CNTNAP2: isoform- and context-specific functions in neurological disorders and cancer.

Autoimmune encephalitis can be classified into antibody-defined subtypes, which can manifest with immunotherapy-responsive movement disorders sometimes mimicking non-inflammatory aetiologies. In the elderly, anti-LGI1 and contactin associated protein like 2 (CASPR2) antibody-associated diseases compose a relevant fraction of autoimmune encephalitis. Patients with LGI1 autoantibodies are known to present with limbic encephalitis and additionally faciobrachial dystonic seizures may occur. However, the clinical spectrum of CASPR2 autoantibody-associated disorders is more diverse including limbic encephalitis, Morvan's syndrome, peripheral nerve hyperexcitability syndrome, ataxia, pain and sleep disorders. Reports on unusual, sometimes isolated and immunotherapy-responsive movement disorders in CASPR2 autoantibody-associated syndromes have caused substantial concern regarding necessity of autoantibody testing in patients with movement disorders. Therefore, we aimed to systematically assess their prevalence and manifestation in patients with CASPR2 autoimmunity. This international, retrospective cohort study included patients with CASPR2 autoimmunity from participating expert centres in Europe. Patients with ataxia and/or movement disorders were analysed in detail using questionnaires and video recordings. We recruited a comparator group with anti-LGI1 encephalitis from the GENERATE network. Characteristics were compared according to serostatus. We identified 164 patients with CASPR2 autoantibodies. Of these, 149 (90.8%) had only CASPR2 and 15 (9.1%) both CASPR2 and LGI1 autoantibodies. Compared to 105 patients with LGI1 encephalitis, patients with CASPR2 autoantibodies more often had movement disorders and/or ataxia (35.6 versus 3.8%; P < 0.001). This was evident in all subgroups: ataxia 22.6 versus 0.0%, myoclonus 14.6 versus 0.0%, tremor 11.0 versus 1.9%, or combinations thereof 9.8 versus 0.0% (all P < 0.001). The small group of patients double-positive for LGI1/CASPR2 autoantibodies (15/164) significantly more frequently had myoclonus, tremor, 'mixed movement disorders', Morvan's syndrome and underlying tumours. We observed distinct movement disorders in CASPR2 autoimmunity (14.6%): episodic ataxia (6.7%), paroxysmal orthostatic segmental myoclonus of the legs (3.7%) and continuous segmental spinal myoclonus (4.3%). These occurred together with further associated symptoms or signs suggestive of CASPR2 autoimmunity. However, 2/164 patients (1.2%) had isolated segmental spinal myoclonus. Movement disorders and ataxia are highly prevalent in CASPR2 autoimmunity. Paroxysmal orthostatic segmental myoclonus of the legs is a novel albeit rare manifestation. Further distinct movement disorders include isolated and combined segmental spinal myoclonus and autoimmune episodic ataxia.

Contactin-associated protein-like 2 (CASPR2) is a cell adhesion protein of the neurexin family. Proteins of this family have been shown to play a role in the development of the nervous system, in synaptic functions, and in neurological diseases. Over recent years, CASPR2 function has gained an increasing interest as demonstrated by the growing number of publications. Here, we gather published data to comprehensively review CASPR2 functions within the nervous system in relation to CASPR2-related diseases in humans. On the one hand, studies on Cntnap2 (coding for CASPR2) knockout mice revealed its role during development, especially, in setting-up the inhibitory network. Consistent with this result, mutations in the CNTNAP2 gene coding for CASPR2 in human have been identified in neurodevelopmental disorders such as autism, intellectual disability, and epilepsy. On the other hand, CASPR2 was shown to play a role beyond development, in the localization of voltage-gated potassium channel (VGKC) complex that is composed of TAG-1, Kv1.1, and Kv1.2. This complex was found in several subcellular compartments essential for action potential propagation: the node of Ranvier, the axon initial segment, and the synapse. In line with a role of CASPR2 in the mature nervous system, neurological autoimmune diseases have been described in patients without neurodevelopmental disorders but with antibodies directed against CASPR2. These autoimmune diseases were of two types: central with memory disorders and temporal lobe seizures, or peripheral with muscular hyperactivity. Overall, we review the up-to-date knowledge on CASPR2 function and pinpoint confused or lacking information that will need further investigation.

