Islet-specific antibody seroconversion in patients with long duration of permanent neonatal diabetes caused by mutations in the KCNJ11 gene

Congenital beta cell defects are not associated with markers of islet autoimmunity, even in the context of high genetic risk for type 1 diabetes

AIMS/HYPOTHESIS

A key unanswered question in type 1 diabetes is whether beta cells initiate their own destruction or are victims of an aberrant immune response (beta cell suicide or homicide?). To investigate this, we assessed islet autoantibodies in individuals with congenital beta cell defects causing neonatal diabetes mellitus (NDM).

METHODS

We measured autoantibodies to GAD (GADA), islet antigen-2 (IA-2A) and zinc transporter 8 (ZnT8A) in 242 individuals with NDM (median age diagnosed 1.8 months [IQR 0.39-2.9 months]; median age collected 4.6 months [IQR 1.8-27.6 months]; median diabetes duration 2 months [IQR 0.6-23 months]), including 75 whose NDM resulted from severe beta cell endoplasmic reticulum (ER) stress. As a control cohort we also tested samples from 69 diabetes-free individuals (median age collected 9.9 months [IQR 9.0-48.6 months]) for autoantibodies.

RESULTS

We found low prevalence of islet autoantibodies in individuals with monogenic NDM; 13/242 (5.4% [95% CI 2.9, 9.0%]) had detectable GADA, IA-2A and/or ZnT8A. This was similar to the proportion in the control participants who did not have diabetes (1/69 positive [1.4%, 95% CI 0.03, 7.8%], p=0.3). Importantly, monogenic individuals with beta cell ER stress had a similar rate of GADA/IA-2A/ZnT8A positivity to non-ER stress aetiologies (2.7% [95% CI 0.3, 9.3%] vs 6.6% [95% CI 3.3, 11.5%] p=0.4). We observed no association between islet autoimmunity and genetic risk, age at testing (including 30 individuals >10 years at testing) or diabetes duration (p>0.4 for all).

CONCLUSIONS/INTERPRETATION

Our data support the hypothesis that beta cell stress/dysfunction alone does not lead to the production of islet autoantibodies, even in the context of high-risk HLA types. This suggests that additional factors are required to trigger an autoimmune response towards beta cells.

Zinc transporter 8 autoantibodies (ZnT8-ab) are associated with higher prevalence of multiple diabetes-related autoantibodies in adults with type 1 diabetes

AIM

The study aimed to assess the prevalence of zinc transporter 8 autoantibodies (ZnT8-ab), other diabetes-related autoantibodies and clinical manifestation of type 1 diabetes in adults, depending on age of the onset of disease.

METHODS

119 patients with type 1 diabetes, 66 at age <35 years (T1DM < 35) and 53 T1DM at age ≥35 years (T1DM ≥ 35). We assessed clinical features, GAD-ab, IA2-ab, ICA, ZnT8-ab and thyroid peroxidase antibodies (ATPO).

RESULTS

In T1DM < 35 lower initial serum C-peptide concentration was observed and diabetes ketoacidosis (DKA) was more common. ATPO positivity was more prevalent in T1DM ≥ 35 (35.8 vs 21.2%, p = 0.04). The prevalence of GAD-ab, IA2-ab and ZnT8-ab was similar in both groups, the titres of IA2-ab and ICA were higher in T1DM < 35 but titre of ZnT8-ab was higher in T1DM ≥ 35. The majority of T1DM < 35 patients were positive for three autoantibodies (40.9%), while T1DM ≥ 35 subjects most often presented with only one (30.2%) antibody, most commonly GAD-ab (81.2%). 45% T1DM < 35 and 34% T1DM ≥ 35 subjects were positive for ZnT8-ab. ZnT8-ab positive patients had higher titre and more frequent occurrence of multiple diabetes-related autoantibodies than ZnT8-ab negative patients.

CONCLUSIONS

Adults with T1DM < 35 and T1DM ≥ 35 differ in the severity of autoimmune response at diagnosis. ZnT8-ab positivity is related to higher titre and more frequent occurrence of multiple diabetes-related autoantibodies.

