Gene Panel Sequencing of Patients With Monogenic Diabetes Brings to Light Genes Typically Associated With Syndromic Presentations

Rare forms of monogenic diabetes in non-European individuals. First reports of CEL and RFX6 mutations from the Indian subcontinent

AIMS

Monogenic diabetes is one of the few examples in metabolic diseases in which a real precision medicine approach can be implemented in daily clinical work. Unfortunately, most of what is known today comes from studies in Whites, thus leaving much uncertainty about the genetics and the clinical presentation of monogenic diabetes in non-Europeans. To fill this gap, we report here two pedigrees from Bangladesh with CEL- and RFX6- diabetes, two rare types of monogenic diabetes which have never been described so far in individuals of the Indian subcontinent.

METHODS

Next generation, Sanger sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA) were performed. Variants' interpretation was according to the American College of Medical Genetics and Genomics guidelines.

RESULTS

In the pedigree with CEL-diabetes, a large and never described deletion of exon 2-11 of CEL (confirmed by MLPA) affecting the entire catalytic domain and being likely pathogenic (LP) was observed in both the proband (who had diabetes at 16) and his mother (diabetes at 31), but not in relatives with normoglycemia. In the pedigree with RFX6-diabetes, a LP protein truncation variant (PTV, p.Tyr192*) in RFX6 was found in both the proband (diabetes at 9) and his mother (diabetes at 30), thus suggesting high heterogeneity in disease onset. Normoglycemic relatives were not available for genetic testing.

CONCLUSIONS

We report genetic features and clinical presentation of the first two cases of CEL- and RFX6-diabetes from the Indian subcontinent, thus contributing to fill the gap of knowledge on monogenic diabetes in non-Europeans.

The genomic mosaic of mitochondrial dysfunction: Decoding nuclear and mitochondrial epigenetic contributions to maternally inherited diabetes and deafness pathogenesis

Aims

Maternally inherited diabetes and deafness (MIDD) is a complex disorder characterized by multiorgan clinical manifestations, including diabetes, hearing loss, and ophthalmic complications. This pilot study aimed to elucidate the intricate interplay between nuclear and mitochondrial genetics, epigenetic modifications, and their potential implications in the pathogenesis of MIDD.

Main methods

A comprehensive genomic approach was employed to analyze a Sicilian family affected by clinically characterized MIDD, negative to the only known causative m.3243 A > G variant, integrating whole-exome sequencing and whole-genome bisulfite sequencing of both nuclear and mitochondrial analyses.

Key findings

Rare and deleterious variants were identified across multiple nuclear genes involved in retinal homeostasis, mitochondrial function, and epigenetic regulation, while complementary mitochondrial DNA analysis revealed a rich tapestry of genetic diversity across genes encoding components of the electron transport chain and ATP synthesis machinery. Epigenetic analyses uncovered significant differentially methylated regions across the genome and within the mitochondrial genome, suggesting a nuanced landscape of epigenetic modulation.

Significance

The integration of genetic and epigenetic data highlighted the potential crosstalk between nuclear and mitochondrial regulation, with specific mtDNA variants influencing methylation patterns and potentially impacting the expression and regulation of mitochondrial genes. This pilot study provides valuable insights into the complex molecular mechanisms underlying MIDD, emphasizing the interplay between nucleus and mitochondrion, tracing the way for future research into targeted therapeutic interventions and personalized approaches for disease management.

