Myasthenia gravis is a condition that happens when communication between nerves and muscles breaks down. This causes muscles to feel weak and get tired quickly. This condition may affect any of the muscles you control, called voluntary muscles. Certain muscle groups are more commonly affected than others. These include muscles in the face, throat, arms and legs. Your eyelids may droop, you may have double vision, trouble speaking or eating, or you may have trouble holding up your head because of weak neck muscles. Myasthenia gravis can happen at any age. But it's more common in people younger than 40 who were assigned female at birth and people older than 60 who were assigned male at birth. There's no way to prevent or cure myasthenia gravis. But treatment can help manage symptoms.