Nonconvulsive Status Epilepticus and Ring Chromosome 20
ABSTRACT & COMMENTARY
Source: Inoue Y, et al. Ring chromosome 20 and nonconvulsive status epilepticus. A new epileptic syndrome. Brain 1997;120:939-953.
Ring chromosome 20 (rc 20) has been considered a rare abnormality. Inoue et al, however, now report that the abnormal gene causes recurrent complex partial status epilepticus (CPSE) and raises the possibility that RC 20 may be more common than previously recognized.
The authors performed chromosome analysis on two patients with recurrent CPSE (one because of short stature and the other because of a family history of heart disease). Both had RC 20.
To expand their series, the authors then examined eight patients who had been admitted to their Epilepsy Center with nonconvulsive status epilepticus in the preceding year. Remarkably, four of these had RC 20.
RC 20 has been considered rare. Previously, only 22 cases have been reported. However, since Inoue et al easily found four cases of RC 20 in their own hospital in one year, it may be more common than we currently recognize. Alternatively, there may be a geographic cluster of this genetic abnormality in central Japan.
Inoue et al reviewed the 22 earlier case reports of RC 20. Among the 22 patients, 20 had seizures. From the available information derived from those 20 plus their own six patients, Inoue et al provide the following clinical profile of the RC 20 epilepsy syndrome:
1. Prolonged complex partial seizures lasting 10-50 minutes
2. Daily seizures
3. Ictal EEG predominated by high-voltage slow (delta frequency) waves with occasional unilateral or bifrontal spike-waves
4. Medication-resistant seizures
5. Average age of onset = 4.5 years (range, 1 day-14 years)
6. Normal neurological examination and neuro-imaging
RC 20 causes epilepsy by an unknown mechanism. However, chromosomal region 20q appears to make a particularly significant contribution to the genetics of epilepsy. Benign familial neonatal convulsions and autosomal dominant nocturnal frontal lobe epilepsy also map to this region (Phillips, et al. Nat Genet 1995; 10:117-118; Leppert, et al. Nature 1989;337:647-648).
COMMENTARY
Future studies of patients with the RC 20 epilepsy syndrome may yield information concerning molecular genetic mechanisms by which these and other inherited seizure disorders are produced. For the present, early identification of RC 20 in patients with complex partial seizures might prove of practical value. Since such patients are normal save for their severe epilepsy and would be expected to have normal reproductive lives, genetic counseling concerning risks to offspring would be important. With medication-resistant seizures to be expected, earlier-than-usual consideration of epilepsy surgery or vagus nerve stimulation might be appropriate. Since seizures related to RC 20 typically last for many minutes, at-home administration of benzodiazepines at ictal onset could be implemented if circumstances permit. drl
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