MODY probability calculator for GCK and HNF1A screening in a multiethnic background population

MODY calculator applied in patients with clinical diagnosis of type 1 diabetes mellitus: Is a higher cutoff needed?

Aim

This study aimed to evaluate the mean post-test probability (PTP) of the Maturity-onset diabetes of the young (MODY) calculator in a multiethnic cohort of patients previously diagnosed with type 1 diabetes (T1DM).

Materials and methods

The MODY probability calculator proposed by Shields and colleagues (2012) was applied to 117 patients from a T1DM outpatient clinic at a tertiary hospital in Brazil. Additionally, two exons of the HNF1A gene were sequenced in eight patients who hadn't received insulin treatment within six months after the diagnosis.

Results

17.1 % of patients achieved PTP >10 %; 11.1 % achieved PTP >25 % (and all patients >30 %), and 7.7 % achieved PTP >40 %. Among the patients who were selected for genetic sequencing, 100 % presented PTP >30 %, with 66.6 % achieving PTP >40 % and 41.6 % achieving PTP >75 %. These cutoffs are as suggested for the Brazilian population, according to previous investigations. No mutation was observed in the sequenced exons.

Conclusion

Considering that only around 10 % of the evaluated cases achieved PTP >30 %, it is highly probable that the most suitable cutoff to select patients for genetic sequencing in a Brazilian cohort of T1DM is higher than the cutoff used in Caucasian populations.

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.

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.

MODY Probability Ratios in Patients Diagnosed with Type 2 Diabetes Mellitus at a Young Age

Objective

Maturity-onset diabetes of the young (MODY) is a non-rare group of monogenic inherited diabetes which is commonly confused with type 1 and type 2 diabetes. Due to high costs of genetic tests that provide a definitive diagnosis, some screening scales are used to identify the high-risk patients. In this study, we aimed to evaluate whether (MODY Probability Calculator [MPC]) which is one of the screening tests will be helpful in identifying our high-risk patients among young patients with type 2 diabetes

Method

The patients received the diagnosis of type 2 diabetes aged <35 years were included in the study. The anthropometric characteristics of the patients, the treatments they received at the time of diagnosis, and the current treatments were recorded by retrospectively scanning patient files.The patients with the diagnosis of type 1 diabetes having autoantibodies to the pancreas were excluded from the study. The probability of MODY was calculated using MPC..

Results

The mean age of 72 patients (40% female) was 41.5±7.2 years. Eighteen of the patients (25%) were using insulin at the time of diagnosis. The mean HbA1c was 8.6±2.2% and C-peptide was 2.35±1.52 ng/ml. The mean MODY positive predictive score calculated by MPC for risk of MODY was 11.23 percent. There were 61 patients (84.7%) with a risk of ≤20%, 9 patients (12.5%) with a risk of 20-50%, and 2 patients (2.8%) with ≥50%. In the group with MODY PPV score >20%, the age of onset of diabetes and the body mass index was significantly lower than the others (p<0.05, for both). There was no significant difference between current treatments of both groups.

Conclusion

It has been reported that MODY risk calculated by MPC may yield different results in different populations. The results of this study showed that 15% of our young-onset diabetes patients had an MPC score above 20 percent. Requesting MODY genetic tests in this 15% of the patient group can be presented as a practical suggestion.

Identification of the First PAX4-MODY Family Reported in Brazil

PURPOSE

The aim of this study was to sequence the coding region of the PAX4 gene in a Brazilian cohort with clinical manifestations of monogenic diabetes.

PATIENTS AND METHODS

This study included 31 patients with autosomal dominant history of diabetes, age at diagnosis ≤40 years, BMI <30 kg/m2, and no mutations in GCK or HNF1A, HNF4A, and HNF1B. Screening of the PAX4 coding region was performed by Sanger sequencing. In silico algorithms were used to assess the potential impact of amino acid substitutions on protein structure and function. Additionally, PAX4-MODY family members and 158 control subjects without diabetes were analyzed for the identified mutation.

RESULTS

The molecular analysis of PAX4 has detected one missense mutation, p.Arg164Gln (c.491G>A), segregating with diabetes in a large Brazilian family. The mutation was absent among the control group. The index case is a woman diagnosed at 32 years of age with polyneuropathy and treated with insulin. She did not present diabetic renal disease or retinopathy. Family members with the PAX4 p.Arg164Gln mutation have a heterogeneous clinical manifestation and treatment response, with age at diagnosis ranging from 24 years to 50 years.

CONCLUSION

To the best of our knowledge, this is the first study to report a PAX4-MODY family in Brazil. The age of PAX4-MODY diagnosis in the Brazilian family seems to be higher than the classical criteria for MODY. Our results reinforce the importance of screening large monogenic diabetes families for the understanding of the clinical manifestations of rare forms of diabetes for the specific and personalized treatment.