rapid and affordable genetic screening, and significant clinical implications suggest that genetic screening for MODY could be considered for all children with diabetes, irrespective of other clinical features.

Cost-effectiveness Analysis of Routine Screening Using Massively Parallel Sequencing for Maturity-Onset Diabetes of the Young in a Pediatric Diabetes Cohort: Reduced Health System Costs and Improved Patient Quality of Life

OBJECTIVE

Maturity-onset diabetes of the young (MODY) is an autosomal dominant form of diabetes, with multiple causative genes. Some MODY subtypes can be treated with sulfonylureas instead of insulin, improving glycemic control, complication rates, quality of life (QoL), and costs. Using massively parallel sequencing (MPS), we recently determined the prevalence of pathogenic/likely pathogenic MODY variants in an Australian pediatric diabetes cohort. Here, these data are used to estimate cost-effectiveness of using MPS for MODY in all pediatric diabetes cases compared with standard practice (sequencing limited to individuals with specific clinical features).

RESEARCH DESIGN AND METHODS

A Markov decision model was developed to estimate incremental costs and quality-adjusted life-years (QALYs) of MPS screening, modeled over 30 years. We used our observed prevalence of 2.14% compared with 0.7% for standard practice, based on published data. The probabilities and utility weightings of long-term diabetes complications were based on HbA_1c and estimated from published data. A series of one-way sensitivity analyses were performed using the net monetary benefit framework.

RESULTS

Routine MPS screening for MODY was more effective and less costly than standard care screening, with 26 QALYs gained and 1,016,000 AUD (782,000 USD) saved per 1,000 patients. Cost of screening was fully offset within 10 years. Routine MPS screening remained dominant until MODY prevalence fell to <1.1%.

CONCLUSIONS

Routine MPS screening for MODY in the pediatric population with diabetes could reduce health system costs and improve patient QoL. Our results make a compelling argument for routine genetic screening in all children with presumed type 1 diabetes mellitus.

A Systematic Review of Childhood Diabetes Research in the Middle East Region

Background: Diabetes mellitus (DM) is a common chronic disorder in children and is caused by absolute or relative insulin deficiency, with or without insulin resistance. There are several different forms of childhood DM. Children can suffer from neonatal diabetes mellitus (NDM), type 1 diabetes (T1DM), type 2 diabetes (T2DM), Maturity Onset Diabetes of the Young (MODY), autoimmune monogenic, mitochondrial, syndromic and as yet unclassified forms of DM. The Middle East has one of the highest incidences of several types of DM in children; however, it is unclear whether pediatric diabetes is an active area of research in the Middle East and if ongoing, which research areas are of priority for DM in children. Objectives: To review the literature on childhood DM related to research in the Middle East, summarize results, identify opportunities for research and make observations and recommendations for collaborative studies in pediatric DM. Methods: We conducted a thorough and systematic literature review by adhering to a list recommended by PRISMA. We retrieved original papers written in English that focus on childhood DM research, using electronic bibliographic databases containing publications from the year 2000 until October 2018. For our final assessment, we retrieved 429 full-text articles and selected 95 articles, based on our inclusion and exclusion criteria. Results: Our literature review suggests that childhood DM research undertaken in the Middle East has focused mainly on reporting retrospective review of case notes, a few prospective case studies, systemic reviews, questionnaire-based studies, and case reports. These reported studies have focused mostly on the incidence/prevalence of different types of DM in childhood. No studies report on the establishment of National Childhood Diabetes Registries. There is a lack of consolidated studies focusing on national epidemiology data of different types of childhood DM (such as NDM, T1DM, T2DM, MODY, and syndromic forms) and no studies reporting on clinical trials in children with DM. Conclusions: Investing in and funding basic and translational childhood diabetes research and encouraging collaborative studies, will bring enormous benefits financially, economically, and socially for the whole of the Middle East region.

