Print OverviewCongenital myasthenic syndromes are rare hereditary (genetic) conditions resulting from a defect at the junction where your nerve stimulates muscle activity. That defect causes muscle weakness. Congenital myasthenic syndromes may affect your nerve cells (presynaptic), your muscle cells (postsynaptic), or the space between your nerve and muscle cells (synaptic).Products & ServicesA Book: Mayo Clinic Family Health Book, 5th EditionNewsletter: Mayo Clinic Health Letter — Digital EditionShow more products from Mayo Clinic By Mayo Clinic Staff Congenital myasthenic syndromes care at Mayo Clinic Request an appointment Doctors & departments Nov. 19, 2016 Print Show references Engel AG, et al. Congenital myasthenic syndromes: Pathogenesis, diagnosis, and treatment. The Lancet. Neurology. 2015;14:420. De Souza PBS, et al. Clinical and genetic basis of congenital myasthenic syndromes. Arch Neuropsiquiatria. 2016;74:750. Engel AG. Congenital myasthenic syndromes. In: Neuromuscular Disorders of Infancy, Childhood, and Adolescence. 2nd ed. Philadelphia, Pa.: Elsevier; 2015. http://www.clinicalkey.com. Accessed Oct. 13, 2016. Riggin EA. Decision Support System. Mayo Clinic, Rochester, Minn. July 1, 2016. Related Products & Services A Book: Mayo Clinic Family Health Book, 5th Edition Newsletter: Mayo Clinic Health Letter — Digital Edition Show more products and services from Mayo Clinic Congenital myasthenic syndromesSymptoms&causesDoctors&departmentsCare atMayoClinic Advertisement Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. Advertising & Sponsorship Policy Opportunities Ad Choices Mayo Clinic Press Check out these best-sellers and special offers on books and newsletters from Mayo Clinic Press. Mayo Clinic on Incontinence - Mayo Clinic PressMayo Clinic on IncontinenceThe Essential Diabetes Book - Mayo Clinic PressThe Essential Diabetes BookMayo Clinic on Hearing and Balance - Mayo Clinic PressMayo Clinic on Hearing and BalanceFREE Mayo Clinic Diet Assessment - Mayo Clinic PressFREE Mayo Clinic Diet AssessmentMayo Clinic Health Letter - FREE book - Mayo Clinic PressMayo Clinic Health Letter - FREE book CON-20209446 Patient Care & Health Information Diseases & Conditions Congenital myasthenic syndromes