Successful sulfonylurea treatment in a patient with permanent neonatal diabetes mellitus with a novel KCNJ11 mutation

Permanent neonatal diabetes mellitus refers to diabetes that occurs before the age of 6 months and persists through life. It is a rare disorder affecting one in 0.2-0.5 million live births. Mutations in the gene KCNJ11, encoding the subunit Kir6.2, and ABCC8, encoding SUR1 of the ATP-sensitive potassium (K_ATP) channel, are the most common causes of permanent neonatal diabetes mellitus. Sulfonylureas close the K_ATP channel and increase insulin secretion. KCNJ11 and ABCC8 mutations have important therapeutic implications because sulfonylurea therapy can be effective in treating patients with mutations in the potassium channel subunits. The mutation type, the presence of neurological features, and the duration of diabetes are known to be the major factors affecting the treatment outcome after switching to sulfonylurea therapy. More than 30 mutations in the KCNJ11 gene have been identified. Here, we present our experience with a patient carrying a novel p.H186D heterozygous mutation in the KCNJ11 gene who was successfully treated with oral sulfonylurea.

Challenges in diagnosing type 1 diabetes in different populations

Diabetes affects today an estimated 366 million people world-wide, including 20 million to 40 million of patients with type 1 diabetes (T1D). While T1D accounts for 5% to 20% of those with diabetes, it is associated with higher morbidity, mortality and health care cost than the more prevalent type 2 diabetes. Patients with T1D require exogenous insulin for survival and should be identified as soon as possible after diagnosis to avoid high morbidity due to a delay in insulin treatment. It is also important to present to the patient correct prognosis that differs by the type of diabetes. From the research point of view, correct classification should help to identify the etiologies and to develop specific prevention for T1D. This review summarizes evidence that may be helpful in diagnosing T1D in various ethnic groups. Challenges in interpretation of results commonly used to determine the type of diabetes are highlighted.

Neonatal diabetes: an expanding list of genes allows for improved diagnosis and treatment

There has been major progress in recent years uncovering the genetic causes of diabetes presenting in the first year of life. Twenty genes have been identified to date. The most common causes accounting for the majority of cases are mutations in the genes encoding the two subunits of the ATP-sensitive potassium channel (K(ATP)), KCNJ11 and ABCC8, and the insulin gene (INS), as well as abnormalities in chromosome 6q24. Patients with activating mutations in KCNJ11 and ABCC8 can be treated with oral sulfonylureas in lieu of insulin injections. This compelling example of personalized genetic medicine leading to improved glucose regulation and quality of life may-with continued research-be repeated for other forms of neonatal diabetes in the future.

Mother and daughter carrying the same KCNJ11 mutation but with a different response to switching from insulin to sulfonylurea

KCNJ11 gene mutations are related to permanent neonatal diabetes mellitus (PNDM). Glycemic stability minimizes the risk of complications. Sulfonylureas (SU) are the proven best therapeutic option. We report a 18-month follow-up of switching from insulin to SU in a mother and her daughter with PNDM due to KCNJ11 mutation.

Genetics and pathophysiology of neonatal diabetes mellitus

Neonatal diabetes mellitus (NDM) is the term commonly used to describe diabetes with onset before 6 months-of-age. It occurs in approximately one out of every 100,000-300,000 live births. Although this term encompasses diabetes of any etiology, it is recognized that NDM diagnosed before 6 months-of-age is most often monogenic in nature. Clinically, NDM subgroups include transient (TNDM) and permanent NDM (PNDM), as well as syndromic cases of NDM. TNDM often develops within the first few weeks of life and remits by a few months of age. However, relapse occurs in 50% of cases, typically in adolescence or adulthood. TNDM is most frequently caused by abnormalities in the imprinted region of chromosome 6q24, leading to overexpression of paternally derived genes. Mutations in KCNJ11 and ABCC8, encoding the two subunits of the adenosine triphosphate-sensitive potassium channel on the β-cell membrane, can cause TNDM, but more often result in PNDM. NDM as a result of mutations in KCNJ11 and ABCC8 often responds to sulfonylureas, allowing transition from insulin therapy. Mutations in other genes important to β-cell function and regulation, and in the insulin gene itself, also cause NDM. In 40% of NDM cases, the genetic cause remains unknown. Correctly identifying monogenic NDM has important implications for appropriate treatment, expected disease course and associated conditions, and genetic testing for at-risk family members. Early recognition of monogenic NDM allows for the implementation of appropriate therapy, leading to improved outcomes and potential societal cost savings. (J Diabetes Invest, doi:10.1111/j.2040-1124.2011.00106.x, 2011).