Autosomal Dominant, Long-Standing Dysglycemia in 2 Families with Unique Phenotypic Features

We describe 2 families with 5 members from 2 generations whose clinical and laboratory characteristics over up to 15 years were consistent with dysglycemia/impaired glucose tolerance. In both families (2 probands and 3 family members), long-term follow-up excluded diabetes type 1 and type 2. Diabetes type 1 antibodies were persistently negative and C-peptide levels were normal. In Family 1, the proband, during a follow-up of 7 years (10.3-17.5 years of age), exhibited persistently high HbA1c (>5.7%) with fasting blood glucose levels mostly higher than 100 mg/dl and postprandial glucose levels up to 180 mg/dl. She eventually required oral anti-diabetics with an improvement in glycemic balance. The father and sister also had persistent mild hyperglycemia with borderline high HbA1c (mostly > 5.7%) levels over 15 and 6.2 years respectively. In Family 2, the proband exhibited borderline high fasting hyperglycemia (>100 mg/dl) at age 16.2 years with increasing HbA1c levels (from 5.6%-5.9%) and impaired glucose tolerance at age 18.3 years (2 h blood glucose 156 mg/dl after 75 g glucose). His sister also exhibited borderline hyperglycemia with borderline high HbA1c over 2 years (13.6-15.4 years). These subjects shared a unique phenotype. They are tall and slim with decreased BMI. Three subjects from Generation II failed to thrive during infancy. In view of the data from 2 generations suggesting maturity-onset diabetes of the young (MODY) with autosomal dominant inheritance, we sought to analyze the MODY genes. In Family 1, the molecular analysis by the MODY panel including 11 genes and whole exome sequencing did not detect any mutation in the proband. In Family 2, the MODY panel was also negative in the proband's sister. These families may represent a hitherto unidentified syndrome. Unique features described in this report may help to reveal additional families with similar characteristics and to decipher the molecular basis of this syndrome. In selected cases, oral antidiabetics in adolescents may improve the glycemic balance.

HNF1A gene mutations and premature ovarian failure (POF): evidence from a clinical paradigm combining MODY 3 and POF

Premature ovarian failure (POF) defines the occurrence of ovarian failure prior to the age of 40. It occurs in one out of 100 women but is very rare before age 20 (1:10,000). Maturity-onset diabetes of the young (MODY), caused by mutations in the HNF1A gene, is also a rare disorder; all types of MODY account for 1-2% of adult diabetic cases. These two rare nosologic entities coexisted in an adolescent girl evaluated for delayed puberty. Although this combination could represent a chance association, an interrelation might exist. We examined HNF1A expression in human fetal and adult ovaries by immunohistochemistry using a polyclonal HNF1A antibody. HNF1A protein was expressed in both the fetal and adult human ovaries. Based on these findings, we hypothesize that HNF1A participates in ovarian organogenesis and/or function and that mutations in the HNF1A gene might represent another molecular defect causing POF, possibly in combination with other genetic factors. The study underlines the importance of rare clinical paradigms in leading the way to elucidation of the pathogenetic mechanisms of rare diseases.

High Frequency of Recessive WFS1 Mutations Among Indian Children With Islet Antibody-negative Type 1 Diabetes

BACKGROUND

While the frequency of islet antibody-negative (idiopathic) type 1 diabetes mellitus (T1DM) is reported to be increased in Indian children, its aetiology has not been studied. We investigated the role of monogenic diabetes in the causation of islet antibody-negative T1DM.

METHODS

We conducted a multicenter, prospective, observational study of 169 Indian children (age 1-18 years) with recent-onset T1DM. All were tested for antibodies against GAD65, islet antigen-2, and zinc transporter 8 using validated ELISA. Thirty-four islet antibody-negative children underwent targeted next-generation sequencing for 31 genes implicated in monogenic diabetes using the Illumina platform. All mutations were confirmed by Sanger sequencing.

RESULTS

Thirty-five (21%) children were negative for all islet antibodies. Twelve patients (7% of entire cohort, 34% of patients with islet antibody-negative T1DM) were detected to have pathogenic or likely pathogenic genetic variants. The most frequently affected locus was WFS1, with 9 patients (5% of entire cohort, 26% of islet antibody-negative). These included 7 children with homozygous and 1 patient each with a compound heterozygous and heterozygous mutation. Children with Wolfram syndrome 1 (WS) presented with severe insulin-requiring diabetes (including 3 patients with ketoacidosis), but other syndromic manifestations were not detected. In 3 patients, heterozygous mutations in HNF4A, ABCC8, and PTF1A loci were detected.

