Certain gene mutations lead to weakness and fatigability in muscles. There are a large number of recognized syndromes with these symptoms, collectively called myasthenia gravis and some are present at birth in which case they are referred to as congenital myasthenic syndromes. They are usually nonprogressive conditions.
In many cases mothers are aware of decreased fetal movements. At birth in the majority of these syndromes, the cry is weak and infants may struggle to breath. Sucking is weak and overall muscle tone is decreased. Motor development is often delayed and many children are unable to run and keep up with their peers. The upper eyelids droop (ptosis) and patients may not be able to move their eyes in all directions (ophthalmoparesis). As they grow, difficulties in swallowing, weakness of the tongue, and difficulty speaking often become apparent. All of these signs and symptoms may worsen dramatically during an acute illness.
In some cases, ventilators are required for adequate oxygenation and tube feeding may become necessary for adequate nutrition.
The majority of these myasthenic syndromes are inherited in autosomal recessive patterns. Both parents are normal but if they are both carriers, then each of their children will have a 25% chance of inheriting both mutations which cause myasthenia.
Pediatricians are likely to make the diagnosis since the symptoms begin at birth. Breathing must be monitored and care taken to ensure that the airways are clear; sometimes a ventilator is required acutely. Depending upon the type of gene mutation, certain drugs can improve muscle function and reduce fatigue. Many individuals live a nearly normal lifespan but sudden death, especially in infants, is a constant risk. There is a wide variation in the severity of weakness and some patients are confined to a wheelchair. Acute illnesses need prompt attention and respiratory infections especially should be treated vigorously. Lifelong monitoring and clinical care are required.