We predefined three CSF metabolite ratios that might change in the presence of specific predicted derangements of the KP—3‐HK:KYNA as a reflection of the ratio of the main protective and neurotoxic metabolites whose synthetic enzymes have been implicated in HD; KYNA:KYN as a measure of the activity of the KATs and 3‐HK:KYN as a measure of the activity of KMO. The gene discussed is KMO; the disease is Huntington disease.