CONCLUSION

Nearly one-quarter of Indian children with islet antibody-negative T1DM had recessive mutations in the WFS1 gene. These patients did not exhibit other features of WS at the time of diagnosis. Testing for monogenic diabetes, especially WS, should be considered in Indian children with antibody-negative T1DM.

Identification of monogenic diabetes in an Australian cohort using the Exeter maturity-onset diabetes of the young (MODY) probability calculator and next-generation sequencing gene panel testing

AIMS

This study aims to describe the prevalence of monogenic diabetes in an Australian referral cohort, in relation to Exeter maturity-onset diabetes of the young (MODY) probability calculator (EMPC) scores and next-generation sequencing with updated testing where relevant.

METHODS

State-wide 5-year retrospective cohort study of individuals referred for monogenic diabetes genetic testing.

RESULTS

After excluding individuals who had cascade testing for a familial variant (21) or declined research involvement (1), the final cohort comprised 40 probands. Incorporating updated testing, the final genetic result was positive (likely pathogenic/pathogenic variant) in 11/40 (27.5%), uncertain (variant of uncertain significance) in 8/40 (20%) and negative in 21/40 (52.5%) participants. Causative variants were found in GCK, HNF1A, MT-TL1 and HNF4A. Variants of uncertain significance included a novel multi-exonic GCK duplication. Amongst participants with EMPC scores ≥ 25%, a causative variant was identified in 37%. Cascade testing was positive in 9/10 tested relatives with diabetes and 0/6 tested relatives with no history of diabetes.

CONCLUSIONS

Contemporary genetic testing produces a high yield of positive results in individuals with clinically suspected monogenic diabetes and their relatives with diabetes, highlighting the value of genetic testing for this condition. An EMPC score cutoff of ≥ 25% correctly yielded a positive predictive value of ≥ 25% in this multiethnic demographic. This is the first Australian study to describe EMPC scores in the Australian clinic setting, albeit a biased referral cohort. Larger studies may help characterise EMPC performance between ethnic subsets, noting differences in the expected probability of monogenic diabetes relative to type 2 diabetes.

The genetic and clinical characteristics of WFS1 related diabetes in Chinese early onset type 2 diabetes

Diabetes is one of the most common phenotypes of Wolfram syndrome owing to the presence of the variants of the WFS1 gene and is often misdiagnosed as other types of diabetes. We aimed to explore the prevalence of WFS1-related diabetes (WFS1-DM) and its clinical characteristics in a Chinese population with early-onset type 2 diabetes (EOD). We sequenced all exons of the WFS1 gene in 690 patients with EOD (age at diagnosis ≤ 40 years) for rare variants. Pathogenicity was defined according to the standards and guidelines of the American College of Medical Genetics and Genomics. We identified 33 rare variants predicted to be deleterious in 39 patients. The fasting [1.57(1.06-2.22) ng/ml] and postprandial C-peptide levels [2.8(1.75-4.46) ng/ml] of the patients with such WFS1 variations were lower than those of the patients without WFS1 variation [2.09(1.43-3.05) and 4.29(2.76-6.07) respectively, ng/ml]. Six (0.9%) patients carried pathogenic or likely pathogenic variants; they met the diagnostic criteria for WFS1-DM according to the latest guidelines, but typical phenotypes of Wolfram syndrome were seldom observed. They were diagnosed at an earlier age and usually presented with an absence of obesity, impaired beta cell function, and the need for insulin treatment. WFS1-DM is usually mistakenly diagnosed as type 2 diabetes, and genetic testing is helpful for individualized treatment.

