KCNJ11 activating Mutation in an Indian Family with ... - MedIND

1 downloads 0 Views 177KB Size Report
Sep 12, 2009 - To identify the genetic cause of transient neonatal diabetes mellitus in three siblings from an Indian family. Methods. Case reports with clinical ...
Original Article

KCNJ11 activating Mutation in an Indian Family with Remitting and Relapsing Diabetes V.V. Khadilkar, A.V. Khadilkar, R.R. Kapoor1, K. Hussain1, A.T. Hattersley2 and S. Ellard2 Hirabai Cowasji Jehangir Medical Research Institute, Pune, India, 1Institute of Child Health & Great Ormond Street Hospital, London WC1N 1EH and 2Institute of Biomedical and Clinical Science, Peninsula Medical School, Exeter EX2 5DW

ABSTRACT Objective. To identify the genetic cause of transient neonatal diabetes mellitus in three siblings from an Indian family. Methods. Case reports with clinical and molecular evaluation of an activating mutation in the KCNJ11 gene are presented. We describe an Indian family with two asymptomatic parents with 3 children presenting with hyperglycemia at 6, 1.5 and 1 month of age respectively. Blood glucose levels at presentation were 22.2, 18.3 and 20 mmol/L and the diabetes remitted in all three children by 5 years of age. None of the affected siblings had dysmorphism or neurological abnormalities. Diabetes relapsed in the oldest sibling at 9.4 years of age and she is now euglycemic on 1mg/Kg of Glibenclamide twice a day. Results. A novel heterozygous missense mutation (G53V) in the KCNJ11 gene was identified in all 3 affected children and the father. Conclusions. The report suggests that screening for KCNJ11 mutations is appropriate in patients diagnosed with neonatal diabetes as it provides valuable information concerning possible course of the disease and choice of treatment. [Indian J Pediatr 2010; 77 (5) : 551-554] E-mail: [email protected]; [email protected]

Key words: KCNJ11; Neonatal diabetes; Relapse; Remit

Diabetes diagnosed in the neonatal period is usually associated with altered β-cell number or function and is often a single gene disorder. 1 Heterozygous gain-of function mutations in KCNJ11, situated on chromosome 11, are the commonest cause of permanent neonatal diabetes (in almost 50% patients) in multiple populations and ethnic groups. KCNJ11 encodes Kir6.2, the poreforming subunit of the ATP-sensitive potassium channel (KATP channel). Gloyn et al first reported that Kir6.2 mutations result in neonatal diabetes2. There is a spectrum of phenotypes associated with activating mutations in Kir6.2 varying from transient neonatal diabetes to permanent diabetes in childhood or adulthood.3,4,5 In addition to neonatal diabetes, some patients also have neurological features, including the DEND syndrome where neonatal diabetes is associated with developmental delay and epilepsy.2,3,6,7 Correspondence and Reprint requests : Dr. V.V. Khadilkar, Pediatric Endocrinologist, Hirabai Cowasji Jehangir Medical Research Institute, Jehangir Hospital, 32 Sassoon Road, Pune 411 001, India. [DOI-10.1007/s12098-010-0062-9]

Most patients with Kir6.2 mutations present with symptomatic hyperglycemia and many present in ketoacidosis. KATP channel mutations account for a unique sub-type of diabetes that can be treated with sulfonylureas.4,6,8 We describe here an Indian family with three children with transient neonatal diabetes mellitus (TNDM), where these children and their father were heterozygous for a missense mutation (G53V) in the KCNJ11 gene. Three siblings presented with neonatal diabetes which remitted, and has now relapsed in the oldest child who is well controlled on an oral hypoglycemic agent. Written informed consent was obtained from parents before publication of this report.

