<prompt> MCardles syndrome is due toDeficiency of glucose-6-phosphataseAbsence of muscle phosphorylaseDeficiency of liver phosphorylaseDeficiency of liver phosphorylase kinase  <response>: McArdle disease also known as glycogen storage disease type V is a disorder affecting muscle metabolism. The condition is caused by the lack of an enzyme called muscle phosphorylase. This results in an inability to break down glycogen fuel stores. McArdle disease leads to pain and fatigue with strenuous exercise. Ref Robbins 9e pg 153 