From glucose sensing to exocytosis: takes from maturity onset diabetes of the young

Monogenic diabetes gave us simplified models of complex molecular processes occurring within β-cells, which allowed to explore the roles of numerous proteins from single protein perspective. Constellation of characteristic phenotypic features and wide application of genetic sequencing techniques to clinical practice, made the major form of monogenic diabetes - the Maturity Onset Diabetes of the Young to be distinguishable from type 1, type 2 as well as neonatal diabetes mellitus and understanding underlying molecular events for each type of MODY contributed to the advancements of antidiabetic therapy and stem cell research tremendously. The functional analysis of MODY-causing proteins in diabetes development, not only provided better care for patients suffering from diabetes, but also enriched our comprehension regarding the universal cellular processes including transcriptional and translational regulation, behavior of ion channels and transporters, cargo trafficking, exocytosis. In this review, we will overview structure and function of MODY-causing proteins, alterations in a particular protein arising from the deleterious mutations to the corresponding gene and their consequences, and translation of this knowledge into new treatment strategies.

Genetic testing for misclassified monogenic diabetes in Māori and Pacific peoples in Aōtearoa New Zealand with early-onset type 2 diabetes

Aims

Monogenic diabetes accounts for 1-2% of diabetes cases yet is often misdiagnosed as type 2 diabetes. The aim of this study was to examine in Māori and Pacific adults clinically diagnosed with type 2 diabetes within 40 years of age, (a) the prevalence of monogenic diabetes in this population (b) the prevalence of beta-cell autoantibodies and (c) the pre-test probability of monogenic diabetes.

Methods

Targeted sequencing data of 38 known monogenic diabetes genes was analyzed in 199 Māori and Pacific peoples with BMI of 37.9 ± 8.6 kg/m² who had been diagnosed with type 2 diabetes between 3 and 40 years of age. A triple-screen combined autoantibody assay was used to test for GAD, IA-2, and ZnT8. MODY probability calculator score was generated in those with sufficient clinical information (55/199).

Results

No genetic variants curated as likely pathogenic or pathogenic were found. One individual (1/199) tested positive for GAD/IA-2/ZnT8 antibodies. The pre-test probability of monogenic diabetes was calculated in 55 individuals with 17/55 (31%) scoring above the 20% threshold considered for diagnostic testing referral.

Discussion

Our findings suggest that monogenic diabetes is rare in Māori and Pacific people with clinical age, and the MODY probability calculator likely overestimates the likelihood of a monogenic cause for diabetes in this population.

Prevalence, clinical features and complications of common forms of Maturity Onset Diabetes of the Young (MODY) seen at a tertiary diabetes centre in south India

BACKGROUND

Maturity Onset Diabetes of the Young (MODY) is a form of monogenic diabetes caused by mutations in single genes, affecting adolescents or young adults. MODY is frequently misdiagnosed as type 1 diabetes (T1). Though several studies from India have reported on the genetic aspects of MODY, the clinical profile, complications and treatments given have not been reported so far, nor compared with T1D and type 2 diabetes (T2D).

AIM

To determine the prevalence, clinical features, and complications of common forms of genetically proven MODY seen at a tertiary diabetes centre in South India and compare them with matched individuals with T1D and T2D.

METHODS

Five hundred and thirty individuals identified as 'possible MODY' based on clinical criteria, underwent genetic testing for MODY. Diagnosis of MODY was confirmed based on pathogenic or likely pathogenic variants found using Genome Aggregation Database (gnomAD) and American College of Medical Genetics (ACMG) criteria. The clinical profile of MODY was compared with individuals with type 1 (T1D) and type 2 (T2D) diabetes, matched for duration of diabetes. Retinopathy was diagnosed by retinal photography; nephropathy by urinary albumin excretion > 30 µg/mg of creatinine and neuropathy by vibration perception threshold > 20 v on biothesiometry.

RESULTS

Fifty-eight patients were confirmed to have MODY (10.9%). HNF1A-MODY (n = 25) was the most common subtype followed by HNF4A-MODY (n = 11), ABCC8-MODY (n = 11), GCK-MODY (n = 6) and HNF1B-MODY (n = 5). For comparison of clinical profile, only the three 'actionable' subtypes - defined as those who may respond to sulphonylureas, namely, HNF1A, HNF4A and ABCC8-MODY, were included. Age at onset of diabetes was lower among HNF4A-MODY and HNF1A-MODY than ABCC8-MODY, T1D and T2D. Prevalence of retinopathy and nephropathy was higher among the three MODY subtypes taken together (n = 47) as compared to T1D (n = 86) and T2D (n = 86).

