CNTN4 modulates neural elongation through interplay with APP.

The neuronal cell adhesion molecule contactin-4 (CNTN4) is genetically associated with autism spectrum disorder (ASD) and other psychiatric disorders. Cntn4-deficient mouse models have previously shown that CNTN4 plays important roles in axon guidance and synaptic plasticity in the hippocampus. However, the pathogenesis and functional role of CNTN4 in the cortex has not yet been investigated. Our study found a reduction in cortical thickness in the motor cortex of Cntn4 -/- mice, but cortical cell migration and differentiation were unaffected. Significant morphological changes were observed in neurons in the M1 region of the motor cortex, indicating that CNTN4 is also involved in the morphology and spine density of neurons in the motor cortex. Furthermore, mass spectrometry analysis identified an interaction partner for CNTN4, confirming an interaction between CNTN4 and amyloid-precursor protein (APP). Knockout human cells for CNTN4 and/or APP revealed a relationship between CNTN4 and APP. This study demonstrates that CNTN4 contributes to cortical development and that binding and interplay with APP controls neural elongation. This is an important finding for understanding the physiological function of APP, a key protein for Alzheimer's disease. The binding between CNTN4 and APP, which is involved in neurodevelopment, is essential for healthy nerve outgrowth.

Contactin 5 and Apolipoproteins Interplay in Alzheimer's Disease.

Background: Apolipoproteins and contactin 5 are proteins associated with Alzheimer's disease (AD) pathophysiology. Apolipoproteins act on transport and clearance of cholesterol and phospholipids during synaptic turnover and terminal proliferation. Contactin 5 is a neuronal membrane protein involved in key processes of neurodevelopment. Objective: To investigate the interactions between contactin 5 and apolipoproteins in AD, and the role of these proteins in response to neuronal damage. Methods: Apolipoproteins (measured by Luminex), contactin 5 (measured by Olink's proximity extension assay), and cholesterol (measured by liquid chromatography mass spectrometry) were assessed in the cerebrospinal fluid (CSF) and plasma of cognitively unimpaired participants (n = 93). Gene expression was measured using polymerase chain reaction in the frontal cortex of autopsied-confirmed AD (n = 57) and control subjects (n = 31) and in the hippocampi of mice following entorhinal cortex lesions. Results: Contactin 5 positively correlated with apolipoproteins B (p = 5.4×10-8), D (p = 1.86×10-4), E (p = 2.92×10-9), J (p = 2.65×10-9), and with cholesterol (p = 0.0096) in the CSF, and with cholesterol (p = 0.02), HDL (p = 0.0143), and LDL (p = 0.0121) in the plasma. Negative correlations were seen between CNTN5, APOB (p = 0.034) and APOE (p = 0.015) mRNA levels in the brains of control subjects. In the mouse model, apoe and apoj gene expression increased during the reinnervation phase (p <  0.05), while apob (p = 0.023) and apod (p = 0.006) increased in the deafferentation stage. Conclusions: Extensive interactions were observed between contactin 5 and apolipoproteins and cholesterol, possibly due to neuronal damage. The alterations in gene expression of apolipoproteins suggest a role in axonal, terminal, and synaptic remodeling in response to entorhinal cortex damage.

Gene-gene interaction network analysis indicates CNTN2 is a candidate gene for idiopathic generalized epilepsy.

