GAD65 autoantibody characteristics in patients with co-occurring type 1 diabetes and epilepsy may help identify underlying epilepsy etiologies

  • Suvi Liimatainen
  • Jerome Honnorat
  • Sean J. Pittock
  • Andrew McKeon
  • Mario Manto
  • Jared R. Radtke
  • T1D Exchange Biobank
  • Christiane S. Hampe
Open Access
Research
Part of the following topical collections:
  1. Rare neurological diseases

Abstract

Background

Autoantibodies against the smaller isoform of glutamate decarboxylase (GAD65Ab) reflect autoimmune etiologies in Type 1 diabetes (T1D) and several neurological disorders, including Stiff Person Syndrome (SPS). GAD65Ab are also reported in cases of epilepsy, indicating an autoimmune component. GAD65Ab in patients with co-occurring T1D, epilepsy or SPS may be part of either autoimmune pathogenesis. To dissect the etiologies associated with GAD65Ab, we analyzed GAD65Ab titer, epitope specificity and enzyme inhibition in GAD65Ab-positive patients diagnosed with epilepsy (n = 28), patients with epilepsy and T1D (n = 10), patients with SPS (n = 20), and patients with T1D (n = 42).

Results

GAD65Ab epitope pattern in epilepsy differed from T1D and SPS patients. Four of 10 patients with co-occurring T1D and epilepsy showed GAD65Ab profiles similar to T1D patients, while lacking GAD65Ab characteristics found in GAD65Ab-positive epilepsy patients. One of these patients responded well to anti-epileptic drugs (AEDs), while another patient did not require medication for seizure control. The third patient was refractory due to a diagnosis of meningioma. The response of the remaining patient to AEDs was unknown. GAD65Ab in the remaining six patients with T1D and epilepsy showed profiles similar to those in epilepsy patients.

Conclusions

Different autoimmune responses associated with T1D, epilepsy and SPS are reflected by disease-specific GAD65Ab patterns. Moreover, the epileptic etiology in patients diagnosed with both T1D and epilepsy may present two different etiologies regarding their epileptic condition. In one group T1D co-occurs with non-autoimmune epilepsy. In the other group GAD65Ab are part of an autoimmune epileptic condition.

Keywords

Autoimmune epilepsy Type 1 diabetes GAD65Ab Epitope mapping GAD65 enzyme activity 

Abbreviations

AEDs

Anti-epileptic drugs

DASP

Diabetes Autoantibody Standardization Program

ES-RBA

Epitope-specific radioligand binding assay

GABA

Gamma-aminobutyric acid

GAD65Ab

Autoantibody directed against the 65 kDa isoform of glutamate decarboxylase

rFab

Recombinant Fab

SPS

Stiff Person Syndrome

T1D

Type 1 diabetes

Background

The observation that nearly 20% of patients with epilepsy have a coexisting autoimmune disorder has led to the hypothesis of an autoimmune mechanism contributing to the pathogenesis of some forms of epilepsy [1, 2]. Autoimmune epilepsy is particularly prevalent in patients with refractory seizures [3, 4] and the underlying autoimmune etiology may contribute to the failure of anti-epileptic drug treatment in these patients. Autoimmune mechanisms have been suggested for other neurological diseases including Stiff Person Syndrome (SPS), cerebellar ataxia, and autoimmune encephalitis, where autoantibodies directed against neuronal antigens may have a pathological effect on neurotransmission [5, 6, 7]. Autoantibodies directed against the smaller isoform of glutamate decarboxylase (GAD65) have been found in patients with encephalitis and epilepsy [8, 9] and in rarer cases in association with epileptic status [10]. GAD65 is one of two enzymes that catalyzes the formation of the major neuroinhibitor gamma-aminobutyric acid (GABA). A possible role of GAD65 in the pathogenesis of epilepsy is supported by reports of abnormalities of GABAergic neurotransmission in animal models of epilepsy [11], epileptic seizures in GAD65-knock-out mice [12], reduction of GABA levels in CSF and brain tissue of epileptic patients [13], and epileptic syndromes associated with GAD65Ab [14]. However, no direct evidence for a pathogenic role of GAD65Ab has been demonstrated in epileptic conditions. GAD65 autoimmunity may exert epileptogenic activity by decreasing the conversion of glutamate into GABA, and/or interference with the release of GABAergic synaptic vesicles, thus increasing the dominance of excitatory neurotransmitters [15]. Such interference with GABAergic neurotransmission in the hippocampus is supported by studies carried out in hippocampal neurons incubated with GAD65Ab-positive sera from patients with epilepsy [16].