CONCLUSION

This is one of the first reports of MODY subtypes from India based on ACMG and gnomAD criteria. The high prevalence of retinopathy and nephropathy in MODY points to the need for earlier diagnosis and better control of diabetes in individuals with MODY.

Monogenic diabetes

Monogenic diabetes includes several clinical conditions generally characterized by early-onset diabetes, such as neonatal diabetes, maturity-onset diabetes of the young (MODY) and various diabetes-associated syndromes. However, patients with apparent type 2 diabetes mellitus may actually have monogenic diabetes. Indeed, the same monogenic diabetes gene can contribute to different forms of diabetes with early or late onset, depending on the functional impact of the variant, and the same pathogenic variant can produce variable diabetes phenotypes, even in the same family. Monogenic diabetes is mostly caused by impaired function or development of pancreatic islets, with defective insulin secretion in the absence of obesity. The most prevalent form of monogenic diabetes is MODY, which may account for 0.5-5% of patients diagnosed with non-autoimmune diabetes but is probably underdiagnosed owing to insufficient genetic testing. Most patients with neonatal diabetes or MODY have autosomal dominant diabetes. More than 40 subtypes of monogenic diabetes have been identified to date, the most prevalent being deficiencies of GCK and HNF1A. Precision medicine approaches (including specific treatments for hyperglycaemia, monitoring associated extra-pancreatic phenotypes and/or following up clinical trajectories, especially during pregnancy) are available for some forms of monogenic diabetes (including GCK- and HNF1A-diabetes) and increase patients' quality of life. Next-generation sequencing has made genetic diagnosis affordable, enabling effective genomic medicine in monogenic diabetes.

The Landscape of HNF1B Deficiency: A Syndrome Not Yet Fully Explored

The hepatocyte nuclear factor 1β (HNF1B) gene is involved in the development of specialized epithelia of several organs during the early and late phases of embryogenesis, performing its function mainly by regulating the cell cycle and apoptosis pathways. The first pathogenic variant of HNF1B (namely, R177X) was reported in 1997 and is associated with the maturity-onset diabetes of the young. Since then, more than 230 different HNF1B variants have been reported, revealing a multifaceted syndrome with complex and heterogenous genetic, pathologic, and clinical profiles, mainly affecting the pediatric population. The pancreas and kidneys are the most frequently affected organs, resulting in diabetes, renal cysts, and a decrease in renal function, leading, in 2001, to the definition of HNF1B deficiency syndrome, including renal cysts and diabetes. However, several other organs and systems have since emerged as being affected by HNF1B defect, while diabetes and renal cysts are not always present. Especially, liver involvement has generally been overlooked but recently emerged as particularly relevant (mostly showing chronically elevated liver enzymes) and with a putative relation with tumor development, thus requiring a more granular analysis. Nowadays, HNF1B-associated disease has been recognized as a clinical entity with a broader and more variable multisystem phenotype, but the reasons for the phenotypic heterogeneity are still poorly understood. In this review, we aimed to describe the multifaceted nature of HNF1B deficiency in the pediatric and adult populations: we analyzed the genetic, phenotypic, and clinical features of this complex and misdiagnosed syndrome, covering the most frequent, unusual, and recently identified traits.

Maturity-onset diabetes of the young in a large Portuguese cohort

AIMS

Monogenic forms of diabetes that develop with autosomal dominant inheritance are classically aggregated in the Maturity-Onset Diabetes of the Young (MODY) categories. Despite increasing awareness, its true prevalence remains largely underestimated. We describe a Portuguese cohort of individuals with suspected monogenic diabetes who were genetically evaluated for MODY-causing genes.

