Metabolomic associations of impaired awareness of hypoglycaemia in type 1 diabetes

This study investigates impaired awareness of hypoglycaemia (IAH), a complication of insulin therapy affecting 20-40% of individuals with type 1 diabetes. The exact pathophysiology is unclear, therefore we sought to identify metabolic signatures in IAH to elucidate potential pathophysiological pathways. Plasma samples from 578 individuals of the Dutch type 1 diabetes biomarker cohort, 67 with IAH and 108 without IAH (NAH) were analysed using the targeted metabolomics Biocrates AbsoluteIDQ p180 assay. Eleven metabolites were significantly associated with IAH. Genome-wide association studies of these 11 metabolites identified significant single nucleotide polymorphisms (SNPs) in C22:1-OH and phosphatidylcholine diacyl C36:6. After adjusting for the SNPs, 11 sphingomyelins and phosphatidylcholines were significantly higher in the IAH group in comparison to NAH. These metabolites are important components of the cell membrane and have been implicated to play a role in cell signalling in diabetes. These findings demonstrate the potential role of phosphatidylcholine and sphingomyelins in IAH.

[Diabetes, not harmless in young adults]

A recent publication in JAMA again demonstrates that a significant proportion of young adults with type-1 or type-2 diabetes develop diabetes-related complications and comorbidities. These complications and comorbidities already occur after a relative short disease duration and is most frequently seen in young adults with type-2 diabetes. Future research should focus on medical, social and psychological factors that will improve diabetes care.

Dendritic Cells Guide Islet Autoimmunity through a Restricted and Uniquely Processed Peptidome Presented by High-Risk HLA-DR

Identifying T cell epitopes of islet autoantigens is important for understanding type 1 diabetes (T1D) immunopathogenesis and to design immune monitoring and intervention strategies in relationship to disease progression. Naturally processed T cell epitopes have been discovered by elution from HLA-DR4 of pulsed B lymphocytes. The designated professional APC directing immune responses is the dendritic cell (DC). To identify naturally processed epitopes, monocyte-derived DC were pulsed with preproinsulin (PPI), glutamic acid decarboxylase (65-kDa isoform; GAD65), and insulinoma-associated Ag-2 (IA-2), and peptides were eluted of HLA-DR3 and -DR4, which are associated with highest risk for T1D development. Proteome analysis confirmed uptake and processing of islet Ags by DC. PPI peptides generated by DC differed from those processed by B lymphocytes; PPI signal-sequence peptides were eluted from HLA-DR4 and -DR3/4 that proved completely identical to a primary target epitope of diabetogenic HLA-A2-restricted CD8 T cells. HLA-DR4 binding was confirmed. GAD65 peptides, eluted from HLA-DR3 and -DR4, encompassed two core regions overlapping the two most immunodominant and frequently studied CD4 T cell targets. GAD65 peptides bound to HLA-DR3. Strikingly, the IA-2 ligandome of HLA-DR was exclusively generated from the extracellular part of IA-2, whereas most previous immune studies have focused on intracellular IA-2 epitopes. The newly identified IA-2 peptides bound to HLA-DR3 and -DR4. Differential T cell responses were detected against the newly identified IA-2 epitopes in blood from T1D patients. The core regions to which DC may draw attention from autoreactive T cells are largely distinct and more restricted than are those of B cells. GAD65 peptides presented by DC focus on highly immunogenic T cell targets, whereas HLA-DR-binding peptides derived from IA-2 are distinct from the target regions of IA-2 autoantibodies.

Discovery of a Selective Islet Peptidome Presented by the Highest-Risk HLA-DQ8trans Molecule

HLA-DQ2/8 heterozygous individuals are at far greater risk for type 1 diabetes (T1D) development by expressing HLA-DQ8trans on antigen-presenting cells compared with HLA-DQ2 or -DQ8 homozygous individuals. Dendritic cells (DC) initiate and shape adaptive immune responses by presenting HLA-epitope complexes to naïve T cells. To dissect the role of HLA-DQ8trans in presenting natural islet epitopes, we analyzed the islet peptidome of HLA-DQ2, -DQ8, and -DQ2/8 by pulsing DC with preproinsulin (PPI), IA-2, and GAD65. Quality and quantity of islet epitopes presented by HLA-DQ2/8 differed from -DQ2 or -DQ8. We identified two PPI epitopes solely processed and presented by HLA-DQ2/8 DC: an HLA-DQ8trans-binding signal-sequence epitope previously identified as CD8 T-cell epitope and a second epitope that we previously identified as CD4 T-cell epitope with increased binding to HLA-DQ8trans upon posttranslational modification. IA-2 epitopes retrieved from HLA-DQ2/8 and -DQ8 DC bound to HLA-DQ8cis/trans. No GAD65 epitopes were eluted from HLA-DQ. T-cell responses were detected against the novel islet epitopes in blood from patients with T1D but scantly detected in healthy donor subjects. We report the first PPI and IA-2 natural epitopes presented by highest-risk HLA-DQ8trans. The selective processing and presentation of HLA-DQ8trans-binding islet epitopes provides insight in the mechanism of excessive genetic risk imposed by HLA-DQ2/8 heterozygosity and may assist immune monitoring of disease progression and therapeutic intervention as well as provide therapeutic targets for immunotherapy in subjects at risk for T1D.

Decreased excitability of the distal motor nerve of young patients with type 1 diabetes mellitus

OBJECTIVE

The compound muscle action potential (CMAP) scan is a novel neurophysiological technique that appears more sensitive in detecting peripheral motor neuropathy than conventional methods. This study explores the value of the CMAP scan for the detection of subclinical diabetic peripheral motor neuropathy.

METHODS

In this cross-sectional pilot study, CMAP scanning of the peroneal nerve was performed in (i) 13 well-controlled patients (8-25 yr old) with type 1 diabetes mellitus (T1DM) duration between 2.5 and 5 yr; (ii) 17 patients (10-25 yr old) with a duration of T1DM of at least 10 yr, poorly controlled and/or with microvascular complications and (iii) 13 adults with T1DM and established clinical diabetic peripheral neuropathy (DPN). Various CMAP scan variables, including measures of axonal excitability and axonal loss and reinnervation, were compared between patients and healthy controls.

RESULTS

Axonal excitability was significantly decreased in the young patient groups as compared to their controls. The CMAP scan measures of axonal loss and reinnervation differed only between patients with clinical DPN and their controls.

CONCLUSIONS

Motor nerve axonal excitability seems to be reduced early in T1DM, even in well-controlled young patients, and probably before (irreversible) axonal damage occurs. These changes can be measured by the CMAP scan, which makes this a promising tool for detecting nerve dysfunction in T1DM.

Metabolic outcomes in young children with type 1 diabetes differ between treatment centers: the Hvidoere Study in Young Children 2009

OBJECTIVE

To investigate whether center differences in glycemic control are present in prepubertal children <11 yr with type 1 diabetes mellitus.

RESEARCH DESIGN AND METHODS

This cross-sectional study involved 18 pediatric centers worldwide. All children, <11 y with a diabetes duration ≥12 months were invited to participate. Case Record Forms included information on clinical characteristics, insulin regimens, diabetic ketoacidosis (DKA), severe hypoglycemia, language difficulties, and comorbidities. Hemoglobin A1c (HbA1c) was measured centrally by liquid chromatography (DCCT aligned, range: 4.4-6.3%; IFFC: 25-45 mmol/mol).