Monogenic Forms of Diabetes Mellitus

In addition to the common types of diabetes mellitus, two major monogenic diabetes forms exist. Maturity-onset diabetes of the young (MODY) represents a heterogenous group of monogenic, autosomal dominant diseases. MODY accounts for 1-2% of all diabetes cases, and it is not just underdiagnosed but often misdiagnosed to type 1 or type 2 diabetes. More than a dozen MODY genes have been identified to date, and their molecular classification is of great importance in the correct treatment decision and in the judgment of the prognosis. The most prevalent subtypes are HNF1A, GCK, and HNF4A. Genetic testing for MODY has changed recently due to the technological advancements, as contrary to the sequential testing performed in the past, nowadays all MODY genes can be tested simultaneously by next-generation sequencing. The other major group of monogenic diabetes is neonatal diabetes mellitus which can be transient or permanent, and often the diabetes is a part of a syndrome. It is a severe monogenic disease appearing in the first 6 months of life. The hyperglycemia usually requires insulin. There are two forms, permanent neonatal diabetes mellitus (PNDM) and transient neonatal diabetes mellitus (TNDM). In TNDM, the diabetes usually reverts within several months but might relapse later in life. The incidence of NDM is 1:100,000-1:400,000 live births, and PNDM accounts for half of the cases. Most commonly, neonatal diabetes is caused by mutations in KCNJ11 and ABCC8 genes encoding the ATP-dependent potassium channel of the β cell. Neonatal diabetes has experienced a quick and successful transition into the clinical practice since the discovery of the molecular background. In case of both genetic diabetes groups, recent guidelines recommend genetic testing.

A UK nationwide prospective study of treatment change in MODY: genetic subtype and clinical characteristics predict optimal glycaemic control after discontinuing insulin and metformin

AIMS/HYPOTHESIS

Treatment change following a genetic diagnosis of MODY is frequently indicated, but little is known about the factors predicting future treatment success. We therefore conducted the first prospective study to determine the impact of a genetic diagnosis on individuals with GCK-, HNF1A- or HNF4A-MODY in the UK, and to identify clinical characteristics predicting treatment success (i.e. HbA_1c ≤58 mmol/mol [≤7.5%]) with the recommended treatment at 2 years.

METHODS

This was an observational, prospective, non-selective study of individuals referred to the Exeter Molecular Genetic Laboratory for genetic testing from December 2010 to December 2012. Individuals from the UK with GCK- or HNF1A/HNF4A-MODY who were not on recommended treatment at the time of genetic diagnosis, and who were diagnosed below the age of 30 years and were currently aged less than 50 years, were eligible to participate.

RESULTS

A total of 44 of 58 individuals (75.9%) changed treatment following their genetic diagnosis. Eight individuals diagnosed with GCK-MODY stopped all diabetes medication without experiencing any change in HbA_1c (49.5 mmol/mol [6.6%] both before the genetic diagnosis and at a median of 1.25 years' follow-up without treatment, p = 0.88). A total of 36 of 49 individuals (73.5%) diagnosed with HNF1A/HNF4A-MODY changed treatment; however, of the 21 of these individuals who were being managed with diet or sulfonylurea alone at 2 years, only 13 (36.1% of the population that changed treatment) had an HbA_1c ≤58 mmol/mol (≤7.5%). These individuals had a shorter diabetes duration (median 4.6 vs 18.1 years), lower HbA_1c (58 vs 73 mmol/mol [7.5% vs 8.8%]) and lower BMI (median 24.2 vs 26.0 kg/m²) at the time of genetic diagnosis, compared with individuals (n = 23/36) with an HbA_1c >58 mmol/mol (>7.5%) (or <58 mmol/mol [<7.5%] on additional treatment) at the 2 year follow-up. Overall, 64% (7/11) individuals with a diabetes duration of ≤11 years and an HbA_1c of ≤69 mmol/mol (≤8.5%) at time of the genetic test achieved good glycaemic control (HbA_1c ≤58 mmol/mol [≤7.5%]) with diet or sulfonylurea alone at 2 years, compared with no participants with a diabetes duration of >11 years and an HbA_1c of >69 mmol/mol (>8.5%) at the time of genetic diagnosis.

CONCLUSIONS/INTERPRETATION

In participants with GCK-MODY, treatment cessation was universally successful, with no change in HbA_1c at follow-up. In those with HNF1A/HNF4A-MODY, a shorter diabetes duration, lower HbA_1c and lower BMI at genetic diagnosis predicted successful treatment with sulfonylurea/diet alone, supporting the need for early genetic diagnosis and treatment change. Our study suggests that, in individuals with HNF1A/HNF4A-MODY with a longer duration of diabetes (>11 years) at time of genetic test, rather than ceasing current treatment, a sulfonylurea should be added to existing therapy, particularly in those who are overweight or obese and have a high HbA_1c.