Twin and family studies have established the genetic contribution to idiopathic generalized epilepsy (IGE). The genetic architecture of IGE is generally complex and heterogeneous, and the majority of the genetic burden in IGE remains unsolved. We hypothesize that gene-gene interactions contribute to the complex inheritance of IGE. CNTN2 (OMIM* 615,400) variants have been identified in cases with familial adult myoclonic epilepsy and other epilepsies. To explore the gene-gene interaction network in IGE, we took the CNTN2 gene as an example and investigated its co-occurrent genetic variants in IGE cases. We performed whole-exome sequencing in 114 unrelated IGE cases and 296 healthy controls. Variants were qualified with sequencing quality, minor allele frequency, in silico prediction, genetic phenotype, and recurrent case numbers. The STRING_TOP25 gene interaction network analysis was introduced with the bait gene CNTN2 (denoted as A). The gene-gene interaction pair mode was presumed to be A + c, A + d, A + e, with a leading gene A, or A + B + f, A + B + g, A + B + h, with a double-gene A + B, or other combinations. We compared the number of gene interaction pairs between the case and control groups. We identified three pairs in the case group, CNTN2 + PTPN18, CNTN2 + CNTN1 + ANK2 + ANK3 + SNTG2, and CNTN2 + PTPRZ1, while we did not discover any pairs in the control group. The number of gene interaction pairs in the case group was much more than in the control group (p = 0.021). Taking together the genetic bioinformatics, reported epilepsy cases, and statistical evidence in the study, we supposed CNTN2 as a candidate pathogenic gene for IGE. The gene interaction network analysis might help screen candidate genes for IGE or other complex genetic disorders.

Early B Cell Factor 3 (EBF3) attenuates Parkinson's disease through directly regulating contactin-associated protein-like 4 (CNTNAP4) transcription: An experimental study.

Parkinson's disease (PD) is a gradually debilitating neurodegenerative syndrome. Here, we analyzed GSE7621 chip data obtained from the Gene Expression Omnibus (GEO) database to explore the pathogenesis of PD. Early B Cell Factor 3 (EBF3), a member of the highly evolutionarily conserved EBF-transcription factor family, is involved in neuronal development. EBF3 expression is low in the substantia nigra of patients with PD. However, whether EBF3 is implicated in dopaminergic neuron death during PD has not yet been investigated. Therefore, we aimed to reveal the potential anti-apoptotic effect and molecular mechanism of EBF3 in PD. We established a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse model in vivo and a 1-methyl-4-phenylpyridine (MPP+)-induced SH-SY5Y cell model in vitro. EBF3 was downregulated in the substantia nigra of PD mice and SH-SY5Y cells treated with MPP+, and the m6A methylation modification level was low. Fat mass and obesity-associated protein (FTO) siRNA upregulated m6A methylation modification of EBF3 and extended the EBF3 mRNA half-life. Functionally, as demonstrated by the results of the open-field test, pole test and gait analysis, EBF3 overexpression ameliorated MPTP-induced behavioral disorder. Further, EBF3 overexpression suppressed neuronal apoptosis in vivo, as evidenced by decreased TUNEL+ cells, and the increased activation of caspase-3 and caspase-9. Similar results were obtained in vitro, as reflected by increased cell viability, decreased LDH activity and restored mitochondrial function, collectively protecting SH-SY5Y cells from MPP+-induced apoptosis. Mechanistically, the results of luciferase reporter, ch-IP and DNA pull-down assays confirmed that, as a transcription factor, EBF3 bound to the promoter of CNTNAP4 (a protein associated with neuronal differentiation) and directly regulated CNTNAP4 transcription. Strikingly, CNTNAP4 knockdown markedly abolished the effect of EBF3 on cell apoptosis, thus aggravating PD. In conclusion, the low level of m6A methylation modification may contribute to the low expression of EBF3 during PD. Additionally, EBF3 attenuates PD by activating CNTNAP4 transcription, suggesting that EBF3 may be a novel therapeutic target in PD.

Contactin-associated protein-like 2 (CNTNAP2) mutations impair the essential α-secretase cleavages, leading to autism-like phenotypes.

