The anti-CASPR2 antibody-associated syndrome is a rare immune-mediated disorder. Most case reports describe neurologic symptoms that include encephalic signs, peripheral nerve hyperexcitability, dysautonomia, or neuropathic pain. We report the case of a 70-year-old man, admitted to the emergency department with complaints of slurred speech and imbalance. Neurological examination was relevant for dysarthria, hyperreflexia, and pancerebellar syndrome. Cranial CT and basic laboratory tests were normal and he spontaneously recovered after 14 hours. Over the next four months, the patient experienced three similar episodes in relation to stressful events (emotional and organic disturbances like prolonged fasting and vaccination). A contrast-enhanced MRI was performed, along with extensive laboratory testing, analysis of cerebrospinal fluid (CSF), paraneoplastic investigation, and next-generation sequencing panel for episodic ataxias. The results revealed oligoclonal bands in the CSF and positive anti-CASPR2 antibodies both in serum and CSF. Three-day-IV- methylprednisolone pulse followed by plasmapheresis and monthly intravenous immunoglobulins was performed with good response. In conclusion, the neurological manifestations that led to the diagnosis of anti-CASPR2 antibody-associated syndrome were intermittent self-limiting episodes of ataxia, often triggered by concurrent stress-inducing factors. This case supports the aim of other authors to add paroxysmal cerebellar ataxia to the spectrum of the anti-CASPR2 antibody syndrome.

Episodic ataxia is an umbrella term for a group of nervous system disorders that adversely and episodically affect movement. Episodes are recurrent, characterized by loss of balance and coordination and can be accompanied by other symptoms ranging from nausea to hemiplegia. Episodic Ataxia Type 1 (EA1) is an inherited, autosomal dominant disease caused by sequence variants in KCNA1, which encodes the voltage-gated potassium channel, KCNA1 (Kv1.1). Here we report a novel loss-of-function KCNA1 pathogenic variant [c.464T>C/p.Leu155Phe] causing frequent, sudden onset of clumsiness or staggering gait in the young female proband. The gene variant was maternally inherited and the mother, whose symptoms also began in childhood, has a normal MRI and EEG, slurred speech and dystonic movements involving upper extremities and mouth. Both mother and daughter are responsive to carbamazepine. Cellular electrophysiology studies of KCNA1-L155P potassium channels revealed complete but non-dominant loss of function, with reduced current and altered gating in heterozygous channels. To our knowledge this is the first EA1-associated pathogenic variant located in the KCNA1 cytoplasmic N-terminus, expanding the reported clinically sensitive domains of the channel.

