Pediatric Monogenic Diabetes: A Unique Challenge and Opportunity

Monogenic diabetes affects approximately 120,000 people in the United States but continues to be misdiagnosed. Within the pediatric population, 1% to 3% of diabetes is monogenic, and early diagnosis and genetically targeted management of congenital diabetes and maturity onset diabetes of the young (MODY) can have a tremendous impact on future health outcomes and quality of life. In some of the more common monogenic diabetes types, patients can switch from insulin therapy to sulfonylureas or even discontinue glucose-lowering therapy with stable glycemic control. Advancements in the field have identified tools and resources to aid in distinguishing patients likely to have monogenic diabetes from the more common forms of type 1 and type 2 diabetes. However, genetic testing with accurate interpretation of results is necessary to confirm a diagnosis and direct treatment selection and disease management. This article discusses challenges and opportunities in monogenic diabetes in the pediatric population. [Pediatr Ann. 2019;48(8):e319-e325.].

RETINAL VEIN OCCLUSION IN A PATIENT WITH MATERNALLY INHERITED DIABETES AND DEAFNESS

PURPOSE

To report a case of maternally inherited diabetes and deafness complicated by branch retinal vein occlusion and cystoid macular edema.

METHODS

Retrospective case report. Multimodal imaging including spectral domain optical coherence tomography, en face optical coherence tomography, and fundus autofluorescence was preformed, and the findings are presented.

FINDINGS

A 58-year-old female with a history of diabetes mellitus, hearing loss, and a previous diagnosis of age-related macular degeneration presented with decreased vision in the right eye. Clinical examination and multimodal imaging demonstrated a right inferior branch retinal vein occlusion complicated by cystoid macular edema and bilateral maculopathy suspicious for maternally inherited diabetes and deafness. Genetic testing confirmed an A3243G mitochondrial mutation.

CONCLUSION

Multimodal retinal imaging is a key to guide diagnosis of rare genetic diseases such as maternally inherited diabetes and deafness. We report the unusual presentation of maternally inherited diabetes and deafness complicated by branch retinal vein occlusion and cystoid macular edema.

GATA6 mutations cause a broad phenotypic spectrum of diabetes from pancreatic agenesis to adult-onset diabetes without exocrine insufficiency

We recently reported de novo GATA6 mutations as the most common cause of pancreatic agenesis, accounting for 15 of 27 (56%) patients with insulin-treated neonatal diabetes and exocrine pancreatic insufficiency requiring enzyme replacement therapy. We investigated the role of GATA6 mutations in 171 subjects with neonatal diabetes of unknown genetic etiology from a cohort of 795 patients with neonatal diabetes. Mutations in known genes had been confirmed in 624 patients (including 15 GATA6 mutations). Sequencing of the remaining 171 patients identified nine new case subjects (24 of 795, 3%). Pancreatic agenesis was present in 21 case subjects (six new); two patients had permanent neonatal diabetes with no enzyme supplementation and one had transient neonatal diabetes. Four parents with heterozygous GATA6 mutations were diagnosed with diabetes outside the neonatal period (12-46 years). Subclinical exocrine insufficiency was demonstrated by low fecal elastase in three of four diabetic patients who did not receive enzyme supplementation. One parent with a mosaic mutation was not diabetic but had a heart malformation. Extrapancreatic features were observed in all 24 probands and three parents, with congenital heart defects most frequent (83%). Heterozygous GATA6 mutations cause a wide spectrum of diabetes manifestations, ranging from pancreatic agenesis to adult-onset diabetes with subclinical or no exocrine insufficiency.

