ring chromosome 20

This catastrophic epileptic syndrome was first described by Atkins et al. in 1972.

The clinical presentation is characterized by mental retardation, behavioral disorders, and epilepsy.

The absence of (or only minimal) dysmorphic features usually delay accurate diagnosis.

The seizures typically start around age 5 years, are of several types, and are refractory to therapy. However, nocturnal frontal lobe seizures are frequently encountered, as well as nonconvulsive status epilepticus and prolonged confusional states.

The electroencephalogram is characterized by a slow background and fronto-temporal interictal epileptiform activity, and ictally by generalized spikes and waves, subtle frontal seizures, or nonconvulsive status epilepticus.

Several pathophysiologic mechanisms were suggested to explain this intractable epilepsy. Among these, the possibility of a channelopathy involving the delection of two known epilepsy genes during chromosome ring formation has been raised: the CHRNA4 gene (acetylcholine receptor), known to cause autosomal-dominant nocturnal frontal lobe epilepsy, and the KCNQ2 (potassium channel) gene, known to cause benign familial neonatal convulsions, both located at 20qter.

References

 Bernard G, Shevell MI. Channelopathies: a review. Pediatr Neurol. 2008 Feb;38(2):73-85. ReviPMID: 18206787