RESULTS

A total of 1133 children participated (mean age: 8.0 ± 2.1 y; females: 47.5%, mean diabetes duration: 3.8 ± 2.1 y). HbA1c (overall mean: 8.0 ± 1.0%; range: 7.3-8.9%) and severe hypoglycemia frequency (mean 21.7 events per 100 patient-years), but not DKA, differed significantly between centers (p < 0.001 resp. p = 0.179). Language difficulties showed a negative relationship with HbA1c (8.3 ± 1.2% vs. 8.0 ± 1.0%; p = 0.036). Frequency of blood glucose monitoring demonstrated a significant but weak association with HbA1c (r = -0.17; p < 0.0001). Although significant different HbA1c levels were obtained with diverse insulin regimens (range: 7.3-8.5%; p < 0.001), center differences remained after adjusting for insulin regimen (p < 0.001). Differences between insulin regimens were no longer significant after adjusting for center effect (p = 0.199).

CONCLUSIONS

Center differences in metabolic outcomes are present in children <11 yr, irrespective of diabetes duration, age, or gender. The incidence of severe hypoglycemia is lower than in adolescents despite achieving better glycemic control. Insulin regimens show a significant relationship with HbA1c but do not explain center differences. Each center's effectiveness in using specific treatment strategies remains the key factor for outcome.

Frequent delay of coeliac disease diagnosis in symptomatic patients with type 1 diabetes mellitus: clinical and genetic characteristics

BACKGROUND

Patients with type 1 diabetes mellitus (T1DM) are more prone to develop other auto-immune diseases, including coeliac disease (CD). Paediatric patients with T1DM are screened for CD, whereas in adult T1DM patients screening programs for CD are not standardised. The aim of this study was to investigate clinical and genetic characteristics of patients with both diagnoses so as to lead to better detection of CD in adult patients with T1DM.

METHODS

We studied 118 patients with both T1DM and CD identified in The Netherlands. We retrospectively collected data on sex distribution, age of onset of T1DM, age of CD diagnosis, CD complaints, duration of CD complaints before CD diagnosis, family history of CD or T1DM, comorbidity and HLA-DQ type.

RESULTS

Thirty-three percent of T1DM+CD patients reported CD related complaints for at least 5 years before CD diagnosis. Two peaks in the age of CD diagnosis in T1DM patients were observed: around 10 and 45 years of age. Women were diagnosed with CD at a younger age than men (median 25 years (IQR 9-38) versus 39 (12-55) years, respectively, P<0.05).

CONCLUSION

A delay of CD diagnosis is frequently found in adult T1DM patients and two peaks in the age of CD diagnosis are present in T1DM patients. This observational study emphasises that more frequent screening for CD in particularly adult T1DM patients is required, preferably by a 5 years interval.

Overweight children with type 1 diabetes have a more favourable lipid profile than overweight non-diabetic children

In the present article, we aimed to compare the cardiometabolic risk between overweight children with and without type 1 diabetes (T1DM). Therefore, data with regard to cardiometabolic risk parameters of 44 overweight Caucasian children (3-18 years) with T1DM were matched with 44 overweight peers without T1DM for sex, ethnicity, age and standard deviation score of BMI (Z-BMI). Detailed history was taken, information regarding anthropometrics and family history were collected and blood pressure was measured. Blood samples were collected for evaluation of lipid profiles (fasting in controls, non-fasting in T1DM children), alanine aminotransferase and HbA1c (in children with T1DM). It was found that overweight children with T1DM had lower median standard deviation score of waist circumference (Z-WC) as compared to the overweight control group [median, 2.0 (interquartile range, IQR, 1.5-2.3) vs. 2.6 (IQR, 2.0-2.9), P < 0.001]. After adjustment for Z-WC, in children with T1DM, median high-density lipoprotein cholesterol levels were significantly higher and median low-density lipoprotein cholesterol lower in T1DM children, as compared to their peers without T1DM [1.40 (IQR, 1.2-1.5) vs. 1.2 (IQR, 1.0-1.3) and 2.7 (IQR, 2.5-3.2) vs. 3.0 (IQR, 2.5-3.4), respectively, all P < 0.01]. When dividing children according to glycaemic status, children with suboptimal glycaemic control had higher values of triglycerides as compared to well-controlled children [1.3 (IQR, 1.0-1.8) vs. 0.96 (IQR, 0.80-1.2), P = 0.036]. In conclusion, overweight children with T1DM have a more favourable lipid profile, as compared to non-diabetic overweight controls, in spite of a higher frequency of a positive family history of CVD, T2DM and hypertension. Still, paediatricians should give extra attention to cardiometabolic risk factors within this vulnerable group, taking into account the already high cardiometabolic risk.

Overweight is highly prevalent in children with type 1 diabetes and associates with cardiometabolic risk

OBJECTIVES

To determine the prevalence of traditional cardiometabolic risk factors and to assess the effect of overweight/obesity on the occurrence of these risk factors in a cohort of children with type 1 diabetes mellitus (T1DM).

STUDY DESIGN

Two hundred eighty-three consecutive patients (3 to 18 years of age) attending an outpatient clinic for T1DM care were included. The prevalence of cardiometabolic risk factors, the metabolic syndrome, and high alanine aminotransferase, were assessed before and after stratification for weight status.

RESULTS

Of all children (median age, 12.8 years; interquartile range, 9.9 to 16.0; median diabetes duration, 5.3 years; interquartile range, 2.9 to 8.6), 38.5% were overweight/obese (Z-body mass index > or =1.1). Overall, median HbA1c levels were 8.2% (interquartile range, 7.4 to 9.8), and HbA1c > or =7.5% was present in 73.9%. Microalbuminuria was found in 17.7%, high triglycerides (>1.7 mmol/L) in 17.3%, high LDL-cholesterol (>2.6 mmol/L) in 28.6%, low HDL-cholesterol (<1.1 mmol/L) in 21.2%, and hypertension in 13.1% of patients. In the overweight/obese children with T1DM, versus normal-weight children, a higher prevalence of hypertension (23.9% vs 5.7%), the metabolic syndrome (25.7% vs 6.3%), and alanine aminotransferase >30 IU/L (15.6% vs 4.5%) was found (all P < .05).

CONCLUSIONS

Overweight/obesity and cardiometabolic risk factors were highly prevalent in a pediatric cohort with T1DM. Hypertension, the metabolic syndrome, and high alanine aminotransferase were significantly more prevalent in overweight/obese compared with normal-weight children with T1DM.

Continuing stability of center differences in pediatric diabetes care: do advances in diabetes treatment improve outcome? The Hvidoere Study Group on Childhood Diabetes

OBJECTIVE

To reevaluate the persistence and stability of previously observed differences between pediatric diabetes centers and to investigate the influence of demography, language communication problems, and changes in insulin regimens on metabolic outcome, hypoglycemia, and ketoacidosis.

RESEARCH DESIGN AND METHODS

This was an observational cross-sectional international study in 21 centers, with clinical data obtained from all participants and A1C levels assayed in one central laboratory. All individuals with diabetes aged 11-18 years (49.4% female), with duration of diabetes of at least 1 year, were invited to participate. Fourteen of the centers participated in previous Hvidoere Studies, allowing direct comparison of glycemic control across centers between 1998 and 2005.

