Congenital myopathy with myasthenic-like onset is a rare neuromuscular disorder characterized by muscle weakness and fatigue that begins in infancy or early childhood. It is caused by mutations in the gene that codes for the protein titin, which is involved in muscle contraction. Symptoms include muscle weakness, fatigue, and difficulty with movement. In some cases, the disorder can progress to respiratory failure. Treatment is supportive and may include physical therapy, medications, and assistive devices.