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Myasthenia gravis is an autoimmune disease of man characterized by remitting and relapsing muscle fatigability. Although the etiology and pathogenesis are incompletely understood, the presence of circulating antibodies directed against the nicotinic acetylcholine (ACh) receptor in 80--90% of patients with myasthenia gravis and the identification of immune complexes at their neuromuscular junction have helped explain the altered neuromuscular transmission. The ACh receptor antibodies do not block access of ACh to the receptor, but do decrease the number of receptors by accelerating their degradation both in rat myotube cultures and in vivo models. In vitro these antibodies play a major role in myasthenia gravis. However, correlations of antibody titers with the clinical state following thymectomy or in neonatal myasthenia suggest that host factors may be equally important in determining whether the ACh receptor antibodies will result in clinical myasthenia.

Two women, heterozygous for X-linked adrenoleukodystrophy, contained striated adrenocortical cells without inflammation and central nervous system demyelinative lesions. Only one was symptomatic neurologically; neither exhibited hypoadrenalism. These findings further document the variability of adrenoleukodystrophy heterozygotes and provide evidence that the major pathologic differences between hemizygote and heterozygote are quantitative in nature.