10 years old Ramu has increasing muscle weakness and raised CPK levels. The most likely defect is in plasma membrane of –

Increase in CPK level with muscle weakness suggests muscle cell damage. Creatine kinase is an enzyme found mainly in → Skeletal muscle, Heart, Brain Its levels will be raised in the serum when any of the above mentioned cell is damaged. There are various isotypes of the enzyme which are specific for difference cells.                 Enzyme                                             Tissue Creatine kinase (MB isoenzyme)           Heart Creatine kinase (BB isoenzyme)             Brain Creatine kinase (MM isoenzyme)         Skeletal muscle Other enzymes elevated in muscle diseases   → Aldolase, Aminotransferases specially (ACT), Lactate dehydrogenase