Mutations in the Contactin-associated protein-like 2 (CNTNAP2) gene are associated with autism spectrum disorder (ASD), and ectodomain shedding of the CNTNAP2 protein plays a role in its function. However, key enzymes involved in the C-terminal cleavage of CNTNAP2 remain largely unknown, and the effect of ASD-associated mutations on this process and its role in ASD pathogenesis remain elusive. In this report we showed that CNTNAP2 undergoes sequential cleavages by furin, ADAM10/17-dependent α-secretase and presenilin-dependent γ-secretase. We identified that the cleavage sites of ADAM10 and ADAM17 in CNTNAP2 locate at its C-terminal residue I79 and L96, and the main α-cleavage product C79 by ADAM10 is required for the subsequent γ-secretase cleavage to generate CNTNAP2 intracellular domain (CICD). ASD-associated CNTNAP2 mutations impair the α-cleavage to generate C79, and the inhibition leads to ASD-like repetitive and social behavior abnormalities in the Cntnap2-I1254T knock-in mice. Finally, exogenous expression of C79 improves autism-like phenotypes in the Cntnap2-I1254T knock-in and Cntnap2-/- knockout mice. This data demonstrates that the α-secretase is essential for CNTNAP2 processing and its function. Our study indicates that inhibition of the cleavage by pathogenic mutations underlies ASD pathogenesis, and upregulation of its C-terminal fragments could have therapeutical potentials for ASD treatment.

Interplay between intrinsic flexibility and sugar coating in Contactin-2 homodimerization.

In this issue of Structure, Chataigner et al. reveal that Contactin-2's homotypic interaction, a glycosylation-dependent process, generates a broad conformational landscape. This structural plasticity, driven by conformational equilibria and sugar coating, facilitates adaptation to diverse ligands and environmental conditions, highlighting its dynamic role in neuronal function.

Contactin 6, A Novel Causative Gene for Congenital Hypothyroidism, Mediates Thyroid Hormone Biosynthesis Through Notch Signaling.

Background: Congenital hypothyroidism (CH) is the most common neonatal metabolic disorder. In patients with CH in China, thyroid dyshormonogenesis is more common than thyroid dysgenesis; however, the genetic causes of CH due to thyroid dyshormonogenesis remain largely unknown. Therefore, we aimed at identifying novel candidate causative genes for CH. Methods: To identify novel CH candidate genes, a total of 599 patients with CH were enrolled and next-generation sequencing was performed. The functions of the identified variants were confirmed using HEK293T and FTC-133 cell lines in vitro and in a mouse model organism in vivo. Results: Three pathogenic contactin 6 (CNTN6) variants were identified in two patients with CH. Pedigree analysis showed that CH caused by CNTN6 variants was inherited in an autosomal recessive pattern. The CNTN6 gene was highly expressed in the thyroid in humans and mice. Cntn6 knockout mice presented with thyroid dyshormonogenesis and CH due to the decreased expression of crucial genes for thyroid hormone biosynthesis (Slc5a5, Tpo, and Duox2). All three CNTN6 variants resulted in the blocking of the release of the Notch intracellular domain, which could not translocate into the nucleus, impaired NOTCH1 transcriptional activity, and decreased expression of SLC5A5, TPO, and DUOX2. Further, we found that DTX1 was required for CNTN6 to promote thyroid hormone biosynthesis through Notch signaling. Conclusions: This study demonstrated that CNTN6 is a novel causative gene for CH through the mediation of thyroid hormone biosynthesis via Notch signaling, which provides new insights into the genetic background and mechanisms involved in CH and thyroid dyshormonogenesis.

Clinical, neurophysiological and serological clues for the diagnosis of neuromyotonia and distinction from cramp-fasciculation syndrome.

