Most are complex ie clonic movements, minor changes in tone (eg head drops, or held object dropped),
automatisms (repetitive movements of eyes, mouth).
No myoclonus (else likely to be juvenile myoclonic epilepsy). Some get generalised tonic-clonic seizures in adolescence but these are infrequent and respond well to treatment.
Precipitated by flashing lights, sleep deprivation, hyperventilation (90% detected after 3 minutes – get them to count aloud)
Atypical have more gradual onset, last longer, have more obvious changes in tone – but continuum
The SLC2A1 gene codes for the glucose transporter protein type 1 (GLUT1), involved in glucose transfer across blood-brain barrier. Heterozygous mutations are mostly de novo but may be inherited as AD trait. There may be mild learning and motor delay, but more often it presents with early absence seizures – GLUT1 mutations are present in up to 10% of early childhood absence epilepsy (ie under 5yrs). The importance of the diagnosis is that the seizure are often intractable to valproate and ethosuximide, whereas a ketogenic diet will be effective.
EEG shows sudden onset 3Hz spike and wave, esp with photic stimulation/hyperventilation. Interictal is often normal.
Clinically apparent if more than 3 seconds of activity, but detailed neuropsych assessment suggests that non-clinical absences do cause functional impairment. Atypical have slower spike waves and rarely have normal interictal.
60-80% full remission, usually during puberty; in most cases, absences disappear on monotherapy but there are resistant cases (unpredictable, other than SLC2A mutations).