Abstract: Compounds of general formula (I) wherein (I) R1-R4 are each independently selected from H and deuterium; and at least one of R1-R4 is deuterium. The compounds have been found to be particularly useful for treating neurodegenerative conditions and in particular but not exclusively conditions such as motor neurone disease.

Abstract: A reagent selected from cholestenoic acid or an inhibitor of an enzyme in the cholestenoic acid biosynthetic or metabolic pathway for use in the treatment of neurodegenerative conditions. In particular, the reagent is a cholestenoic acid of a particular form, such as 3?,7?-dihydroxycholest-5-en-26-oic (3?,7?-diHCA), not previously associated with neural tissue or CSF. Pharmaceutical compositions, methods of treatment or prevention of neurodegenerative conditions as well as diagnostic methods and novel biomarkers form further aspects of the invention.