Neuromyotonia and cramp-fasciculation syndrome diagnosis currently relies on neurophysiological examination. In this study we investigated the clinical features and neural antibody profile of patients with neuromyotonia and cramp-fasciculation syndrome to assess the diagnostic value of serological testing. Available sera from adult patients with electromyography-defined neuromyotonia and cramp-fasciculation syndrome were tested for neural antibodies by indirect immunofluorescence on mouse brain sections and live cell-based assays. Forty patients were included, 14 with neuromyotonia and 26 with cramp-fasciculation syndrome. Neural antibodies were detected in 10/10 neuromyotonia sera, most commonly against contactin-associated protein 2 (7/10, 70%), and in 1/20 (5%) cramp-fasciculation syndrome sera. Clinical myokymia, hyperhidrosis, and paresthesia or neuropathic pain were more common in neuromyotonia and mostly associated with contactin-associated protein 2 antibodies. Central nervous system involvement was present in 4/14 (29%) neuromyotonia patients. A tumor was detected in 13/14 (93%) neuromyotonia patients (thymoma, 13), and in 4/26 (15%) with cramp-fasciculation syndrome (thymoma, 1; other neoplasms, 3). Twenty-one/27 (78%) patients achieved a significant improvement or complete remission. Our findings highlight clinical, neurophysiological and serological clues that can be useful in the diagnosis of neuromyotonia and cramp-fasciculation syndrome. Antibody testing is valuable for neuromyotonia diagnosis, while its usefulness in cramp-fasciculation syndrome confirmation is limited.

The autoimmune vulnerability of the node of Ranvier.

The nodes of Ranvier (NoR) are essential domains for nerve conduction and their disruption plays a key role in the pathophysiology of immune-mediated neuropathies. Our understanding of the specialized nodal regions and the immune mechanisms that affect them is growing and has led to the update of peripheral neuropathy classification to include the autoimmune nodopathies, defined by the site of the autoimmune attack. Autoantibodies directed against molecules of the nodal region (as neurofascin-140/186, neurofascin-155, contactin-1, contactin-associated protein 1, contactin-associated protein 2, gangliosides, LGI4, or myelin-associated glycoprotein), macrophage-induced paranodal demyelination, and phenotypic changes of the nodal domains of Schwann cells have been identified as key mechanisms in the pathogenesis of the autoimmune neuropathies. This review explores the current knowledge of the autoimmune vulnerability of the NoR, including the underlying mechanisms leading to dysfunction in the diverse autoimmune disorders.

Genotype-phenotype correlation in contactin-associated protein-like 2 (CNTNAP-2) developmental disorder.

Contactin-associated protein-like 2 (CNTNAP2) gene encodes for CASPR2, a presynaptic type 1 transmembrane protein, involved in cell-cell adhesion and synaptic interactions. Biallelic CNTNAP2 loss has been associated with "Pitt-Hopkins-like syndrome-1" (MIM#610042), while the pathogenic role of heterozygous variants remains controversial. We report 22 novel patients harboring mono- (n = 2) and bi-allelic (n = 20) CNTNAP2 variants and carried out a literature review to characterize the genotype-phenotype correlation. Patients (M:F 14:8) were aged between 3 and 19 years and affected by global developmental delay (GDD) (n = 21), moderate to profound intellectual disability (n = 17) and epilepsy (n = 21). Seizures mainly started in the first two years of life (median 22.5 months). Antiseizure medications were successful in controlling the seizures in about two-thirds of the patients. Autism spectrum disorder (ASD) and/or other neuropsychiatric comorbidities were present in nine patients (40.9%). Nonspecific midline brain anomalies were noted in most patients while focal signal abnormalities in the temporal lobes were noted in three subjects. Genotype-phenotype correlation was performed by also including 50 previously published patients (15 mono- and 35 bi-allelic variants). Overall, GDD (p < 0.0001), epilepsy (p < 0.0001), hyporeflexia (p = 0.012), ASD (p = 0.009), language impairment (p = 0.020) and severe cognitive impairment (p = 0.031) were significantly associated with the presence of biallelic versus monoallelic variants. We have defined the main features associated with biallelic CNTNAP2 variants, as severe cognitive impairment, epilepsy and behavioral abnormalities. We propose CASPR2-deficiency neurodevelopmental disorder as an exclusively recessive disease while the contribution of heterozygous variants is less likely to follow an autosomal dominant inheritance pattern.

