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Metabolic reasoning
Whole-map thinking. Each case is a chain of cause → effect that ends in the labs: why DKA has ketones and hyperglycemia, why a drinker goes hypoglycemic, why an infant with MCAD deficiency spills no ketones. Walk through the chain on the map, then order it yourself, answer the why questions, or diagnose from the labs.
Lactic acidosis in an infant that improves on a fat diet
A 4-month-old boy has severe developmental delay, hypotonia, seizures and a persistent lactic acidosis that worsens with carbohydrate feeds and improves on a high-fat diet.
| Lactate | ↑↑ | ↑ |
| Pyruvate | ↑↑ | ↑ |
| Lactate:pyruvate ratio | normal (<20) | |
| Alanine | ↑ | ↑ |
| Glucose | normal |
Pyruvate dehydrogenase complex deficiency (E1α, X-linked)
Pyruvate has three exits — acetyl-CoA, lactate, alanine. Close the first and the other two overflow; feed fat to bypass it.
Condition card: Pyruvate dehydrogenase complex (PDHC) deficiency →Pathway map →
- Glucose → glycolysis → pyruvate normally; PDH E1α (needs TPP) is deficient → pyruvate can't become acetyl-CoA.
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Pathways involved: PDH & TCA cycle, Glycolysis, Ketogenesis & ketone body use. Drill them one at a time in Metabolic pathways.