RESULTS

Mean A1C was 8.2 +/- 1.4%, with substantial variation between centers (mean A1C range 7.4-9.2%; P < 0.001). There were no significant differences between centers in rates of severe hypoglycemia or diabetic ketoacidosis. Language difficulties had a significant negative impact on metabolic outcome (A1C 8.5 +/- 2.0% vs. 8.2 +/- 1.4% for those with language difficulties vs. those without, respectively; P < 0.05). After adjustement for significant confounders of age, sex, duration of diabetes, insulin regimen, insulin dose, BMI, and language difficulties, the center differences persisted, and the effect size for center was not reduced. Relative center ranking since 1998 has remained stable, with no significant change in A1C.

CONCLUSIONS

Despite many changes in diabetes management, major differences in metabolic outcome between 21 international pediatric diabetes centers persist. Different application between centers in the implementation of insulin treatment appears to be of more importance and needs further exploration.

Prediction and diagnosis of type 1 diabetes using beta-cell autoantibodies

The clinical manifestation of type 1 diabetes is the endpoint of a long-lasting immune-mediated destruction process of the B-cells. Autoantibodies originating from this process can be applied in the diagnosis and clinical discrimination of autoimmune diabetes as well as in the prediction of this disease. At clinical diagnosis between 80-90% of patients with type 1 diabetes are positive for antibodies to B-cell antigens, such as ICA and antibodies to glutamic acid decarboxylase or IA2. These antibodies can also be detected in the presymptomatic period before onset of the disease, and can thus be used to predict type 1 diabetes. Using a combination of antibodies, diabetes can be predicted in 70-80% of future cases of diabetes, with a positive predictive value between 30-80%, depending on the type of antibody tested for and the population studied. Between 5 and 30% of patients initially diagnosed with type 2 diabetes will show progression to insulin dependency and turn out to have type 1 within three years of diagnosis. It is clinically relevant to identify these patients early in the course of disease, as deterioration of metabolic control results in an increased risk for macro- and micro-vascular complications. Autoantibodies to glutamic acid decarboxylase or ICA are of high diagnostic sensitivity in these cases and are better predictors for future insulin dependency than biochemical or clinical parameters. Increasing knowledge on the applicability of antibodies for diabetes prediction and diagnosis and the development of commercial assays for antibodies to glutamic acid decarboxylase and IA2 antibodies has enabled the implementation of B-cell autoantibodies in routine diagnostic settings.

Good metabolic control is associated with better quality of life in 2,101 adolescents with type 1 diabetes

OBJECTIVE

It is unclear whether the demands of good metabolic control or the consequences of poor control have a greater influence on quality of life (QOL) for adolescents with diabetes. This study aimed to assess these relations in a large international cohort of adolescents with diabetes and their families.

RESEARCH DESIGN AND METHODS

The study involved 2,101 adolescents, aged 10-18 years, from 21 centers in 17 countries in Europe, Japan, and North America. Clinical and demographic data were collected from March through August 1998. HbA(1c) was analyzed centrally (normal range 4.4-6.3%; mean 5.4%). Adolescent QOL was assessed by a previously developed Diabetes Quality of Life (DQOL) questionnaire for adolescents, measuring the impact of diabetes, worries about diabetes, satisfaction with life, and health perception. Parents and health professionals assessed family burden using newly constructed questionnaires.

RESULTS

Mean HbA(1c) was 8.7% (range 4.8-17.4). Lower HbA(1c) was associated with lower impact (P < 0.0001), fewer worries (P < 0.05), greater satisfaction (P < 0.0001), and better health perception (P < 0.0001) for adolescents. Girls showed increased worries (P < 0.01), less satisfaction, and poorer health perception (P < 0.01) earlier than boys. Parent and health professional perceptions of burden decreased with age of adolescent (P < 0.0001). Patients from ethnic minorities had poorer scores for impact (P < 0.0001), worries (P < 0.05), and health perception (P < 0.01). There was no correlation between adolescent and parent or between adolescent and professional scores.

CONCLUSIONS

In a multiple regression model, lower HbA(1c) was significantly associated with better adolescent-rated QOL on all four subscales and with lower perceived family burden as assessed by parents and health professionals.

Low prevalence of GAD and IA2 antibodies in schoolchildren from a village in the southwestern section of the Netherlands

Glutamic acid decarboxylase (GAD) and insulinoma antigen 2 (IA2) antibodies are increasingly used as a tool to predict type I diabetes in children and as a differential diagnostic tool to distinguish type I and type II diabetes in adults. However, the background frequency of these antibodies in the general population has not been extensively studied and may differ between countries. The current study aims to establish the frequency of GAD and IA2 antibodies in an unselected population of schoolchildren and confirm the previously reported low prevalence of islet cell antibodies (ICA) in the general Dutch population. The study population consisted of 1403 unselected schoolchildren. All children were tested for GAD antibodies, and 1085 children were analyzed for IA2 antibodies by radiobinding assay. Development of diabetes was recorded during a 7-year follow-up. Five children (0.4%) were positive for GAD antibodies, one child (0.1%) was positive for IA2 antibodies. Two children developed diabetes during follow-up, one was positive for GAD antibodies only, the second was positive for both GAD and IA2 antibodies. The frequency of GAD and IA2 antibodies in the southwestern part of The Netherlands is low. This observation is in concordance with earlier studies on ICA in Dutch schoolchildren. For future diabetes prediction and intervention trials it is important to establish the background frequencies and predictive power of antibody screening in different populations.

Persistent differences among centers over 3 years in glycemic control and hypoglycemia in a study of 3,805 children and adolescents with type 1 diabetes from the Hvidøre Study Group

OBJECTIVE

Twenty-one international pediatric diabetes centers from 17 countries investigated the effect of simple feedback about the grand mean HbA(1c) level of all centers and the average value of each center on changes in metabolic control, rate of severe hypoglycemia, and insulin therapy over a 3-year period.

RESEARCH DESIGN AND METHODS

Clinical data collection and determination of HbA(1c) levels were conducted at a central location in 1995 (n = 2,780, age 0-18 years) and 1998 (n = 2,101, age 11-18 years).

RESULTS

Striking differences in average HbA(1c) concentrations were found among centers; these differences remained after adjustment for the significant confounders of sex, age, and diabetes duration. They were apparent even in patients with short diabetes duration and remained stable 3 years later (mean adjusted HbA(1c) level: 8.62 +/- 0.03 vs. 8.67 +/- 0.04 [1995 vs. 1998, respectively]). Three centers had improved significantly, four centers had deteriorated significantly in their overall adjusted HbA(1c) levels, and 14 centers had not changed in glycemic control. During the observation period, there were increases in the adjusted insulin dose by 0.076 U/kg, the adjusted number of injections by 0.23 injections per day, and the adjusted BMI by 0.95 kg/m(2). The 1995 versus 1998 difference in glycemic control for the seven centers could not be explained by prevailing insulin regimens or rates of hypoglycemia.

CONCLUSIONS

This study reveals significant outcome differences among large international pediatric diabetes centers. Feedback and comparison of HbA(1c) levels led to an intensification of insulin therapy in most centers, but improved glycemic control in only a few.

