A 2-Month-Old Boy With Yellow Eyes: Osmosis USMLE Study Question of the Week

October 30, 2020

Pyruvate kinase deficiency is an inherited metabolic disorder of the enzyme pyruvate kinase, which affects the survival of erythrocytes. Both autosomal dominant and recessive inheritance have been observed with the disorder; classically, and more commonly, the inheritance is autosomal recessive. Pyruvate kinase deficiency is the second most common cause of enzyme-deficient hemolytic anemia, following glucose-6-phosphate dehydrogenase deficiency.

Erythrocytes manufacture adenosine triphosphate (ATP) through glycolysis. A deficiency in pyruvate kinase, the enzyme that potentiates the last step of glycolysis results in erythrocytes with decreased ATP. Due to the unavailability of adequate ATP, all active processes in the erythrocyte to a halt. Sodium potassium ATPase pumps are the first to stop, and because the cell membrane is more permeable to potassium than sodium, potassium leaks out. Water moves this potassium out down its concentration gradient out of the cells, resulting in cellular desiccation.

Echinocytes (from the Greek word echinos, meaning "hedgehog" or "sea urchin"), which are seen in pyruvate kinase deficiency, are a type of erythrocyte that have an abnormal cell membrane characterized by many small, evenly spaced thorny projections.

Major Takeaway: Pyruvate kinase deficiency is an inherited metabolic disorder of the enzyme pyruvate kinase which affects the survival of erythrocytes. It is characterized by the presence of echinocytes.

Read more on pyruvate kinase deficiency.

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