Incidental mild hyperglycemia in children: two MODY 2 families identified in Brazilian subjects

Identification of Variants Responsible for Monogenic Forms of Diabetes in Brazil

Monogenic forms of diabetes mellitus may affect a significant number of patients of this disease, and it is an important molecular cause to be investigated. However, studies of the genetic causes of monogenic diabetes, especially in populations with mixed ethnic backgrounds, such as the one in Brazil, are scarce. The aim of this study was to screen several genes associated with monogenic diabetes in fifty-seven Brazilian patients with recurrence of the disease in their families and thirty-four relatives. Inclusion criteria were: Age of onset ≤ 40 years old, BMI < 30 kg/m², at least two affected generations and negative anti-GAD and anti-IA2 antibodies. MODY genes HNF4A, GCK, HNF1A, HNF1B, NEUROD1, KLF11, PAX4, INS, KCNJ11, and MT-TL1 were sequenced by Sanger sequencing. We identified a total of 20 patients with variants, 13 GCK-MODY, four HNF1A-MODY, and one variant in each of the following genes, HNF4A, HNF1B and MT-TL1. Segregation analysis was performed in 13 families. Four variants were novel, two in GCK (p.(Met115Val) [c.343A>G] and p.(Asp365GlufsTer95) [c.1094_1095insGCGA]) and two in HNF1A (p.(Tyr163Ter) [c.489C>G] and p.(Val380CysfsTer39) [c.1136_1137insC]). Here we highlight the importance of screening for monogenic diabetes in admixed populations.

Tunisian Maturity-Onset Diabetes of the Young: A Short Review and a New Molecular and Clinical Investigation

INTRODUCTION/AIMS

Maturity-Onset Diabetes of the Young (MODY) is a monogenic non-autoimmune diabetes with 14 different genetic forms. MODY-related mutations are rarely found in the Tunisian population. Here, we explored MODY related genes sequences among seventeen unrelated Tunisian probands qualifying the MODY clinical criteria.

MATERIALS AND METHODS

The GCK and HNF1A genes were systematically analyzed by direct sequencing in all probands. Then, clinical exome sequencing of 4,813 genes was performed on three unrelated patients. Among them, 130 genes have been reported to be involved in the regulation of glucose metabolism, β-cell development, differentiation and function. All identified variants were analyzed according to their frequencies in the GnomAD database and validated by direct sequencing.

RESULTS

We identified the previously reported GCK mutation (rs1085307455) in one patient. The clinical features of the MODY2 proband were similar to previous reports. In this study, we revealed rare and novel alterations in GCK (rs780806456) and ABCC8 (rs201499958) genes with uncertain significance. We also found two likely benign alterations in HNF1A (rs1800574) and KLF11 (rs35927125) genes with minor allele frequencies similar to those depicted in public databases. No pathogenic variants have been identified through clinical exome analysis.

CONCLUSIONS

The most appropriate patients were selected, following a strict clinical screening approach, for genetic testing. However, the known MODY1-13 genes could not explain most of the Tunisian MODY cases, suggesting the involvement of unidentified genes in the majority of Tunisian affected families.

A rare splice site mutation in the gene encoding glucokinase/hexokinase 4 in a patient with MODY type 2

The article presents a variant of maturity onset diabetes of the young type 2, caused by a rare mutation in the GCK gene. Maturity onset diabetes of the young (MODY) is a hereditary form of diabetes with an autosomal dominant type of inheritance, an onset at a young age, and a primary defect in pancreatic β-cell function. This type of diabetes is different from classical types of diabetes mellitus (DM1 and DM2) in its clinical course, treatment strategies, and prognosis. Clinical manifestations of MODY are heterogeneous and may vary even among members of the same family, i. e., carriers of identical mutations. This phenotypic variation is due to the interaction of mutations with different genetic backgrounds and the influence of environmental factors (e. g., lifestyle). Using next-generation sequencing technology, the c.580–1G>A substitution (IVS5 –1G>A, rs1554335421) located in an acceptor splice site of intron 5 of the GCK gene was found in a proband. The identified variant cosegregated with a pathological phenotype in the examined family members. The GCK gene encodes glucokinase (hexokinase 4), which catalyzes the first step in a large number of glucose metabolic pathways such as glycolysis. Mutations in this gene are the cause of MODY2. The illness is characterized by an insignificant increase in the fasting glucose level, is a well-controlled disease without medication, and has a low prevalence of micro- and macrovascular complications of diabetes. The presented case of MODY2 reveals the clinical significance of a mutation in the splice site of the GCK gene. When nonclassical diabetes mellitus is being diagnosed in young people and pregnant women, genetic testing is needed to verify the diagnosis and to select the optimal treatment method. Key words: human; maturity onset diabetes of the young; MODY2; glucokinase gene; next-generation sequencing; genetic analysis; bioinformatics.

