Metabolic syndrome biomarkers relate to rate of cognitive decline in MCI and dementia stages of Alzheimer's disease

BACKGROUND

The relationship between biomarkers of metabolic syndrome and insulin resistance, plasma triglyceride/HDL cholesterol (TG/HDL-C) ratio, on the rate of cognitive decline in mild cognitive impairment (MCI) and dementia stages of Alzheimer's disease (AD) is unknown. The role of peripheral and cerebrospinal fluid (CSF) levels of Apolipoprotein A1 (ApoA1), a key functional component of HDL, on cognitive decline also remains unclear among them. Here we evaluate baseline plasma TG/HDL-C ratio and CSF and plasma ApoA1 levels and their relation with cognitive decline in the MCI and Dementia stages of AD.

PATIENTS AND METHODS

A retrospective longitudinal study (156 participants; 106 MCI, 50 AD dementia) from the Alzheimer's Disease Neuroimaging Initiative, with an average of 4.0 (SD 2.8) years follow-up. Baseline plasma TG/HDL-C, plasma, and CSF ApoA1 and their relationship to inflammation and blood-brain barrier (BBB) biomarkers and longitudinal cognitive outcomes were evaluated. Multivariable linear mixed effect models were used to assess the effect of baseline analytes with longitudinal changes in Mini-Mental State Exam (MMSE), Clinical Dementia Rating-Sum of Boxes (CDR-SB), and Logical Memory delayed recall (LM) score after controlling for well-known covariates.

RESULTS

A total of 156 participants included 98 women, 63%; mean age was 74.9 (SD 7.3) years. At baseline, MCI and dementia groups did not differ significantly in TG/HDL-C (Wilcoxon W statistic = 0.39, p = 0.39) and CSF ApoA1 levels (W = 3642, p = 0.29), but the dementia group had higher plasma ApoA1 than the MCI group (W = 4615, p = 0.01). Higher TG/HDL-C ratio was associated with faster decline in CDR-SB among MCI and dementia groups. Higher plasma ApoA1 was associated with faster decline in MMSE and LM among MCI, while in contrast higher CSF ApoA1 levels related to slower cognitive decline in MMSE among MCI. CSF and plasma ApoA1 also show opposite directional correlations with biomarkers of BBB integrity. CSF but not plasma levels of ApoA1 positively correlated to inflammation analytes in the AGE-RAGE signaling pathway in diabetic complications (KEGG ID:KO04933).

CONCLUSIONS

Biomarkers of metabolic syndrome relate to rate of cognitive decline among MCI and dementia individuals. Elevated plasma TG/HDL-C ratio and plasma ApoA1 are associated with worse cognitive outcomes in MCI and dementia participants. CSF ApoA1 and plasma ApoA1 likely have different roles in AD progression in MCI stage.

The Alzheimer's Cell Atlas (TACA): A single-cell molecular map for translational therapeutics accelerator in Alzheimer's disease

Introduction

Recent advances in generating massive single-cell/nucleus transcriptomic data have shown great potential for facilitating the identification of cell type-specific Alzheimer's disease (AD) pathobiology and drug-target discovery for therapeutic development.

Methods

We developed The Alzheimer's Cell Atlas (TACA) by compiling an AD brain cell atlas consisting of over 1.1 million cells/nuclei across 26 data sets, covering major brain regions (hippocampus, cerebellum, prefrontal cortex, and so on) and cell types (astrocyte, microglia, neuron, oligodendrocytes, and so on). We conducted nearly 1400 differential expression comparisons to identify cell type-specific molecular alterations (e.g., case vs healthy control, sex-specific, apolipoprotein E (APOE) ε4/ε4, and TREM2 mutations). Each comparison was followed by protein-protein interaction module detection, functional enrichment analysis, and omics-informed target and drug (over 700,000 perturbation profiles) screening. Over 400 cell-cell interaction analyses using 6000 ligand-receptor interactions were conducted to identify the cell-cell communication networks in AD.

Results

All results are integrated into TACA (https://taca.lerner.ccf.org/), a new web portal with cell type-specific, abundant transcriptomic information, and 12 interactive visualization tools for AD.

Discussion

We envision that TACA will be a highly valuable resource for both basic and translational research in AD, as it provides abundant information for AD pathobiology and actionable systems biology tools for drug discovery.