Genetics of Monogenic Diabetes: Present Clinical Challenges

PURPOSE OF REVIEW

Monogenic forms of diabetes have specific treatments that differ from the standard care provided for type 1 and type 2 diabetes, making the appropriate diagnosis essential. In this review, we discuss current clinical challenges that remain, including improving case-finding strategies, particularly those that have transethnic applicability, and understanding the interpretation of genetic variants as pathogenic, with clinically meaningful impacts.

RECENT FINDINGS

Biomarker approaches to the stratification for genetic testing now appear to be most effective in identifying cases of monogenic diabetes, and use of genetic risk scores may also prove useful. However, applicability in all ethnic groups is lacking. Challenges remain in the classification of genes as diabetes-causing and the interpretation of genetic variants at the clinical interface. Since the discovery that genetic defects can cause neonatal or young-onset diabetes, multiple causal genes have been identified and there have been many advances in strategies to detect genetic forms of diabetes and their treatments. Approaches learnt from monogenic diabetes are now being translated to polygenic diabetes.

Genetic causes and treatment of neonatal diabetes and early childhood diabetes

Diabetes mellitus and impaired fasting glucose associated with single gene mutations are less rare than previously thought and may account for more than 6% of patients attending a pediatric diabetes clinic. The number of loci involved in monogenic diabetes exceed 25, and appropriate genetic diagnosis is crucial to direct therapy, for genetic counseling and for prognosis of short- and long-term complications. Among patients with neonatal diabetes (i.e. with onset within first 6 months of life) and patients with Maturity Onset Diabetes of the Young (MODY; an autosomal dominant form of diabetes), those carrying mutations in KCNJ11, ABCC8, HNF1A and HNF4A genes usually respond to oral therapy with sulphonylurea, while those bearing GCK mutations do not necessitate any treatment. Sensor-augmented continuous subcutaneous insulin infusion has been successfully employed in neonatal diabetes, and long-lasting effectiveness of sulfonylurea in KCNJ11 mutation carriers with neonatal diabetes well documented.

Comprehensive screening for monogenic diabetes in 89 Japanese children with insulin-requiring antibody-negative type 1 diabetes

BACKGROUND

Mutations in causative genes for neonatal diabetes or maturity-onset diabetes of the young have been identified in multiple patients with autoantibody-negative type 1 diabetes (T1D).

OBJECTIVES

We aimed to clarify the prevalence and phenotypic characteristics of monogenic abnormalities among 89 children with autoantibody-negative insulin-requiring T1D.

METHODS

Mutations in 30 genes were screened using next-generation sequencing, and copy-number alterations of 4 major causative genes were examined using multiplex-ligation-dependent probe amplification. We compared the clinical characteristics between mutation carriers and non-carriers.

RESULTS

We identified 11 probable pathogenic substitutions (6 in INS , 2 in HNF1A , 2 in HNF4A , and 1 in HNF1B ) in 11 cases, but no copy-number abnormalities. Only 2 mutation carriers had affected parents. De novo occurrence was confirmed for 3 mutations. The non-carrier group, but not the carrier group, was enriched with susceptible HLA alleles. Mutation carriers exhibited comparable phenotypes to those of non-carriers, except for a relatively normal body mass index (BMI) at diagnosis.

CONCLUSIONS

This study demonstrated significant genetic overlap between autoantibody-negative T1D and monogenic diabetes. Mutations in INS and HNF genes, but not those in GCK and other monogenic diabetes genes, likely play critical roles in children with insulin-requiring T1D. This study also suggests the relatively high de novo rates of INS and HNF mutations, and the etiological link between autoimmune abnormalities and T1D in the non-carrier group. Carriers of monogenic mutations show non-specific phenotypes among all T1D cases, although they are more likely to have a normal BMI at diagnosis than non-carriers.

Familial diabetes of adulthood: A bin of ignorance that needs to be addressed

AIMS

The aim of this article was to share with a wide readership some data and related reasoning about a multigenerational form of diabetes mellitus of adulthood.

DATA SYNTHESIS

We have recently described a familial form of diabetes mellitus, which in the routine clinical setting of adult individuals is simplistically diagnosed as type 2 diabetes. Such misdiagnosis involves as much as 3% of adult unrelated diabetic patients with no evidence of autoimmune disease. More recent data, obtained by means of a next-generation sequencing, indicate that approximately 25% of such patients carry mutations in the genes involved in monogenic diabetes, thus leaving unraveled the molecular causes of the remaining 75% individuals.

