Voyager Therapeutics Inc., the gene therapy startup led by erstwhile Biogen Inc. executive Al Sandrock, has a new deal with a San Diego biotech that's worth up to $4.2 billion. By 1 p.m. Monday, Voyager share prices had risen slightly, though not quite enough to match that valuation: They were trading at $7.72 each, an 11% increase over the day. That enzyme breaks down a large molecule, glucocerebroside, into a sugar and a simple fat molecule. Mutations in GBA1 disrupt that breakdown process, playing a role in Parkinson's as well as Gaucher disease and others. Engineered capsids are thought to enable gene therapies -- which are typically delivered inside of harmless viruses called adeno-associated viruses, or AAVs -- to get to their cellular destinations more safely and precisely. The two were in fact working on a Parkinson's program until last February, when, following an FDA-mandated clinical hold, Neurocrine decided to terminate the agreement. That program had a different target, though: the aromatic L-amino acid decarboxylase enzyme, or AADC, not GBA1. 'We look forward to expanding our engagement with Neurocrine Biosciences, with whom we already enjoy a strong relationship."