Highlights

We compiled an Alzheimer's disease (AD) brain cell atlas consisting of more than 1.1 million cells/nuclei transcriptomes from 26 data sets, covering major brain regions (cortex, hippocampus, cerebellum) and cell types (e.g., neuron, oligodendrocyte, astrocyte, and microglia).We conducted over 1400 differential expression (DE) comparisons to identify cell type-specific gene expression alterations. Major comparison types are (1) AD versus healthy control; (2) sex-specific DE, (3) genotype-driven DE (i.e., apolipoprotein E [APOE] ε4/ε4 vs APOE ε3/ε3; TREM2R47H vs common variants) analysis; and (4) others. Each comparison was further followed by (1) human protein-protein interactome network module analysis, (2) pathway enrichment analysis, and (3) gene-set enrichment analysis.For drug screening, we conducted gene set enrichment analysis for all the comparisons with over 700,000 drug perturbation profiles connecting more than 10,000 human genes and 13,000 drugs/compounds.A total of over 400 analyses of cell-cell interactions against 6000 experimentally validated ligand-receptor interactions were conducted to reveal the disease-relevant cell-cell communications in AD.

421 Elucidating Circadian and Sleep Phenotypes and Relation to Cognitive Impairment in Alzheimer’s Dementia

Introduction

Although sleep disruption in Alzheimer’s disease (AD) pathogenesis has been described, the role of circadian rhythm dysfunction (CRD) is less understood. We hypothesize greater CRD and sleep disruption with poorer cognitive function in AD compared to normal cognition.

Methods

We examined 3 groups:1)mild cognitive impairment with positive AD biomarkers(MCI-AD),n=18, 2)cognitively normal at high risk for AD(HR)(APOEƐ4 carriers),n=19, 3)cognitively normal APOEƐ4 non-carriers(CL),n=16 (National Institute of Aging, IMMUNE-AD). DNA extraction and APOEƐ4 genotyping were performed under the Cleveland Clinic Lou Ruvo Center for Brain Health Aging and Neurodegenerative Disease Biobank. We evaluated actigraphy-based (Motionlogger MicroWatch, Ambulatory Monitoring,Inc®) sleep (wake episodes(WE), total sleep time(TST), sleep efficiency(SE), sleep fragmentation index(SFI)) and circadian (mesor, amplitude, robustness, sleep regulatory index(SRI), intradaily stability) predictors and sleep study-based (ApneaLink Air by ResMed®) predictors (apnea hypopnea index(AHI,3% desaturation) and recording time<90%SaO2) across the groups and assessed association with cognition (Mini-Mental State Exam(MMSE)). Analysis of variance (ANOVA) or Kruskal-Wallis with Bonferroni adjustment was used for cross-group comparisons. ANCOVA assessed cross-group association of MMSE and sleep/circadian indices. Models were adjusted for age, sex, race, education, and BMI.

Results

Age differed across MCI-AD, HR, and CL groups (68.4±6.2,71.2±3.7,73.7±3.7 respectively,p=0.008). MCI-AD had more WE than HR and CL (14.4±5.6,10.9±3.9,10.9±3.5 respectively,p=0.033). In MCI-AD, the following associations were observed: 5% increase in SE was associated with 0.49 point higher MMSE (coefficient0.49, 95%CI[0.03,0.95],p=0.038), 1 hour increase in TST was associated with 0.81 point higher MMSE (coefficient0.81, 95%CI[0.24,1.37],p=0.006), and 1 unit increase in SFI was associated with 0.36 point lower MMSE (coefficient-0.36, 95%CI[-0.64,-0.08],p=0.013). Key measures differed: CLs had lower AHI, MCI-AD had less TST SaO2<90%, MCI-AD had the largest and HR the lowest SFI, and MCI-AD had lesser robustness but higher mesor and amplitude.

Conclusion

In this comparative study of carefully AD biomarker-phenotyped and APOEƐ4-genotyped patients and normal cognition controls, less sleep time and more fragmented sleep are associated with poorer MMSE scores in MCI-AD. Preliminary results show cognitively normal participants at risk of AD(HR) do not show CRD seen in MCI-AD and are more consistent with controls (CL).

Support (if any)

Catalyst Award. MCI cohort: Alzheimer’s Association, 2014-NIRG-305310. IMMUNE-AD, R01AG022304. CADRC, P30 AG062428. Jane and Lee Seidman Fund.