CONCLUSIONS

Our proposal is to define the latter patients as being affected by familial diabetes of adulthood (FDA), a clear admission of ignorance and a limbo where adult patients with multigenerational diabetes with no genetic definition of their hyperglycemia have to wait for better times.

Juvenile-Onset Diabetes and Congenital Cataract: "Double-Gene" Mutations Mimicking a Syndromic Diabetes Presentation

Monogenic forms of diabetes may account for 1–5% of all cases of diabetes, and may occur in the context of syndromic presentations. We investigated the case of a girl affected by insulin-dependent diabetes, diagnosed at 6 years old, associated with congenital cataract. Her consanguineous parents and her four other siblings did not have diabetes or cataract, suggesting a recessive syndrome. Using whole exome sequencing of the affected proband, we identified a heterozygous p.R825Q ABCC8 mutation, located at the exact same amino-acid position as the p.R825W recurring diabetes mutation, hence likely responsible for the diabetes condition, and a homozygous p.G71S mutation in CRYBB1, a gene known to be responsible for congenital cataract. Both mutations were predicted to be damaging and were absent or extremely rare in public databases. Unexpectedly, we found that the mother was also homozygous for the CRYBB1 mutation, and both the mother and one unaffected sibling were heterozygous for the ABCC8 mutation, suggesting incomplete penetrance of both mutations. Incomplete penetrance of ABCC8 mutations is well documented, but this is the first report of an incomplete penetrance of a CRYBB1 mutation, manifesting between susceptible subjects (unaffected mother vs. affected child) and to some extent within the patient herself, who had distinct cataract severities in both eyes. Our finding illustrates the importance of family studies to unmask the role of confounding factors such as double-gene mutations and incomplete penetrance that may mimic monogenic syndromes including in the case of strongly evocative family structure with consanguinity.

MODY in Ukraine: genes, clinical phenotypes and treatment

BACKGROUND

Maturity-onset diabetes of the young (MODY) has not been previously studied in Ukraine. We investigated the genetic etiology in a selected cohort of patients with diabetes diagnosed before 18 years of age, and in their family members.

METHODS

Genetic testing of the most prevalent MODY genes (GCK, HNF1A, HNF4A, HNF1B and INS) was undertaken for 36 families (39 affected individuals) by Sanger or targeted next generation sequencing.

RESULTS

A genetic diagnosis of MODY was made in 15/39 affected individuals from 12/36 families (33%). HNF1A and HNF4A MODY were the most common subtypes, accounting for 9/15 of MODY cases. Eight patients with HNF1A or HNF4A MODY and inadequate glycemic control were successfully transferred to sulfonylureas. Median HbA1c decreased from 67 mmol/mol (range 58-69) to 47 mmol/mol (range 43-50) (8.3% [7.5-8.5] to 6.4% [6.1-6.7]) 3 months after transfer (p=0.006).

CONCLUSIONS

Genetic testing identified pathogenic HNF1A and HNF4A variants as the most common cause of MODY in Ukraine. Transfer to sulfonylureas substantially improved the glycemic control of these patients.

Population-Based Assessment of a Biomarker-Based Screening Pathway to Aid Diagnosis of Monogenic Diabetes in Young-Onset Patients

OBJECTIVE

Monogenic diabetes, a young-onset form of diabetes, is often misdiagnosed as type 1 diabetes, resulting in unnecessary treatment with insulin. A screening approach for monogenic diabetes is needed to accurately select suitable patients for expensive diagnostic genetic testing. We used C-peptide and islet autoantibodies, highly sensitive and specific biomarkers for discriminating type 1 from non-type 1 diabetes, in a biomarker screening pathway for monogenic diabetes.

RESEARCH DESIGN AND METHODS

We studied patients diagnosed at age 30 years or younger, currently younger than 50 years, in two U.K. regions with existing high detection of monogenic diabetes. The biomarker screening pathway comprised three stages: 1) assessment of endogenous insulin secretion using urinary C-peptide/creatinine ratio (UCPCR); 2) if UCPCR was ≥0.2 nmol/mmol, measurement of GAD and IA2 islet autoantibodies; and 3) if negative for both autoantibodies, molecular genetic diagnostic testing for 35 monogenic diabetes subtypes.

