Alnylam Pharmaceuticals Inc. and Genzyme, both of Cambridge, said Monday that they have formed an exclusive alliance to develop and commercialize RNAi therapeutics for the treatment of transthyretin-mediated amyloidosis, or ATTR, in Japan and other Asia-Pacific countries.

ATTR is a rare, debilitating, hereditary disease that damages the nervous system and heart, resulting in a life expectancy of 5 to 15 years.