Hyperglycemia in pediatric age: could it be maturity onset diabetes of the young? Case reports and review of the literature

Maturity Onset Diabetes of the Young (MODY) includes a clinically and genetically heterogeneous group of diabetes subtypes with MODY-2 being the second most prevalent form. We report 2 cases of MODY-2 identified during the investigation of asymptomatic hyperglycemia. A 12-year-old girl with a familiar history of diabetes (mother, maternal aunt, and maternal grandfather) was referred due to hypercholesterolemia, abnormal fasting glucose (114 mg/dL), and increased levels of glycated haemoglobin (HbA1c) (6%) presenting with negative β-cell antibodies. A glucokinase (GCK) heterozygous missense mutation c.364C&gt;T (p.Leu122Phe) in exon 4 was identified in the index patient and in the 3 family members. An obese 9-year-old boy was investigated for elevated fasting glycemic levels (99-126 mg/dL), HbA1c rise (6.6%-7.6%), and negative β-cell antibodies. The patient's father, paternal aunt, and paternal grandfather had a history of diabetes during their childhood. A GCK heterozygous missense mutation c.698G&gt;A (p.Cys233Tyr) in exon 7 was identified in the index patient. This variant was only described in another family strongly affected by both MODY and classic autoimmune mediated diabetes, contrary to our case. MODY-2 should be suspected in the presence of early onset of persistent mild fasting hyperglycemia and negative β-cell antibodies associated with a positive family history of diabetes. These cases illustrate the challenging aspects of MODY diagnosis due to possible phenotypic overlap with other types of diabetes. The diagnosis requires a high level of suspicion and GCK genetic screening should be performed in the presence of compatible features. An early diagnosis allows for appropriate management, genetic counselling, and the identification of affected family members.

Clinical application of ACMG-AMP guidelines in HNF1A and GCK variants in a cohort of MODY families

Maturity-onset diabetes of the young (MODY) is a form of monogenic diabetes with autosomal dominant inheritance. GCK -MODY and HNF1A -MODY are the prevalent subtypes. Currently, there is growing concern regarding the correct interpretation of molecular genetic findings. The American College of Medical Genetics and Genomics (ACMG) updated guidelines to interpret and classify molecular variants. This study aimed to determine the prevalence of MODY ( GCK / HNF1A ) in a large cohort of Brazilian families, to report variants related to phenotype, and to classify them according to ACMG guidelines. One hundred and nine probands were investigated, 45% with clinical suspicion of GCK -MODY and 55% with suspicion of HNF1A -MODY. Twenty-five different variants were identified in GCK gene (30 probands-61% of positivity), and 7 variants in HNF1A (10 probands-17% of positivity). Fourteen of them were novel (12- GCK /2- HNF1A ). ACMG guidelines were able to classify a large portion of variants as pathogenic (36%- GCK /86%- HNF1A ) and likely pathogenic (44%- GCK /14%- HNF1A ), with 16% (5/32) as uncertain significance. This allows us to determine the pathogenicity classification more efficiently, and also reinforces the suspected associations with the phenotype among novel variants.

Maturity-onset diabetes of the young (MODY) in Brazil: Establishment of a national registry and appraisal of available genetic and clinical data

AIMS

Maturity-Onset Diabetes of the Young (MODY) comprises a heterogeneous group of monogenic forms of diabetes caused by mutations in at least 14 genes, but mostly by mutations in Glucokinase (GCK) and hepatocyte nuclear factor-1 homeobox A (HNF1A). This study aims to establish a national registry of MODY cases in Brazilian patients, assessing published and unpublished data.

METHODS

311 patients with clinical characteristics of MODY were analyzed, with unpublished data on 298 individuals described in 12 previous publications and 13 newly described cases in this report.

RESULTS

72 individuals had GCK mutations, 9 described in Brazilian individuals for the first time. One previously unpublished novel GCK mutation, Gly178Ala, was found in one family. 31 individuals had HNF1A mutations, 2 described for the first time in Brazilian individuals. Comparisons of GCK probands vs HNF1A: age 16±11 vs 35±20years; age at diagnosis 11±8 vs 21±7years; BMI 19±6 vs 25±6kg/m²; sulfonylurea users 5 vs 83%; insulin users 5 vs 17%; presence of arterial hypertension 0 vs. 33%, all p<0.05. No differences were observed in lipids and C-peptide.

CONCLUSIONS

Most MODY cases in Brazil are due to GCK mutations. In agreement with other studied populations, novel mutations are common. Only 14% of patients with familial diabetes carry a HNF1A mutation. Diagnosis of other rare forms of MODY is still a challenge in Brazilian population, as well as adequate strategies to screen individuals for molecular diagnosis.

Maturity onset diabetes of young type 2 due to a novel de novo GKC mutation

Maturity Onset Diabetes of Young (MODY) is a heterogeneous group of monogenic disorders that result in β-cell dysfunction, with an estimated prevalence of 1%-2% in industrialized countries. MODY generally occurs in non-obese patients with negative autoantibodies presenting with mild to moderate hyperglycemia. The clinical features of the patients are heterogeneous, depending on the different genetic subtypes. We pretend to report a case of MODY type 2 caused by a novel de novo CGK mutation, highlighting the importance of the differential diagnosis in pediatric diabetes. A 13-year-old, healthy and non-obese girl was admitted for investigation of recurrent hyperglycemia episodes. She presented with persistent high levels of fasting blood glycemia (> 11.1 mmol/L) and had no familial history of diabetes. The blood glucose profile revealed an impaired fasting glucose of 124 mg/dL (6,9 mmol/L) with a normal oral glucose tolerance test. Fasting insulinemia was 15 mg/dL (90.1 pmol/L), HOMA-IR was 3.9 and hemoglobin A1c was 7.1%. Pancreatic autoantibodies were negative. Genetic testing identified a novel missense heterozygous mutation in exon 5 of GCK gene c.509G > T (p.Gly170Val), not present on the parents. This result established the diagnosis of MODY type 2. Clinical identification of patients with MODY remains a diagnostic challenge, especially when familial history is absent. Molecular diagnosis is very important for establishing an individualized treatment and providing a long term prognosis for each type of MODY.