Episodic ataxia (EA) is a group of disorders characterized by recurrent spells of vertigo, truncal ataxia, and dysarthria. Episodic ataxia type 2 (EA2), the most common subtype of EA, is an autosomal dominant disease caused by mutation of the CACNA1A gene. EA2 has been rarely reported in the Chinese population. Here we present an EA2 family admitted to Xiangya Hospital in October 2018. The proband was a 22-year-old male who complained of recurrent spells of vertigo, slurred speech, and incoordination for 4 years. Brain magnetic resonance imaging (MRI) showed cerebellar atrophy. He had neuropsychological development disorder in childhood, and cognitive assessment in adulthood showed cognitive impairment. The proband's mother and grandmother had a similar history. Peripheral blood samples from the proband and family members were collected, and genomic DNA was isolated. Whole exome sequencing of the proband detected a heterozygous frameshift mutation c.2042_2043del (p.Q681Rfs*100) of CACNA1A gene. This mutation was verified in the proband and 2 family members using Sanger sequencing. One family member carrying this mutation was free of symptoms and signs, suggesting an incomplete penetrance of the mutation. We reported a variant c.2042_2043del of CACNA1A gene as the pathogenic mutation in a Chinese EA2 family for the first time. This case enriched the clinical spectrum of CACNA1A related EA2, and contributed to the understanding of clinical and genetic characteristics of EA2 to reduce misdiagnosis. 发作性共济失调(episodic ataxia，EA)是一组以反复发作性眩晕、构音障碍、共济失调为主要临床特征的疾病。发作性共济失调2型(episodic ataxia type 2，EA2)是EA最常见的亚型，致病基因为CACNA1A，遗传方式为常染色体显性遗传。在中国人群中，CACNA1A突变导致EA2的报道罕见。中南大学湘雅医院于2018年10月收治了1个EA2家系。先证者，男，22岁，因“反复发作性头晕4年，加重1年”入院。临床表现为反复发作性眩晕伴有言语含糊和肢体共济失调，发作间期存在进行性加重的构音障碍，头颅MRI显示小脑萎缩。患者幼年时有神经心理发育障碍表现，成年期认知评估显示存在认知障碍。先证者的母亲和外婆有类似的发作性症状。提取患者及家系成员外周血基因组DNA，对先证者进行全外显子测序，发现杂合移码突变c.2042_2043del(p.Q681Rfs*100)。进一步采用Sanger测序技术对先证者以及家系成员进行该位点测序验证，在先证者及2个家系成员中发现该杂合移码突变，其中1名家系成员携带此突变但无临床表现，提示存在不完全外显。本研究明确了CACNA1A基因c.2042_2043del突变为该EA2家系的致病突变，该突变可能存在不完全外显，在中国汉族人群中为首次报道。本研究丰富了CACNA1A突变相关EA2的临床表型特征，有助于认识该病临床表现及遗传学特点，减少误诊和漏诊。. Episodic ataxia (EA) is a group of disorders characterized by recurrent spells of vertigo, truncal ataxia, and dysarthria. Episodic ataxia type 2 (EA2), the most common subtype of EA, is an autosomal dominant disease caused by mutation of the CACNA1A gene. EA2 has been rarely reported in the Chinese population. Here we present an EA2 family admitted to Xiangya Hospital in October 2018. The proband was a 22-year-old male who complained of recurrent spells of vertigo, slurred speech, and incoordination for 4 years. Brain magnetic resonance imaging (MRI) showed cerebellar atrophy. He had neuropsychological development disorder in childhood, and cognitive assessment in adulthood showed cognitive impairment. The proband’s mother and grandmother had a similar history. Peripheral blood samples from the proband and family members were collected, and genomic DNA was isolated. Whole exome sequencing of the proband detected a heterozygous frameshift mutation c.2042_2043del (p.Q681Rfs*100) of CACNA1A gene. This mutation was verified in the proband and 2 family members using Sanger sequencing. One family member carrying this mutation was free of symptoms and signs, suggesting an incomplete penetrance of the mutation. We reported a variant c.2042_2043del of CACNA1A gene as the pathogenic mutation in a Chinese EA2 family for the first time. This case enriched the clinical spectrum of CACNA1A related EA2, and contributed to the understanding of clinical and genetic characteristics of EA2 to reduce misdiagnosis.

Episodic ataxia type 1 and 2 (EA1 and EA2) are the most well-described of the episodic ataxias. They are autosomal dominantly inherited early-onset diseases characterized by attacks of cerebellar dysfunction. EA1 is clinically characterized by short episodes of ataxia with interictal myokymia, whereas EA2 is characterized by longer-lasting recurrent ataxia, slurred speech, and interictal nystagmus. We report on a patient with EA2 with interictal focal dystonia and also interictal myokymia, which is hitherto not reported as an interictal feature associated to EA2. The patient carries a previously described heterozygous pathogenic de novo frameshift variant in the CACNA1A gene, establishing the diagnosis of EA2. She had symptom onset at age 13 and from age 48 she developed interictal myokymia and focal dystonia as illustrated in Supplemental Movie S1. We conclude that interictal myokymia and focal dystonia may be interictal features associated to EA2 caused by the cerebellar pathophysiology of EA2. Episodes of ataxia were successfully treated with acetazolamide in low dose, whereas the interictal features were unresponsive to acetazolamide.

Pathogenic KCNA1 variants have been linked to episodic ataxia type 1 (EA1), a rare neurological syndrome characterized by continuous myokymia and attacks of generalized ataxia that can be triggered by fever, abrupt movements, emotional stress, and fatigue. Currently, over 40 KCNA1 variants have been identified in individuals with EA1. A male patient displayed partial seizures in addition to EA1 symptoms, often triggered by fever. A sibling presented with typical EA1 symptoms, seizures, and learning difficulties. In addition, the older brother displayed cognitive impairment, developmental delay, and slurred speech, which were absent in his younger sister. Whole-exome sequencing was performed for the patients. A novel de novo missense variant in KCNA1 (p.Ala261Thr) was identified in the male patient, which is located in a base of the 3rd transmembrane domain (S3). The other novel KCNA1 variant (p.Gly376Ser) was identified in the sibling and was inherited from an unaffected father with low-level mosaicism. The variant was located in the S5-S6 extracellular linker of the voltage sensor domain of the Kv channel. Next, we systematically reviewed the available clinical phenotypes of individuals with EA1 and observed that individuals with KCNA1 variants at the C-terminus were more likely to suffer from seizures and neurodevelopmental disorders than those with variants at the N-terminus. Our study expands the mutation spectrum of KCNA1 and improves our understanding of the genotype-phenotype correlations of KCNA1. Definitive genetic diagnosis is beneficial for the genetic counseling and clinical management of individuals with EA1.