RESULTS

A total of 1,407 patients participated (1,365 with no known genetic cause, 34 with monogenic diabetes, and 8 with cystic fibrosis-related diabetes). A total of 386 out of 1,365 (28%) patients had a UCPCR ≥0.2 nmol/mmol, and 216 out of 386 (56%) were negative for GAD and IA2 and underwent molecular genetic testing. Seventeen new cases of monogenic diabetes were diagnosed (8 common Maturity Onset Diabetes of the Young [Sanger sequencing] and 9 rarer causes [next-generation sequencing]) in addition to the 34 known cases (estimated prevalence of 3.6% [51/1,407] [95% CI 2.7-4.7%]). The positive predictive value was 20%, suggesting a 1-in-5 detection rate for the pathway. The negative predictive value was 99.9%.

CONCLUSIONS

The biomarker screening pathway for monogenic diabetes is an effective, cheap, and easily implemented approach to systematically screening all young-onset patients. The minimum prevalence of monogenic diabetes is 3.6% of patients diagnosed at age 30 years or younger.

Identification of Maturity-Onset Diabetes of the Young Caused by Glucokinase Mutations Detected Using Whole-Exome Sequencing

Glucokinase maturity-onset diabetes of the young (GCK-MODY) represents a distinct subgroup of MODY that does not require hyperglycemia-lowering treatment and has very few diabetes-related complications. Three patients from two families who presented with clinical signs of GCK-MODY were evaluated. Whole-exome sequencing was performed and the effects of the identified mutations were assessed using bioinformatics tools, such as PolyPhen-2, SIFT, and in silico modeling. We identified two mutations: p.Leu30Pro and p.Ser383Leu. In silico analyses predicted that these mutations result in structural conformational changes, protein destabilization, and thermal instability. Our findings may inform future GCK-MODY diagnosis; furthermore, the two mutations detected in two Korean families with GCK-MODY improve our understanding of the genetic basis of the disease.

Towards a systematic nationwide screening strategy for MODY

MODY is an early-onset monogenic form of diabetes. Correctly identifying MODY is of considerable importance as diagnosing the specific genetic subtype can inform the optimal treatment, with many patients being able to discontinue unnecessary insulin treatment. Diagnostic molecular genetic testing to confirm MODY is expensive, so screening strategies are required to identify the most appropriate patients for testing. In this issue of Diabetologia, Johansson and colleagues (DOI 10.1007/s00125-016-4167-1 ) describe a nationwide systematic screening approach to identify individuals with MODY in the paediatric age range. They focused testing on patients negative for both GAD and islet antigen 2 (IA-2) islet autoantibodies, thereby ruling out those with markers of type 1 diabetes, the most common form of diabetes in this age group. This commentary discusses the advantages and limitations of the approach, and the caution required when interpreting variants of uncertain pathogenicity identified from testing whole populations rather than targeting only patients with a strong MODY phenotype.

Type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM), also known as autoimmune diabetes, is a chronic disease characterized by insulin deficiency due to pancreatic β-cell loss and leads to hyperglycaemia. Although the age of symptomatic onset is usually during childhood or adolescence, symptoms can sometimes develop much later. Although the aetiology of T1DM is not completely understood, the pathogenesis of the disease is thought to involve T cell-mediated destruction of β-cells. Islet-targeting autoantibodies that target insulin, 65 kDa glutamic acid decarboxylase, insulinoma-associated protein 2 and zinc transporter 8 - all of which are proteins associated with secretory granules in β-cells - are biomarkers of T1DM-associated autoimmunity that are found months to years before symptom onset, and can be used to identify and study individuals who are at risk of developing T1DM. The type of autoantibody that appears first depends on the environmental trigger and on genetic factors. The pathogenesis of T1DM can be divided into three stages depending on the absence or presence of hyperglycaemia and hyperglycaemia-associated symptoms (such as polyuria and thirst). A cure is not available, and patients depend on lifelong insulin injections; novel approaches to insulin treatment, such as insulin pumps, continuous glucose monitoring and hybrid closed-loop systems, are in development. Although intensive glycaemic control has reduced the incidence of microvascular and macrovascular complications, the majority of patients with T1DM are still developing these complications. Major research efforts are needed to achieve early diagnosis, prevent β-cell loss and develop better treatment options to improve the quality of life and prognosis of those affected.