REPORT OF CASES Proband: The proband was born at 32 weeks of gestation with a birth weight of 1.8 kg to nonconsanguineous parents (Fig 1). At 6 month of age she was admitted with vomiting, dehydration and metabolic acidosis. On admission, she weighed 5.8 Kg (-2.3 standard deviation score for age and sex). Initial investigations revealed an

[Received September 12, 2009; Accepted December 18, 2009]

Indian Journal of Pediatrics, Volume 77—May, 2010

551

V.V Khadilkar et al was treated with antibiotic and s/c short acting insulin. Her urinary ketones were negative and other investigations were normal. She was discharged on s/c intermediate acting insulin on twice daily dose and was on insulin for the next 4 months. Parents and the clinician (VK) once again found a downward trend in sugars. By 6 months of age she was euglycemic without insulin and all treatment was discontinued. Sibling 4 (S4): Sibling 4 was born at full term with a birth weight of 2.6 kg. He has been completely asymptomatic to date. Random blood glucose levels tested with his affected siblings have all been normal. Sibling 5 (S5): Sibling 5 was born at full term with a birth weight of 2.5 kg. He was admitted with vomiting and metabolic acidosis at one month of age. He, like the other siblings was diagnosed with transient neonatal diabetes and was put on s/c insulin which was administered for a month. His blood glucose levels started gradually declining till he was completely off therapy by two months of age. Fig 1. Family tree with three affected and one unaffected sibling.

elevated blood glucose concentration of 22.2 mmol/L (400 mg/dl), c-peptide of 66.6 pmol/L (0.2 ng/ml) (ref range 119-1189 pmol/L), venous blood pH of 7.10 with presence of ketones in the urine; consistent with a diagnosis of diabetic ketoacidosis (DKA). The HbA1c on presentation was elevated at 10%. An ultrasound scan of the abdomen revealed a normally placed pancreas. A diagnosis of Type I diabetes was made and after successful treatment of the DKA, she was discharged on thrice daily subcutaneous (s/c) insulin. Parents monitored capillary blood glucose concentrations regularly at home and found a downward trend in blood glucose levels with several episodes of hypoglycemia over the next few years. Insulin treatment was discontinued at 5 year of age. However, she re-presented at 9.5 year of age with symptoms of weight loss, fatigue, polyuria and polydipsia. A diagnosis of diabetes mellitus was re-established and the patient was commenced on insulin therapy. After initial stabilization, glibencamide was introduced and gradually increased to investigate whether it could replace insulin. Insulin was successfully stopped at a dose of 1mg/kg/day. Currently, her median premeal blood glucose concentrations are below 6.7 (120 mg/dl) and post meal are below 7.8 mmol/L (140 mg/dl) with an HbA1c of 5%. Sibling 2: The second baby was born prematurely and died due to unknown cause in the early neonatal period. Sibling 3 : The proband’s sibling 3 (S3) was born at full term with a birth weight of 2.5 kg. She presented at 1 and a half months of age with vomiting and dehydration. At admission her blood glucose concentration was 18.3 mmol/L(329 mg/dl), C-peptide was 99.9 pmol/L(0.3 ng/ ml), HbA1c was 9% and her blood pH was normal. She 552

Mutation analysis Genomic DNA was extracted from peripheral leukocytes using standard procedures. The KCNJ11, ABCC8 and INS genes were amplified by PCR and the products sequenced using a BigDye Terminator cycler sequencing Kit v3.1 (Applied Biosystems, Warrington, UK). The sequencing reactions were analysed on an ABI 3730 capillary sequencer (Applied Biosytems, Warrington, UK) and sequences were compared to the published sequences using Mutation Surveyor version 2.61 (Softgenetics PA, USA).

RESULTS A novel heterozygous missense mutation (G53V) was identified in the proband’s KCNJ11 gene. Her two affected siblings were also heterozygous for the same mutation which was inherited from their unaffected father. This G>T mutation at nucleotide 158 (c.158G>T) results in the substitution of the amino acid valine for glycine at codon 53 (p.Gly53Val). The G53V mutation is likely to be pathogenic since the glycine residue is conserved across species and four different mutations at this codon; G53R, G53S, G53D and G53N have previously been reported.3, 5,9 Functional studies have also been conducted on KATP channel with mutations in Kir6.2 at this residue that have shown an altered response to ATP5.