Caspr1 antibodies autoimmune paranodopathy with severe tetraparesis: Potential relevance of antibody titers in monitoring treatment response.

AIM: Nodopathies and paranodopathies are autoimmune neuropathies associated with antibodies to nodal-paranodal antigens (neurofascin 140/186 and 155, contactin-1, contactin-associated protein 1 [Caspr1]) characterized by peculiar clinical features, poor response to standard immunotherapies (e.g., intravenous immunoglobulins, IVIg). Improvement after anti-CD20 monoclonal antibody therapy has been reported. Data on Caspr1 antibodies pathogenicity are still preliminary, and longitudinal titers have been poorly described. METHODS: We report on a young woman who developed a disabling neuropathy with antibodies to the Caspr1/contactin-1 complex showing a dramatic improvement after rituximab therapy, mirrored by the decrease of antibody titers. RESULTS: A 26-year-old woman presented with ataxic-stepping gait, severe motor weakness at four limbs, and low frequency postural tremor. For neurophysiological evidence of demyelinating neuropathy, she was diagnosed with chronic inflammatory demyelinating polyradiculoneuropathy and treated with IVIg without benefit. MRI showed symmetrical hypertrophy and marked signal hyperintensity of brachial and lumbosacral plexi. Cerebrospinal fluid showed 710 mg/dL protein. Despite intravenous methylprednisolone, the patient progressively worsened, and became wheelchair-bound. Antibodies to nodal-paranodal antigens were searched for by ELISA and cell-based assay. Anticontactin/Caspr1 IgG4 antibodies resulted positive. The patient underwent rituximab therapy with slow progressive improvement that mirrored the antibodies titer, measured throughout the disease course. CONCLUSIONS: Our patient had a severe progressive course with early disability and axonal damage, and slow recovery starting only a few months after antibody-depleting therapy. The close correlation between titer, disability, and treatment, supports the pathogenicity of Caspr1 antibodies, and suggest that their longitudinal evaluation might provide a potential biomarker to evaluate treatment response.

Differences in Startle and Prepulse Inhibition in Contactin-associated Protein-like 2 Knock-out Rats are Associated with Sex-specific Alterations in Brainstem Neural Activity.

The contactin-associated protein-like 2 (CNTNAP2) gene encodes for the CASPR2 protein, which plays an essential role in neurodevelopment. Mutations in CNTNAP2 are associated with neurodevelopmental disorders, including autism spectrum disorder and schizophrenia. Rats with a loss of function mutation in the Cntnap2 gene show increased acoustic startle response (ASR) and decreased prepulse inhibition (PPI). The neural basis of this altered auditory processing in Cntnap2 knock-out rats is currently unknown. Auditory brainstem recordings previously revealed no differences between the genotypes. The next step is to investigate brainstem structures outside of the primary auditory pathway that mediate ASR and PPI, which are the pontine reticular nucleus (PnC) and pedunculopontine tegmentum (PPTg), respectively. Multi-unit responses from the PnC and PPTg in vivo of the same rats revealed sex-specific effects of loss of CASPR2 expression on PnC activity, but no effects on PPTg activity. Female Cntnap2-/- rats showed considerably increased PnC firing rates compared with female wildtypes, whereas the difference between the genotypes was modest in male rats. In contrast, for both females and males we found meager differences between the genotypes for PPTg firing rates and inhibition of PnC firing rates, indicating that altered firing rates of these brainstem structures are not responsible for decreased PPI in Cntnap2-/- rats. We conclude that the auditory processing changes seen in Cntnap2-/- rats are associated with, but cannot be fully explained by, differences in PnC firing rates, and that a loss of function mutation in the Cntnap2 gene has differential effects depending on sex.

Contactin-associated protein-like 2 antibody-associated autoimmune encephalitis in children: case reports and systematic review of literature.