GAD65Ab is also found in 80% of new onset Type 1 diabetes (T1D) patients [17] and in 60% of patients with SPS [18]. Importantly, epilepsy is 4–6 fold more prevalent in patients with T1D than in the general population [19, 20, 21] and patients with epilepsy have a 4-fold higher prevalence of T1D than the general population [14]. It remains unclear whether GAD65Ab has a pathogenic role in patients with T1D and epilepsy [20, 22, 23].

Specific differences in GAD65Ab titer [24], epitope specificity [25, 26, 27], binding pattern to specific brain structures [28], tissue distribution [29, 30], and inhibition of GAD65 enzyme activity [29] have been observed in different diseases. Here we investigated whether GAD65Ab in autoimmune epilepsy differed in epitopes specificity, inhibition of enzyme activity, and/or titer from GAD65Ab in T1D or SPS. Such differences would possibly allow the identification of individuals at risk for autoimmune epilepsy and aid in the treatment of patients with autoimmune epilepsy [31].

Methods

Patients

Sera from patients with autoimmune epilepsy (n = 38) were collected by the T1D Exchange program [32], the Outpatient Clinic of Neurology and Rehabilitation, Tampere University Hospital, Finland [33], the University Claude Bernard, Lyon [34], and the Mayo Clinic, Rochester, USA. Two patients had confirmed hippocampal atrophy, three patients had epilepsy after head trauma, and one patient developed epilepsy in association with meningioma. The majority of patients responded poorly to standard anti-epileptic therapy. Ten of the epileptic patients were also diagnosed with T1D. Clinical parameters, including responsiveness to anti-epileptic therapy are shown in Table 1. Sera from 42 patients with established T1D without other autoimmune disorders [35], and sera from 20 patients diagnosed with SPS were included [34]. All experiments were performed in accordance with relevant guidelines and regulations, and local institutional ethics committee approval and subjects’ consent were obtained prior to collection of all serum samples (T1D Exchange Biobank, Benaroya Research Institute, Seattle, WA and JAEB Center for Health Research, Tampa, FL; University Claude Bernard Lyon, Hospices Civils de Lyon, Tampere University Hospital, Finland, Mayo Clinic, Rochester, USA).
Table 1

Characteristics of patients diagnosed with epilepsy

Patient #

Other Autoimmune disorder

Age at study (years)

Sex

Response to anti-epileptic drug (AED) treatment

GAD65Ab Titer (U/ml)

1

T1D, MS-like disorder

57

Female

Refractory

2 × 104

2

Celiac disease

43

Female

Refractory

4 × 105

3

None

52

Female

Refractory

2 × 104

4

Thyroiditis

36

Female

Refractory

1 × 106

5

None

72

Female

Refractory

1 × 102

6

None

48

Female

Refractory

4 × 102

7

None

84

Female

Refractory

1 × 105

8

None

29

Female

Refractory

4 × 102

9

None

81

Male

Refractory

3 × 105

10

Hashimoto’s, Alopecia Areata

unknown

Female

Refractory

4 × 105

11

None

unknown

Female

Refractory

9 × 104

12

Graves’ disease

unknown

Female

Refractory

2 × 104

13

T1D

66

NA

Responsive

2 × 107

14

T1D

45

NA

Refractory

2 × 107

15

T1D

6

NA

No medication

1 × 103

16

T1D

16

NA

Responsive

9 × 103

17

None

37

Female

NA

5 × 103

18

None

38

Female

NA

8 × 105

19

None

32

Female

NA

6 × 105

20

None

47

Female

NA

8 × 105

21

None

63

Female

NA

5 × 102

22

None

81

Male

Responsive

6 × 102

23

None

54

Male

Refractory

6 × 102

24

None

13

Female

NA

1 × 103

25

None

4

Female

NA

3 × 103

26

None

22

Female

Refractory

2 × 103

27

None

62

Male

NA

3 × 103

28

None

67

Male

NA

3 × 103

29

None

68

Male

NA

2 × 103

30

None

73

Male

NA

2 × 104

31

None

43

Female

NA

8 × 104

32

None

30

Female

Refractory

2 × 105

33*

T1D

78

Female

NA

2 × 103

34*

T1D

47

Female

NA

2 × 103

35*

T1D

53

Female

Refractory

6 × 103

36*

T1D

35

Female

NA

2 × 104

37*

T1D

22

Female

Refractory

3 × 106

Patients with both T1D and epilepsy are indicated with an asterisk

All serum samples were confirmed to be GAD65Ab-positive by radioligand binding assay.