DISCUSSION Neonatal diabetes has been defined as hyperglycemia presenting in the first six month of life.4 This condition Indian Journal of Pediatrics, Volume 77—May, 2010

KCNJ11 activating Mutation in an Indian Family with Remitting and Relapsing Diabetes may be transient or permanent. The majority of cases of transient neonatal diabetes mellitus (TNDM) are due to abnormalities of an imprinted locus on chromosome 6q244. Permanent neonatal diabetes are most commonly caused by heterozygous activating KCNJ11 mutations6,10, followed by mutations in the INS gene.11 Mutations in the KCNJ11 gene can also cause TNDM that remits and relapses.5 This is in line with our findings of a heterozygous missense mutation G53V in the KCJN11 gene which has resulted in TNDM in three siblings in one family with the diabetes having relapsed in the oldest sibling. Mutations at the same residue as found in our family have, in fact been described to cause varying phenotypes from TNDM (G53R, G53S)5 to PNDM9 to severe diabetes with DEND (developmental delay, epilepsy and neonatal diabetes) syndrome.3 None of the children in the present study showed any neurological abnormalities, developmental delay or dysmorphic features (Fig. 2). Interestingly, despite inheriting the same heterozygous missense mutation, the father is currently asymptomatic aged 40years This suggests that the same mutation can cause a variable phenotype within the same family (Table 1), as has been reported previously.4 He is at increased risk of developing diabetes. At low glucose concentrations, K+ efflux through open KATP channels maintains the β-cell membrane in a hyperpolarized state, thus the voltage- gated Ca+2 channels remain closed. Increase in the blood glucose concentration increases glucose uptake by the β-cell, producing changes in cytosolic nucleotide concentrations resulting in closure of the KATP channel. Mutations in the KCJN11 gene cause neonatal diabetes by reducing KATP channel ATP sensitivity and increasing the KATP current, which inhibits β-cell electrical activity and insulin secretion. 1 In the family studied, the heterozygous missense mutation resulting in neonatal diabetes in the

Fig. 2. All four siblings from affected family.

three of the siblings was transmitted by the father. Patients with activating mutations in the KCJN11 have been reported to have low birth weight reflecting impaired intrauterine and postnatal insulin secretion. Also in the family studied, the first siblings birth weight was below the 1st percentile (-2.8 Z score), S3 was on the 5th percentile (-1.4 Z score) and S5 was on the 3rd percentile (-1.5 Z score). The median age at diagnosis has been reported to be 6 week with all patients being diagnosed by 6 month. 1 This is in line with age at diagnosis of siblings in the present study, who were diagnosed at 6 month, 6 week and 4 week respectively. At diagnosis all had hyperglycemia and low C-peptide levels and two of the siblings presented with ketoacidosis. Studies have suggested that KATP channels that are insensitive to ATP as a consequence of Kir6.2 mutations could be closed by an ATP-independent mechanism (e.g. by sulphonylureas) and insulin secretion might be restored. It has

TABLE 1. Clinical Characteristics, Mutation and Current Status of Siblings from Affected Family Clinical presentation

Age at diabetes diagnosis

Blood glucose at presentation mmol/L

Birth Weigh t Kg

Clinical picture at diagnosis

Mutation

Current status

Sibling 1 Female

Transient Neonatal Diabetes, remitted, then relapsed at 9.4 yrs

6 months

22.2

1.8

DKA, treated with Insulin

Missense mutation (G53V) in the KCNJ11

Diabetic on glibenclamide

Sibling 2 Male

Born premature (27 weeks),died in immediate post natal period

-

-

-

-

-

-

Sibling 3 Female

Transient Neonatal Diabetes

1.5 months

18.3

2.5

Vomitting, dehydration

Normal, off all therapy

Sibling 4 Male

Normal

-

-

2.6

-

Sibling 5 Female

Transient Neonatal Diabetes

1 month

20

2.5

DKA, treated with Insulin

Missense mutation (G53V) in the KCNJ11 Missense mutation (G53V) in the KCNJ11 Missense mutation (G53V) in the KCNJ11

Indian Journal of Pediatrics, Volume 77—May, 2010

Normal, off all therapy Normal, off all therapy

553

V.V Khadilkar et al thus been reported that many patients can discontinue insulin injections and show improved glycemic control when treated with high-dose sulfonylurea tablets. 8 While two of the siblings studied have shown remission and are off all treatment, the oldest sibling had a relapse and is now well controlled on glibenclamide. CONCLUSIONS In conclusion, we report a novel KCNJ11 mutation, G53V, in a family with three siblings affected with transient neonatal diabetes. This report highlights the importance of genetic analysis in neonatal diabetes and demonstrates that it provides valuable information regarding outcome and choice of treatment.

