Claims about a treatment for Alzheimer’s should be met with caution

A DRUG THAT slowed the progress of Alzheimer’s disease would be both a boon to humanity and a cash cow for the firm that developed it. Hence the rollercoaster ride enjoyed by the shares of Biogen, a biotechnology company based in Cambridge, Massachusetts, which hopes to be the firm in question. The recent surge in its share price (see chart) followed its announcement, on October 22nd, that it would soon seek approval in America for aducanumab, a molecule it believes will fit the bill.Aducanumab is a type of drug known as a monoclonal antibody. Antibodies are specialised protein molecules that form part of the immune system. They include so-called hypervariable regions, the exact chemistry of which differs from one type of antibody to another. The specifics of the hypervariable region cause it to bind with great fidelity to some other molecule, usually part of a pathogen, stopping that molecule working and marking it for destruction by other parts of the immune system.