Kv5.1 antibody in epilepsy patients with unknown etiology

BACKGROUND

Neuronal autoantibodies and favorable response to immunosuppressive treatment have been described in patients with chronic epilepsy of unknown cause, suggesting autoimmune etiology. Our aim was to identify novel epilepsy-specific autoantibodies reactive with neuronal surface antigens.

METHODS

Sera of 172 epilepsy patients with unknown cause and 30 healthy controls were screened with indirect immunofluorescence to identify IgG reacting with primary rat neuronal cultures. Putative target autoantigens were investigated with immunoprecipitation (IP) and liquid chromatography-mass/mass spectrometry (LC-MS/MS) studies using SH-SY5Y cells. Validation of LC-MS/MS results was carried out by IP and immunocytochemistry assays.

RESULTS

Antibodies to neuronal cell surface antigens were detected in 18 epilepsy patients. LC-MS/MS analysis identified voltage-gated potassium channel modifier subfamily F member 1 (KCNF1, Kv5.1) as the single common cell surface antigen in 4 patients with Lennox-Gastaut syndrome (n = 2), focal epilepsy of unknown cause (n = 1) and mesial temporal lobe epilepsy with hippocampal sclerosis (n = 1). These patients had the common features of early seizure onset and treatment-resistance. IP assays and co-localization (serum IgG and commercial Kv5.1-antibody) studies done with non-fixed Kv5.1-transfected HEK293 cells and primary neuronal cultures confirmed the presence of Kv5.1-antibody in 4 epilepsy patients identified by LC-MS/MS. Similar findings were not obtained by sera of other patients with epilepsy, patients with autoimmune encephalitis and healthy controls.

CONCLUSION

The herein described novel neuronal surface antibody to Kv5.1 appears to be associated with treatment-resistant epilepsy of unknown cause. Exact clinical and pathogenic significance of this antibody remains to be elucidated.

The Complex Genetic Landscape of Hereditary Ataxias in Turkey and Implications in Clinical Practice

BACKGROUND

The genetic and epidemiological features of hereditary ataxias have been reported in several populations; however, Turkey is still unexplored. Due to high consanguinity, recessive ataxias are more common in Turkey than in Western European populations.

OBJECTIVE

To identify the prevalence and genetic structure of hereditary ataxias in the Turkish population.

METHODS

Our cohort consisted of 1296 index cases and 324 affected family members. Polymerase chain reaction followed by Sanger sequencing or fragment analysis were performed to screen for the trinucleotide repeat expansions in families with a dominant inheritance pattern, as well as in sporadic cases. The expansion in the frataxin (FXN) gene was tested in all autosomal recessive cases and in sporadic cases with a compatible phenotype. Whole-exome sequencing was applied to 251 probands, selected based on the family history, age of onset, and phenotype.

RESULTS

Mutations in known ataxia genes were identified in 30% of 1296 probands. Friedreich's ataxia was found to be the most common recessive ataxia in Turkey, followed by autosomal recessive spastic ataxia of Charlevoix-Saguenay. Spinocerebellar ataxia types 2 and 1 were the most common dominant ataxias. Whole-exome sequencing was performed in 251 probands with an approximate diagnostic yield of 50%. Forty-eight novel variants were found in a plethora of genes, suggesting a high heterogeneity. Variants of unknown significance were discussed in light of clinical data.

CONCLUSION

With the large sample size recruited across the country, we consider that our results provide an accurate picture of the frequency of hereditary ataxias in Turkey. © 2021 International Parkinson and Movement Disorder Society.

Calcium channel antibodies in patients with absence epilepsy

Autoimmunity has aroused interest in the last years as a contributory mechanism of epilepsy, especially in epilepsies with unknown cause or therapy resistance. Since the relationship of absence epilepsy (AE) with calcium channels is well established, we aimed to investigate related antibodies in patients diagnosed with AE. Consecutive patients with typical absence seizures having either childhood absence epilepsy (CAE) or juvenile absence epilepsy (JAE) with generalized spike and wave discharges on electroencephalography (EEG) were included after their consent. The patients were diagnosed according to the International League Against Epilepsy (ILAE) 2010 criteria. Antibodies against P-Q type voltage gated calcium channels (VGCC) and T-type VGCC subunit Cav3.2 (encoded by the CACNA1H gene) were investigated by RIA and ELISA, respectively. We searched for these antibodies in 32 patients with AE and 53 patients with focal epilepsy of unknown cause (FEOUC) as the disease control group; furthermore, 30 healthy persons served as the healthy controls. Eleven patients (34.3%) with AE had CAE and the remaining patients had JAE. Only a 47-year-old female FEOUC patient, who also had systemic lupus erythematosus with normal MRI scans showed antibodies against P-Q type VGCC, whereas no antibody positivity could be found in other FEOUC and AE patients and healthy controls. Our results might suggest that calcium channel antibodies do not play an important role in the pathophysiology of AE. Further studies with larger groups of other epileptic syndromes are needed to confirm our results.