There are two distinct subtypes of NDM: (i) permanent; and (ii) transient form characterized by resolution of diabetes within weeks to months [4]. Activating mutations in the genes ABCC8 and KCNJ11, which encode for the Kir6.2 and SUR1 subunits, respectively, of the ATP-sensitive potassium (KATP) channel of the pancreatic beta cells are the commonest cause of permanent NDM [2]. Of the transient NDM cases, nearly 70% of are caused by loss of methylation at the differentially imprinted locus on chromosome 6q24 [4], while KCNJ11 and ABCC8 mutations account for majority of the remaining cases [5]. The present study was conducted with the objective of describing the genetic mutation profile and the clinical presentation, management and outcome of children with neonatal diabetes mellitus at our institute over the last seven years.

We reviewed the case records of all infants with NDM presenting to All India Institute of Medical Sciences (AIIMS), New Delhi from January 2009 to December 2015. NDM was diagnosed when the child presented within the first 6 months of life with symptoms of polyuria and dehydration with random blood sugar more than 200 mg/dL, or when the presentation was later in the first year but proven to be of monogenic etiology [1,2].

All infants were hospitalized at presentation. Diabetic ketoacidosis (DKA) was managed as per protocol [6]. Subsequent management was with 0.3 to 0.7 U/kg/day of subcutaneous insulin in multiple divided doses. Majority of the infants needed 1-2 doses of Neutral Protamine Hagedorn (NPH) insulin and 3-4 doses of Regular insulin. Parents were instructed to dilute the insulin with normal saline and administer it using insulin syringe. They were given simple written instructions to monitor blood glucose at home, manage hypo- and hyper-glycemia, and check urinary ketones when baby was sick [7]; close follow-up was maintained.

Genetic mutation analysis was done after obtaining informed consent from the parents. Genetic testing for six infants (cases 1, 6, 7, 8, 9 and 11 in Table I) was carried out at Department of Molecular Genetics, Royal Devon and Exeter NHS Foundation Trust, Exeter, UK. It consisted of rapid Sanger sequencing of the KCNJ11, ABCC8 and INS genes with additional EIF2AK3 analysis in infants born to related parents. In patient 8, a custom designed targeted next generation sequencing of all known NDM genes [3] was also done; and methylation analysis for chromosome 6q24 was conducted at Wessex Regional Genetics Laboratory, Salisbury [8,9]. Mutation testing for cases 2, 3, 4 and 5 was done at Department of Molecular Genetics, Madras Diabetes Research foundation, Chennai. Sequencing was carried out on ABI 3500 Genetic Analyzer (Applied Biosystems, Foster City, CA) using the Big Dye terminator V3.1, and the sequences were compared with the database. Published primers were used to amplify the DNA for KCNJ11, ABCC8 and INS [10,11].

TABLE I  Summary of the Clinical Profile and Mutations in the Patients with Neonatal Diabetes Mellitus

After receiving the genetic report, four infants with mutations in KCNJ11 or ABCC8 were switched to oral sulfonylureas as per the protocol [12]. All children were followed-up for growth, development and glycemic control.

Eleven infants (8 boys) were diagnosed with NDM. The clinical, demographic and genetic mutation profile of the cases is summarized in Table I. The median (range) age at initial presentation was 8 (1- 44) weeks. Mean (SD) birth weight was 2.4 (0.5) kg, with 7 (63.6%) infants being low birth weight. Six (54.5%) infants had presented with DKA; 4 (36.4%) with polyuria, irritability and increased demand for feeds, and one was diagnosed by surveillance of blood glucose in view of previous sibling’s death with NDM.

Eight (72.7%) infants in our cohort had permanent NDM, 2 had transient NDM and the type was uncertain in one child who died at 3 months. Pathogenic genetic mutations were identified in seven (63.6%) infants (Table I). The most commonly affected gene was KCNJ11 in three cases, followed by INS gene in two cases. One patient each had mutation in ABCC8 and ZFP57 genes. None of the common mutations were identified in three infants. In one patient, initial sample was insufficient and the baby died before repeat sample could be obtained.

