The invention relates to the use of angiogenin, or a fragment or variant thereof, to treat diseases or conditions characterised by neuronal injury or death, or axonal degeneration, especially neurodegenerative diseases such as Amyotrophic Lateral Sclerosis (ALS). The invention also describes a plurality of mutations of the human angiogenin gene which are associated with a neurodegenerative disease phenotype, and particularly a ALS phenotype. Also described is a method of assessing whether an individual is afflicted with, or generically predisposed to develop, a disease or condition characterised by neuronal injury or death, or axonal degeneration.