Table 3.

Phenotypes and electrophysiological changes associated with KCNC1 variants.

Phenotype	Progressive myoclonus epilepsy	Developmental and epileptic encephalopathy	Developmental encephalopathy without seizures
KCNC1 variant	p.Arg320His	p.Ala421Val	p.Arg339X	p.Gln492X	p.Arg317His
Seizure types	Myoclonic tonic‐clonic (infrequent)	Myoclonic other generalized focal	Nil	Nil	Nil
Cognitive function	Normal with mild late decline in some	Moderate‐severe ID	Moderate ID	Mild‐moderate ID	Mild ID
Electrophysiological characteristics
Whole‐cell current	Marked reduction	Marked reduction	Marked reduction	Moderate reduction	Marked reduction
Current‐voltage relationship	Gain of function	No change	No change	No change	No change
Dominant negative effect	Yes	No	Yes	Unknowna	Yes

^aNot assessed as current with mutant was not markedly reduced (see Methods).