GAD65Ab radioligand binding assay

Sera were analyzed using a radioligand binding assay as previously described [36]. The cutoff for GAD65Ab positivity was 65 U/mL established as the 98th percentile of 50 healthy sera (standard curve’s range: 30–1000 U/mL). The sensitivity and specificity of the assay were 86 and 93%, respectively in the 2007 Diabetes Autoantibody Standardization Program (DASP) Workshop [37].

Epitope-specific radioligand binding assay

GAD65Ab epitope specificities were tested in a competitive epitope-specific radioligand binding assay (ES-RBA) as described [36]. All sera and a GAD65Ab-positive control were analyzed for their binding to GAD65 in the presence of GAD65-specific recombinant Fab (rFab). rFab used in this study were derived from GAD65-specific monoclonal antibodies. DPA, DPC, and DPD were isolated from a patient with T1D and recognize epitopes located at amino acids 483–585, 195–412, and 96–173, respectively [38]. Monoclonal antibodies b96.11 and b78 were derived from a patient with autoimmune polyendocrine syndrome type 1 and recognize epitopes located at amino acid residues 308–365 and 451–585, respectively [39]. Monoclonal antibodies N-GAD65mAb and 221–442 were raised in mice and recognize linear epitopes at amino acid residues 4–22 [40], and conformational epitopes at amino acid residues 221–442 [41], respectively.

Monoclonal antibody b96.11 shares its epitope specificity with the majority of T1D patients [36], while b78 is a prototypical epitope for GAD65Ab in SPS patients and only rarely bound by GAD65Ab present in T1D patients [27].

The cutoff for specific competition was > 15% as determined by control rFab D1.3 [36]. Binding of GAD65Ab to GAD65 in the presence of rFab was expressed as: counts per minute (cpm) in the presence of rFab/cpm in the absence of rFab × 100.

GAD65 enzyme activity assay

GAD65 enzyme activity was measured by the 14CO2-trapping method described previously [42]. The results are presented as: % residual activity = cpm in the presence of IgG/cpm in the absence of IgG × 100.

Statistics

For two group comparisons, we used Student’s t-test for normally distributed values or Mann-Whitney U test as a non-parametric test. All statistical testing was two-sided, and p-values less than 0.05 were considered statistically significant. Statistical analyses were performed using the Prism® program (GraphPad Software, Inc., San Diego, USA).

Results

All sera were analyzed for GAD65Ab titer, GAD65Ab epitope recognition and inhibition of GAD65 enzyme activity.

GAD65Ab titer

GAD65Ab titers of T1D patients (median 978 U/ml) was significantly lower compared to SPS patients (median 345,042 U/ml, p < 0.0001) and epilepsy patients (median 17,000 U/ml, p = 0.0004) (Fig. 1a, Table 2).
Fig. 1

a GAD65Ab titers in patients with SPS, T1D, and epilepsy. GAD65Ab titers were determined for all patients in RBA and are reported for SPS patients (n = 20) (open diamonds), T1D patients (n = 42) (open circles), and patients diagnosed with epilepsy (n = 38) (triangles). In the epilepsy group, patients diagnosed with both T1D and epilepsy (n = 10) are shown as filled triangles, while patients diagnosed with epilepsy only are shown as open triangles. Individual patient titers and median binding for each group are shown. Significant differences in GAD65Ab titers are indicated by horizontal bars. b GAD65 enzyme activity inhibition by patients’ sera. GAD65 enzymatic activity in the presence of patients’ sera was determined for SPS patients (n = 20) (open diamonds), T1D patients (n = 42) (open circles), and patients diagnosed with epilepsy (n = 38) (triangles). In the epilepsy group, patients diagnosed with both T1D and epilepsy (n = 10) are shown as filled triangles, while patients diagnosed with epilepsy only are shown as open triangles. GAD65 enzyme activity is presented as remaining activity, related to un-inhibited activity (set at 100%). Individual patient data and median enzyme activity are shown. Significant differences in GAD65 enzyme activity are indicated by the horizontal bar

Table 2

Epitope binding specificities and enzyme inhibition

Patient (#)

DPA (%)

b96.11 (%)

b78 (%)

N-GAD65Ab (%)

DPC (%)

221-442 (%)

DPD (%)

Remaining Enzyme activity (%)

