What causes restless leg syndrome?

See below. Maybe genetic, but more often is sporadic without family history. May be related to problems with iron metabolism.
A few things. To say the least, there are quite a few things that cause rls. First can be genetics especially if symptoms begin earlier than age 45. Other things iron deficiency, thyroid issues, b12/folate deficiencies. Also a lot of medications can cause. This is not to mention a number of other medical problems including diabetes, chronic pain issue and absorption problems that go with it.
Veins or neurologic. Can either be a primary neurologic condition of unknown cause, or due to leaking of valves in veins of the legs, i.e. Venous insufficiency, which is very treatable. Neurologic type is treated only with medications but procedures to close leaking veins ('ablation') can improve or cure the venous type! See a vein doctor and a sleep or neurology md...