Phenotype variability and neonatal diabetes in a large family with heterozygous mutation of the glucokinase gene

Monogenic diabetes caused by mutations in the glucokinase gene (GCK-MODY) is usually characterized by a mild clinical phenotype. The clinical course of diabetes may be, however, highly variable. The authors present a child with diabetes manifesting with ketoacidosis during the neonatal period, born in a large family with ten members bearing a heterozygous p.Gly223Ser mutation in GCK. DNA sequencing and multiplex ligation-dependent probe amplification were used to confirm GCK mutation and exclude other de novo mutations in other known genes associated with monogenic diabetes. Continuous glucose monitoring (CGM) was used to assess daily glycemic profiles. At the onset of diabetes the child had hyperglycemia 765 mg/dl with pH 7.09. Her glycated hemoglobin level was 8.6% (70.5 mmol/mol). The C-peptide level was below normal range (<0.5 pmol/ml) at onset, and the three- and 6-month follow-up examinations. Current evaluation at age 3 still showed unsatisfactory metabolic control with HbA1c level equal to 8.1% (65.0 mmol/mol). CGM data showed glucose concentrations profile similar to poorly controlled type 1 diabetes. The patient was confirmed to be heterozygous for the p.Gly223Ser mutation and did not show any point mutations or deletions within other monogenic diabetes genes. Other family members with p.Gly223Ser mutation had retained C-peptide levels and mild diabetes manageable with diet (five individuals), oral hypoglycemizing agents (five patients), or insulin (one patient). This mutation was absent within all healthy family members. Heterozygous mutations of the GCK gene may result in neonatal diabetes similar to type 1 diabetes, the cause of such phenotype variety is still unknown. The possibility of other additional, unknown mutations seems to be the most likely explanation for the unusual presentation of GCK-MODY.

Mutations in pancreatic ß-cell Glucokinase as a cause of hyperinsulinaemic hypoglycaemia and neonatal diabetes mellitus

Glucokinase is a key enzyme involved in regulating insulin secretion from the pancreatic ß-cell. The unique role of glucokinase in human glucose physiology is illustrated by the fact that genetic mutations in glucokinase can either cause hyperglycaemia or hypoglycaemia. Heterozygous inactivating mutations in glucokinase cause maturity-onset diabetes of the young (MODY), homozygous inactivating in glucokinase mutations result in permanent neonatal diabetes whereas heterozygous activating glucokinase mutations cause hyperinsulinaemic hypoglycaemia.

An in-frame deletion in Kir6.2 (KCNJ11) causing neonatal diabetes reveals a site of interaction between Kir6.2 and SUR1

CONTEXT

Activating mutations in genes encoding the Kir6.2 (KCNJ11) and SUR1 (ABCC8) subunits of the pancreatic ATP-sensitive K(+) channel are a common cause of permanent neonatal diabetes (PNDM). All Kir6.2 mutations identified to date are missense mutations. We describe here a novel in-frame deletion (residues 28-32) in Kir6.2 in a heterozygous patient with PNDM without neurological problems that are detectable by standard evaluation.

OBJECTIVE

The aim of the study was to identify the mutation responsible for neonatal diabetes in this patient and characterize its functional effects.

DESIGN

Wild-type and mutant Kir6.2/SUR1 channels were examined by heterologous expression in Xenopus oocytes.

RESULTS

The Kir6.2-28Delta32 mutation produced a significant decrease in ATP inhibition and an increase in whole-cell K(ATP) currents, explaining the diabetes of the patient. Tolbutamide block was only slightly reduced in the simulated heterozygous state, suggesting that the patient should respond to sulfonylurea therapy. The mutation decreased ATP inhibition indirectly, by increasing the intrinsic (unliganded) channel open probability. Neither effect was observed when Kir6.2 was expressed in the absence of SUR1, suggesting that the mutation impairs coupling between SUR1 and Kir6.2. Coimmunoprecipitation studies further revealed that the mutation disrupted a physical interaction between Kir6.2 and residues 1-288 (but not residues 1-196) of SUR1.

CONCLUSIONS

We report a novel KCNJ11 mutation causing PNDM. Our results show that residues 28-32 in the N terminus of Kir6.2 interact both physically and functionally with SUR1 and suggest that residues 196-288 of SUR1 are important in this interaction.

