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Invited Review
2 (
1
); 23-30
doi:
10.25259/JPED_6_2022

Genetics for the pediatric endocrinologists – 1

Diagnosis of monogenic diabetes among children and adolescents
Department of Molecular Genetics, Madras Diabetes Research Foundation, Chennai, Tamil Nadu, India
Department of Diabetology, Madras Diabetes Research Foundation, Chennai, Tamil Nadu, India
Department of Pediatric Endocrinology and Diabetes Unit, Department of Pediatrics, Postgraduate Institute of Medical Education and Research, Chandigarh, India
Corresponding author: Radha Venkatesan, Department of Molecular Genetics, Madras Diabetes Research Foundation, Chennai, Tamil Nadu, India. radharv@yahoo.co.in
Licence
This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

How to cite this article: Venkatesan R, Mohan V, Kumar R. Genetics for the pediatric endocrinologists – 1. Diagnosis of monogenic diabetes among children and adolescents. J Pediatr Endocrinol Diabetes 2022;2:23-30.

Abstract

The advancement in genetic laboratory technology has helped immensely in the diagnosis of many genetic disorders which could not hitherto be diagnosed. Monogenic diabetes among children and adolescents is not uncommon and needs a high index of clinical suspicion to diagnose. With the availability of genetic diagnostic laboratories with the latest technology, more and more patients should benefit from early diagnosis, specific targeted treatment, and better outcomes. The pediatricians and pediatric endocrinologists managing children with diabetes need to clinically suspect and advise appropriate genetic tests to confirm the diagnosis of monogenic diabetes. Neonatal diabetes mellitus is one of the most rewarding diagnoses, if we pick up a specific genetic abnormality that could respond to sulfonylurea. The child with KCNJ11 or ABCC8 gene mutation responding to sulfonylurea could escape from the life-long insulin injections and complications of diabetes. It is equally important to identify other forms of monogenic diabetes as the specific diagnosis can have implications in the treatment, genetic counseling, and identifying other family members harboring the same gene mutation.

Keywords

Monogenic diabetes
Maturity-onset diabetes of young
Neonatal diabetes
Glibenclamide

CASE PROFILE

A 6-week-old male baby was brought to the emergency department with rapid breathing, vomiting and an episode of seizure. He was diagnosed with diabetic ketoacidosis (DKA) with the first random blood glucose value of 527 mg/dL. The HbA1c at diagnosis was 10% and fasting C-peptide level was 0.01 ng/mL (normal range: 1.1–4.4 ng/mL). The child was born at term small-for-gestational age (SGA) with a birth weight of 1900 g, by normal vaginal delivery. The antenatal and perinatal periods were uneventful. After successfully managing DKA, the baby was started on treatment with injections of glargine and human regular insulin along with self-monitoring of blood glucose 4–6 times/day. However, the glycemic control remained poor with wide fluctuations of blood glucose.

He was referred to a tertiary care center for the advice of a pediatric endocrinologist. The insulin regimen was continued, and genetic testing was advised to look for genetic mutations in the KCNJ11 or ABCC8 genes. These two genes encode the subunits of the ATP-sensitive K+ (KATP channel) present in insulin-secreting pancreatic β-cells. A heterozygous disease-causing variant was identified in the KCNJ11 gene (Location: Exon 1; DNA Description: c.602G>T Protein Description: p. [Arg201Leu]).

He was started on glibenclamide, (an antidiabetic drug that binds to and inhibits the sulfonylurea receptor 1, SUR1 in pancreatic beta cells, and stimulates insulin release) and the clinical response was monitored with frequent blood glucose levels. Over the next 4 weeks, the baby responded to glibenclamide and insulin was slowly tapered off.

During the follow-up, the baby continued to have blood glucose levels below 150 mg/dL with HbA1c below 6.1% and the C-peptide levels of 0.57 ng/mL after 3 months of starting glibenclamide. At the last follow-up at 2.5 years of age, the baby was doing well with normal growth and development for his age. The last HbA1c and C-peptide were 6.0% and 0.90 ng/mL, respectively.

