The type of Ab determines the age of onset (for example patients with AChR Abs typically have a bimodal early-onset or late-onset disease), frequency of associated thymoma (very common in the forms associated with AChR Abs, exceptional in those associated with MuSK Abs), clinical phenotype and severity (anti-MuSK myasthenia gravis has often more severe weakness and involves bulbar muscles more often than anti-AChR forms), and response to treatment (MuSK-associated forms usually have less favourable response to symptomatic treatment and immunotherapies, see below). The gene discussed is MUSK; the disease is thymoma.