Clinical electrophysiological characteristics of cyclin-dependent kinase-like 5 gene induced developmental and...

To delineate the clinical and electrophysiological characteristics of the cyclin-dependent kinase-like 5 gene-induced developmental and epileptic encephalopathy.

We retrospectively analyzed serial video-EEG recordings and clinical data from 22 patients with pathogenic CDKL5 variants at a single center.

All CDKL5 variants were de novo. The age of onset of epileptic seizures ranged from 8 days (d) to 1 year (Y) and 10 months (m), with a median age of 2 months. The types of epileptic seizures at onset were as follows: 7 focal seizures (median age: 3 m); 5 tonic seizures (median age: 20 d); 5 epileptic spasms (median age: 4 m); 3 bilateral tonic-clonic seizures (median age: 40 d); and 2 focal seizures accompanied by epileptic spasms (median age: 2 m). Serial monitoring (87 sessions) revealed that background activity was normal in all patients under 6 months, with prominent occipital interictal discharges. Notably, both background activity and interictal discharges deteriorated with age. The main seizure type evolved to epileptic spasms in most patients. Six patients already had developmental delay before the onset of epileptic seizures. As of the last follow-up (July 2025), a total of 21 patients had experienced developmental delay or regression after seizure onset.

EEG features in patients with cyclin-dependent kinase-like 5 gene-induced developmental and epileptic encephalopathy: physiological rhythms are normal within 6 months of age, with a progressive deterioration in background activity and interictal discharges as the disease advances. Seizure types are diverse from the onset, with focal seizures being the most common at the beginning; epileptic spasms are the most prevalent seizure type during the disease course and can persist, whereas the previously recognized characteristic hyperkinetic-tonic-clustered epileptic spasm seizures are uncommon.