The above case profile highlights the importance of localizing the genetic abnormality in infants with neonatal diabetes mellitus (NDM). The success story of managing this index patient in terms of effective switching to oral sulfonylurea (glibenclamide) from otherwise lifelong insulin injections was made possible only due to the recognition of a specific gene mutation responding to sulfonylurea. This is an example of offering “personalized medicine” to patients with monogenic diabetes and was possible only due to the advances in genetic diagnosis in the recent years. In this short review, we discuss the clinically relevant issues which pediatricians may encounter in day-to-day management of children with suspected monogenic diabetes.

What is Monogenic Diabetes Mellitus?

Monogenic diabetes mellitus is a heterogeneous group of disorders of diabetes caused by mutations in single genes. The mutations primarily affect the pancreatic β-cells leading to reduced insulin secretion. This is in contrast to the polygenic forms of diabetes such as type 1 and type 2 diabetes mellitus which are caused by a number of genes and environmental factors.[1] As of date, 14 different forms of maturity-onset diabetes of the young (MODY) have been recognized.

What are the common forms of monogenic diabetes observed during childhood and adolescence?

The common forms of monogenic diabetes presenting during childhood and adolescence are NDM, MODY, mitochondrial diabetes, and the rare diabetes-associated syndromic diseases [Figure 1].

Figure 1:: Common types of monogenic diabetes mellitus: NDM: Neonatal diabetes mellitus; TNDM: Transient neonatal diabetes mellitus; PNDM: Permanent neonatal diabetes mellitus; MODY: Maturity onset diabetes of young; IPEX: Immunodysregulation, Polyendocrinopathy, Enteropathy, X-linked.

What are the common forms of monogenic diabetes seen among Indian population?

In India, all the four forms mentioned above, namely, NDM, MODY, mitochondrial diabetes, and diabetes-associated syndromic diseases are seen. Tables 1 and 2 summarize the important published data on the occurrence of different types of monogenic diabetes in India.[2-16]

Table 1:: Studies reporting frequency of MODY among Indian population.
Author Study population and age group Study participants Gene mutations/syndromes frequency
Mohan et al. 1985[2] <25 years 4560 individuals with diabetes onset <25 years 219 suspected to have MODY (only based on clinical profile)
Radha et al. 2009[3] 25±4 years 96 individuals with clinically suspected MODY HNF-1α mutations accounted for 9 of 96 (9.6%)
Anuradha et al. 2011[4] 21±4 years 87 individuals with clinically suspected MODY 3 of 87 (3.4%) subjects had MODY 1 while none of these subjects had GCK mutation (MODY 2)
Kanthimathi et al. 2014[5] <18 years 49 individuals with mild hyperglycemia 2 of 49 (4.08%) were found to have GCK mutation
Chapla et al. 2015[6] <35 years 56 individuals with clinically diagnosed MODY 11 (19%) positive for mutations in 10 gene panel targeted NGS
Mohan et al. 2018[7] 20.85±5.9 years 152 individuals with clinically diagnosed MODY HNF-1α {MODY 3} -7.2%; ABCC8 {MODY 12} -3.3%. Additional variants reported in AKT2, WFS1, RFX6, NKX6-1 could be related to MODY.
Lakshmanan et al. 2021[8] Children and adolescents (<18 years) 327 individuals with diabetes 37 (11%) were monogenic diabetes, out of which 15 NDM, 5 MODY, 13 Wolfram syndrome, 2 H-Syndrome, 1 Mitochondrial DM, 1 TRMA

MODY: Maturity Onset Diabetes of Young, DM: Diabetes mellitus, NDM: Neonatal diabetes mellitus, TRMA: Thiamine-responsive megaloblastic anemia, GCK: Glucokinase, NGS: Next generation sequencing