Harnessing endophenotypes and network medicine for Alzheimer's drug repurposing

Following two decades of more than 400 clinical trials centered on the "one drug, one target, one disease" paradigm, there is still no effective disease-modifying therapy for Alzheimer's disease (AD). The inherent complexity of AD may challenge this reductionist strategy. Recent observations and advances in network medicine further indicate that AD likely shares common underlying mechanisms and intermediate pathophenotypes, or endophenotypes, with other diseases. In this review, we consider AD pathobiology, disease comorbidity, pleiotropy, and therapeutic development, and construct relevant endophenotype networks to guide future therapeutic development. Specifically, we discuss six main endophenotype hypotheses in AD: amyloidosis, tauopathy, neuroinflammation, mitochondrial dysfunction, vascular dysfunction, and lysosomal dysfunction. We further consider how this endophenotype network framework can provide advances in computational and experimental strategies for drug-repurposing and identification of new candidate therapeutic strategies for patients suffering from or at risk for AD. We highlight new opportunities for endophenotype-informed, drug discovery in AD, by exploiting multi-omics data. Integration of genomics, transcriptomics, radiomics, pharmacogenomics, and interactomics (protein-protein interactions) are essential for successful drug discovery. We describe experimental technologies for AD drug discovery including human induced pluripotent stem cells, transgenic mouse/rat models, and population-based retrospective case-control studies that may be integrated with multi-omics in a network medicine methodology. In summary, endophenotype-based network medicine methodologies will promote AD therapeutic development that will optimize the usefulness of available data and support deep phenotyping of the patient heterogeneity for personalized medicine in AD.

0057 Actigraphy-Based Circadian Measures and Cerebrospinal Fluid Biomarkers of Neurodegeneration in Alzheimer’s Disease with Mild Cognitive Impairment

Introduction

Although recent data implicates sleep and circadian disruption to neurodegeneration in Alzheimer’s Disease (AD), the association of objective circadian biomarkers and neurodegeneration remains understudied. We hypothesize that actigraphy-based circadian measures are associated with cerebrospinal fluid (CSF) biomarkers of neurodegeneration in those mild cognitive impairment due to AD (MCI-AD).

Methods

Eighteen patients with CSF biomarker-confirmed MCI-AD underwent actigraphy monitoring generating the following circadian measures: amplitude, F-ratio and mesor and morning collection of CSF biomarkers of neurodegeneration (Aβ42,t-tau,p-tau). Linear models were used to evaluate the association of circadian and CSF measures; logarithmic transformations were performed on neurodegenerative markers for greater normality. Analysis was performed using SAS software. A significance level of 0.05 was assumed for all tests.

Results

Eighteen MCI-AD patients who were 68± 6.2 years, 44% female, with median AHI=12 and underwent actigraphy monitoring for 8.2+/-3.2 days were included. There was no significant association of circadian measures and Aβ42 nor with mesor and neurodegeneration biomarkers. Amplitude was associated with both p-tau and t-tau, such that each 10 unit increase in amplitude resulted in a predicted increase in p-tau of 8% (95% CI:1%-15%, p=0.018) and an increase of 13% (3%-23%; p=0.01) in t-tau. F-ratio was positively associated with p-tau and t-tau; each 1000 unit increase in F-ratio resulted in a predicted 12% (4%-22%; p=0.007) increase in P-tau and 20%(6%-35%; p=0.005) increase in t-tau. Associations of these circadian measures and CSF levels of p-tau and t-tau remained statistically significant after adjustment for age and sex.

Conclusion

Among patients with symptomatic MCI stages of AD, objective measures of circadian rhythm disruption are associated with CSF-based biomarkers of neurodegeneration even after consideration of age and sex. Future investigation should clarify directionality of this association and potential utility of circadian-based interventions in the mitigation of AD progression.

Support

N/A

Longitudinal change in regional brain volumes with exposure to repetitive head impacts

Objective

This study tests the hypothesis that certain MRI-based regional brain volumes will show reductions over time in a cohort exposed to repetitive head impacts (RHI).

Methods

Participants were drawn from the Professional Fighters Brain Health Study, a longitudinal observational study of professional fighters and controls. Participants underwent annual 3T brain MRI, computerized cognitive testing, and blood sampling for determination of neurofilament light (NfL) and tau levels. Yearly change in regional brain volume was calculated for several predetermined cortical and subcortical brain volumes and the relationship with NfL and tau levels determined.

Results

A total of 204 participants who had at least 2 assessments were included in the analyses. Compared to controls, the active boxers had an average yearly rate of decline in volumes of the left thalamus (102.3 mm³/y [p = 0.0004], mid anterior corpus callosum (10.2 mm³/y [p = 0.018]), and central corpus callosum (16.5 mm³/y [p = <0.0001]). Retired boxers showed the most significant volumetric declines compared to controls in left (32.1 mm³/y [p = 0.002]) and right (30.6 mm³/y [p = 0.008]) amygdala and right hippocampus (33.5 mm³/y [p = 0.01]). Higher baseline NfL levels were associated with greater volumetric decline in left hippocampus and mid anterior corpus callosum.