Autoantibodies to a 38-kDa glycosylated islet cell membrane-associated antigen in (pre)type 1 diabetes: association with IA-2 and islet cell autoantibodies

OBJECTIVE

To study the association of autoantibodies against a 38-kDa glycated islet cell membrane-associated (GLIMA) protein with (pre)type 1 diabetes, patient characteristics, and other immune and genetic markers of the disease and to evaluate the possible added value of GLIMA antibody determinations for disease prediction and classification.

RESEARCH DESIGN AND METHODS

Recent-onset type 1 diabetic patients (n = 100), prediabetic siblings (n = 23), and nondiabetic control subjects (n = 100) were consecutively recruited by the Belgian Diabetes Registry. GLIMA antibodies were determined by immunoprecipitation of radiolabeled islet cell proteins; islet cell antibodies (ICAs) were determined by indirect immunofluorescence; and insulin autoantibodies (IAAs), insulinoma-associated protein-2 antibodies (IA-2As), and GAD antibodies (GADAs) were determined by radioligand assays.

RESULTS

GLIMA antibodies were detected in 38% of type 1 diabetic patients and 35% of prediabetic siblings (during follow-up) vs. 0% in control subjects (P < 0.001). Their prevalence was lower than that of other antibodies and was significantly associated with high levels of IA-2A and ICA (P < 0.0001). In (pre)diabetes, GLIMA antibodies could only be demonstrated in sera positive for > or = 1 other autoantibody.

CONCLUSIONS

GLIMA antibodies are strongly associated with type 1 diabetes and antibody markers of rapid progression to clinical onset but have a lower diagnostic sensitivity for the disease than IAA, ICA, IA-2A, or GADA. In its present form, the GLIMA antibody assay does not provide much additional information for prediction or classification of diabetes, compared with that obtained from the measurement of IA-2As alone or in combination with IAAs, ICAs, and GADAs.

Carbohydrate metabolism during long-term growth hormone treatment in children with short stature born small for gestational age

OBJECTIVE

To assess possible side-effects of long-term continuous growth hormone (GH) treatment on carbohydrate (CH) metabolism in children with short stature born small for gestational age.

DESIGN

In a prospective, randomised double-blind, dose-response multicentre trial, the effect of GH treatment on CH metabolism was evaluated, comparing two GH dosages [3 vs. 6 IU/(m(2) body surface.day)].

PATIENTS

Seventy-eight children with short stature (height SD-score < - 1.88) born small for gestational age (birth length SD-score < - 1.88) being all prepubertal with a mean (SD) chronological age of 7.3 (2.2) years before start of treatment.

MEASUREMENTS

Glucose and insulin concentrations during oral glucose tolerance tests (OGTTs) and glycosylated haemoglobin (HbA(1c)) were measured before and during 6 years of GH treatment.

RESULTS

Before treatment, the glucose response to oral glucose after 120 min was in six of the 78 children (8%) above 7.8 mmol/l but below 11.1 mmol/l, indicating impaired glucose tolerance (IGT), whereas after 6 years of GH treatment, IGT was found in 4% of the children. None of the children developed diabetes mellitus. Mean fasting glucose levels had increased significantly by 0.5 mmol/l after 1 year of GH treatment, without a further increase thereafter. The 2-h area under the curve adjusted for fasting levels (AUCab) for glucose and the HbA(1c) levels were lower after 6 years of GH treatment compared to baseline. During GH treatment, all HbA(1c) levels were in the normal range. In contrast to the effects on glucose levels, GH treatment induced considerably higher fasting insulin levels and glucose-stimulated insulin levels. The increase in AUCab for insulin occurred particularly during the first year of treatment, whereas the fasting insulin levels showed a further increase from one to six years. As a result, the 30- and 120-min ratios of insulin to glucose were higher during GH treatment compared to the start of treatment. The children who remained prepubertal during the entire study period showed similar patterns in glucose and insulin levels compared to the children who entered puberty. None of the observed changes were different between the GH dosage groups.

CONCLUSIONS

Continuous GH treatment during 6 years in children with short stature born small for gestational age has no adverse effects on glucose levels, even with dosages up to 6 IU/(m(2) d). However, as has been reported in other patient groups, GH treatment induces higher fasting insulin levels and glucose-stimulated insulin levels, indicating relative insulin resistance. Since the consequences of long-term hyperinsulinism during childhood are unknown, careful follow-up of these GH-treated children born small for gestational age is required.

Absence of a PDX-1 mutation and normal gastroduodenal immunohistology in a child with pancreatic agenesis

Pancreatic agenesis is a rare condition, of which only a limited number of cases have been described. One recent paper reported a homozygous mutation in the pancreatic duodenal homeobox gene 1 (PDX-1) in a child with pancreatic agenesis. We report a 6-year-old boy with pancreatic agenesis, treated medically, without abnormalities in the PDX-1 gene coding sequence and with normal gastroduodenal endocrine cell distribution. Genes other than PDX-1 also appear to be involved in human pancreatic agenesis.

Laboratory standards in the assessment of the quality of care

Diabetes mellitus requires constant care. The main goal of this is prevention of interference with daily life and prevention of long-term complications. Laboratory methods mostly used include HbAlc and microalbuminuria testing. Several methods exist for these determinations. Moreover, no worldwide standards are available. Studies have shown that with the current techniques improvement of laboratory standardization is clearly required, but have also shown that this is possible even without 'synthetic standards', the ultimate standards which will not be available within the next 3-5 years.

Carbohydrate metabolism during growth hormone treatment and after discontinuation of growth hormone treatment in girls with Turner syndrome treated with once or twice daily growth hormone injections

OBJECTIVE

To assess possible side-effects of treatment with supraphysiological GH dosages on carbohydrate (CH) metabolism in girls with Turner syndrome (TS) during GH treatment until adult height is reached as well as after discontinuation of GH treatment.

DESIGN

In a prospective, randomized injection frequency-response study, the effect of GH treatment in combination with low dose ethinyl oestradiol on CH metabolism was evaluated, comparing twice daily (BID) with once daily (OD) injections of a total GH dose of 6 U/m2/day until adult height was reached.

PATIENTS

Nineteen untreated girls with TS, mean (SD) pretreatment age 13.3 (1.7) (range 11.0-17.6) year.

MEASUREMENTS

Glucose and insulin concentrations during oral glucose tolerance tests (OGTT) were measured before and during GH treatment, as well as at 6 months after discontinuation of GH treatment.

RESULTS

GH treatment was discontinued after a mean of 43 (range 27-57) months. In one of the 19 girls, a different girl at each time point before, during and after discontinuation of GH treatment, the glucose response to OGTT after 120 minutes was above 7.8 mmol/l but below 11.1 mmol/l, indicating impaired glucose tolerance. None of the girls developed diabetes mellitus. Fasting glucose levels did not significantly change during, or after discontinuation of GH treatment. The 3 h area under the curve for time-concentration adjusted for fasting levels during the OGTT for glucose showed a significant decrease during GH treatment. In contrast to the glucose levels, GH treatment induced considerably higher insulin levels compared to pretreatment values. After discontinuation of GH insulin levels decreased to values comparable with pretreatment levels. None of these observed changes were different between the GH injection frequency groups. The changes in CH variables during and after discontinuation of GH were not related to changes in body mass index.