Table 2:: Studies reporting NDM among Indian population.
Author Study Population Region/City Gene Mutations/Syndromes frequency
Varadarajan 2013[9] 40 Infants with DM
29 tested for genetic mutations
Chennai Wolcott-Rallison syndrome (EIF2AK3) -9
Berardinelli-Seip lipodystrophy -1
Fanconi-Bickel syndrome -1
ABCC8 gene mutation -5
KCNJ11 gene mutation -2
GCK gene mutation -1
INS1 gene mutation -1
Jahnavi et al. 2014[10] 33 subjects with infantile-onset DM Chennai ABCC8 - 7
KCNJ11 -3
INS gene mutation -2
Berardinelli-Seip syndrome (AGPAT2) -1
Fanconi-Bickel syndrome (SLC2A2) -1
Ganesh et al. 2016[11] 10 children with NDM (onset <6 months) Chennai Transient NDM -1
Chromosome 6q24
Permanent NDM -9
KCNJ11 gene mutation -1
ABCC8 gene mutation -2
INS gene mutation -2
EIF2AK3 gene mutation -1
PDX1 gene mutation -1
SLC19A2 gene mutation -1
NEUROD1 gene mutation -1
Jain et al. 2017[12] 11 infants with NDM
9 tested for genetic mutations
New Delhi Permanent NDM -8
KCNJ11 gene mutation -3
ABCC8 gene mutation -1
INS gene mutation-1
Transient NDM -1
ZFP57 gene mutation -1
Kumar et al. 2019[13] 34 subjects with infantile-onset DM
29 children underwent genetic testing
Chandigarh Permanent NDM -9
KCNJ11 gene mutation -7
(5 out of 7 switched to sulfonylurea)
Wolcott–Rallison syndrome (EIF2AK3) -1
Homozygous GCK mutation -1
Transient NDM -3
KCNJ11 gene mutation -2
ABCC8 gene mutation -1
Gopi et al. 2021[14] 181 children with permanent NDM Chennai Permanent NDM
KCNJ11 gene mutation -20
(DEND Syndrome in 3/20)
ABCC8 gene mutation -19
33 out of total 39 (84%) patients (KCNJ11+ABCC8) switched to sulfonylurea
Nayak et al. 2021[15] 12 infants with NDM
8 presented at <6 months
Lucknow Transient NDM -3
KCNJ11 gene mutation -1
INS gene mutation-1
ABCC8 gene mutation-1
Permanent NDM -7
Homozygous GCK gene mutation -2 (siblings)
TRMA gene mutation -2 (siblings)
IPEX syndrome -1
Wolcott-Rallison syndrome -2
Gopi et al. 2021[16] 189 children with permanent NDM Chennai Permanent NDM
9 INS gene mutations in 8 children

DM: Diabetes mellitus, NDM: Neonatal diabetes mellitus

Are there regional differences in the way monogenic diabetes presents in India?

Regional differences are likely to be there in India in the way the children with monogenic diabetes present to the pediatrician, particularly with regard to the syndromic forms of neonatal diabetes especially in regions where consanguineous marriages are more prevalent, but more data are needed.

When should I suspect monogenic diabetes if a child was initially thought to have type 1 diabetes?

As per the available literature, mostly from the West, around 1–4% of all individuals with diabetes will have one or other form of monogenic diabetes.

The features specific for monogenic diabetes include the following:

  1. Diabetes onset before the age of 6 months

  2. Diagnosis of diabetes before 30 years of age with the following features:

    1. Family history with at least one affected parent with diabetes mellitus and often affecting three generations in the family

    2. Significant β-cell reserve is present outside the honeymoon phase (even after 3 years of the diagnosis): C-peptide >300 pmol/L (>0.9 ng/mL)

    3. Absence of pancreatic islet autoantibodies such as glutamic acid decarboxylase and zinc transporter, especially at diagnosis

    4. Presence of extra-pancreatic dysmorphic features suggesting a specific subtype of monogenic diabetes

    5. Non-requirement of insulin to manage diabetes for at least 2 years after the diagnosis f) Absence of ketosis.

When should I suspect monogenic diabetes if a child was initially diagnosed with type 2 diabetes?

