A genome-wide association study in autoimmune neurological syndromes with anti-GAD65 autoantibodies

Abstract

Autoimmune neurological syndromes (AINS) with autoantibodies against the 65 kDa isoform of the glutamic acid decarboxylase (GAD65) present with limbic encephalitis including temporal lobe seizures or epilepsy, cerebellitis with ataxia, and stiff-person-syndrome, or overlap forms. Anti-GAD65 autoantibodies are also detected in autoimmune diabetes mellitus, which has a strong genetic susceptibility conferred by human leukocyte antigen (HLA) and non-HLA genomic regions. We investigated the genetic predisposition in patients with anti-GAD65 AINS. We performed a genome-wide association study (GWAS) and an association analysis of the HLA region in a large German cohort of 1,214 individuals. These included 167 patients with anti-GAD65 AINS, recruited by the German Network for Research on Autoimmune Encephalitis (GENERATE), and 1,047 individuals without neurological or endocrine disease as population-based controls. Predictions of protein expression changes based on GWAS findings were further explored and validated in the CSF proteome of a virtually independent cohort of 10 patients with GAD65-AINS and 10 controls. Our GWAS identified 16 genome-wide significant (p < 5 × 10−8) loci for the susceptibility to anti-GAD65 AINS. The top variant, rs2535288 (p = 4.42 × 10−16, odds ratio-OR = 0.26, 95%CI= 0.187-0.358), localized to an intergenic segment in the middle of the HLA class I region. The great majority of variants in these loci (>90%) mapped to non-coding regions of the genome. Over 40% of the variants have known regulatory functions on the expression of 48 genes in disease relevant cells and tissues, mainly CD4+ T cells and the cerebral cortex. The annotation of epigenomic marks suggested specificity for neural and immune cells. A network analysis of the implicated protein-coding genes highlighted the role of protein kinase C beta (PRKCB) and identified an enrichment of numerous biological pathways participating in immunity and neural function. Analysis of the classical HLA alleles and haplotypes showed no genome-wide significant associations. The strongest associations were found for the DQA1*03:01-DQB1*03:02-DRB1*04:01HLA haplotype (p = 4.39 × 10−4, OR = 2.5, 95%CI= 1.499-4.157), and DRB1*04:01 allele (p = 8.3 × 10−5, OR = 2.4, 95%CI = 1.548-3.682) identified in our cohort. As predicted, the CSF proteome showed differential levels of five proteins (HLA-A/B, C4A, ATG4D and NEO1) of eQTL genes from our GWAS in the CSF proteome of anti-GAD65 AINS. These findings suggest a strong genetic predisposition with direct functional implications for immunity and neural function in anti-GAD65 AINS, mainly conferred by genomic regions outside the classical HLA alleles.

Autoimmune encephalitis—An update

“…Hohe Titer (> 10.000 IU/ml) sind bei einer GAD-Enzephalitis mit limbischer Enzephalitis, Stiff-Person-Syndrom, zerebellärer Ataxie oder therapierefraktären epileptischen Anfällen assoziiert [ 42 ]. Die GAD-Enzephalitis hat häufig eine chronische Verlaufsform mit unvollständiger Genesung und spricht nur eingeschränkt auf eine Immuntherapie an [ 57 ]. Im Gegensatz dazu gehen niedrigere Titer mit einem heterogenen Symptomspektrum einher, bei denen in Abwesenheit der typischen Klinik Differenzialdiagnosen erwogen werden sollten.…”

Cerebrospinal fluid proteomics indicates immune dysregulation and neuronal dysfunction in antibody associated autoimmune encephalitis

“…Patients with IgG-autoantibodies against NMDAR in CSF ± serum, LGI1 in serum ± CSF, and GAD in serum ± CSF (detected by immunohistochemistry on rodent or non-human primate brain tissue and cell-based assays) were included. All GAD-patients had high serum GAD-antibody levels as defined by the presence of a typical staining pattern on rodent or non-human primate brain tissue and pancreas [21,28] We focused on these as they present the most common examples of AE with autoantibodies against cell-surface antigens (LGI1, NMDAR) and the most common form of AE with autoantibodies against a predominantly intracellular antigen (GAD65). Patients with signs of acute infectionassessed by routine blood and CSF analysis -, known comorbid systemic autoimmune disease or chronic infections (e.g.…”

“…post-infectious AE [17]) and tumors (i.e. paraneoplastic AE [18]) in combination with a genetic susceptibility [19][20][21] with different individual weight [9]. However, the exact, in particular the subtype-specific, mechanisms have not been fully understood.…”

Stiff Person Spectrum Disorders—An Update and Outlook on Clinical, Pathophysiological and Treatment Perspectives

“…Isolated case reports also describe an occurrence of SPS in HLA-B27-positive patients of non-neurological concomitant diseases (HLA B27 and spondyloarthropathy [ 70 ]; HLA B27 and Hodgkin’s lymphoma [ 71 ]). Recently, Strippel and colleagues performed a genome-wide association study (GWAS) and an associated analysis of the HLA region in a large German cohort of 167 patients with anti-GAD65 AINS, 48 of which with SPS, and 1047 control patients without neurological or endocrine disease [ 72 ]. The authors did not find any genome-wide significant associations to specific anti-GAD65 AINS, however, 400 associations at the nominal level of significance.…”