Conclusion

Volumetric loss in different brain regions may reflect different pathologic processes at different times among individuals exposed to RHI.

TREM2 deficiency eliminates TREM2+ inflammatory macrophages and ameliorates pathology in Alzheimer's disease mouse models

Jay and colleagues show that TREM2 deficiency reduces the number of macrophages infiltrating the brain and is protective against disease pathogenesis in mouse models of Alzheimer’s disease.

Variants in triggering receptor expressed on myeloid cells 2 (TREM2) confer high risk for Alzheimer’s disease (AD) and other neurodegenerative diseases. However, the cell types and mechanisms underlying TREM2’s involvement in neurodegeneration remain to be established. Here, we report that TREM2 is up-regulated on myeloid cells surrounding amyloid deposits in AD mouse models and human AD tissue. TREM2 was detected on CD45^hiLy6C⁺ myeloid cells, but not on P2RY12⁺ parenchymal microglia. In AD mice deficient for TREM2, the CD45^hiLy6C⁺ macrophages are virtually eliminated, resulting in reduced inflammation and ameliorated amyloid and tau pathologies. These data suggest a functionally important role for TREM2⁺ macrophages in AD pathogenesis and an unexpected, detrimental role of TREM2 in AD pathology. These findings have direct implications for future development of TREM2-targeted therapeutics.

Effects of Duration of Type 2 Diabetes Mellitus on Insulin Secretion

OBJECTIVE

To gain insight into the effects of duration of type 2 diabetes on insulin secretion in patients with type 2 diabetes mellitus.

METHODS

C-peptide concentrations were measured every 2 years before and after intravenous injection of 1 mg of glucagon in 89 patients with type 2 diabetes (51 men and 38 women) as part of the Rochester Diabetic Neuropathy Study in those subjects who participated in follow-up (median, 12 years; range, 6 to 14).

RESULTS

Although insulin secretion decreased over time (P<0.001) in the group as a whole, both the pattern and the rate of decline in C-peptide concentration differed considerably among the study subjects. Insulin secretion, whether measured as fasting C-peptide, 6-minute C-peptide, or postglucagon increment in C-peptide concentrations, declined with increasing duration of diabetes in approximately half of the patients but either increased or remained essentially constant over time in the other half. The decrease in insulin secretion was not associated with a deterioration in glycemic control because hemoglobin A1c also declined (P<0.005) during the same interval.

CONCLUSION

We conclude that insulin secretion decreases over time in many patients with type 2 diabetes. Because the rate of decline is variable, the predictive value of any single measurement is limited. These data indicate that although a decrease in insulin secretion over time is characteristic of type 2 diabetes mellitus, it is not inevitable.

Epitope-restricted 65-kilodalton glutamic acid decarboxylase autoantibodies among new-onset Sardinian type 2 diabetes patients define phenotypes of autoimmune diabetes

The 65-kDa glutamic acid decarboxylase (GAD65) autoantibodies (GAD65Abs), commonly found in type 1 diabetes mellitus (T1DM) patients, are also found at lower frequencies in type 2 diabetes mellitus (T2DM) patients. GAD65Abs in T1DM patients are epitope specific, in contrast to those found in other GAD65Ab-positive individuals, including T2DM patients. Our aim was to assess whether epitope-specific GAD65Abs, or the additional presence of islet antigen 2 (IA-2) autoantibodies, better define T1DM phenotypes among T2DM patients. GAD65 and IA-2 autoantibodies were analyzed in 1436 Sardinian subjects classified with T2DM and in 384 nondiabetic patient controls. Autoantibody binding specificity to the N-terminal, middle (M), and C-terminal (C) portions of the GAD65 molecule was evaluated. Among the T2DM patients, 5.1% had GAD65 (P < 0.001) and 2.4% had IA-2 autoantibodies, compared with 1.3 and 1.6%, respectively, among the controls. GAD65Ab-positive T2DM patients with M+C (epitope-specific) reactivity were found to have the lowest body mass index (P < 0.001), followed by GAD65Ab/IA-2Ab-positive patients (P < 0.01), and non-M+C-reactive (non-epitope-specific) patients (P < 0.02). In GAD65Ab-positive T2DM patients, c-peptide levels were lower in M+C-reactive compared with non-M+C-reactive patients. Sardinian T2DM patients with M+C-predominant GAD65Ab reactivity have clinical features more similar to those of T1DM patients. Thus, GAD65Ab epitope analysis may help to define T1DM phenotypes among newly diagnosed GAD65Ab-positive patients classified with T2DM.