The features specific for monogenic diabetes in children include:

  • Not significantly obese and/or the family members who are diabetic are of normal weight

  • Acanthosis nigricans is not detected on clinical evaluation

  • Ethnic background is from a race with known low occurrence of type 2 diabetes

  • There is no evidence of insulin resistance, and the fasting C-peptide levels are within normal range (300–1000 pmol/L or 0.9–3.0 ng/mL)

  • Extra-pancreatic dysmorphic features of a specific subtype of monogenic diabetes are present.

What are the different tests or technology available for the genetic diagnosis of monogenic diabetes?

There are two main technologies available for the genetic diagnosis of monogenic diabetes. One is direct gene sequencing by Sanger method and the other is high throughput next generation sequencing (NGS). In Sanger method, sequencing is done typically of one gene at a time choosing the most relevant genes for monogenic diabetes. This is very time-consuming, laborious, and cost-intensive. NGS includes targeted sequencing (tNGS) using gene panels, whole exome sequencing (WES), and whole genome sequencing (WGS).

These days, tNGS using gene panels of relevant genes is preferred over Sanger sequencing. This method facilitates the investigation of a large number of genes at the same time, making it rapid and economical. However, when a mutation is detected in a gene through this method, we validate for just that particular mutation using Sanger method as this serves as a gold standard.

In general, gene panels will be the appropriate test to order for monogenic diabetes, but there are cases where the clinical features clearly fit with a mutation of a distinct gene, as in syndromes of monogenic diabetes. In such cases, it is enough to do Sanger sequencing of the specific relevant genes in question.

WES or WGS are generally performed as gene discovery methods for detecting novel genes. They are high throughput and labor-intensive because of the volume of data that are generated.

At the Madras Diabetes Research Foundation and Dr. Mohan’s Diabetes Specialties Centre, we have set up a separate department of “Monogenic Diabetes.” This is a first such department in India. In our laboratory, we perform genetic testing for all the known and relevant genes for monogenic diabetes. The genetic testing for neonatal diabetes and syndromes of NDM is done free of cost by us. (Websites: www.mdrf.in ; www.monogenicdiabetes.in ).

How can we improve the diagnosis of monogenic diabetes in India?

First, it is important to correctly identify the genetic cause of monogenic diabetes since it has implications for treatment, surveillance of complications, associated extra-pancreatic disorders, and identification of affected and at-risk family members.[17] Each genetic subtype of monogenic diabetes demands different management and treatment and entails proper interpretation of pathogenicity. A strategy to perform differential diagnosis of monogenic diabetes is presented in [Figure 2].

Figure 2:: Strategy for differential diagnosis of monogenic diabetes mellitus. NDM: Neonatal diabetes mellitus, TNDM: Transient neonatal diabetes mellitus, PNDM: Permanent neonatal diabetes mellitus, MODY: Maturity onset diabetes of young, IPEX: Immunodysregulation, Polyendocrinopathy, Enteropathy, X-linked, WFS: Wolfram Syndrome, TRMA: Thiamine-responsive megaloblastic anemia, WRS: Wolcott Rallison Syndrome.

Another important aspect is raising the awareness of monogenic diabetes and making the diagnosis more accessible, which will certainly improve disease prognosis and management in affected children and their families.[18]

Should parents and unaffected siblings be tested?

This is a very important aspect in genetic studies. Genetics studies talk about the inheritance pattern of the mutations and testing the parents will add information regarding from whom the mutation was inherited and whether the mutation co-segregates with the disease. In addition, testing of the unaffected children enhances the predictive ability and will provide the information about the at-risk status of the siblings. This kind of testing is called cascade testing.

Are there any recent advances in diagnosis and management for the pediatrician?

The field of diabetes genetics has advanced so much that it is now possible to deliver on precision medicine. Assessing whether the identified variation in a gene is truly disease-causing or clinically actionable has been a big challenge for the molecular geneticist. However, these are being done now and they are the recent advances in this field.