METHODS

This single-center retrospective cohort study enrolled patients with positive genetic testing for MODY between 2015 and 2021. Automatic sequencing and, in case of initial negative results, next-generation sequencing were performed. Their clinical and molecular characteristics were described.

RESULTS

Eighty individuals were included, 55 with likely pathogenic/pathogenic variants in one of the MODY genes and 25 MODY-positive family members, identified by cascade genetic testing. The median age at diabetes diagnosis was 23 years, with a median HbA1c of 6.5%. The most frequently mutated genes were identified in HNF1A (40%), GCK (34%) and HNF4A (13%), followed by PDX1, HNF1B, INS, KCNJ11 and APPL1. Thirty-six unique variants were found (29 missense and 7 frameshift variants), of which ten (28%) were novel.

CONCLUSIONS

Our data highlights the importance of genetic testing in the diagnosis of MODY and the establishment of its subtypes, leading to more personalized treatment and follow-up strategies.

Monogenic diabetes in New Zealand - An audit based revision of the monogenic diabetes genetic testing pathway in New Zealand

AIMS

To evaluate (a) the diagnostic yield of genetic testing for monogenic diabetes when using single gene and gene panel-based testing approaches in the New Zealand (NZ) population, (b) whether the MODY (Maturity Onset Diabetes of the Young) pre-test probability calculator can be used to guide referrals for testing in NZ, (c) the number of referrals for testing for Māori/Pacific ethnicities compared to NZ European, and (d) the volume of proband vs cascade tests being requested.

METHODS

A retrospective audit of 495 referrals, from NZ, for testing of monogenic diabetes genes was performed. Referrals sent to LabPlus (Auckland) laboratory for single gene testing or small multi-gene panel testing, or to the Exeter Genomics Laboratory, UK, for a large gene panel, received from January 2014 - December 2021 were included. Detection rates of single gene, small multi-gene and large gene panels (neonatal and non-neonatal), and cascade testing were analysed. Pre-test probability was calculated using the Exeter MODY probability calculator and ethnicity data was also collected.

RESULTS

The diagnostic detection rate varied across genes, from 32% in GCK, to 2% in HNF4A, with single gene or small gene panel testing averaging a 12% detection rate. Detection rate by type of panel was 9% for small gene panel, 23% for non-neonatal monogenic diabetes large gene panel and 40% for neonatal monogenic diabetes large gene panel. 45% (67/147) of patients aged 1-35 years at diabetes diagnosis scored <20% on MODY pre-test probability, of whom 3 had class 4/5 variants in HNF1A, HNF4A or HNF1B. Ethnicity data of those selected for genetic testing correlated with population diabetes prevalence for Māori (15% vs 16%), but Pacific People appeared under-represented (8% vs 14%). Only 1 in 6 probands generated a cascade test.

CONCLUSIONS

A new monogenic diabetes testing algorithm for NZ is proposed, which directs clinicians to choose a large gene panel in patients without syndromic features who score a pre-test MODY probability of above 20%.

Monogenic diabetes clinic (MDC): 3-year experience

AIM

In the pediatric diabetes clinic, patients with type 1 diabetes mellitus (T1D) account for more than 90% of cases, while monogenic forms represent about 6%. Many monogenic diabetes subtypes may respond to therapies other than insulin and have chronic diabetes complication prognosis that is different from T1D. With the aim of providing a better diagnostic pipeline and a tailored care for patients with monogenic diabetes, we set up a monogenic diabetes clinic (MDC).

METHODS

In the first 3 years of activity 97 patients with non-autoimmune forms of hyperglycemia were referred to MDC. Genetic testing was requested for 80 patients and 68 genetic reports were available for review.

