Complex/polygenic inheritance with variable penetrance.
A minority of cases may be explained by variants in SCN1A and SLC2A1.
There is frequently a family history of febrile seizures (in 50% of cases); other seizures/epilepsy syndromes may also occur in families. Epilepsy with myoclonic-atonic seizures is seen in families with other individuals with genetic epilepsy with febrile seizures plus, suggesting common genetic etiological factors.