Differentiating forms of autoimmune encephalitis (AE) from other causes of seizures helps expedite immunotherapies in AE patients and informs studies regarding their contrasting pathophysiology. We aimed to investigate whether and how Nuclear Magnetic Resonance (NMR)-based metabolomics could differentiate AE from drug-resistant epilepsy (DRE), and stratify AE subtypes. This study recruited 238 patients: 162 with DRE and 76 AE, including 27 with contactin-associated protein-like 2 (CASPR2), 29 with leucine-rich glioma inactivated 1 (LGI1) and 20 with N-methyl-d-aspartate receptor (NMDAR) antibodies. Plasma samples across the groups were analyzed using NMR spectroscopy and compared with multivariate statistical techniques, such as orthogonal partial least squares discriminant analysis (OPLS-DA). The OPLS-DA model successfully distinguished AE from DRE patients with a high predictive accuracy of 87.0 ± 3.1% (87.9 ± 3.4% sensitivity and 86.3 ± 3.6% specificity). Further, pairwise OPLS-DA models were able to stratify the three AE subtypes. Plasma metabolomic signatures of AE included decreased high-density lipoprotein (HDL, -(CH2)n-, -CH3), phosphatidylcholine and albumin (lysyl moiety). AE subtype-specific metabolomic signatures were also observed, with increased lactate in CASPR2, increased lactate, glucose, and decreased unsaturated fatty acids (UFA, -CH2CH=) in LGI1, and increased glycoprotein A (GlycA) in NMDAR-antibody patients. This study presents the first non-antibody-based biomarker for differentiating DRE, AE and AE subtypes. These metabolomics signatures underscore the potential relevance of lipid metabolism and glucose regulation in these neurological disorders, offering a promising adjunct to facilitate the diagnosis and therapeutics.

Objective To explore the clinical features, auxiliary examinations, therapies and prognoses of patients with antibodies against contactin-associated protein-like 2 (CASPR2). Methods The clinical data of 11 anti-CASPR2 encephalitis patients who were admited to the People′s Hospital of Zhengzhou University from March 2015 to April 2018 were retrospectively analyzed. Results The age of these 11 cases was (35.6±19.4) years (ranged 20-74 years), and eight cases were females. There were seven cases with limbic encephalitis which included six cases of epilepsy, four cases of memory impairment, two cases of mental and behavioral abnormalities. Four cases had peripheral nerve hyperexcitability. Four cases had neuropathic pain. There were six cases with autonomic dysfunction including five cases of constipation, three cases of tachycardia, two cases of hyperhidrosis, two cases of urinary disorder. Seven cases had sleep disorder. Four cases had weight loss. Two cases showed cerebellar symptoms and two cases had hyponatremia. Magnetic resonance imaging scan of the brain showed abnormal signal in two cases, mainly involved medial temporal lobe and the hippocampus. Six cases underwent 18F-fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) examination, and three cases showed abnormalities, including two with temporal hypermetabolism and one with cortical hypermetabolism. Chest enhanced CT and PET-CT showed thymoma in one case. All cases received immunotherapy, and after treatment their symptoms were improved. Long-term follow-up was performed in nine cases, and three cases relapsed. Conclusions The major clinical manifestations of anti-CASPR2 encephalitis were limbic encephalitis, peripheral nerve hyperexcitability, neuropathic pain, autonomic dysfunction, insomnia and so on. Immunotherapy was effective and some patients may have recurrence. Key words: Autoantibodies; Encephalitis; Autoimmune encephalitis; Contactin associated protein-like 2

