Restless legs syndrome in monozygotic twins: clinical correlates.

To better understand genetic characteristics of restless legs syndrome (RLS) and identify nongenetic factors that may influence phenotype, the authors studied 12 identical twins in which at least one member expressed RLS. Ten of the 12 twin pairs were concordant for RLS symptoms. Despite the high concordance rate, the disease severity, age at onset, and symptom descriptions often varied between twins. Birth order, birth weight, and serum ferritin levels did not predict RLS severity or age at onset.