1*

69

67

65

84

95

100

78

98

2

88

67

65

84

98

98

74

80

3

45

42

48

88

98

98

26

64

4

71

45

72

88

92

103

32

32

5

100

60

100

99

88

102

71

84

6

101

61

76

95

99

100

68

92

7

52

57

60

106

103

99

44

59

8

100

67

65

95

92

100

46

96

9

54

62

86

74

82

96

47

46

10

72

63

52

101

98

95

63

100

11

86

49

65

101

96

100

51

85

12

40

26

53

97

96

102

18

100

13*

52

45

65

88

88

99

34

36

14*

39

55

66

99

82

100

22

26

15*

99

67

90

91

92

89

80

100

16*

97

58

83

100

98

95

79

80

17

76

63

92

NA

NA

NA

76

NA

18

57

17

93

NA

NA

NA

22

NA

19

39

42

49

NA

NA

NA

14

NA

20

37

20

34

NA

NA

NA

12

NA

21

103

94

108

NA

NA

NA

90

63

22

101

100

105

NA

NA

NA

98

81

23

96

102

100

NA

NA

NA

98

54

24

105

102

96

NA

NA

NA

87

13

25

90

84

89

NA

NA

NA

46

4

26

97

64

95

NA

NA

NA

63

22

27

104

85

105

NA

NA

NA

81

62

28

96

96

100

NA

NA

NA

90

67

29

93

71

69

NA

NA

NA

76

68

30

82

74

89

NA

NA

NA

84

73

31

74

58

87

NA

NA

NA

70

43

32

90

96

93

NA

NA

NA

98

30

33*

102

65

78

NA

NA

NA

67

78

34*

100

96

106

NA

NA

NA

92

47

35*

83

91

83

NA

NA

NA

100

53

36*

89

71

82

NA

NA

NA

71

35

37*

95

70

89

NA

NA

NA

88

22

Patients with both T1D and epilepsy are indicated with an asterisk. Samples with highest binding to the DPD-defined epitope and inhibition of enzyme activity are emphasized in bold

GAD65Ab epitope specificity

All serum samples were analyzed for GAD65Ab epitope recognition at half-maximal binding concentration. Binding specificity to six conformational epitopes (defined by rFab DPA, b96.11, DPC, DPD, 221–442, and b78), and one linear epitope (defined by rFab N-GAD65mAb) was investigated.

Our epitope analysis revealed significant differences in GAD65Ab epitopes recognized from sera obtained from epileptic patients, patients with T1D, and patients with SPS (Fig. 2, Table 2).
Fig. 2

GAD65Ab epitope pattern in patients diagnosed with SPS (n = 20) (open diamonds), T1D (n = 42) (open circles), epilepsy (n = 38) (triangles). In the epilepsy group, patients diagnosed with both T1D and epilepsy (n = 10) are shown as filled triangles, while patients diagnosed with epilepsy only are shown as open triangles. Binding of serum samples to GAD65 was evaluated in the presence of rFab DPA, b96.11, DPD, DPC, b78, 221-442, and N-GAD65mAb. Binding was related to un-competed binding (set at 100%). Remaining binding is presented for each sample. Median binding is indicated. Significant differences in binding are indicated by horizontal bars

GAD65Ab in patients with epilepsy recognized GAD65Ab epitopes that differ significantly from those recognized in patients with T1D. Particularly, binding of GAD65Ab in patients with epilepsy was significantly more reduced by rFab DPD (median binding 71% vs 90%, p < 0.0001), and b78 (median binding 83% vs 97%, p < 0.0001) as compared to patients with T1D, while binding was less reduced by rFab 221–442 (median binding 100% vs 73%, p < 0.0001) and rFab DPC (median binding 95% vs 83%, p = 0.0003). Binding of GAD65Ab in epilepsy patients was less reduced by rFab DPC- and rFab N-GAD65mAb- as compared to that in patients with SPS (median binding 95% vs 76%, p = 0.0003, median binding 95% vs 75%, p < 0.0001, respectively).

GAD65 enzyme inhibition by patients’ sera

Inhibition of GAD65 enzyme activity by patients’ sera was investigated (Fig. 1b, Table 2).

As expected, all SPS patient sera inhibited GAD65 enzyme activity (median inhibition 43%, range: 24–87%), while GAD65Ab-positive sera in T1D patients caused no significant inhibition of GAD65 enzyme activity (median inhibition 4%, range 0–13%). Patients with epilepsy significantly inhibited GAD65 enzyme activity (median inhibition 47%, range: 0–96%). However, ten patients with epilepsy showed no inhibition of enzyme activity.

