Congenital myasthenic syndrome (Jack Russell terrier type) is an inherited Neuromuscular Disease affecting dogs. Affected dogs typically present around 6-7 weeks of age with severe exercise-induced weakness leading to collapse. During episodes of weakness dogs will have decreased reflexes in all limbs and a short-strided gait that progressively worsens until they collapse. Weakness resolves after rest and dogs are clinically normal between episodes of weakness. Dogs develop resistance to treatments used for a similar, acquired form of the disease known as myasthenia gravis, and may be humanely euthanized within 3 months of age due to disease severity.