OBJECTIVES: To ascertain the clinical characteristics of pediatric patients with contactin-associated protein-like 2 (CASPR2) antibody-associated autoimmune encephalitis (AEs). METHODS: Two cases of CASPR2 antibody-associated AEs have been reported. In addition, a systematic search of literature published between January 2010 and March 2022 through six online databases was conducted to identify the pediatric patients with CASPR2 antibody-associated AEs. Data on demographics, clinical symptoms, laboratory examinations, imaging, treatment, and outcome were collected. RESULTS: Our updated literature search yielded 1,837 publications, of which 21 were selected, and 40 patients in this study met the diagnostic criteria for AE. There were 25 males and 15 females with a mean age of 9.2 years. The most common presenting symptoms are psychiatric symptoms (72.5%), sleep changes (62.5%), and movement disorders (60%). The psychiatric symptoms included mood changes (39.1%), behavior changes (25%), and hallucination (7.5%). In total, 23 cases (57.5%) combined with autonomic dysfunction, such as gastrointestinal dysmotility, cardiovascular-related symptoms, and sweating. No tumors were observed in children. Thirty-eight patients received first-line immunotherapy, and eight received first-line and second-line immunotherapy. All patients had a good clinical response to immune therapy. Mean mRS at onset was 3.4; It was 0.88 at the last follow-up. There was no recurrence during follow-up. CONCLUSION: Psychiatric symptoms, sleep disorders, movement disorders, and cardiovascular-related symptoms are the most common presentation in pediatric patients with CASPR2 antibody-associated AEs. Tumor, particularly with thymoma, is uncommon in children diagnosed with CASPR2 antibody-associated AEs. In addition, prompt diagnosis and immunotherapy can relieve symptoms and improve the prognosis.

Neuroaxonal and Glial Markers in Patients of the Same Age With Multiple Sclerosis.

BACKGROUND AND OBJECTIVES: The specificity of novel blood biomarkers for multiple sclerosis (MS)-related neurodegeneration is unclear because neurodegeneration also occurs during normal aging. To understand which aspects of neurodegeneration the serum biomarkers neurofilament light (sNfL), serum glial fibrillary acidic protein (sGFAP), and serum contactin-1 (sCNTN1) reflect, we here explore their cross-sectional association with disability outcome measures and MRI volumes in a unique cohort of people with MS (PwMS) of the same age. METHODS: sNfL, sGFAP (both singe-molecule array technology) and sCNTN1 (Luminex) were measured in serum samples of 288 PwMS and 125 healthy controls (HCs) of the Project Y cohort, a population-based cross-sectional study of PwMS born in the Netherlands in 1966 and age-matched HC. RESULTS: sNfL (9.83 pg/mL [interquartile range {IQR}: 7.8-12.0]) and sGFAP (63.7 pg/mL [IQR: 48.5-84.5]) were higher in PwMS compared with HC (sNfL: 8.8 pg/mL [IQR: 7.0-10.5]; sGFAP: 51.7 pg/mL [IQR: 40.1-68.3]) (p < 0.001), whereas contactin-1 (7,461.3 pg/mL [IQR: 5,951.8-9,488.6]) did not significantly differ between PwMS compared with HC (7,891.2 pg/mL [IQR: 6,120.0-10,265.8]) (p = 0.068). sNfL and sGFAP levels were 1.2-fold higher in secondary progressive patients (SPMS) compared with relapsing remitting patients (p = 0.009 and p = 0.043). Stratified by MS subtype, no relations were seen for CNTN1, whereas sNfL and sGFAP correlated with the Expanded Disability Status Scale (ρ = 0.43 and ρ = 0.39), Nine-Hole Peg Test, Timed 25-Foot Walk Test, and Symbol Digit Modalities Test (average ρ = 0.38) only in patients with SPMS. Parallel to these clinical findings, correlations were only found for sNfL and sGFAP with MRI volumes. The strongest correlations were observed between sNfL and thalamic volume (ρ = -0.52) and between sGFAP with deep gray matter volume (ρ = - 0.56) in primary progressive patients. DISCUSSION: In our cohort of patients of the same age, we report consistent correlations of sNfL and sGFAP with a range of metrics, especially in progressive MS, whereas contactin-1 was not related to clinical or MRI measures. This demonstrates the potential of sNfL and sGFAP as complementary biomarkers of neurodegeneration, reflected by disability, in progressive MS.

