Epilepsia
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Severe early onset epilepsies are often caused by de novo pathogenic variants. Few studies have reported the frequency of somatic mosaicism in parents of children with severe epileptic encephalopathies. Here we aim to investigate the frequency of mosaicism in the parents of children with epilepsy caused by alleged de novo variants. ⋯ Our results show that de novo events can occur already in parental tissue and in some cases can be detected in peripheral blood. Consequently, parents affected by low-grade mosaicism are faced with an increased recurrence risk for transmitting the pathogenic variant, compared to the overall recurrence risk for a second affected child estimated at approximately 1%. However, testing for parental somatic mosaicism will help identifying those parents who truly are at higher risk and will significantly improve genetic counseling in the respective families.