RESULTS

In 58 subjects hyperglycemia was discovered beyond 1 year of age (Group 1) and in 10 before 1 year of age (Group 2). Genetic variants considered causative of hyperglycemia were identified in 25 and 6 patients of Group 1 and 2, respectively, with a pick up rate of 43.1% (25/58) for Group 1 and 60% (6/10) for Group 2 (global pick-up rate: 45.5%; 31/68). When we considered probands of Group 1 with a parental history of hyperglycemia, 58.3% (21/36) had a positive genetic test for GCK or HNF1A genes, while pick-up rate was 18.1% (4/22) in patients with mute family history for diabetes. Specific treatments for each condition were administered in most cases.

CONCLUSION

We conclude that MDC may contribute to provide a better diabetes care in the pediatric setting.

Achievements, prospects and challenges in precision care for monogenic insulin-deficient and insulin-resistant diabetes

Integration of genomic and other data has begun to stratify type 2 diabetes in prognostically meaningful ways, but this has yet to impact on mainstream diabetes practice. The subgroup of diabetes caused by single gene defects thus provides the best example to date of the vision of 'precision diabetes'. Monogenic diabetes may be divided into primary pancreatic beta cell failure, and primary insulin resistance. In both groups, clear examples of genotype-selective responses to therapy have been advanced. The benign trajectory of diabetes due to pathogenic GCK mutations, and the sulfonylurea-hyperresponsiveness conferred by activating KCNJ11 or ABCC8 mutations, or loss-of-function HNF1A or HNF4A mutations, often decisively guide clinical management. In monogenic insulin-resistant diabetes, subcutaneous leptin therapy is beneficial in some severe lipodystrophy. Increasing evidence also supports use of 'obesity therapies' in lipodystrophic people even without obesity. In beta cell diabetes the main challenge is now implementation of the precision diabetes vision at scale. In monogenic insulin-resistant diabetes genotype-specific benefits are proven in far fewer patients to date, although further genotype-targeted therapies are being evaluated. The conceptual paradigm established by the insulin-resistant subgroup with 'adipose failure' may have a wider influence on precision therapy for common type 2 diabetes, however. For all forms of monogenic diabetes, population-wide genome sequencing is currently forcing reappraisal of the importance assigned to pathogenic mutations when gene sequencing is uncoupled from prior suspicion of monogenic diabetes.

Search for a time- and cost-saving genetic testing strategy for maturity-onset diabetes of the young

AIMS

Correct genetic diagnosis of maturity-onset diabetes of the young (MODY) is beneficial for person's diabetes management compared to no genetic testing. Aim of the present study was a search for optimal time- and cost-saving strategies by comparing two approaches of genetic testing of participants with clinical suspicion of MODY.

METHODS

A total of 121 consecutive probands referred for suspicion of MODY (Group A) were screened using targeted NGS (tNGS), while the other 112 consecutive probands (Group B) underwent a single gene test based on phenotype, and in cases of negative findings, tNGS was conducted. The study was performed in two subsequent years. The genetic results, time until reporting of the final results and financial expenses were compared between the groups.

RESULTS

MODY was confirmed in 30.6% and 40.2% probands from Groups A and B, respectively; GCK-MODY was predominant (72.2% in Group A and 77.8% in Group B). The median number of days until results reporting was 184 days (IQR 122-258) in Group A and 91 days (44-174) in Group B (p < 0.00001). Mean costs per person were higher for Group A (639 ± 30 USD) than for Group B (584 ± 296 USD; p = 0.044).

CONCLUSIONS

The two-step approach represented a better strategy for genetic investigation of MODY concerning time and costs compared to direct tNGS. Although a single-gene investigation clarified the diabetes aetiology in the majority of cases, tNGS could reveal rare causes of MODY and expose possible limitations of both standard genetic techniques and clinical evaluation.

MODY probability calculator utility in individuals' selection for genetic testing: Its accuracy and performance

Introduction

MODY probability calculator (MPC) represents an easy‐to‐use tool developed by Exeter University to help clinicians prioritize which individuals should be oriented to genetic testing. We aimed to assess the utility of MPC in a Portuguese cohort with early‐onset monogenic diabetes.