Salidroside Alleviates Diabetic Cognitive Dysfunction Via B3galt2/F3/Contactin Signaling Pathway in Mice.

Diabetes is frequently accompanied by cognitive impairment with insidious onset, and progressive cognitive and behavioral changes. ß-1, 3-galactosyltransferase 2 (B3galt2) contributes to glycosylation, showing a clue for neuronal apoptosis, proliferation and differentiation. However, the role of B3galt2 in diabetic cognitive dysfunction (DCD) has not been investigated. In the present study, we aimed to explore the role of B3galt2 in DCD. Additionally, the potential therapeutic effects of salidroside on DCD was also explored. Diabetic C57BL/6J mice showed cognitive dysfunction together with down-regulated B3galt2. Overexpression of B3galt2 reversed the cognitive decline of diabetic C57BL/6J. Moreover, cognitive impairment was aggravated in B3galt2+/- diabetic mice compared with C57BL/6J diabetic mice. Immunohistochemistry fluorescence indicated that B3galt2 and F3/Contactin were co-localized in the hippocampal regions. Importantly, the expression of F3/Contactin can be regulated by the manipulation of B3galt2, overexpression of which assuaged hippocampal neuronal damage, protected the synapsin, and reduced neuronal apoptosis in diabetic mice. Interestingly, SAL alleviated DCD and reversed the expression of B3galt2 in diabetic C57BL/6J mice. These findings indicate that inhibition of B3galt2/F3/Contactin pathway contributes to DCD, and participates in SAL reversed DCD.

Characterization of the contactin 5 protein and its risk-associated polymorphic variant throughout the Alzheimer's disease spectrum.

INTRODUCTION: We investigate the CNTN5 rs1461684 G variant and the contactin 5 protein in sporadic Alzheimer's disease (sAD). METHODS: Contactin 5, sAD biomarkers, and synaptic markers were measured in the cerebrospinal fluid (CSF). Amyloid and tau deposition were assessed using positron emission tomography. Contactin 5 protein and mRNA levels were measured in brain tissue. RESULTS: CSF contactin 5 increases progressively in cognitively unimpaired individuals and is decreased in mild cognitive impairment and sAD. CSF contactin 5 correlates with sAD biomarkers and with synaptic markers. The rs1461684 G variant associates with faster disease progression in cognitively unimpaired subjects. Cortical full-length and isoform 3 CNTN5 mRNAs are decreased in the presence of the G allele and as a function of Consortium to Establish a Registry for Alzheimer's Disease stages. DISCUSSION: The newly identified rs1461684 G variant associates with sAD risk, rate of disease progression, and gene expression. Contactin 5 protein and mRNA are affected particularly in the early stages of the disease.

Early-Stage Contactin-Associated Protein-like 2 Limbic Encephalitis: Clues for Diagnosis.

