Elevated concentrations of elements and abnormalities of neuromuscular junctions in tongue muscles of Down's syndrome.

X-ray spectrometry was used to measure the concentrations of calcium, iron, copper and zinc in tongue muscles from patients with Down's syndrome (DS) undergoing partial glossectomy. Similar measurements on samples from autopsies served as controls. Electron microscopy was used to examine neuromuscular junctions. The calcium and copper were significantly elevated and correlated in DS while the iron and zinc showed little change. The copper increase is probably connected with the known high level of Zn-Cu superoxide dismutase (SOD), coded for by chromosome 21. (In DS there is a trisomy 21). The excess of SOD may interfere with free radicals needed for excitation-contraction coupling and may be instrumental in damaging junctional membranes. The high calcium may result from such membrane damage. It is suggested that neuromuscular junction pathology, either genetic or free radical induced, may cause the tongue weakness in DS.