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Kind of confused here. The concepts discussed here are from 2 similar questions on UWorld but no question details will be posted.
One UW question (in the explanation) states that homocystinuria is most commonly caused by cystathionine beta synthase mutations and presents with marfanoid habitus, ectopia lentis, developmental delay, and thromboembolic complications.
Another UW question states that the most common genetic cause of hyperhomocysteinemia is methylene THF reductase (MTHFR) mutations and presents with thromboembolic complications, but also can be caused by mutations in methionine synthase, B12 deficiency, or folate deficiency.
I realize you can distinguish the causes of elevated homocysteine with low methionine by looking at other sx :
- MTHFR defect or folate deficiency MAY show megaloblastic anemia but there will be normal MMA levels and no periph neuropathy
- Methionine Synthase defect will show no anemia
- B12 deficiency will show megaloblastic anemia with elevated MMA / neuropathy
But I am just so confused at the naming. Why are they named differently (e.g. one elevated in the urine vs one in the blood), and are there any other differences (such as presentation) obviously besides buildup of Methionine + cysteine becoming essential AA in CBS mutations/B6 deficiency vs lack of Methionine and need for its supplementation in MTHFR mutations/Methionine Synthase Mutations/B12 deficiency? Like, does one just have elevated homocystiene in the urine and one in the blood?
One UW question (in the explanation) states that homocystinuria is most commonly caused by cystathionine beta synthase mutations and presents with marfanoid habitus, ectopia lentis, developmental delay, and thromboembolic complications.
Another UW question states that the most common genetic cause of hyperhomocysteinemia is methylene THF reductase (MTHFR) mutations and presents with thromboembolic complications, but also can be caused by mutations in methionine synthase, B12 deficiency, or folate deficiency.
I realize you can distinguish the causes of elevated homocysteine with low methionine by looking at other sx :
- MTHFR defect or folate deficiency MAY show megaloblastic anemia but there will be normal MMA levels and no periph neuropathy
- Methionine Synthase defect will show no anemia
- B12 deficiency will show megaloblastic anemia with elevated MMA / neuropathy
But I am just so confused at the naming. Why are they named differently (e.g. one elevated in the urine vs one in the blood), and are there any other differences (such as presentation) obviously besides buildup of Methionine + cysteine becoming essential AA in CBS mutations/B6 deficiency vs lack of Methionine and need for its supplementation in MTHFR mutations/Methionine Synthase Mutations/B12 deficiency? Like, does one just have elevated homocystiene in the urine and one in the blood?
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