BACKGROUND AND OBJECTIVES: Previous studies suggested that autoimmune limbic encephalitis with antibodies against contactin-associated protein-like 2 (CASPR2-encephalitis) is clinically heterogeneous and progresses slowly, preventing its early recognition. We aimed to describe the onset and progression of CASPR2-encephalitis and to assess long-term outcomes. METHODS: We retrospectively analyzed the medical records of all patients whose CSF tested positive for anti-CASPR2 antibodies in our center between 2006 and 2020. Standardized telephone interviews of all available patients and relatives were conducted, assessing long-term functional independence using the Functional Activity Questionnaire (FAQ) and quality of life using the 36-Item Short-Form Survey (SF36). RESULTS: Forty-eight patients were included (98% males; median age 64 years), and 35 participated in telephone interviews (73%). At onset, 81% had at least 1 neurologic symptom among the following: limbic (54%), peripheral nerve hyperexcitability (PNH; 21%), and/or cerebellar symptoms (17%). Most of the patients (75%) had initially symptoms of only one of these categories. Limbic symptoms at onset included mostly seizures (33%), while memory disturbances were less frequent (10%). PNH signs were mostly neuropathic pain (9/10 patients). Other symptoms seen at onset included asthenia (33%), mood disorders (25%), and insomnia (21%); 19% of patients did not show any limbic, peripheral, or cerebellar symptom at onset but only asthenia (15%), mood disorders (6%), weight loss (8%), dysautonomia (4%), and/or insomnia (2%). The peak of the disease was attained in median 16.7 months after onset. Over the study period (median follow-up, 58.8 months, range 10.6-189.1), 77% of patients developed ≥3 core CASPR2 symptoms and 42% fulfilled the diagnostic criteria for autoimmune limbic encephalitis, although all patients ultimately developed limbic symptoms. At the last visit, most interviewed patients (28/35 patients, 80%; median, 5 years after onset) had recovered functional independence (FAQ <9) while only the vitality subscore of the SF36 was lower than normative data (mean 49.9 vs 58.0, p = 0.0369). DISCUSSION: CASPR2-encephalitis has a progressive course and is highly heterogeneous at the early stage. In men older than 50 years, otherwise unexplained seizures, cerebellar ataxia, and/or neuropathic pain are suggestive of early-stage CASPR2-encephalitis, especially if they coincide with recent asthenia, mood disorders, or insomnia.

Leucine-rich Glioma-inactivated 1 Encephalitis Followed by Isaacs Syndrome: Alternating Presence of Pathogenic Autoantibodies to Leucine-rich Glioma-inactivated 1 and Contactin-associated Protein-like 2.

The coexistence of leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (CASPR2) autoantibodies in the same individual is surprisingly often observed. We herein report the first case of LGI1 encephalitis followed by Isaacs syndrome in which LGI1 and CASPR2 antibodies in the serum and cerebrospinal fluid (CSF) were measured during the entire disease course. After the resolution of limbic encephalitis, LGI1 antibodies disappeared from the CSF simultaneously with the appearance of CASPR2 antibodies in the serum. The alternating presence of these pathogenic autoantibodies along with the clinical and phenotypic alternations suggested that LGI1 encephalitis was associated with CASPR2 autoantibody production in the peripheral tissue, leading to CASPR2-associated Isaacs syndrome.

Distinct movement disorders in contactin-associated-protein-like-2 antibody-associated autoimmune encephalitis.

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.

Structural insights into the contactin 1 - neurofascin 155 adhesion complex.

Cell-surface expressed contactin 1 and neurofascin 155 control wiring of the nervous system and interact across cells to form and maintain paranodal myelin-axon junctions. The molecular mechanism of contactin 1 - neurofascin 155 adhesion complex formation is unresolved. Crystallographic structures of complexed and individual contactin 1 and neurofascin 155 binding regions presented here, provide a rich picture of how competing and complementary interfaces, post-translational glycosylation, splice differences and structural plasticity enable formation of diverse adhesion sites. Structural, biophysical, and cell-clustering analysis reveal how conserved Ig1-2 interfaces form competing heterophilic contactin 1 - neurofascin 155 and homophilic neurofascin 155 complexes whereas contactin 1 forms low-affinity clusters through interfaces on Ig3-6. The structures explain how the heterophilic Ig1-Ig4 horseshoe's in the contactin 1 - neurofascin 155 complex define the 7.4 nm paranodal spacing and how the remaining six domains enable bridging of distinct intercellular distances.