How should you manage specific subtypes of monogenic diabetes?

Many of the common forms of monogenic diabetes have specific management strategies. These are based on specific mutations in the genes, leading to precision treatment. Therefore, the treatment is based on genetic etiology.

The common gene mutations responsible for NDM are in KCNJ11, ABCC8, INS, and 6q24 region.[19] NDM could be transient (45%), permanent (45%), and syndromic (10%). However, the relative frequency of the three forms of NDM is different in the Indian studies with transient <10–20%, permanent 60–70%, and syndromic NDM 20–50%. The Indian studies reporting neonatal diabetes are summarized in Table 2.[9-16] The different forms of neonatal diabetes are listed in Box 1.

Box 1:: Common forms of transient and permanent NDM.
Subtype Relative frequency Common genes affected Specific phenotype
Transient NDM
TNDM1 6q24 related 70% PLAGL, HYMAI Umbilical hernia, macroglossia
TNDM2 15% KCNJ11 Developmental delay
10% ABCC8 Developmental delay
5% INS, HNF-1B, SLCA2A Pancreatic hypoplasia, renal abnormalities (HNF-1B) Rickets, round facies, mild hyperglycemia (SLCA2A)
Permanent NDM 50% KCNJ11 ± DEND syndrome
30% INS No dysmorphism
15% ABCC8 ± DEND syndrome
3% GCK-homozygous No dysmorphism
2% PDX-1, HNF-1B homozygous Pancreatic hypoplasia and renal abnormalities (HNF-1B)

NDM: Neonatal diabetes mellitus

In those children with PNDM having INS mutations, insulin is the only treatment. A few forms of PNDM are a part of complex syndromes, having multisystemic extra-pancreatic manifestations. Wolcott-Rallison syndrome is one of the common syndromic forms of NDM seen in India and in populations with high consanguinity. Common syndromes and the associated genetic mutations presenting with NDM are listed in Box 3.

Mutations in KCNJ11 and ABCC8 genes (which encode the 2 subunits of KATP channel, KIR6.2, and SUR, respectively) lead to NDM and can manifest as transient (TNDM) or permanent (PNDM) forms. In general, TNDM have an average onset at 4 weeks and undergoes remission by around 36 weeks and has high chances of relapse later in life. The salient features of TNDM and PNDM are listed in Box 2.

Box 2:: Clinical differences between transient and permanent NDM.
Transient NDM Permanent NDM
  • Earlier age at onset (<1 month)

  • IUGR: more frequent/severe

  • Less initial insulin requirement

  • Less frequency of DKA

  • Onset usually >1 month

  • Less severe IUGR

  • Higher insulin requirement

  • Higher rates of developing DKA

DKA: Diabetic ketoacidosis, IUGR: Intrauterine growth restriction, NDM: Neonatal diabetes mellitus, DKA: Diabetic ketoacidosis

PNDM manifests around first week of life and remains life-long. Although to bring the glucose down, insulin is administered as soon as a clinical diagnosis is made, genetic testing may reveal KATP related neonatal diabetes, and then patient can be shifted to sulfonylureas (SU). Since the KIR6.2 channels are also present in the brain neurons, SU drugs also help improve neurodevelopmental problems including seizures, a common feature of these mutations, and in achieving excellent glycemic control.

6q24-related TNDM is more severe than the KATP-related TNDM with severe restriction of intrauterine growth and early onset of diabetes, but likely to have earlier remission. Affected individuals can have macroglossia and/or umbilical hernia. Insulin is the only treatment option, as these children do not respond to sulfonylurea.

In TNDM, the need for insulin gradually declines and remission is achieved at an average of 4–12 months; relapse occurs very often usually in adolescence, pregnancy, or adulthood. This is the remitting-relapsing diabetes. The relapsed diabetes usually responds to sulfonylurea and/or dipeptidyl peptidase-4 (DPP-4) inhibitors, insulin therapy may not be required.

In the case of MODY, treatment and management strategies are dependent on the subtype of MODY.[7] This is detailed below.

