The Food and Drug Administration has approved Aegerion Pharmaceuticals’ request to market its first drug, a treatment for a rare inherited genetic disorder that can raise cholesterol to life-threatening levels. The condition is resistant to statins and other medications typically used to bring high cholesterol under control. The Cambridge biotech’s drug, Juxtapid, does carry a risk of liver toxicity, so it will come with a “black box” label — the FDA’s most serious warning level.