CONCLUSIONS

GH treatment with 6 U/m2/day in combination with low dose ethinyl oestradiol in girls with Turner syndrome aged > or =11 years did not negatively influence glucose levels, but induced higher levels of insulin indicating relative insulin resistance. These changes in insulin levels were independent of the frequency of the GH injections (once vs. twice daily). After discontinuation of GH treatment, insulin values decreased to baseline levels.

Carbohydrate metabolism during long-term growth hormone (GH) treatment and after discontinuation of GH treatment in girls with Turner syndrome participating in a randomized dose-response study. Dutch Advisory Group on Growth Hormone

To assess possible side-effects of GH treatment with supraphysiological doses on carbohydrate (CH) metabolism in girls with Turner syndrome (TS) during long term GH treatment and after discontinuation of GH treatment, the results of oral glucose tolerance tests and hemoglobin A1c measurements were analyzed in 68 girls with TS participating in a randomized dose-response trial. These previously untreated girls, aged 2-11 yr, were randomly assigned to 1 of 3 GH dosage groups: group A, 4 IU/m2 x day (-0.045 mg/kg x day); group B, first year ,4 IU/m2 day; thereafter, 6 IU/m2 x day (approximately 0.0675 mg/kg x day); group C, first year, 4 IU/m2 x day; second year, 6 IU/m2 x day; thereafter, 8 IU/m2 x day (approximately 0.090 mg/kg x day). After the first 4 yr, girls 12 yr of age or older started with 5 microg/kg BW-day 17beta-estradiol for induction of puberty. To assess the effects of long term high dose GH treatment on CH metabolism, the 7-yr data from the oral glucose tolerance tests in 9 girls of group C were evaluated (group C1). To determine whether the changes in CH metabolism during GH treatment would persist after discontinuation of GH treatment, the data for 28 girls who had reached adult height (group A, n = 9; group B, n = 10; group C, n = 9) were evaluated at baseline, after 4 yr of GH treatment, and 6 months after discontinuation of GH. Seven-year data for group C1 showed that glucose levels did not significantly change during GH treatment, whereas fasting insulin levels as well as glucose-induced insulin levels increased significantly. The data for the 28 girls who were treated with GH for a mean (SD) period of 85.3 (13.3) months demonstrated that the GH-induced higher insulin levels decreased to values close to or equal to pretreatment values after discontinuation of GH treatment. Changes in CH variables were not significantly related to the GH dose. Hemoglobin A1c levels never showed an abnormal value. The prevalence of impaired glucose tolerance was low, and none of the girls developed diabetes mellitus. In conclusion, long term GH treatment with dosages up to 8 IU/m2 x day in girls with TS has no adverse effects on glucose levels, but induced higher levels of insulin, indicating relative insulin resistance. The increased insulin levels during long term GH treatment decreased after discontinuation of GH treatment to values close to or equal to pretreatment values. Although the reversibility of the effects of long term GH is reassuring, the consequence of long term hyperinsulinism is still unknown.

Analysis of antibody responses against coxsackie virus B4 protein 2C and the diabetes autoantigen GAD(65)

Type I diabetes mellitus results from the autoimmune destruction of insulin producing beta cells in the pancreas. Certain viral infections, especially those caused by coxsackie B viruses and related enteroviruses, have been associated with the development of type I diabetes. The sequence homology between the coxsackie B4 virus nonstructural protein 2C (CVB4 p2C) and the major diabetes autoantigen glutamic acid decarboxylase (GAD(65)) provides a basis for the hypothesis of molecular mimicry. In this study, we investigated the prevalence of antibodies directed against nonstructural enterovirus proteins. In addition, a correlation of antibodies against CVB4 p2C and GAD(65) was studied in diabetes patients and in healthy controls. Antibody reactivity against CVB proteins was detected by immunoprecipitation of [(35)S]-methionine-labelled viral proteins and GAD(65) antibodies were measured in a quantitative radio-immunoassay. It was shown that antibodies raised against the nonstructural proteins of CVB4 are very common in the population and a high degree of heterotypic cross-reactivity exists between different enterovirus types. CVB4 p2C-specific antibodies were not only detectable in GAD(65) antibody-positive diabetes patients but also in GAD(65) antibody-negative healthy blood donors. Furthermore, GAD(65) antibodies could not be detected in p2C-positive subjects who had various enterovirus infections, indicating that an antibody response to CVB4 p2C does not necessarily induce a cross-reactive immune response against GAD(65). A correlation was not found between antibodies against GAD(65) and p2C.

Circulating semicarbazide-sensitive amine oxidase is raised both in type I (insulin-dependent), in type II (non-insulin-dependent) diabetes mellitus and even in childhood type I diabetes at first clinical diagnosis

Plasma semicarbazide-sensitive amine oxidase is raised in patients with Type I (insulin-dependent) diabetes mellitus. It has been suggested that this enzyme is involved in the development of microvascular damage through its ability to convert amines (e.g. methylamine and aminoacetone) into aldehydes, hydrogen peroxide and ammonia. Plasma semicarbazide-sensitive amine oxidase was found to be equally raised both in patients with Type I diabetes (n = 73) and Type II (non-insulin-dependent) diabetes mellitus (n = 88) compared with control subjects (621 +/- 209 and 619 +/- 202 vs 352 +/- 102 mU/l, p < 0.0001) and to correlate in multiple regression analysis with HbA1c. Since the enzyme could protect the islets from the inhibitory effects of methylamine on insulin secretion, we also tested sera of 100 children, collected consecutively at first diagnosis of Type I diabetes, for semicarbazide-sensitive amine oxidase. The activity was greatly increased compared with serum values of 76 control (siblings) children (757 +/- 300 vs 455 +/- 138 mU/l, p < 0.0001), but not associated with HbA1c. Our study confirms the increase of plasma semicarbazide-sensitive amine oxidase in Type I diabetes and extends this finding to Type II diabetes as well as to childhood Type I at first clinical diagnosis. In the last case increased enzyme activities could serve to protect the islets from inhibitory effects of methylamine but cause damage by generation of hydrogen peroxide, aldehydes and ammonia. In the long run the increased enzyme activities could also contribute to vascular damage by direct cytotoxic action on endothelial cells, including increased oxidative stress and glycosylation of proteins.

Carbohydrate and lipid metabolism during various growth hormone dosing regimens in girls with Turner syndrome. Dutch Working Group on Growth Hormone

To analyze the effects of supraphysiological dosages of growth hormone (GH) on carbohydrate (CH) and lipid metabolism, we investigated 87 girls with Turner syndrome (TS) in two studies: (1) a 4-year GH dose-response (DR) study comparing three groups with stepwise GH dosage increases up to 8 IU/m2/d in girls aged 2 to 11 years, and (2) a 2-year GH administration frequency-response (FR) study in girls aged 11 to 17 years, comparing once-daily (OD) and twice-daily (BID) injections of a total GH dose of 6 IU/m2/d in combination with low-dose ethinyl estradiol (50 ng/kg/d orally). At baseline, impaired glucose tolerance (IGT) was present in 6% of the girls, and at the end of the studies, in 5%. In the DR study, the area under the curve for time-concentration (AUCab) for glucose after an oral glucose tolerance test (OGTT) showed no change over time and no significant difference between any of the study groups. However, in all three DR groups, the AUCab for insulin, fasting glucose, the insulinogenic index, hemoglobin A1c (HbA1c), and urinary C-peptide (uCp) were all significantly higher after 4 years compared with pretreatment (P<.05). In the FR study, group differences were not observed. Compared with healthy Dutch control subjects, the median baseline levels in relatively young girls in the DR study were similar for total cholesterol (TC) and lower for high-density lipoprotein (HDL) cholesterol. In contrast, the median TC levels of relatively older girls in the FR study were higher and HDL levels were similar. With increasing GH dosage in the DR study, median TC and low-density lipoprotein (LDL) levels decreased, whereas median HDL levels increased. The changes after 4 years were significant, including a decrease in the atherogenic index. GH treatment at the supraphysiological dosages used in this study did not increase the frequency of IGT or clinical diabetes. However, we observed an increased insulinogenic index indicative of insulin resistance. Therefore, long-term follow-up study is warranted in these otherwise healthy subjects. OD injection regimens changed the lipid profile toward a more cardioprotective direction with a significant reduction of the TC/HDL cholesterol ratio.

