Pyruvate carboxylase deficiency

Pyruvate carboxylase deficiency (PCD) is a rare, inherited metabolic disorder caused by deficient activity of the enzyme pyruvate carboxylase, which plays a critical role in gluconeogenesis (the production of glucose), lipogenesis, and the replenishment of citric acid cycle intermediates (anaplerosis). The enzyme is encoded by the PC gene located on chromosome 11q13.2. Because pyruvate carboxylase is essential for energy metabolism in multiple organ systems, its deficiency leads to the accumulation of lactic acid and other metabolic byproducts in the blood, primarily affecting the brain, liver, and kidneys. Three clinical forms are recognized. Type A (infantile form) is characterized by moderate lactic acidemia, developmental delay, and intellectual disability, with onset typically in the first months of life. Type B (severe neonatal form) presents shortly after birth with severe lactic acidosis, hyperammonemia, hepatomegaly, and rapidly progressive neurological deterioration, often leading to death in early infancy. Type C (benign or intermittent form) is the mildest, with episodic metabolic acidosis but relatively preserved neurological function. Common symptoms across types include lactic acidosis, hypoglycemia, failure to thrive, seizures, hypotonia, and psychomotor retardation. There is currently no cure for pyruvate carboxylase deficiency. Treatment is largely supportive and aims to manage metabolic crises, correct acidosis, and optimize nutrition. Dietary strategies may include supplementation with citrate or aspartate to replenish citric acid cycle intermediates, avoidance of prolonged fasting, and a diet with controlled protein and carbohydrate intake. Biotin supplementation has been tried but is generally ineffective since the enzyme deficiency is not due to biotin deficiency. Prognosis varies significantly by type, with Type B carrying the poorest outcome and Type C having the most favorable long-term prognosis.

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