Immune reactivity to glutamic acid decarboxylase 65 in stiff-man syndrome and type 1 diabetes mellitus

doi:10.1016/S0140-6736(00)02431-4

The Lancet

Volume 356, Issue 9223, 1 July 2000, Pages 31-35

https://doi.org/10.1016/S0140-6736(00)02431-4 Get rights and content

Summary

Background

The immune response to an isoform of glutamic acid decarboxylase (GAD), GAD65, is associated with two clinically distinct diseases, stiff-man syndrome (SMS) and type 1 (insulin-dependent) diabetes mellitus. We sought to identify differences in the cellular and humoral immune responses to GAD in these two diseases.

Methods

We compared T-cell responses in 14 SMS patients with axial disease and 17 patients with type 1 diabetes.

Findings

Peripheral blood T cells of eight SMS patients recognised different immunodominant epitopes of GAD65 compared with T cells from 17 patients with type 1 diabetes. GAD regions 81–171 and 313–403 induced a dominant T-cell response in six of eight patients with SMS but in only one of 17 patients with type 1 diabetes (p=0·001). No SMS patients responded dominantly to GAD fragments 161–243 and 473–555 compared with ten patients with type 1 diabetes (p=0·008). GAD antibodies were detected in 11 of 14 SMS patients (seven with diabetes) and 11 of 17 patients with type 1 diabetes; IgG1 was dominant in both groups. SMS patients, however, were more likely than patients with diabetes to have isotypes other than IgG1 (p=0·03), in particular, IgG4 or IgE isotypes, which were not detected in patients with type 1 diabetes (p=0·012).

Interpretation

Our findings indicate differences between patients with SMS and type 1 diabetes in cellular (epitope recognition) and humoral (isotype pattern) responses to GAD65. Thus the same autoantigen can elicit distinct immune responses in patients with SMS, even when associated with diabetes, compared with patients with type 1 diabetes.

Introduction

Glutamic acid decarboxylase (GAD) isoform 65 is a major autoantigen in type 1 (insulin-dependent) diabetes mellitus and stiff-man syndrome (SMS), a rare neurological disorder that causes painful muscle spasms and rigidity. An immune response to islet-cell antigens, including GAD65, is thought to be involved in the destruction of insulin-secreting cells that causes type 1 diabetes,1, 2, 3 and may also cause SMS, which is associated with impairment of neurotransmission.4, 5 Most patients with type 1 diabetes do not have SMS, but about 50% of SMS patients have diabetes.⁴ Differences between the involvement of GAD in these two disorders might explain why individuals develop diabetes but rarely develop both diabetes and SMS.⁶

The epitopes of GAD recognised by antibodies from patients with type 1 diabetes and SMS patients have been identified and the dominant epitopes are distinct.6, 7, 8, 9, 10 In type 1 diabetes these epitopes include peptides in the middle (amino acids 245–449) and at the carboxyl terminus (amino acids 450–570) of GAD, whereas in SMS the epitope is often at the amino-terminus (first eight aminoacids) of the molecule.6, 7 In type 1 diabetes the epitopes tend to be conformational, whereas in SMS they are linear.⁶ The distinct pattern of staining on human beta cells with GAD-positive sera in patients with SMS,¹¹ the higher titres of GAD antibodies,4, 6 and different effects on gamma-amino butyric acid synthesis, indicate that these antibodies recognise GAD differently compared with type 1 diabetes.¹²

The GAD epitopes involved in the cellular immune response in type 1 diabetes have also been mapped to the middle and carboxyl terminus of the molecule,13, 14, 15 whereas T cells from controls respond to the middle of the molecule. T-cell GAD epitope mapping in SMS has not been done, although T cells in SMS patients do respond to GAD.16, 17

GAD antibody isotype can reflect the type of T-helper-cell response generated.¹⁸ Islet-cell antibodies, which include GAD antibody reactivity, are usually restricted to IgG1 subclass.19, 20 The isotype profile of GAD65 antibodies has not been characterised in SMS and in type 1 diabetes, although GAD65 antibodies are dominantly IgG1 in prediabetic individuals.²¹ Moreover, monoclonal antibodies isolated from patients with type 1 diabetes are usually of the IgG1 isotype.²²

We studied differences in the cellular (epitoperecognition) and humoral (isotype profile) immune response to GAD65 in patients with SMS and type 1 diabetes to characterise the possible mechanisms that lead to their distinct clinical outcome.

Section snippets

Patients

A consecutive series of 14 patients (mean age 45 years, range 23–67; four men, ten women) with clinical and neurological features of axial SMS, seven of whom had diabetes mellitus, were referred to us for study. Diagnosis of axial SMS was confirmed independently by a consultant neurologist and was based on typical clinical symptoms, electromyogram findings, clinical improvement on diazepam, and the presence of GAD antibodies, according to recent criteria.²³ None of the patients had diseases

Results

Sera for autoantibody analysis were available from all patients. However, because of difficulty in obtaining fresh blood cells, sufficient peripheral blood mononuclear cells for HLA genotype were available from 13 of 14 SMS patients, and for T-cell studies from only eight SMS patients.

We did not detect GAD65 antibodies in three SMS patients. Of the seven SMS patients with diabetes, six were on insulin treatment and the mean duration of their diabetes was 8·4 years (range 0–22). SMS was

Discussion

We found that the GAD antibody response in type 1 diabetes and SMS commonly includes IgG1. In type 1 diabetes, GAD65 autoantibodies were highly restricted, comprising only IgG1 and IgG3, which are thought to be associated with a cell-mediated T-helper type 1 response in human beings. By contrast, there were no IgE or IgG4 GAD isotype antibodies, which are thought to be associated with a humoral T-helper type 2 response, so there was no evidence of a humoral response in type 1 diabetes. The main

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ArticlesImmune reactivity to glutamic acid decarboxylase 65 in stiff-man syndrome and type 1 diabetes mellitus

Summary

Background

Methods

Findings

Interpretation

Introduction

Section snippets

Patients

Results

Discussion

Lancet

Lancet

J Autoimmun

Hum Immunol

Lancet

Control of autoimmune diabetes in NOD mice by GAD expression or suppression in beta cells

Science

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

Nature

Autoantibodies to GABA-ergic neurons and pancreatic beta cells in stiff-man syndrome

N Engl J Med

Autoantibodies to glutamic acid decarboxylase in a patient with stiff-man syndrome, epilepsy, and type I diabetes mellitus

N Engl J Med

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

J Exp Med

Autoreactive epitopes defined by diabetes-associated human monoclonal antibodies are localized in the middle and C-terminal domains of the smaller form of glutamate decarboxylase

Proc Natl Acad Sci USA

GAD autoantibodies in IDDM, stiff-man syndrome, and autoimmune polyendocrine syndrome type I recognize different epitopes

Diabetes

Identification of autoantibody epitopes of glutamic acid decarboxylase in stiff-man syndrome patients

J Immunol

Identification of a dominant epitope of glutamic acid decarboxylase (GAD-65) recognized by autoantibodies in stiff-man syndrome

J Exp Med

Association of HLADQB1*0201 with stiff-man syndrome

J Clin Endocrinol Metab

Inhibition of gamma-aminobutyric acid synthesis by glutamic acid decarboxylase autoantibodies in stiff-man syndrome

Ann Neurol

Articles
Immune reactivity to glutamic acid decarboxylase 65 in stiff-man syndrome and type 1 diabetes mellitus

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

Association of HLADQB1^*0201 with stiff-man syndrome