Permanent neonatal diabetes due to mutations in KCNJ11 encoding Kir6.2: patient characteristics and initial response to sulfonylurea therapy

Permanent neonatal diabetes (PND) can be caused by mutations in the transcription factors insulin promoter factor (IPF)-1, eukaryotic translation initiation factor-2alpha kinase 3 (EIF2AK3), and forkhead box-P3 and in key components of insulin secretion: glucokinase (GCK) and the ATP-sensitive K(+) channel subunit Kir6.2. We sequenced the gene encoding Kir6.2 (KCNJ11) in 11 probands with GCK-negative PND. Heterozygous mutations were identified in seven probands, causing three novel (F35V, Y330C, and F333I) and two known (V59M and R201H) Kir6.2 amino acid substitutions. Only two probands had a family history of diabetes. Subjects with the V59M mutation had neurological features including motor delay. Three mutation carriers tested had an insulin secretory response to tolbutamide, but not to glucose or glucagon. Glibenclamide was introduced in increasing doses to investigate whether sulfonylurea could replace insulin. At a glibenclamide dose of 0.3-0.4 mg. kg(-1). day(-1), insulin was discontinued. Blood glucose did not deteriorate, and HbA(1c) was stable or fell during 2-6 months of follow-up. An oral glucose tolerance test performed in one subject revealed that glucose-stimulated insulin release was restored. Mutations in Kir6.2 were the most frequent cause of PND in our cohort. Apparently insulin-dependent patients with mutations in Kir6.2 may be managed on an oral sulfonylurea with sustained metabolic control rather than insulin injections, illustrating the principle of pharmacogenetics applied in diabetes treatment.

Insulin sensitivity, glucose effectiveness, and insulin secretion in nondiabetic offspring of patients with non-insulin-dependent diabetes mellitus: a cross-sectional study

To evaluate the factors that determine the worsening of intravenous glucose tolerance in subjects at high risk for developing non-insulin-dependent diabetes mellitus (NIDDM), 15 glucose-tolerant offspring of NIDDM patients and 21 control subjects were studied. Each subject underwent a frequently sampled intravenous glucose tolerance (FSIGT) test. The intravenous glucose tolerance index (K(G) index) was calculated between minutes 10 and 40 of a FSIGT test. Insulin sensitivity (S(I)), glucose effectiveness at zero insulin (GEZI), and first- and second-phase insulin responsiveness (phi1 and phi2) were estimated using glucose and insulin kinetic minimal models. The acute insulin response to glucose (AIRg) was calculated as the area under the insulin curve above the basal level between 0 and 10 minutes, and the suprabasal insulin effect was determined by the product of S(I) times AIRg. Offspring had a lower S(I) than control subjects (14.1 +/- 7.5 v 9.25 +/- 4.20 x 10(-5) x min(-1)(pmol x L(-1))(-1), P < .01), and their AIRg was similar (3,284 +/- 2,280 v 3,105 +/- 1,499 pmol x L(-1), NS). Sample division according to the median K(G) value showed that control subjects with low tolerance had a lower AIRg (4,417 +/- 2,531 v 2,043 +/- 1,068 pmol x L(-1), P < .05) and a lower suprabasal insulin effect (0.057 +/- 0.03 v 0.023 +/- 0.009 min(-1), P < .05) than control subjects with high tolerance. Offspring with low tolerance had a lower AIRg (2,574 +/- 1,197 v 3,707 +/- 1,656 pmol x L(-1), P < .05) and a lower GEZI (0.101 +/- 0.05 v 0.212 +/- 0.08 x 10(-1) x min(-1), P < .05) than offspring with high tolerance. Offspring with high and low tolerance showed lower phi1 (375 +/- 155 v 272 +/- 181 v 698 +/- 336 (pmol x L(-1))min(mmol x L(-1)), NS) than control subjects with high tolerance. In conclusion, our data suggest that decreases in GEZI and AIRg are the main factors responsible for the worsening of intravenous glucose tolerance in the offspring of NIDDM patients.