The contactin-associated protein-like 2 (CNTNAP2) gene is a member of the neurexin superfamily. CNTNAP2 was first implicated in the cortical dysplasia-focal epilepsy (CDFE) syndrome, a recessive disease characterized by intellectual disability, epilepsy, language impairments and autistic features. Associated SNPs and heterozygous deletions in CNTNAP2 were subsequently reported in autism, schizophrenia and other psychiatric or neurological disorders. We aimed to comprehensively examine evidence for the role of CNTNAP2 in susceptibility to psychiatric disorders, by the analysis of multiple classes of genetic variation in large genomic datasets. In this study we used: i) summary statistics from the Psychiatric Genomics Consortium (PGC) GWAS for seven psychiatric disorders; ii) examined all reported CNTNAP2 structural variants in patients and controls; iii) performed cross-disorder analysis of functional or previously associated SNPs; and iv) conducted burden tests for pathogenic rare variants using sequencing data (4,483 ASD and 6,135 schizophrenia cases, and 13,042 controls). The distribution of CNVs across CNTNAP2 in psychiatric cases from previous reports was no different from controls of the database of genomic variants. Gene-based association testing did not implicate common variants in autism, schizophrenia or other psychiatric phenotypes. The association of proposed functional SNPs rs7794745 and rs2710102, reported to influence brain connectivity, was not replicated; nor did predicted functional SNPs yield significant results in meta-analysis across psychiatric disorders at either SNP-level or gene-level. Disrupting CNTNAP2 rare variant burden was not higher in autism or schizophrenia compared to controls. Finally, in a CNV mircroarray study of an extended bipolar disorder family with 5 affected relatives we previously identified a 131kb deletion in CNTNAP2 intron 1, removing a FOXP2 transcription factor binding site. Quantitative-PCR validation and segregation analysis of this CNV revealed imperfect segregation with BD.This large comprehensive study indicates that CNTNAP2 may not be a robust risk gene for psychiatric phenotypes.

Impact of anti-CASPR2 autoantibodies from patients with autoimmune encephalitis on CASPR2/TAG-1 interaction and Kv1 expression

CNS autoimmunity: new findings and pending issues

The CNTNAP2-CASK complex modulates GluA1 subcellular distribution in interneurons

Background and ObjectivesPatients with ongoing seizures are usually not allowed to drive. The prognosis for seizure freedom is favorable in patients with autoimmune encephalitis (AIE) with antibodies against NMDA receptor (NMDAR), leucine-rich glioma-inactivated 1 (LGI1), contactin-associated protein-like 2 (CASPR2), and the gamma-aminobutyric-acid B receptor (GABABR). We hypothesized that after a seizure-free period of 3 months, patients with AIE have a seizure recurrence risk of <20% during the subsequent 12 months. This would render them eligible for noncommercial driving according to driving regulations in several countries.MethodsThis retrospective multicenter cohort study analyzed follow-up data from patients aged 15 years or older with seizures resulting from NMDAR-, LGI1-, CASPR2-, or GABABR-AIE, who had been seizure-free for ≥3 months. We used Kaplan-Meier (KM) estimates for the seizure recurrence risk at 12 months for each antibody group and tested for the effects of potential covariates with regression models.ResultsWe included 383 patients with NMDAR-, 440 with LGI1-, 114 with CASPR2-, and 44 with GABABR-AIE from 14 international centers. After being seizure-free for 3 months after an initial seizure period, we calculated the probability of remaining seizure-free for another 12 months (KM estimate) as 0.89 (95% confidence interval [CI] 0.85–0.92) for NMDAR, 0.84 (CI 0.80–0.88) for LGI1, 0.82 (CI 0.75–0.90) for CASPR2, and 0.76 (CI 0.62–0.93) for GABABR.DiscussionTaking a <20% recurrence risk within 12 months as sufficient, patients with NMDAR-AIE and LGI1-AIE could be considered eligible for noncommercial driving after having been seizure-free for 3 months.

Voltage-gated potassium channel (VGKC) and glutamic acid decarboxylase (GAD) antibodies are increasingly tested in patients with suspected autoimmune encephalitis (AE) and other neurological diseases, yet their clinical significance, especially when detected outside of classic contexts, remains poorly defined. This case series of three patients explores an unusual pattern of antibody dynamics in VGKC antibody-positive and leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (CASPR2) antibodies-negative AE. All patients underwent immunotherapy based on clinical suspicion and improved, and had delayed emergence of GAD antibodies during recovery phases.The key observations were that VGKC antibody levels were elevated during the acute presentation and either declined or normalized following treatment. GAD antibodies were absent during acute illness but emerged during the post-treatment/recovery phase, when patients were already recuperating. No patient developed syndromes classically associated with GAD antibodies (e.g., worsening encephalitis, stiff person syndrome, and refractory seizures). LGI1 and CASPR2 antibodies were consistently negative throughout all tested phases.These findings bring up the questions of the role(s) GAD antibody may play in the disease processes in AE and other neurological diseases, including the possibility of GAD antibody positivity not necessarily indicating active or causative disease, and suggest it may, in some contexts, represent a phenomenon of immune remodeling or non-specific activation. Additionally, these cases reinforce the potential clinical utility of initiating immunotherapy based on phenotype and clinical suspicion, particularly in VGKC-positive, LGI1/CASPR2-negative presentations, while emphasizing the need for more nuanced interpretation of antibody dynamics over time.