Insulin management and metabolic control of type 1 diabetes mellitus in childhood and adolescence in 18 countries. Hvidøre Study Group on Childhood Diabetes

Insulin regimens and metabolic control in children and adolescents with Type 1 diabetes mellitus were evaluated in a cross-sectional, non-population-based investigation, involving 22 paediatric departments, from 18 countries in Europe, Japan, and North America. Blood samples and information were collected from 2873 children from March to August 1995. HbA1c was determined once and analysed centrally (normal range 4.4-6.3%, mean 5.4%). Year of birth, sex, duration of diabetes, height, body weight, number of daily insulin injections, types and doses of insulin were recorded. Average HbA1c in children under 11 years was 8.3 +/- 1.3% (mean +/- SD) compared with 8.9 +/- 1.8% in those aged 12-18 years. The average insulin dose per kg body weight was almost constant (0.65 U kg(-1) 24 h(-1)) in children aged 2-9 years for both sexes, but there was a sharp increase during the pubertal years, particularly in girls. The increase in BMI of children with diabetes was much faster during adolescence compared to healthy children, especially in females. Sixty per cent of the children (n = 1707) used two daily insulin injections while 37% (n = 1071) used three or more. Of those on two or three injections daily, 37% used pre-mixed insulins, either alone or in combination with short- and intermediate-acting insulin. Pre-adolescent children on pre-mixed insulin showed similar HbA1c levels to those on a combination of short- and long-acting insulins, whereas in adolescents significantly better HbA1c values were achieved with individual combinations. Very young children were treated with a higher proportion of long-acting insulin. Among adolescent boys, lower HbA1c was related to use of more short-acting insulin. This association was not found in girls. We conclude that numerous insulin injection regimens are currently used in paediatric diabetes centres around the world, with an increasing tendency towards intensive diabetes management, particularly in older adolescents. Nevertheless, the goal of near normoglycaemia is achieved in only a few.

Antibody screening in a population of children

The first large-scale (secondary) intervention trials have been initiated in first-degree family members of patients with insulin-dependent diabetes mellitus (IDDM). Within a few years, data from these studies may suggest that intervention is possible, thereby opening similar approaches in the general population. However, before large-scale intervention studies can be initiated, several problems need to be solved. One of these problems is the lack of knowledge on the natural course of beta-cell autoimmunity. This review analyses this and other issues related to population-based prediction for IDDM. At present, no long-term follow-up studies are available in large-sized populations, but data show that prediction in the general population is both technically feasible and likely to have sufficient power to be useful in prevention trials. More data need to be generated, not only to determine which markers are most likely to give good prediction but also to obtain knowledge on the natural course, psychosocial impact and cost-effectiveness of screening.

Low prevalence of antibodies to GAD65 in a 50- to 74-year-old general Dutch population. The Hoorn Study

OBJECTIVE

To assess the prevalence of antibodies to GAD65 (GAD65-A) in relation to glucose tolerance disturbances and to blood glucose-lowering therapy in a general Dutch population.

RESEARCH DESIGN AND METHODS

A population sample of 2,350 Dutch subjects, age 50-74 years, agreed to undergo an oral glucose tolerance test (OGTT). They were classified as having normal glucose tolerance, impaired glucose tolerance, newly detected diabetes, or known diabetes. GAD65-A levels were measured in serum by means of a standardized radioligand assay and subsequently were expressed as indexes. The prevalence rates were defined as the proportions of individuals of each category of glucose tolerance exceeding the value of the index at the 99th percentile of the entire study population.

RESULTS

The prevalence rates and the 95% CIs of GAD65-A were 0.7% (0.4-1.2%) in cases of normal glucose tolerance, 2.4% (0.9-5.3%) in impaired glucose tolerance, 0% (0-3.3%) in newly detected diabetes, according to the World Health Organization (WHO) criteria, and 3.5% (0.7-10.0%) in known diabetes. A total of 2 out of 3 subjects with GAD65-A indexes above the 99th percentile and 10 out of 18 subjects with GAD65-A indexes above the 85th percentile received insulin therapy for their diabetes, which showed an association between GAD65-A and insulin therapy

CONCLUSIONS

Low prevalence rates of latent autoimmunity to GAD were found in 50- to 74-year-old Dutch subjects with normal and abnormal glucose tolerance, and GAD65-A was associated with insulin use in known diabetic subjects.

Fluctuations in GAD65 antibodies after clinical diagnosis of IDDM in young children

OBJECTIVE

To investigate whether the presence of GAD antibodies at onset of IDDM correlates to a more aggressive rate of beta-cell destruction after clinical onset.

RESEARCH DESIGN AND METHODS

We studied GAD antibodies at onset of disease, after 1 year, and after 6 years in 33 consecutively referred children (mean age 8.08, range 1.7-16.3). In a subset of 11 patients, GAD antibodies were studied very frequently. The correlation between GAD antibodies and clinical parameters, including glycosylated hemoglobin, residual insulin secretion, and insulin dosage, was evaluated.

RESULTS

GAD antibody titers were highly variable. Four patients became GAD antibody positive weeks to years after clinical onset. Other patients switched between testing positive and negative for GAD antibodies shortly after clinical onset. No correlation was found between the presence of GAD antibodies and the rate of beta-cell destruction, but patients with high GAD antibody indexes at onset had significantly higher glycosylated hemoglobin levels.

CONCLUSIONS

GAD antibodies at clinical onset do not predict the rate of beta-cell destruction in young children with newly diagnosed IDDM. The highly variable GAD antibody levels suggest variation of the autoimmune process.

Identification and characterization of glima 38, a glycosylated islet cell membrane antigen, which together with GAD65 and IA2 marks the early phases of autoimmune response in type 1 diabetes

Immunoprecipitating IgG autoantibodies to glutamic acid decarboxylase, GAD65, and/or a tyrosine phosphatase, IA2, are present in the majority of individuals experiencing pancreatic beta cell destruction and development of type 1 diabetes. Here we identify a third islet cell autoantigen, a novel 38-kD protein, which is specifically immunoprecipitated with sera from a subset of prediabetic individuals and newly diagnosed type 1 diabetic patients. The 38-kD autoantigen, named glima 38, is an amphiphilic membrane glycoprotein, specifically expressed in islet and neuronal cell lines, and thus shares the neuroendocrine expression patterns of GAD65 and IA2. Removal of N-linked carbohydrates results in a protein of 22,000 Mr. Glima 38 autoantibodies were detected in 16/86 (19%) of newly diagnosed patients, including three very young children, who had a rapid onset of disease, and in 6/44 (14%) of prediabetic individuals up to several years before clinical onset. The cumulative incidence of GAD65 and glima 38 antibodies in these two groups was 83 and 80%, respectively, and the cumulative incidence of GAD65, glima 38, and IA2 antibodies in the same groups was 91 and 84%, respectively. GAD65, IA2, and glima 38 represent three distinct targets of immunoprecipitating IgG autoantibodies associated with beta cell destruction and type 1 diabetes.

