Task: Question Answering
Input (English): Context: The first step in the management of restless legs syndrome (RLS) is to identify, and if possible to treat any condition which might cause or worsen RLS, such as iron deficiency or some drug treatments. The patients suffering from RLS should be prompted to keep a healthy sleep schedule. Drug treatment should be restricted to patients with a clear clinical diagnosis, decided on an individual basis, when the clinical impact is serious. Four drug classes are central to the treatment of RLS: dopaminergic agents, some antiepileptics, opioids, and benzodiazepines. Dopaminergic agonists are the treatment of choice, especially when daily treatment is indicated, or if the symptoms are severe. Two dopaminergic agonists are licensed in France for the treatment of RLS: ropinirole (Adartrel) and pramipexole (Sifrol). After initiation of treatment, the patients should benefit from a regular follow-up in order to evaluate the efficacy of treatment and to identify possible side-effects. Special care should be given to the detection of augmentation, a phenomenon characterized by a paradoxical worsening of the symptoms with treatment. Some particular conditions, such as RLS comorbid with renal insufficiency, during pregnancy, and in the child are discussed. 
 Question: Which deficiency is the cause of restless leg syndrome?
Output (English): iron