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I respectfully disagree. Receptor tyrosine kinase protein MuSK is a signaling protein involved in the development of the neuromuscular junction, which is also held in place by rapsyn. Antibodies to this protein interfere with the NMJ and cause MG symptoms.
Muscarinic acetylcholine receptors, or mAChRs, are acetylcholine receptors that form G protein-coupled receptor complexes in the cell membranes of certain neurons and other cells. They play several roles, including acting as the main end-receptor stimulated by acetylcholine released from postganglionic fibers in the parasympathetic nervous system. Muscarinic receptors are so named because they are more sensitive to muscarine than to nicotine. Their counterparts are nicotinic acetylcholine receptors (nAChRs), receptor ion channels.
So MuSK and mAChR are two totally different proteins. Antibodies to mAChR may not cause problems with muscle NMJs to contribute to MG, but I strongly suspect they can cause havoc with various organs controlled by the autonomic nervous system, giving rise to many odd symptoms that stump doctors.
Thus drugs that affect the transmission of acetylcholine in the NMJ and help with MG symptoms might also improve non-MG symptoms that might be appearing in the autonomic nervous system, such as gastroparesis in the digestive system. Those not affected with gastroparesis might find pyridostigmine causes digestive upset, but my daughter who had gastroparesis discovered her gut started moving again and acting more normally once she started on pyridostigmine, which implies something going on with the mAChR related to her nAChR antibodies and acetylcholine transmission.
The lungs seems to be a hybrid between the autonomic nervous system (parasympathetic – rest and digest, sympathetic – fight or flight, and enteric) and the central nervous system (conscious control). During the day, many muscles are involved with breathing, and can be consciously controlled but for the most part we don’t think about or notice breathing, but at night, when we fall asleep, the only muscle that stays awake is the diaphragm, when all other muscles enter a sleep based paralyzation. Thus MG antibodies that attack some lung muscles might not be making a noticeable difference during the day, but can cause difficulty breathing during sleep at night, necessitating the need for a BiPAP machine.