A high prevalence of organ-specific autoimmunity in patients with bipolar disorder

BACKGROUND

In a previous study, we reported an increased prevalence of thyroperoxidase antibodies (TPOA) in patients with bipolar disorder. Here we report the prevalence of other organ-specific autoantibodies: H/K adenosine triphosphatase (ATPA), glutamic acid decarboxylase-65 (GAD65A), and GAD-67 (GAD67A).

METHODS

ATPA, GAD65A, and GAD67A were determined (via a commercially available enzyme linked immunosorbent assay for ATPA, and a standardized radio immunoassays for GAD65A and GAD67A)in the sera of 239 patients with DSM-IV bipolar disorder, in 74 patients with DSM-IV schizophrenia, and in 220 healthy control subjects.

RESULTS

The positivity prevalences for ATPA and GAD65A (but not GAD67A) were elevated in bipolar patients compared with those in healthy control subjects (11.7 vs. 6.1% and 11.3 vs. 2.6% respectively; p <.05). Schizophrenia patients did not show such statistically higher prevalence. The elevated prevalence of ATPA and GAD65A in bipolar disorder was associated with neither rapid cycling nor the use of lithium. Interestingly, the presence of GAD65A (and not that of TPOA and ATPA) tended to be associated with the activity of bipolar disorder. The level of TPOA was negatively correlated with the serum level of sIL-2R, a measure of T cell activation.

CONCLUSION

Bipolar disorder is associated with organ-specific autoimmunity to the antigens TPO, H/K ATPase, and GAD65.

Conformation-dependent GAD65 autoantibodies in diabetes

AIMS/HYPOTHESIS

Conformation-dependent autoantibodies directed against GAD65 are markers of Type 1 diabetes. In this study we aimed to determine whether the substitution of GAD65 with GAD67 amino acids would affect the binding of conformation-dependent GAD65 autoantibodies.

METHODS

We used PCR-based site-directed mutagenesis to generate a series of mutated GAD65 cDNA constructs in which specific GAD65 coding sequences for regions of the protein critical for autoantibody binding were replaced with GAD67 coding sequences.

RESULTS

The introduction of a point mutation at position 517, substituting glutamic acid with proline, markedly reduced the binding of disease-associated GAD65 antibodies. The binding of GAD65 antibodies to the E517P mutant was reduced in the sera of all newly diagnosed Type 1 diabetes patients ( n=85) by a mean of 72% ( p<0.0001) compared with binding to wild-type GAD65. Patients with latent autoimmune diabetes in adults ( n=24) showed a similar reduction in binding (79% reduction, p<0.0001). First-degree relatives who subsequently progressed to Type 1 diabetes ( n=12) showed a reduction in binding of 80% compared with a reduction of only 65% among relatives who had not progressed to disease ( n=38; p=0.025). In healthy GAD65Ab-positive individuals who did not progress to diabetes during a 9-year follow-up period ( n=51), binding to GAD65-E517P was reduced by only 28% compared with binding to wild-type GAD65.

CONCLUSIONS/INTERPRETATION

Differences in autoantibody binding to wild-type GAD65 versus GAD65-E517P may provide predictive information about Type 1 diabetes risk beyond that provided by the presence or absence of GAD65 autoantibodies. Lack of binding to mutant GAD65-E517P defines GAD65-positive individuals who are at higher risk of developing diabetes.