Islet cell cytoplasmic antibody reactivity in midgestational human fetal pancreas

The reactivity of islet cell cytoplasmic antibodies (ICA)-positive and ICA-negative sera of recent onset type 1 diabetic patients was studied in human fetal pancreata of 12-18 weeks' gestation and compared with the reactivity of these sera in adult human control pancreata. The aims of the study were: (1) to observe the presence of ICA staining in human fetal islet cells; (2) to compare endpoint titres (in Juvenile Diabetes Foundation units) of ICA-positive patient sera in fetal pancreata and adult human control pancreata. Ten ICA-positive sera and eight ICA-negative sera from newly diagnosed diabetic patients and four sera from healthy controls were tested on three human adult and eight human fetal pancreata. As in the adult control pancreata. ICA-positive sera reacted to insulin-, glucagon-, and somatostatin-positive cells of fetal pancreata of all gestational ages. This was observed both in single cells and in cells in islet-like cell clusters. Dilution of a reference serum gave similar results in both adult and fetal pancreata. In contrast, the ICA-positive patient sera yielded a striking heterogeneity in fetal as well as in adult pancreata. However, end-point titres between adult and fetal pancreata did not differ significantly (P > 0.05). In conclusion, ICA-positive sera from recent onset diabetic patients show that the expression of molecules to which ICA react is present in all islet cells and starts before week 12 of gestation.

Value of antibodies to GAD65 combined with islet cell cytoplasmic antibodies for predicting IDDM in a childhood population

The value of a test for islet cell cytoplasmic antibodies together with a test for GAD65 antibodies to predict the subsequent development of diabetes over a period of 11.5 years was assessed in an open childhood population comprising 2,805 individuals. A single serum sample was obtained from each individual between 1975 and 1977 and screened for islet cell cytoplasmic antibodies for which eight individuals were positive (0.29%). During the average follow-up period of 11.5 years, four of eight islet cell antibody positive and three islet cell antibody negative individuals developed clinical diabetes. Sera from all individuals, who were islet cell antibody positive and/or developed diabetes (total of 11) and from 100 randomly selected control subjects were analysed for GAD65 antibodies. Six of eight islet cell antibody positive individuals were GAD65 antibody positive including all four who subsequently developed IDDM. Furthermore, one of the three islet cell antibody negative individuals who developed IDDM was GAD65 antibody positive both in 1976 and in 1989. Thus, a positive test for GAD65 antibodies alone correctly predicted diabetes in five of seven children, who developed the disease. Only one of the children, who developed diabetes was positive for insulin autoantibodies and this individual was also positive for islet cell cytoplasmic antibodies and GAD65 antibodies. One of the 100 control subjects was positive for GAD65 antibodies (1%). The results suggest that a single GAD65 antibody test may have a higher sensitivity for predicting IDDM than a test for islet cell cytoplasmic antibodies, but that a combined positive test for both antibodies increases the specificity for predicting IDDM over a period of 11.5 years.

Higher autoantibody levels and recognition of a linear NH2-terminal epitope in the autoantigen GAD65, distinguish stiff-man syndrome from insulin-dependent diabetes mellitus

The smaller form of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD65) is a major autoantigen in two human diseases that affect its principal sites of expression. Thus, destruction of pancreatic beta cells, which results in insulin-dependent diabetes mellitus (IDDM), and impairment of GABA-ergic synaptic transmission in Stiff-Man syndrome (SMS) are both characterized by circulating autoantibodies to GAD65. Anti-GAD65 autoantibodies in IDDM are predominantly directed to conformational epitopes. Here we report the characterization of humoral autoimmune responses to GAD65 in 35 SMS patients, of whom 13 (37%) also had IDDM. All SMS patients immunoprecipitated native GAD65 and the main titers were orders of magnitude higher than in IDDM patients. Furthermore, in contrast to the situation in IDDM, autoantibodies in 35 of 35 (100%) of SMS patients recognized denatured GAD65 on Western blots. Two major patterns of epitope specificity were identified on Western blots. The first pattern, detected in 25 of 35 SMS patients (71%), of whom 11 had IDDM (44%), was predominantly reactive with a linear NH2-terminal epitope residing in the first eight amino acids of GAD65. Nine of nine individuals who were HLA-haplotyped in this group carried an IDDM susceptibility haplotype and HLA-DR3, DQw2 was particularly abundant. The second pattern, detected in 10 of 35 patients (29%) of whom two had IDDM (20%), included reactivity with the NH2-terminal epitope plus strong reactivity with one or more additional epitope(s) residing COOH-terminal to amino acid 101. The second epitope pattern may represent epitope spreading in the GAD65 molecule, but may also include some cases of epitope recognition associated with IDDM resistant HLA-haplotypes. The principal NH2-terminal linear epitope in GAD65 distinguishes the reactivity of SMS and IDDM autoantibodies and may be a determinant of pathogenicity for GABA-ergic neurons. The greater magnitude and distinct specificity of the humoral response to GAD65 in SMS may reflect a biased involvement of the T helper cell type 2 (Th2) subset of CD4+ T cells and antibody responses, whereas IDDM is likely mediated by the Th1 subset of CD4+ T cells and cytotoxic T cell responses.

Differential expression of GAD65 and GAD67 in human, rat, and mouse pancreatic islets

The smaller form of the autoantigen glutamic acid decarboxylase, GAD65 (formerly the 64,000 M(r) autoantigen), is a major target of humoral autoimmunity in type I diabetes. Human autoantisera have been used extensively to characterize the GAD65 antigen in both rat and human islets, but the protein has escaped detection in mouse islets. We have now analyzed the expression of GAD65 and GAD67, the larger glutamic acid decarboxylase protein, in human, rat, and mouse islets of Langerhans and brain, using human monoclonal islet cell autoantibodies, human autoantisera, and experimentally raised antibodies to glutamic acid decarboxylase. Human monoclonal autoantibodies and experimentally raised antibodies reacted with mouse GAD65 produced in a baculovirus expression system by Western blotting and immunoprecipitation and with GAD65 in mouse brain by immunohistochemistry but failed to detect GAD65 in mouse islets by the latter two methods. However, analysis of mouse islets by Western blotting technique, using the most sensitive experimentally raised antibody, showed that mouse islets express both GAD65 and GAD67 but at levels that are severalfold lower than those in mouse brain or in human and rat islets. Furthermore, both human and rat islets predominantly express GAD65, whereas GAD67 is the major glutamic acid decarboxylase protein in mouse islets. Human islets are significantly distinct from mouse and rat islets and from brain because they only express GAD65, which is consistent with the predominant role of this form as a target of autoantibodies associated with beta-cell destruction in humans. Human as well as rat islet GAD65 are found in both membrane-bound and soluble forms. The low level of glutamic acid decarboxylase expression in mouse islets compared with human and rat islets is likely to have implications for both the development of tolerance to glutamic acid decarboxylase as well as the homing of glutamic acid decarboxylase-specific lymphocytes to the mouse beta-cell. In this context, the results suggest 1) that the mouse is ideal for studies of the consequences of an expression of high levels of glutamic acid decarboxylase in the beta-cell from a transgene and 2) that the rat may be better suited than the mouse for development of nontransgenic animal models of glutamic acid decarboxylase autoimmunity by immunization.