HbA(1c) levels in schoolchildren with type 1 diabetes are seasonally variable and dependent on weather conditions

AIMS/HYPOTHESIS

We evaluated seasonal HbA(1c) changes in children with type 1 diabetes and its relation with measures of weather conditions.

METHODS

HbA(1c) changes over more than 3 years were evaluated in type 1 diabetic patients who were younger than 18 years and had diabetes duration of more than 12 months, and correlated with measures of weather conditions (ambient temperature, hours of sunshine and solar irradiance). After comparison of autocorrelation patterns, patterns of metabolic control and meteorological data were evaluated using Spearman rank correlation.

RESULTS

A total of 3,935 HbA(1c) measurements in 589 school (≥ 7 years) and 88 preschool (<7 years) children were analysed. Mean (± SD) HbA(1c) level for the whole study period was 7.65 ± 1.12%. The lowest HbA(1c) levels were observed in late summer and the highest in winter months, with differences consistently exceeding 0.44%. Autocorrelation analysis of HbA(1c) levels in schoolchildren showed a sine-wave pattern with a cycle length of roughly 12 months, which mirrored changes in ambient temperature. Strong negative correlations of HbA(1c) with ambient temperature (R = -0.56; p = 0.0002), hours of sunshine (R= -0.52; p = 0.0007) and solar irradiance (R = -0.52; p = 0.0006) were present in schoolchildren, but not in preschoolers (p ≥ 0.29 for each correlation).

CONCLUSIONS/INTERPRETATION

Seasonal changes of HbA(1c) levels in schoolchildren with type 1 diabetes are a significant phenomenon and should be considered in patient education and diabetes management. They may potentially affect the results of clinical trials using HbA(1c) levels as their primary outcome, as well as HbA(1c)-based diagnosis of diabetes.

Autoimmune markers in diabetes

BACKGROUND

Type 1 diabetes (T1DM) results from cell-mediated autoimmune destruction of the β cells of the islets of Langerhans. Autoantibodies directed against the islets are useful clinical tools that allow the recognition and confirmation of β-cell autoimmunity.

CONTENT

In this review we define the term "islet autoantibody," describe the pathogenesis of autoantibody generation, and explain the uses of islet autoantibodies in clinical medicine and in research studies that concern the interruption or prevention of T1DM. We also discuss the biology of islet autoantibodies and their rates of appearance at the time of onset of T1DM and their appearance before the development of T1DM.

SUMMARY

The presence of islet autoantibodies in persons with diabetes confirms an autoimmune etiology. In nondiabetic individuals, islet autoantibodies are strong predictors of the later development of T1DM.

Neonatal diabetes in a child positive for islet cell antibodies at onset and Kir6.2 activating mutation

In contrast to the autoimmune type 1 diabetes, patients with monogenic diabetes due to KCNJ11 mutations do not have pancreatic auto-antibodies at onset. Here we describe a patient diagnosed at the age of 12 weeks that showed ICA at diagnosis, yet has been tested with positive result for KCNJ11 mutation.

Mutations in the ABCC8 (SUR1 subunit of the K(ATP) channel) gene are associated with a variable clinical phenotype

OBJECTIVE

Mutations in the ABCC8 gene encoding the SUR1 subunits of the beta-cell K-ATP channel cause neonatal diabetes (ND) mellitus. We aimed to determine the contribution of ABCC8 gene to ND in Poland, to describe the clinical phenotype associated with its mutations and to examine potential modifying factors.

PATIENTS

The Nationwide Registry of ND in Poland includes patients diagnosed before 6 months of age. In total 16 Kir6.2 negative patients with ND, 14 permanent and 2 relapsed transient, were examined.