GAD2 on chromosome 10p12 is a candidate gene for human obesity

The gene GAD2 encoding the glutamic acid decarboxylase enzyme (GAD65) is a positional candidate gene for obesity on Chromosome 10p11-12, a susceptibility locus for morbid obesity in four independent ethnic populations. GAD65 catalyzes the formation of gamma-aminobutyric acid (GABA), which interacts with neuropeptide Y in the paraventricular nucleus to contribute to stimulate food intake. A case-control study (575 morbidly obese and 646 control subjects) analyzing GAD2 variants identified both a protective haplotype, including the most frequent alleles of single nucleotide polymorphisms (SNPs) +61450 C>A and +83897 T>A (OR = 0.81, 95% CI [0.681-0.972], p = 0.0049) and an at-risk SNP (-243 A>G) for morbid obesity (OR = 1.3, 95% CI [1.053-1.585], p = 0.014). Furthermore, familial-based analyses confirmed the association with the obesity of SNP +61450 C>A and +83897 T>A haplotype (chi(2) = 7.637, p = 0.02). In the murine insulinoma cell line betaTC3, the G at-risk allele of SNP -243 A>G increased six times GAD2 promoter activity (p < 0.0001) and induced a 6-fold higher affinity for nuclear extracts. The -243 A>G SNP was associated with higher hunger scores (p = 0.007) and disinhibition scores (p = 0.028), as assessed by the Stunkard Three-Factor Eating Questionnaire. As GAD2 is highly expressed in pancreatic beta cells, we analyzed GAD65 antibody level as a marker of beta-cell activity and of insulin secretion. In the control group, -243 A>G, +61450 C>A, and +83897 T>A SNPs were associated with lower GAD65 autoantibody levels (p values of 0.003, 0.047, and 0.006, respectively). SNP +83897 T>A was associated with lower fasting insulin and insulin secretion, as assessed by the HOMA-B% homeostasis model of beta-cell function (p = 0.009 and 0.01, respectively). These data support the hypothesis of the orexigenic effect of GABA in humans and of a contribution of genes involved in GABA metabolism in the modulation of food intake and in the development of morbid obesity.

Development of type 1 diabetes in wild bank voles associated with islet autoantibodies and the novel ljungan virus

Wild bank voles (Clethrionomys glareolus) may develop diabetes in laboratory captivity. The aim of this study was to test whether bank voles develop type 1 diabetes in association with Ljungan virus. Two groups of bank voles were analyzed for diabetes, pancreas histology, autoantibodies to glutamic acid decarboxylase (GAD65), IA-2, and insulin by standardized radioligand-binding assays as well as antibodies to in vitro transcribed and translated Ljungan virus antigens. Group A represented 101 trapped bank voles, which were screened for diabetes when euthanized within 24 hours of capture. Group B represented 67 bank voles, which were trapped and kept in the laboratory for 1 month before being euthanized. Group A bank voles did not have diabetes. Bank voles in group B (22/67; 33%) developed diabetes due to specific lysis of pancreatic islet beta cells. Compared to nondiabetic group B bank voles, diabetic animals had increased levels of GAD65 (P < .0001), IA-2 (P < .0001), and insulin (P = .03) autoantibodies. Affected islets stained positive for Ljungan virus, a novel picorna virus isolated from bank voles. Ljungan virus inoculation of nondiabetic wild bank voles induced beta-cell lysis. Compared to group A bank voles, Ljungan virus antibodies were increased in both nondiabetic (P < .0001) and diabetic (P = .0015) group B bank voles. Levels of Ljungan virus antibodies were also increased in young age at onset of newly diagnosed type 1 diabetes in children (P < .01). These findings support the hypothesis that the development of type 1 diabetes in captured wild bank voles is associated with Ljungan virus. It is speculated that bank voles may have a possible zoonotic role as a reservoir and vector for virus that may contribute to the incidence of type 1 diabetes in humans.

Immune reactivity to GAD25 in type 1 diabetes mellitus

While both isoforms of glutamic acid decarboxylase (GAD) function as important autoantigens in autoimmune diabetes mellitus-GAD65 in humans and GAD67 in the NOD mouse-GAD67 is not synthesized in human pancreatic islets and is thought not to be an autoantigen in human diabetes. We have recently shown, however, that human islets contain a GAD67 splice variant: GAD25. Given the evidence that GAD67 could be a key diabetogenic autoantigen in the NOD mouse and the high prevalence of GAD65 autoantibodies in human type 1 diabetes, it became important to ask whether there is also immune reactivity to GAD25 in type 1 diabetes-possibly implicating it in the pathogenesis of the disease-and whether GAD25 reactivity could, like GAD65 reactivity, function as a clinically useful marker for the disease. We also hypothesized that the presence of autoantibodies to the smaller splice variant could be a cause of the up to 30% prevalence of GAD67 autoreactivity associated with type 1 diabetes. We therefore analyzed GAD25 reactivity in 105 newly-diagnosed children with type 1 diabetes and 74 control subjects. While 14 (13%) of the diabetic subjects were positive for GAD67 autoantibodies, only 3 (3%) were positive for GAD25 reactivity, none of which were GAD67 antibody-positive. Analysis of reactivity to a GAD67 chimera was consistent with GAD67 binding activity being due to cross-reactive GAD65 antibodies. Immunostaining confirmed the presence of GAD25 in human islets, revealing GAD25-positive cells to be sparse. Our results indicate that autoreactivity to GAD25 is rare in newly diagnosed type 1 diabetes and does not underlie GAD67 reactivity.