ObjectivesIt is assumed that autoimmune limbic encephalitis (ALE) demonstrates distinct neuropsychological manifestations with differential responses to immunotherapy according to which associated autoantibody (AAB), if any, is identified. Towards investigating whether this is the case, this study aims to summarize respective findings from the primary literature on ALE with AABs binding to cell surface neural antigens and ALE with AABs against intracellular neural antigens. MethodsWe chose ALE with AABs against leucine-rich, glioma inactivated protein 1 (LGI1) and contactin-associated protein-like 2 (CASPR2) as the most frequent cell surface membrane antigens, and ALE with AABs to Embryonic Lethal, Abnormal Vision, Like 1 (ELAVL) proteins (anti-Hu) and glutamic acid decarboxylase 65 (GAD65) as the most frequent intracellular neural antigens. The PubMed and Scopus databases were searched on March 1st, 2021 for neuropsychological test and -screening data from patients with ALE of these AAB-types. Findings were reviewed according to AAB-type and immunotherapy status and are presented in a review section and are further statistically evaluated and presented in a meta-analysis section in this publication. ResultsOf the 1304 initial hits, 32 studies on ALE with AABs against LGI1, CASPR2, and GAD65 reporting cognitive screening data could be included in a review. In ALE with AABs against LGI1, CASPR2 and GAD65, memory deficits are the most frequently reported deficits. However, deficits in attention and executive functions including working memory, fluency, and psychological function have also been reported. This review shows that ALE patients with AABs against both LGI1 and CASPR2 show higher percentages of neuropsychological deficits compared to ALE patients with AABs against GAD65 before and after initiation of immunotherapy. However, the methodologies used in these studies were heterogenous, and longitudinal studies were not comparable. Moreover, 21 studies including ALE patients with AABs against LGI1 and GAD65 were also suitable for meta-analysis. No suitable study on ALE with AABs against ELAVL proteins could be identified. Meta-Analyses could be executed for cognitive screening data and only partially, due to the small number of studies. However, in statistical analysis no consistent effect of AAB or immunotherapy on performance in cognitive screening tests could be found. ConclusionCurrently, there is no definite evidence supporting the notion that different AAB-types of ALE exhibit distinct neuropsychological manifestations and respond differently to immunotherapy. Overall, we could not identify evidence for any effect of immunotherapy on cognition in ALE. More systematic, in-depth and longitudinal neuropsychological assessments of patients with different AAB-types of ALE are required in the future to investigate these aspects.

Implicated in autoimmune encephalitis, neuromyotonia and genetic forms of autism, here we report that contactin-associated protein-like 2 (CNTNAP2) contains a potential autoepitope within the extracellular region. CNTNAP2 sequence-similar regions (CSSRs) from human pathogens were identified. Sera from autistic and control children were obtained and analyzed for the presence of antibodies able to bind CSSRs. One such candidate CSSR was evaluated for evidence of autoimmune responses to CNTNAP2 in a mouse model of acute infection. Autistic and control children sera contained antibodies able to discrete regions of CNTNAP2. In a murine model of acute infection, a CSSR derived from the N-terminal extracellular region of CNTNAP2 resulted in anti-CNTNAP2 antibody production, proinflammatory cytokine elevation, cerebellar and cortical white matter T-cell infiltration as well as motor dysfunction. Taken together, these data suggest that CNTNAP2 contains a potential autoepitope within the extracellular region.

P 92 Limbic encephalitis with Contactin-associated protein like-2 (CASPR2) -antibodies: acute psychosis with late onset and abnormal EEG

