Patients with amyotrophic lateral sclerosis (ALS) have increased arginine dimethylation, and an asymmetrical dimethylarginine (ADMA) to l-arginine ratio could be a predictor of prognosis, say researchers. Ikenada and colleagues report that the immunoreactivity of protein arginine methyltransferase 1 (PRMT1) and its products in post-mortem spinal cord was increased in cord from four patients with ALS compared with cord from four patients without ALS. They also found that the concentration of ADMA in cerebrospinal fluid was significantly higher in 52 patients with ALS than in 21 controls. The team also showed that the ADMA to l-arginine ratio correlated with the rate of decline in the ALS Functional Rating Scale and that the ratio was an independent predictor of overall survival. A high ADMA to l-arginine ratio was a predictor of poor prognosis.