MEASUREMENTS

ABCC8 gene mutations were detected by direct sequencing. Mutation carriers' characteristics included clinical data and biochemical parameters. In addition, we performed the hyperinsulinaemic euglycaemic clamp and tested for islet-specific antibodies in diabetic subjects.

RESULTS

We identified two probands with permanent ND (one heterozygous F132V mutation carrier and one compound heterozygote with N23H and R826W mutations) and two others with relapsed transient ND (heterozygotes for R826W and V86A substitutions, respectively). One subject, a heterozygous relative with the R826W mutation, had adult onset diabetes. There were striking differences in the clinical picture of the mutation carriers as the carrier of two mutations, N23H and R826W, was controlled on diet alone with HbA(1c) of 7.3%, whereas the F132V mutation carrier was on 0.66 IU/kg/day of insulin with HbA(1c) of 11.7%. The C-peptide level varied from 0.1 ng/ml (F132V) to 0.75 ng/ml (V86A). We also observed a variable insulin resistance, from moderate (M = 5.5 and 5.6 mg/kg/min, respectively, in the two R826W mutation carriers) to severe (M = 2.6 mg/kg/min in the F132V mutation carrier). We were able to transfer two patients off insulin to sulphonylurea (SU) and to reduce insulin dose in one other patient. Interestingly, there was no response to SU in the most insulin resistant F132V mutation carrier despite high dose of glibenclamide. All examined auto-antibodies were present in one of the subjects, the V86A mutation carrier, although this did not seem to influence the clinical picture, as we were able to transfer this girl off insulin.

CONCLUSION

Mutations in SUR1 are the cause of about 15% of Kir6.2 negative permanent ND in Poland. The clinical phenotype of SUR1 diabetic mutation carriers is heterogeneous and it appears to be modified by variable sensitivity to insulin.

Diagnosis and treatment of neonatal diabetes: a United States experience

BACKGROUND/OBJECTIVE

Mutations in KCNJ11, ABCC8, or INS are the cause of permanent neonatal diabetes mellitus in about 50% of patients diagnosed with diabetes before 6 months of age and in a small fraction of those diagnosed between 6 and 12 months. The aim of this study was to identify the genetic cause of diabetes in 77 consecutive patients referred to the University of Chicago with diabetes diagnosed before 1 yr of age.

METHODS

We used Oragene DNA Self-Collection kit to obtain a saliva sample for DNA. We sequenced the protein-coding regions of KCNJ11, ABCC8, and INS using standard methods.

RESULTS

We enrolled 32 patients diagnosed with diabetes before 6 months of age and 45 patients diagnosed between 6 and 12 months. We identified a mutation in KCNJ11 in 14 patients from 12 families and in INS in 7 patients from 4 families. Three of the patients with an INS mutation were diagnosed with diabetes between 6 and 12 months of age. Finally, we found that two patients had an abnormality of chromosome 6q24 associated with transient neonatal diabetes mellitus.

CONCLUSIONS

We were able to establish a genetic cause of diabetes in 63% of patients diagnosed with diabetes before 6 months of age and in 7% of patients diagnosed between 6 and 12 months. Genetic testing, which is critical for guiding appropriate management, should be considered in patients diagnosed with diabetes before 1 yr of age, especially if they are autoantibody negative, although the presence of autoantibodies does not rule out a monogenic cause.

Neonatal diabetes mellitus

An explosion of work over the last decade has produced insight into the multiple hereditary causes of a nonimmunological form of diabetes diagnosed most frequently within the first 6 months of life. These studies are providing increased understanding of genes involved in the entire chain of steps that control glucose homeostasis. Neonatal diabetes is now understood to arise from mutations in genes that play critical roles in the development of the pancreas, of beta-cell apoptosis and insulin processing, as well as the regulation of insulin release. For the basic researcher, this work is providing novel tools to explore fundamental molecular and cellular processes. For the clinician, these studies underscore the need to identify the genetic cause underlying each case. It is increasingly clear that the prognosis, therapeutic approach, and genetic counseling a physician provides must be tailored to a specific gene in order to provide the best medical care.