GAD65 and IA-2 autoantibodies are common in a subset of siblings of Sardinian Type 2 diabetes families

Type 1 diabetes in Sardinia is very common in children, and we hypothesized that Latent Autoimmune Diabetes of Adult (LADA) might constitute a significant proportion of diabetes in adult Sardinian subjects. Since Type 2 diabetes is a familial disorder, we tested this hypothesis by investigating the prevalence of GAD65 and IA-2 autoantibodies (Ab) in Type 2 diabetes multiplex families of Sardinian ancestry enrolled in the Study Group for the Genetics of Diabetes in Sardinia.

METHODS

A total of 684 individuals were ascertained from 252 Sardinian Type 2 diabetes multiplex families with 2.4 affected siblings per family comprising 190 families with two affected, 37 with three, 15 with four, 7 with five, and 3 with six, in addition to 80 unaffected siblings. Controls were household contacts representing 204 healthy spouses of affected siblings. Diagnosis was at 35-69 years of age and insulin was not given in the first 4 years after diagnosis. GAD65Ab and IA-2Ab were determined in standard radioligand binding assays.

RESULTS

Among affected siblings GAD65Ab were positive in 8.8% of insulin-treated (n = 137; P = 0.0006), in 2.5% of non-insulin-treated (n = 467), and in 1.2% of non-diabetic siblings (n = 80) compared with 0.5% of controls (n = 204). IA-2Ab was positive in 6.6% insulin-treated (P = 0.04), 2.1% non-insulin-treated, and 2.5% non-diabetic siblings compared with 1.5% of controls.

CONCLUSION

A high frequency of GAD65Ab and IA-2Ab as markers of Type 1 diabetes was found among Type 2 diabetes siblings from Sardinian multiplex families despite excluding those who had been treated with insulin during the first 4 years of disease. Our data support the hypothesis that LADA may be common in Sardinian Type 2 diabetes and stress the importance of investigating markers of Type 1 diabetes in studies of Type 2 diabetes.

Type 1 diabetes-related autoantibodies are rare in Alaska native populations

OBJECTIVES

When clinical data were initially gathered from the Alaskan Eskimos in the 1950's, diabetes mellitus was noted to be quite rare. The prevalence of diabetes has increased significantly since that time, with rates of 10% reported recently in some Alaska native populations. Our goal was to understand the pathogenesis of diabetes among these groups, with the hypothesis that Alaskan Eskimos were predominantly affected by type 2 diabetes, not by latent autoimmune diabetes in adults (LADA).

STUDY DESIGN

Population based case control study

METHODS

We tested sera from subjects in two Eskimo villages for the presence of type 1 diabetes-related autoantibodies against glutamic acid decarboxylase (GAD65Ab) and tyrosine phosphatase-like islet antigen-2 (IA-2Ab).

RESULTS

Among subjects from one Inupiat village (#1) and one SiberianYup'ik village (#2), there were 21 subjects with diabetes mellitus (DM), 17 with impaired glucose tolerance (IGT), and 226 healthy controls with normal glucose tolerance (NGT). In village 1, GAD65 antibodies were not present in either diabetic subjects or those with IGT. One of the healthy controls (1%; 1/97) was positive for GAD65Ab. Similarly, no subjects from this village with DM or IGT had positive IA-2Ab titers, and one healthy control (1%; 1/97) was positive for IA-2Ab. In village 2, no DM subject was GAD65Ab positive. One (10%; 1/10) of the IGT subjects and two (1.6%;2/129) of the healthy controls were positive for GAD65Ab. In this village, two of the DM subjects (12%;2/17), one of the IGT subjects (10%; 1/10), and one of the healthy controls (0.8%;1/129) were IA-2Ab positive. No individual was positive for both GAD65Ab and IA-2Ab.

CONCLUSION

Alaskan Inupiat and Siberian Yup'ik Eskimos appear to be predominantly affected by type 2 diabetes, not LADA.

Stable GAD65 autoantibody epitope patterns in type 1 diabetes children five years after onset

Autoantibodies to GAD65 (GAD65Ab) are prominent in type 1 diabetes. These autoantibodies may be present both years before and after the clinical diagnosis of type 1 diabetes and are widely used as a marker for the disease. Recently it has been demonstrated that progression to type 1 diabetes is accompanied by GAD65Ab epitope maturation. Here we examine whether autoantibody maturation processes also progress after the clinical diagnosis of type 1 diabetes. Antibody reactivity to GAD65, GAD67 and GAD65/67 fusion proteins was measured by radioimmunoassays in 62 children with type 1 diabetes. Samples were taken at diagnosis and five years later. While the overall GAD65Ab level declined over time, the epitope pattern was remarkably stable with no significant changes in binding pattern. Loss of GAD65Ab-positivity was associated with significantly lower GAD65Ab indices at diagnosis compared to patients' sera that remained GAD65Ab-positive. The decrease in GAD65Ab levels did not correlate to residual C-peptide levels. Our data suggest that processes controlling GAD65Ab levels and epitope binding patterns remain stable during the first five years of type 1 diabetes.

