An improved method for diagnosing autoimmune or genetic diseases is provided in this disclosure. In particular, a method to diagnose diseases affecting the tissues of organs selected from the group of spleen, brain, heart, kidney, thyroid, eye, skin, intestine, liver, pancreas, adrenal gland, prostate and lungs or from the tissues selected from the group of muscles and bones or other tissues. More specifically, the present invention provides an improved method for diagnosing diseases affecting neuromuscular junctions.