Methods

This single‐centre retrospective study enrolled 132 participants submitted to genetic testing between 2015 and 2020. Automatic sequencing and, in case of initial negative results, generation sequencing were performed. MODY probability was calculated using the probability calculator available online. Positive and negative predictive values (PPV and NPV, respectively), accuracy, sensitivity and specificity of the calculator were determined for this cohort.

Results

Seventy‐three individuals were included according to inclusion criteria: 20 glucokinase (GCK‐MODY); 16 hepatocyte nuclear factor 1A (HNF1A‐MODY); 2 hepatocyte nuclear factor 4A (HNF4A‐MODY) and 35 DM individuals with no monogenic mutations found. The median probability score of MODY was significantly higher in monogenic diabetes‐positive subgroup (75.5% vs. 24.2%, p < .001). The discriminative accuracy of the calculator, as expressed by area under the curve, was 75% (95% CI: 64%–85%). In our cohort, the best cut‐off value for the MODY calculator was found to be 36%, with a PPV of 74.4%, NPV of 73.5% and corresponding sensitivity and specificity of 76.2% and 71.4%, respectively.

Conclusions

In a highly pre‐selected group of probands qualified for genetic testing, the Exeter MODY probability calculator provided a useful tool in individuals' selection for genetic testing, with good discrimination ability under an optimal probability cut‐off of 36%. Further geographical and population adjustments are warranted for general use.

HNF1B-MODY Masquerading as Type 1 Diabetes: A Pitfall in the Etiological Diagnosis of Diabetes

Hepatocyte nuclear factor-1B (HNF1B) maturity-onset diabetes of the young (MODY), also referred to as “renal cysts and diabetes syndrome” or MODY-5, is a rare form of monogenic diabetes that is caused by a deletion or a point mutation in the HNF1B gene, a developmental gene that plays a key role in regulating urogenital and pancreatic development. HNF1B-MODY has been characterized by its association with renal, hepatic and other extrapancreatic features.

We present the case of a 39-year-old female patient who was first diagnosed with type 1 diabetes, but then, owing to the absence of anti-islet autoantibodies and to the disease’s progression, was labeled later on as having atypical type 2 diabetes. She was finally recognized as having HNF1B-MODY, a diagnosis that had been suggested by the lack of metabolic syndrome and by the presence of unexplained chronically disturbed liver function tests and hypomagnesemia. There was a 10-year delay between the onset of diabetes and the molecular diagnosis. An atypical form of diabetes, especially in patients with multisystem involvement, should raise suspicion for an alternative etiology. A timely diagnosis of HNF1B-MODY is of utmost importance since it can greatly impact diabetes management and disease progression as well as family history.

Diabetes Mellitus Diagnosed in Childhood and Adolescence With Negative Autoimmunity: Results of Genetic Investigation

Monogenic diabetes is a rare form of diabetes, accounting for approximately 1% to 6% of pediatric diabetes patients. Some types of monogenic diabetes can be misdiagnosed as type 1 diabetes in children or adolescents because of similar clinical features. Identification of the correct etiology of diabetes is crucial for clinical, therapeutic, and prognostic issues. Our main objective was to determine the prevalence of monogenic diabetes in patients with diabetes mellitus, diagnosed in childhood or in adolescence, and negative autoimmunity. We retrospectively analyzed clinical data of 275 patients diagnosed with insulin-dependent diabetes at age <18yr in the last 10 years. 8.4% of subjects has negative autoimmunity. Their DNA was sequenced by NGS custom panel composed by 45 candidate genes involved in glucose metabolism disorder. Two novel heterozygous pathogenic or likely pathogenic variants (10,5% of autoantibody negative subjects) were detected: the frameshift variant c.617_618insA in NEUROD1 exon 2 and the missense change c.116T>C in INS exon 2. Our study corroborates previous results of other reports in literature. NGS assays are useful methods for a correct diagnosis of monogenic diabetes, even of rarest forms, highlighting mechanisms of pediatric diabetes pathogenesis.