Recognition of glutamic acid decarboxylase (GAD) by autoantibodies from different GAD antibody-positive phenotypes

Autoantibodies against the smaller isoform of glutamic acid decarboxylase (GAD) are markers for Type 1 diabetes. GAD65 autoantibody (GAD65Ab)-positive individuals in the general population are, however, mostly at low risk of developing Type 1 diabetes, suggesting that GAD65Ab phenotypes may be associated with different underlying pathogenic processes. The aim of this study was to test the hypothesis that Type 1 diabetes patients (n = 243; group I), GAD65Ab-positive healthy individuals (n = 28; group II), and healthy first-degree relatives of Type 1 diabetes patients (n = 41; group III) have antibody phenotypes that recognize different GAD65 epitopes. Sera from groups I-III were tested for their binding to GAD65 and GAD67, as well as six different GAD65/67 fusion proteins. Regardless of group, sera reactive to both GAD65 and GAD67 showed broader epitope reactivity than GAD65-specific sera. Furthermore, Type 1 diabetes patients showed a more restricted epitope binding than healthy individuals and first-degree relatives, demonstrating significantly less binding to the N-terminal part of GAD65 and to GAD67. Our analysis demonstrates that the N-terminal part is essential for full antibody binding to GAD65, in particular, to the middle epitope. It is suggested that Type 1 diabetes is associated with restricted GAD65Ab epitope specificity.

Newly diagnosed latent autoimmune diabetes in adults (LADA) is associated with low level glutamate decarboxylase (GAD65) and IA-2 autoantibodies. Diabetes Incidence Study in Sweden (DISS)

A quantitative assay with microSepharose was used to determine GAD65Ab and IA-2Ab levels in 771 population-based patients diagnosed with diabetes mellitus at 15 to 34 years of age, and in 828 matched controls. Among the patients, 587 (76%) were classified with type I, 108 (14%) with type II, and 76 (10%) with unclassifiable diabetes. The levels above normal demonstrated a prevalence of GAD65Ab in 66% of type I diabetes, 50% of type II diabetes and 54% of unclassifiable patients and for IA-2Ab in 40%, 17% and 21%, respectively. Among the autoantibody-positive sera, the LADA patients had a lower GAD65Ab index (median 0.19, p < 0.0001) and IA-2Ab index (median 0.28, p < 0.0001) than the type I patients (median 0.37 and 0.66). Patients with unclassifiable diabetes had a GAD65Ab (median 0.43) or IA-2Ab (median 0.63) index which was not different from the type I diabetes patients. Our data demonstrate that young adult new-onset LADA patients have low level GAD65Ab and IA-2Ab. The low-level autoantibodies may signify a less aggressive beta-cell autoimmunity, which may explain why these patients are often classified with type II or non-insulin-dependent diabetes.

A simple and rapid microSepharose assay for GAD65 and ICA512 autoantibodies in diabetes. Diabetes Incidence Study in Sweden (DISS)

GAD65Ab and ICA512Ab are strongly associated with insulin-dependent (Type 1) diabetes mellitus. A novel, simple radio-antigen binding assay with microSepharose conjugated with monoclonal antibodies specific for human immunoglobulin light chains was developed to provide diagnostic sensitivity and specificity of GAD65Ab and ICA512Ab for Type 1 diabetes. The Receiver Operating Characteristic (ROC) curve was used to determine the upper level of Normal in 583 new onset Type 1 diabetic patients and in 829 matched controls. The sensitivity of GAD65Ab and ICA512Ab was 66% (384/583) and 41% (211/520), respectively, and the diagnostic specificity was 96% for both autoantibodies. Levels, but not frequency, of GAD65Ab were higher among female Type 1 diabetes patients, whereas ICA512Ab levels did not differ between males and females. Positivity for GAD65Ab. ICA512Ab or both showed a sensitivity of 74% and a specificity of 92% for Type 1 diabetes. This simple, one-step centrifugation, high-capacity radio-antigen binding assay has a high precision and reproducibility to accurately detect both GAD65Ab and ICA512Ab. This assay should also prove useful in other autoantibody assays against conformation-sensitive autoantigens.