ObjectivesThe clinical data of patients with double-positive for leucine-rich glioma-inactivated protein 1 (LGI1) and contactin-associated protein-like 2 (CASPR2) antibodies is limited, particularly for children. This study aimed to investigate and summarize the clinical features and long-term prognosis of children’s LGI1 and CASPR2 antibodies related to neurological disorders.MethodsWe collected the clinical data and prognosis of patients with dual positive antibodies of CASPR2 and LGI1, hospitalized in the Department of Neurology, Children’s Hospital of Chongqing Medical University. Furthermore, we summarized the clinical phenotypes of this disorder in children by reviewing the published literature.ResultsTwo patients presenting with variable neurological symptoms including pain, hypertension, profuse sweating, irritability, and dyssomnia from Children’s Hospital of Chongqing Medical University were enrolled in this study. Together with the two patients, we identified 17 children with dual CASPR2 and LGI1 antibodies, including 12 males and 5 females. At the onset, the median age was 4.1 years (range 1–16, interquartile range 2.5–13.5), with 9 children younger than 5 years and 6 adolescents. Of the 17 patients, 11 were diagnosed with Morvan syndrome, 4 with acquired neuromyotonia, 1 with Guillain-Barré syndrome, and 1 with Guillain-Barré syndrome combined with Morvan syndrome. Dysautonomia (14/17, 82.3%), pain (13/17, 76.4%), sleep disorders (13/17, 76.4%), encephalopathy (12/17, 70.5%), and weight loss (10/17, 58.8%) were the most frequently described symptoms overall. No tumors were identified. Of the 17 patients, 13 received immunotherapy comprising IVIG combination of IVMP during the acute symptomatic phase followed by oral prednisolone to maintain remission (n = 7), the combination of IVIG, IVMP, oral prednisolone and methotrexate (n = 1), the combination of IVIG, IVMP, and mycophenolate mofetil (n = 1), the combination of IVIG, IVMP, oral prednisolone, and rituximab (n = 1), IVIG only (n = 2), IVMP only (n = 1). Median modified Rankin Scale (mRS) scores in the acute phase were 3 (range 1–4) and improved gradually. Over the follow-up (median 8.6 months, range 1–36 months), 52.9% (9/17) of the patients recovered completely; one patient relapsed and showed immunotherapy-dependent.ConclusionLGI1 and CASPR2 double-positive antibodies associated with the neurological diseases can occur in children of all ages and involve multiple nervous systems. Morvan syndrome is the most common phenotype of this disorder. The long-term outcomes are mostly favorable upon immunotherapy.

Contactin-associated protein-like 2 (CASPR2) autoantibody disease has a variable clinical phenotype. We present a case report and performed a systematic review of the literature to summarize: (1) the clinical phenotype of patients with CASPR2 antibodies, (2) the findings in neurological investigations, and (3) the associated neuroimaging findings. A chart review was performed for the case report. A systematic review of the medical literature was performed from first available to June 13, 2018. Abstracts were screened, and full-text peer-reviewed publications for novel patients with CASPR2 positivity in serum or cerebrospinal fluid (CSF) were included. Selected publications were reviewed, and relevant information was collated. Data were analyzed to determine overall frequency for demographic information, clinical presentations, and investigation findings. Our patient was a previously healthy 61-year-old male with both serum and CSF CASPR2 antibodies who presented with limbic encephalitis and refractory epilepsy. He was successfully treated with immunosuppression. For our systematic review, we identified 667 patients from 106 studies. Sixty-nine percent were male. Median age was 54years (IQR 39-65.5). Median disease duration was 12months (IQR 5.6-20). Reported overall clinical syndromes were: autoimmune encephalitis [69/134 (51.5%)], limbic encephalitis [106/274 (38.7%)], peripheral nerve hyperexcitability [72/191 (37.7%)], Morvan syndrome [57/251 (22.7%)], and cerebellar syndrome [24/163 (14.7%)]. Patients had positive serum [642/642 (100%)] and CSF [87/173 (50.3%)] CASPR2 antibodies. MRI was reported as abnormal in 159/299 patients (53.1%), and the most common abnormalities were encephalitis or T2 hyperintensities in the medial temporal lobes, or hippocampal atrophy, mesial temporal sclerosis, or hippocampal sclerosis. FDG-PET was abnormal in 30/35 patients (85.7%), and the most common abnormality was temporomesial hypometabolism. The most commonly associated condition was myasthenia gravis (38 cases). Thymoma occurred in 76/348 patients (21.8%). Non-thymoma malignancies were uncommon [42/397 (10.6%)]. Most patients have autoimmune or limbic encephalitis and corresponding abnormalities on neuroimaging. Other presentations include peripheral nerve hyperexcitability or Morvan syndromes, cerebellar syndromes, behavioral and cognitive changes, and more rarely movement disorders. The most commonly associated malignancy was thymoma and suggests a role for thymoma screening in CASPR2-related diseases.