Patients diagnosed with epilepsy and T1D

Within the patients diagnosed with both T1D and epilepsy (n = 10), six patients (#13, #14 #34, #35, #36, #37) shared GAD65Ab characteristics with patients diagnosed with epilepsy only, and significantly inhibited GAD65 enzyme activity. The remaining four patients (#1, #15, #16, #33) shared GAD65Ab characteristics with patients diagnosed with only T1D in that they had medium or low GAD65Ab titers, their GAD65Ab were only weakly competed by rFab DPD and they did not, or only weakly, inhibit GAD65 enzyme activity (Table 2).

CSF

CSF was available for six patients with epilepsy, two of which were also diagnosed with T1D. The epitope mapping of these samples revealed strong recognition of the DPA-, DPD-, b96.11- and b78-defined epitopes (Fig. 3). Epitope recognition in CSF and sera in the two patients where matching samples were available showed no significant differences (data not shown). Unfortunately, the limited sample volume did not permit to test the effect on GAD65 enzyme activity.
Fig. 3

GAD65Ab epitope pattern and GAD65Ab titer in CSF obtained from patients diagnosed with epilepsy (n = 6). Binding of serum samples to GAD65 was evaluated in the presence of rFab DPA, b96.11, DPD, and b78. Binding was related to un-competed binding (set at 100%). Remaining binding is presented for each sample. Median binding is indicated. Significant differences in binding are indicated by horizontal bars. Patients diagnosed with both T1D and epilepsy (n = 2) are shown as filled symbols

Discussion

The major goal of our investigation was to establish disease-specific GAD65Ab characteristics in patients with autoimmune epilepsy. Our results confirm earlier studies by us and others that GAD65Ab in T1D patients recognize epitopes located in the middle region [36, 43, 44, 45], while GAD65Ab in SPS patients preferably bind to epitopes located at the C-terminus [26, 30] and the N-terminus [24, 27]. GAD65Ab in autoimmune epilepsy differed significantly from those in T1D. While GAD65Ab in patients with autoimmune epilepsy shared several characteristics with GAD65Ab present in SPS patients, they did not recognize the linear epitope located at amino acids 4–22 (represented by N-GAD65mAb), while GAD65Ab in SPS patients did.

Four of ten patients diagnosed with both epilepsy and T1D showed GAD65Ab patterns resembling those in T1D patients. One of these patients responded well to AEDs, while the second patient did not require medication for seizure control. The third patient (#1) did not respond to AEDs, probably due to co-existing meningioma and no information regarding responsiveness to AEDs was available for patient #33. GAD65Ab in the remaining six patients with T1D and epilepsy displayed characteristics similar to GAD65Ab in patients with autoimmune epilepsy. Only one of these patients responded to AEDs, while three patients did not. No information regarding response to AEDs was available for the remaining two patients.

In a previous study Fouka et al. reported no differences in GAD65Ab epitope specificities when analyzing patients with SPS and patients with epilepsy [46]. Our results show that while GAD65Ab profiles in neurological disorders have large overlaps, SPS patients recognized a linear epitope at the N-terminal region of GAD65 significantly better compared to epilepsy patients. These differences in results are likely caused by different epitope mapping assays. Fouka et al. utilized GAD65 fragments which covered several hundred amino acids, likely to contain several epitopes [46]. It is therefore possible that differences in binding to one epitope may be masked by binding to additional sites [47]. In a similar study Gresa-Arribas [48] reported that GAD65Ab in CSF of patients with neurological syndromes showed broader epitope recognition than the corresponding serum samples. In difference to our study, they observed no differences regarding GAD65Ab binding to the N-terminal region between different neurological syndromes. As aforementioned, this difference may be due to different methods used in these studies. Similar to Fouka, Gresa-Arribas used large GAD65 fragments for epitope mapping, which may contain several epitope regions and therefore mask disease-specific differences. Previous studies reported that inhibition of the larger isoform of glutamate decarboxylase - GAD67 - in the hippocampus reduced GABAergic neurotransmission and was associated with seizures, while inhibition of GAD65 in the same location did not induce seizures, possibly due to the low expression of GAD65 in the hippocampal CA1 area [49]. Our analysis showed that patients with neurological disorders had significantly higher frequencies of GAD67Ab compared to that in T1D patients. However, as previously reported [48], we found no differences in GAD67Ab frequency between patients with autoimmune epilepsy and patients with SPS.

