I'll google it for you....
Here's what wikipedia says
a neuromuscular disease leading to fluctuating muscle weakness and fatiguability. It is an autoimmune disorder, in which weakness is caused by circulating antibodies that block acetylcholine receptors at the post-synaptic neuromuscular junction,[1] inhibiting the stimulative effect of the neurotransmitter acetylcholine. Myasthenia is treated medically with cholinesterase inhibitors or immunosuppressants, and, in selected cases, thymectomy. At 200 - 400 cases per million it is one of the less common autoimmune disorders.[1]
and here's the link i found when googling it <img src="i/expressions/face-icon-small-smile.gif" border="0">
<a target=_blank class=ftalternatingbarlinklarge href="http://en.wikipedia.org/wiki/Myasthenia_gravis">http://en.wikipedia.org/wiki/Myasthenia_gravis</a>