HNF1A-MODY (MODY 3): This is the most common form of MODY in India and in many parts of the world.3 It is characterized by progressive β-cell loss, and progressive loss of insulin secretion, with diabetes onset during adolescence or early adulthood. The first-line treatment is low dose sulfonylurea, which will partly bypass the defective insulin secretory response. Some individuals with HNF1A-MODY can be very sensitive to sulfonylurea and experience hypoglycemia even on very small doses. Glucagon-like peptide-1 agonists and DPP-4 inhibitors have been shown to be efficacious and may be useful as adjunctive therapy when glycemic control is inadequate with sulfonylurea monotherapy.

HNF4A-MODY (MODY 1): The treatment modality is the same as HNF1A-MODY.

HNF1B-MODY (MODY 5): Heterozygous mutations in HNF1B gene presents with heterogeneous phenotypes which include developmental cystic kidney disease alone, diabetes alone, or a combination of both. This type of MODY is not sensitive to SU, requiring insulin therapy.

GCK-MODY (MODY 2): This form is distinctive from other MODY types and is characterized by mild hyperglycemia due to an increased threshold for glucose-induced insulin release. It does not require pharmacologic treatment apart from pregnancy in woman with GCK-MODY. In pregnancy, appropriate management is predicted based on the genotype of the fetus. If the fetus inherits GCK mutations, mildly elevated maternal glucose levels are sensed as normal by the fetus and treatment is not required. On the other hand, if the fetus does not carry the mutations, mildly elevated maternal glucose will induce increased insulin secretion by the fetus which can lead to microsomia. In such cases, insulin therapy must be considered.

Box 3:: Common syndromic forms of NDM and their characteristic phenotypes.
Genes affected Specific phenotype
EIF2AK3 Spondyloepiphyseal dysplasia, renal anomalies, liver failure, neutropenia, intellectual disability, and hypothyroidism (Wolcott-Rallison syndrome)
FOXP3 IPEX syndrome presenting as hypothyroidism, diarrhea and eczema
GLIS3 Hypothyroidism, hepatic fibrosis, glaucoma, cystic kidneys, and developmental delay
PTF1A Pancreatic and cerebellum agenesis, and microcephaly
RFX6 Pancreatic hypoplasia, and digestive system defects (Mitchell-Riley syndrome)
NEUROG3 Congenital malabsorptive diarrhea and enteroendocrine cell dysgenesis
GATA6 Pancreatic agenesis and cardiac malformations
MNX1 Developmental delay, neurogenic bladder, sacral agenesis, and imperforate anus
NKX2 Developmental delay, hypotonia, hearing impairment, cortical blindness, and short stature
NEUROD1 Cerebellar hypoplasia, sensorineural deafness, and visual impairment
PAX 6 Central nervous system phenotype – microcephaly and panhypopituitarism
Ocular phenotype – aniridia, keratopathy, optic nerve defects, cataracts, microphthalmia, and anophthalmia
SLC19A2 Recessive mutations lead to NDM, TRMA and deafness with or without cardiac manifestations (Rogers syndrome)
SLC2A2 DM with hepatomegaly, glycosuria, proteinuria, hypophosphatemic rickets (Fanconi–Bickel syndrome)
WFS1 DIDMOAD or Wolfram Syndrome

IPEX: Immunodysregulation, Polyendocrinopathy, Enteropathy, X-linked, NDM: Neonatal diabetes mellitus, TRMA: Thiamine-responsive megaloblastic anemia, DIDMOAD: Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy, and Deafness

CONCLUSION

In a nutshell, gene-based precision treatment for monogenic diabetes has already arrived in the clinical setting. Pediatricians and pediatric endocrinologists managing children with diabetes need to be aware of when to suspect monogenic diabetes in a given child with diabetes. The confirmation of genetic diagnosis has implications in the treatment, genetic counseling, and identifying other family members harboring the same gene mutation.

Declaration of patient consent

Patient’s consent not required as there are no patients in this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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