BioMarin Pharmaceutical Inc. doesn't back down from a tough rare disease. The Novato company (NASDAQ: BMRN), which made its name with enzyme-replacement therapies that tackle virtually unpronounceable orphan diseases like phenylketonuria and versions of mucopolysaccharidosis, expects to enroll the first patient by mid-year in an early-stage clinical trial in Batten Disease. CEO Jean-Jacques Bienaimé said BioMarin will file an investigational new drug application with the Food and Drug Administration…