3.

4.

5.

6.

Acknowledgments We acknowledge funding from the Wellcome Trust for genetic analysis. Genetic testing for neonatal diabetes (diagnosed under 6 month) is available free of charge, see www.diabetesgenes.org for details. Contributions: AVK, VVK, RRK and KH were involved in the clinical work up. ATH, SE, RRK and KH were involved in the genetic work up. All authors were involved in preparing the manuscript. VVK will act as guarantor of the study. Conflict of Interest: None.

7.

8.

9.

Role of Funding Source: None.

REFERENCES 1. Hattersley AT, Ashcroft FM. Activating mutations in Kir6.2 and neonatal diabetes: new clinical syndromes, new scientific insights, and new therapy. Diabetes 2005; 54: 2503-2513. 2. Gloyn AL, Pearson ER, Antcliff JF, Proks P, Bruining GJ,

554

10.

11.

Slingerland AS et al. Activating mutations in the gene encoding the ATP-sensitive potassium- channel subunit Kir6.2 and permanent neonatal diabetes. N Engl J Med 2004; 350: 1838-1849. Flanagan SE, Edghill EL, Gloyn AL, Ellard S, Hattersley AT. Mutations in KCNJ11, which encodes Kir6.2, are a common cause of diabetes diagnosed in the first 6 months of life, with the phenotype determined by genotype. Diabetologia 2006; 49: 1190-1197. Flanagan SE, Patch AM, Mackay DJ, Edghill EL, Gloyn AL, Robinson D et al. Mutations in ATP-sensitive K+ channel genes cause transient neonatal diabetes and permanent diabetes in childhood or adulthood. Diabetes 2007; 56: 19301937. Gloyn AL, Reimann F, Girard C, Edghill EL, Proks P, Pearson ER et al. Relapsing diabetes can result from moderately activating mutations in KCNJ11. Hum Mol Genet 2005; 14: 925934. Sagen JV, Raeder H, Hathout E, Shehadeh N, Gudmundsson K, Baevre H et al. Permanent neonatal diabetes due to mutations in KCNJ11 encoding Kir6.2: patient characteristics and initial response to sulfonylurea therapy. Diabetes 2004; 53: 2713-2718. Proks P, Girard C, Haider S, Gloyn AL, Hattersley AT, Sansom SP et al. A gating mutation at the internal mouth of the Kir6.2 pore is associated with DEND syndrome. EMBO Rep 2005; 6: 470–475. Pearson ER, Flechtner I, Njølstad PR et al. Switching from insulin to oral sulfonylureas in patients with diabetes due to Kir6.2 mutations. N Engl J Med 2006; 355: 467-477. Vaxillaire M, Populaire C, Busiah K, Cavé H, Gloyn AL, Hattersley AT et al. Kir6.2 mutations are a common cause of permanent neonatal diabetes in a large cohort of French patients. Diabetes 2004; 53: 2719-2722. Edghill E, Flanagan S, Patch AM, Boustred C, Parrish, Shields B et al. Insulin Mutation Screening in 1044 Patients with Diabetes: Mutations in the INS gene are a Common Cause of Neonatal Diabetes but a Rarer Cause of Diabetes Diagnosed in Childhood or Adulthood. Diabetes 2008; 57: 1034-1042. Ashcroft FM, Rorsman P. Electrophysiology of the pancreatic b-cell. Prog Biophys Mol Biol 1989; 54: 87–143.

Indian Journal of Pediatrics, Volume 77—May, 2010