SCN5A encodes for cardiac sodium channel conducting the sodium inward current (INa). The first reported SCN5A mutations were clustered in the regions functionally associated with channel inactivation. Subsequently, several allelic variants have been reported (http://pc4.fsm. it:81/cardmoc) and functional expression studies showed that, at variance with LQT1- and LQT2-asociated mutations, LQT3 defects cause a gain of function with an increased INa. Interestingly, SCN5A mutations are also found in other clinical syndromes allelic to LQT3: Brugada syndrome, cardiac conduction defect, and sinus node disease (for a review see Ref. ). The prevalence of LQT3 among LQTS patient is estimated to be 10-15%.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.