Refining of the electroclinical phenotype in familial and sporadic cases of CSNK2B-related Neurodevelopmental Syndrome.

CSNK2B encodes a regulatory subunit of casein kinase II, which is highly expressed in the brain. Heterozygous pathogenic variants in CSNK2B are associated with Poirier-Bienvenu neurodevelopmental syndrome (POBINDS) (OMIM #618732), characterized by facial dysmorphisms, seizures, intellectual disability, and behavioral disturbances. We report ten new patients with CSNK2B-related Neurodevelopmental Syndrome associated with heterozygous variants of CSNK2B. In three patients, a pathogenic variant was inherited from an affected parent. We describe both molecular and clinical features, focusing on epileptic and neurodevelopmental phenotypes. The median age at follow-up was 8.5 years (range 21 months-42 years). All patients had epilepsy, with onset at a median age of 10.5 months range 6 days-10 years). Seizures were both focal and generalized and were resistant to anti-seizure medications in two out of ten patients. Six patients had mild to moderate cognitive delays, whereas four patients had no cognitive disability. Although all previously reported patients had a de novo CSNK2B pathogenic variant, here we report, for the first time, two familial cases of CSNK2B-related Neurodevelopmental Syndrome. We confirmed the highly variable expressivity of the disease among both interfamilial and intrafamilial cases. Furthermore, this study provides information about the long-term outcome in adult patients and underlines the importance of detailed family history collection before performing genetic testing in patients with epilepsy and neurodevelopmental disorders.