The midgestational human fetal pancreas contains cells coexpressing islet hormones

In the fetal development of the mouse pancreas, endocrine cells have been found that express more than one hormone simultaneously. Our objective was to evaluate the existence of such cells in the human fetal pancreas. We found cells coexpressing two of the major pancreatic hormones (insulin, glucagon, and somatostatin) in sections of eight midgestational (12-18 weeks) pancreata and in 0-7% of cells in single-cell suspensions from midgestational pancreata. By electron microscopy, using granule morphology and immunoelectron microscopic techniques, we could confirm these findings and even detect cells containing three hormones. Morphologically different granules contained different immunoreactivities, suggesting parallel regulation of hormone production and packaging. In six newborn pancreata (born after 22-40 weeks of gestation), we could not find any multiple-hormone-containing cells. Subsequently, we evaluated whether multiple-hormone-containing cells proliferate by using pancreatic fragments and single-cell preparations at the light and electron microscopic level (six pancreata). No endocrine hormone-containing cells incorporated bromodeoxyuridine during a 1-hr culture period, indicating that these cells have lost the ability to proliferate under the conditions chosen. We conclude that, as in mice, the human fetal pancreas of 12-18 weeks of gestation contains endocrine cells that express multiple hormones simultaneously. These (multiple) hormone-containing cells do not seem to proliferate under basal conditions.

Membrane anchoring of the autoantigen GAD65 to microvesicles in pancreatic beta-cells by palmitoylation in the NH2-terminal domain

Pancreatic beta-cells and gamma-aminobutyric acid (GABA)-secreting neurons both express the enzyme glutamic acid decarboxylase (GAD) which is a major target of autoantibodies associated with beta-cell destruction and impairment of GABA-ergic neurotransmitter pathways. The predominant form of GAD in pancreatic beta-cells, GAD65, is synthesized as a soluble hydrophilic molecule, which is modified to become firmly membrane anchored. Here we show by immunogold electron microscopy that GAD65 is localized to the membrane of small vesicles which are identical in size to small synaptic-like microvesicles in pancreatic beta-cells. The NH2-terminal domain of GAD65 is the site of a two-step modification, the last of which results in a firm membrane anchoring that involves posttranslational hydroxylamine sensitive palmitoylation. GAD65 can be released from the membrane by an apparent enzyme activity in islets, suggesting that the membrane anchoring step is reversible and potentially regulated. The hydrophobic modifications and consequent membrane anchoring of GAD65 to microvesicles that store its product GABA may be of functional importance and, moreover, significant for its selective role as an autoantigen.

Enrichment of beta cells from the human fetal pancreas by fluorescence activated cell sorting with a new monoclonal antibody

The aim of this study was to produce an antibody reactive to the surface of endocrine pancreatic cells and use this antibody for the purification of endocrine cells from the human fetal pancreas by fluorescence activated cell sorting. We describe such an antibody, called N1, reacting with the surface and cytoplasm of endocrine cells in the adult and fetal human pancreas (12 to 18 weeks gestational age). While unreactive to exocrine and mesenchymal cells, it was not specific for endocrine cells, as evidenced by its staining pattern in tissues other than pancreas. Almost 40% of the N1-positive pancreatic cells contained either insulin, glucagon or somatostatin. Conversely, more than 90% of each of the hormone-containing cells was N1 positive. An additional 40% of N1-positive cells, not containing other pancreatic hormones, was shown to contain islet amyloid polypeptide, synaptophysin, chromogranin, tyrosine hydroxylase or CA812. A two-step collagenase digestion protocol yielded 1.29 +/- 0.17 x 10(5) cells per mg pancreatic tissue. After Percoll gradient centrifugation, the suspension contained 15.6 +/- 5.7% (n = 25, mean +/- SD) cells reactive with N1. By fluorescence activated cell sorting using the antibody N1, the single-cell suspension was enriched from 3.0 +/- 1.4% to 16.2 +/- 4.8% (n = 10, p less than 0.01) Beta cells. Alpha and Delta cells were also enriched significantly by this procedure. The percentage of N1-positive cells increased from 17 +/- 4% to 83 +/- 6%. This preparation enriched for endocrine cells allows future studies on possible endocrine precursor cells.

Pancreatic beta cells express two autoantigenic forms of glutamic acid decarboxylase, a 65-kDa hydrophilic form and a 64-kDa amphiphilic form which can be both membrane-bound and soluble

The 64-kDa pancreatic beta-cell autoantigen, which is a target of autoantibodies associated with early as well as progressive stages of beta-cell destruction, resulting in insulin-dependent diabetes (IDDM) in humans, has been identified as the gamma-aminobutyric acid-synthesizing enzyme glutamic acid decarboxylase. We have identified two autoantigenic forms of this protein in rat pancreatic beta-cells, a Mr 65,000 (GAD65) hydrophilic and soluble form of pI 6.9-7.1 and a Mr 64,000 (GAD64) component of pI 6.7. GAD64 is more abundant than GAD65 and has three distinct forms with regard to cellular compartment and hydrophobicity. A major portion of GAD64 is hydrophobic and firmly membrane-anchored and can only be released from membrane fractions by detergent. A second portion is hydrophobic but soluble or of a low membrane avidity, and a third minor portion is soluble and hydrophilic. All the GAD64 forms have identical pI and mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Results of pulse-chase labeling with [35S]methionine are consistent with GAD64 being synthesized as a soluble protein that is processed into a firmly membrane-anchored form in a process which involves increases in hydrophobicity but no detectable changes in size or charge. All the GAD64 forms can be resolved into two isoforms, alpha and beta, which differ by approximately 1 kDa in mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis but are identical with regard to all other parameters analyzed in this study. GAD65 has a shorter half-life than the GAD64 forms, remains hydrophilic and soluble, and does not resolve into isomers. Comparative analysis of the brain and beta-cell forms of GAD show that GAD65 and GAD64 in pancreatic beta-cells correspond to the larger and smaller forms of GAD in brain, respectively. The expression of different forms and the flexibility in subcellular localization of the GAD autoantigen in beta-cells may have implications for both its function and autoantigenicity.

Identification of the 64K autoantigen in insulin-dependent diabetes as the GABA-synthesizing enzyme glutamic acid decarboxylase

The pancreatic islet beta-cell autoantigen of relative molecular mass 64,000 (64K), which is a major target of autoantibodies associated with the development of insulin-dependent diabetes mellitus (IDDM) has been identified as glutamic acid decarboxylase, the biosynthesizing enzyme of the inhibitory neurotransmitter GABA (gamma-aminobutyric acid). Pancreatic beta cells and a subpopulation of central nervous system neurons express high levels of this enzyme. Autoantibodies against glutamic acid decarboxylase with a higher titre and increased epitope recognition compared with those usually associated with IDDM are found in stiff-man syndrome, a rare neurological disorder characterized by a high coincidence with IDDM.