Myasthenia gravis (MG) is an autoimmune disease in which antibodies bind to acetylcholine receptors or to functionally related molecules in the postsynaptic membrane at the neuromuscular junction. The antibodies induce weakness of skeletal muscles, which is the sole disease manifestation. The weakness can be generalized or localized, is more proximal than distal, and nearly always includes eye muscles, with diplopia and ptosis. The pattern of involvement is usually symmetric, apart from the eye involvement, which is often markedly asymmetric and involves several eye muscles. The weakness typically increases with exercise and repetitive muscle use (fatigue) and varies over the course of a day and from day to day, often with nearly normal muscle strength in the morning (summary by Gilhus, 2016).

Autoimmune polyendocrine syndrome type II (APS2), or Schmidt syndrome, is characterized by the presence of autoimmune Addison disease in association with either autoimmune thyroid disease or type I diabetes mellitus, or both. Chronic candidiasis is not present. APS2 may occur at any age and in both sexes, but is most common in middle-aged females and is very rare in childhood (summary by Betterle et al., 2004). See 240300 for a phenotypic description of autoimmune polyendocrine syndrome type I (APS1).

Thymomas are low-grade epithelial cancers of the thymus. Familial occurrence of thymoma is rare.