We were able to successfully transfer all four children with mutations in either KCNJ11 or ABCC8 genes from insulin to oral glibenclamide. The age at transfer ranged from 2 to 9 months. The initial dose of glibenclamide on which glycemic control was achieved ranged from 0.5 to 2 mg/kg/day, and was reduced on follow-up. Glycemic control was excellent in these children with no episode of DKA or symptomatic hypoglycemia. At last follow-up, the mean (SD) HbA1c level in these 4 children was 6.6 (0.5)%. Two infants having mutations in the INS gene were continued on subcutaneous regular and NPH insulin, and are under regular follow-up.

Limitations of this study are: small sample size and incomplete genetic evaluation for some of the patients. Of the four cases without confirmed genetic mutation, two had undergone evaluation for only the three most common genes (KCNJ11, ABCC8 and INS), one had transient NDM but could not be tested for loss of methylation and one baby died before genetic testing.

In a recent large study, it was reported that in offspring of non-consanguineous parents, mutations in KCNJ11, ABCC8, INS and 6q24 methylation abnormalities accounted for approximately 28%, 18%, 10% and 10%, respectively of the NDM cases; while among children of consanguineous parents, EIF2AK3 mutations were the commonest [2]. In an earlier Indian series, Jahnavi, et al. [14] had reported a total of 12 mutations in 33 children with infancy-onset diabetes; ABCC8 in 7, KCNJ11 in 3 and INS in 2. In another recent series from Chennai [15], mutation profile of 10 children with NDM (six of whom were born to consanguineous parents) was presented. Nine of these had permanent NDM, attributable to mutations in ABCC8 and INS in 2 each, and KCNJ11, EIF2AK3, SLC19A2, NEUROD1 and PDX1 in one each; while one had transient NDM due to loss of methylation in chromosome 6q24.

The identification of mutations in KCNJ11 or ABCC8 genes highlights the importance of establishing early genetic diagnosis, as these patients can be switched over to oral sulfonylureas, that are not only more convenient, but also associated with reduction in episodes of hypo- and hyper-glycemia [12,13]. Insulin gene (INS) mutations are associated with synthesis of misfolded preproinsulin or proinsulin that is retained in endoplasmic reticulum and results in apoptosis of the beta cells, leading to permanent insulin-dependence. The age at onset is variable with many patients presenting beyond 6 months or even beyond infancy. INS mutations are typically sporadic and heterozygous [10], as in both our cases. Abnormalities in 6q24 are typically associated with moderate intrauterine growth retardation and diabetes within first week of life. Hyperglycemia remits by few weeks to months, but may recur during illness [4], and nearly half relapse during adolescence or early adulthood [16].

To conclude, genetic testing is essential in children with neonatal diabetes mellitus. It not only confirms the diagnosis, but also defines the prognosis of the affected child, and predicts the risk in subsequent pregnancies. Since mutations in KCNJ11 and ABCC8 have major therapeutic implications, these genes should be screened first. Testing of 6q24 must be considered in infants with NDM who had intrauterine growth retardation, and go into spontaneous remission. The role of adequate counseling and education of the parents in appropriate management of the young infants with NDM cannot be over-emphasized. Early diagnosis, identification of the genetic defect and appropriate clinical management can be very rewarding.

Acknowledgements: Dr Deborah Mackay and Prof Karen I Temple for performing the methylation specific analysis, and to Mr Anil Kumar for extracting DNA and ensuring safe transport of the clinical samples from AIIMS to the laboratories in Chennai or Exeter.

Contributors: VJ: conceptualized the study design, critically revised the paper and will act as guarantor; VJ, AS: drafted the paper, VJ, AS, JY, RS: acquired the data; VR, VM, EDF, SE: performed and interpreted the mutation analysis. All authors contributed to manuscript writing and approved the final draft.

Competing interests: None stated.

Funding: SE is the recipient of a Wellcome Trust Senior Investigator award (grant number:　WT098395/Z/12/Z). The genetic analysis carried out at Institute of Biomedical and Clinical Science, Exeter has been supported by this grant.

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