Together with the finding that sera of all SPS patients inhibited GAD65 enzyme activity, while only 69% of sera of epileptic patients did, we conclude that GAD65Ab in epilepsy patients differ significantly from GAD65Ab in SPS patients and T1D patients.

A weakness of our study lays in the small number of participants in each group. SPS, GAD65Ab-positive epilepsy and T1D with epilepsy are rare diseases. Therefore, it was necessary for us to combine samples from various locations in this study. All samples were analyzed in the same laboratory to reduce inter-laboratory and inter-assay variations. Moreover, as this study focused on the investigation of GAD65Ab in autoimmune epilepsy, we cannot exclude that other autoantibodies, (e.g. directed to synaptic autoantigens) may be associated with the development of autoimmune epilepsy. Furthermore, patients with GAD65 autoimmune frequently have overlapping autoimmune disorders, both neurological and non-neurological [50]. Also, it is possible that certain patients we studied may go on to develop other GAD65 autoimmune manifestations in the future. Finally, autoimmune epilepsy may also be mediated via innate immune responses (for review see [51]), in which case autoantibodies are unlikely to be associated with the pathology.

We conclude that patients diagnosed with both T1D and epilepsy may present two different epileptic etiologies. In one group T1D may co-occur with non-autoimmune epilepsy without any particular role of the immune system and GAD65Ab in the epileptic condition. These patients are expected to respond well to AEDs. GAD65Ab should be present only in the periphery. For the second group an underlying autoimmune component may contribute to the epileptic condition. Consequently, patients may respond poorly to AEDs therapy but may benefit from immunotherapy. One would expect GAD65Ab to be present both in the periphery and in the CSF. Unfortunately, CSF was not available from the majority of patients in this study.

Larger studies will be necessary to confirm our findings and to further evaluate the mechanisms involved in the pathogenesis of autoimmune epilepsy.

Conclusions

Different autoimmune responses associated with T1D, epilepsy and SPS are reflected by disease-specific GAD65 epitopes. Moreover, the epileptic etiology in patients diagnosed with both T1D and epilepsy may present two different etiologies regarding their epileptic condition. In one group T1D co-occurs with non-autoimmune epilepsy. In the other group GAD65Ab are part of an autoimmune epileptic condition.

Notes

Acknowledgments

We wish to thank Asa Davis, PhD and Carla Greenbaum, MD of the T1D Exchange Biobank Coordinating Center at Benaroya Research Institute, Seattle, as well as investigators and staff in the T1D Exchange Clinic Network for subject recruitments.

Funding

This work was supported by the Leona M. and Harry B. Helmsley Charitable Trust.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Authors’ contributions

SL, JH, MM, AMcK, and SJP took part in interpretation of results and critically revised the manuscript, JRR participated in antibody measurements and enzyme activity experiments, CSH took part in the study design, statistical analysis, interpretation of results and manuscript preparation. All authors read and approved the final manuscript.

Ethics approval and consent to participate

All experiments were performed in accordance with relevant guidelines and regulations, and local institutional ethics committee approval and subjects’ consent were obtained prior to collection of all serum samples (T1D Exchange Biobank, Benaroya Research Institute, Seattle, WA and JAEB Center for Health Research, Tampa, FL; University Claude Bernard Lyon, Hospices Civils de Lyon, and Tampere University Hospital, Finland).

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Authors and Affiliations

  • Suvi Liimatainen
    • 1
    • 2
  • Jerome Honnorat
    • 3
  • Sean J. Pittock
    • 4
    • 5
  • Andrew McKeon
    • 4
    • 5
  • Mario Manto
    • 6
  • Jared R. Radtke
    • 7
  • T1D Exchange Biobank
  • Christiane S. Hampe
    • 7
  1. 1.Department of Neurology and RehabilitationTampere University HospitalTampereFinland
  2. 2.Division 7Tampere University HospitalTampereFinland
  3. 3.University of Lyon - University Claude Bernard LyonLyonFrance
  4. 4.Department of NeurologyCollege of Medicine, Mayo ClinicRochesterUSA
  5. 5.Department of Laboratory Medicine & Pathology College of MedicineMayo ClinicRochesterUSA
  6. 6.Unité d’Etude du Mouvement, Université Libre De BruxellesBrusselsBelgium
  7. 7.Department of MedicineSchool of Medicine, University of WashingtonSeattleUSA

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