▁also ▁be ▁associated ▁with ▁auto imm une ▁dise ases , ▁such ▁as ▁hypoth y roid ism ▁( an ▁under active ▁thy roid ▁g land ) ▁or ▁di ab etes ▁m ell it us ▁type ▁ 1 . ▁My as then ia ▁gra vis , ▁too , ▁may ▁happen ▁in ▁the ▁presence ▁of ▁tum ors ▁( th ym oma , ▁a ▁tum or ▁of ▁the ▁th ym us ▁in ▁the ▁ch est ); ▁people ▁with ▁M G ▁without ▁a ▁tum or ▁and ▁people ▁with ▁LE MS ▁without ▁a ▁tum or ▁have ▁similar ▁gen etic ▁variations ▁that ▁seem ▁to ▁pre dis pose ▁them ▁to ▁these ▁dise ases . ▁H LA - DR 3 - B 8 ▁( an ▁H LA ▁sub type ), ▁in ▁particular , ▁seems ▁to ▁pre dis pose ▁to ▁LE MS . ▁ ▁Mechan ism ▁In ▁normal ▁neur om us cular ▁function , ▁a ▁n erve ▁imp ulse ▁is ▁carried ▁down ▁the ▁ax on ▁( the ▁long ▁projection ▁of ▁a ▁n erve ▁cell ) ▁from ▁the ▁sp inal ▁cord . ▁At ▁the ▁n erve ▁ending ▁in ▁the ▁neur om us cular ▁j unction , ▁where ▁the ▁imp ulse ▁is ▁transferred ▁to ▁the ▁mus cle ▁cell , ▁the ▁n erve ▁imp ulse ▁leads ▁to ▁the ▁opening ▁of ▁voltage - g ated ▁calci um ▁channels ▁( V G CC ), ▁the ▁infl ux ▁of ▁calci um ▁ ions ▁into ▁the ▁n erve ▁terminal , ▁and ▁the ▁calci um - dependent ▁trigger ing ▁of ▁syn apt ic ▁ves icle ▁fusion ▁with ▁pl asma ▁memb rane