Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.
One example: In 1582 the united provinces invited francis, duke of anjou to lead them; but after a failed attempt to take antwerp in 1583, the duke left the netherlands again. after the assassination of william of orange (10 july 1584), both henry iii of france and elizabeth i of england declined the offer of sovereignty. however, the latter agreed to turn the united provinces into a protectorate of england (treaty of nonsuch, 1585), and sent the earl of leicester as governor-general. this was unsuccessful and in 1588 the provinces became a confederacy. the union of utrecht is regarded as the foundation of the republic of the seven united provinces, which was not recognized by the spanish empire until the peace of westphalia in 1648.
Solution is here: In what year did francis, duke of anjou leave the netherlands?
Explanation: The generated question is perfect. Because the question is based on second sentence of the input passage and its answer is 1583.

Now, solve this: Prior studies, all using SPECT techniques, failed to find any differences for dopamine transporter (DAT) in restless legs syndrome (RLS) subjects. The distinct pharmacokinetic properties associated with SPECT-determined DAT along with rapid biodynamic changes in DAT may, however, have missed membrane-bound DAT differences. The current studies assessed real-time DAT binding potentials (BP) in striatum of RLS patients using (11)C-methylphenidate and PET techniques. RLS medications were stopped at least 11 days prior to the PET study. Clinical severity of RLS was also assessed. PET scans were performed at 2 different times of day (starting at 08:30 and 19:30) in separate groups of subjects. The primary outcome measure was total striatal DAT BP. Thirty-six patients with primary RLS and 34 age- and gender-matched controls. RLS subjects had significantly lower DAT binding in the striatum compared to controls on both the Day and the Night scans. DAT was decreased in putamen and caudate but not the ventral striatum of RLS subjects. There were no diurnal differences in DAT for the total group or for control and RLS separately. DAT BP did not correlate with any clinical measures of RLS. The current study found a significant decrease in DAT BP in two independent studies. These results when viewed along with prior RLS SPECT and autopsy studies of DAT, and cell culture studies with iron deficiency and DAT, suggest that membrane-bound striatal DAT, but not total cellular DAT, may be decreased in RLS.
Solution:
Which deficiency is the cause of restless leg syndrome?