A 9 yr old girl has difficulty in combing hairs and climbing upstairs since 6 months. She has Gower’s sign positive and maculopapular rash over metacarphalangeal joints. What should be the next appropriate investigation to be done?
Correct Answer: Creatine kinase
Description: The mitochondrial creatine kinase (CKm) is present in the mitochondrial intermembrane space, where it regenerates phosphocreatine (PCr) from mitochondrially generated ATP and creatine (Cr) impoed from the cytosol. Apa from the two mitochondrial CK isoenzyme forms, that is, ubiquitous mtCK (present in non-muscle tissues) and sarcomeric mtCK (present in sarcomeric muscle), there are three cytosolic CK isoforms present in the cytosol, depending on the tissue. Whereas MM-CK is expressed in sarcomeric muscle, that is, skeletal and cardiac muscle, MB-CK is expressed in cardiac muscle, and BB-CK is expressed in smooth muscle and in most non-muscle tissues. Mitochondrial mtCK and cytosolic CK are connected in a so-called PCr/Cr-shuttle or circuit. PCr generated by mtCK in mitochondria is shuttled to cytosolic CK that is coupled to ATP-dependent processes, e.g. ATPases, such as acto-myosin ATPase and calcium ATPase involved in muscle contraction, and sodium/potassium ATPase involved in sodium retention in the kidney. The bound cytosolic CK accepts the PCr shuttled through the cell and uses ADP to regenerate ATP, which can then be used as energy source by the ATPases (CK is associated intimately with the ATPases, forming a functionally coupled microcompament). PCr is not only an energy buffer but also a cellular transpo form of energy between subcellular sites of energy (ATP) production (mitochondria and glycolysis) and those of energy utilization (ATPases)Thus, CK enhances skeletal, cardiac, and smooth muscle contractility, and is involved in the generation of blood pressure Finally, high CK in the blood may be an indication of damage to CK-rich tissue, such as in rhabdomyolysis, myocardial infarction, myositis and myocarditis. This means creatine kinase in blood may be elevated in a wide range of clinical conditions including the use of medication such as statins; endocrine disorders such as hypothyroidism;and skeletal muscle diseases and disorders including malignant hypehermia,and neuroleptic malignant syndrome Ref Harrison20th edition pg 2567
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