USMLE Step 1 Questions: Nitrates, Vitamin B12 Deficiency & Mitochondrial Inheritance (Review 182)

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Q- Which one of the following classes of drugs decreases preload by increasing venous capacitance?

A- ACE inhibitors

B- Beta blockers

C- Nitrates

D- Thiazide diuretics

C- Nitrates cause dilatation of veins, which decreases preload, leading to reduced cardiac workload.

 

Q- A patient with vitamin B12 deficiency develops neurological symptoms. Which metabolic change is responsible?

A- Increased homocysteine only

B- Increased methylmalonic acid only

C- Increased homocysteine and methylmalonic acid

D- Decreased folate levels

C- Increased homocysteine and methylmalonic acid– B12 deficiency causes accumulation of both homocysteine and methylmalonic acid, leading to neurological dysfunction. B12 vs. folate: Homocysteine is elevated in both. Methylmalonic acid is the key test: it is elevated in B12 deficiency but normal in folate deficiency. Only B12 deficiency causes neurological damage (subacute combined degeneration), so giving folate alone can correct the anemia while the nerve damage continues.

 

Q- A patient has a mutation in mitochondrial DNA. Which pattern of inheritance is expected?

A- Autosomal dominant

B- Autosomal recessive

C- Maternal inheritance

D- X-linked inheritance

C- Maternal inheritance– Mitochondrial DNA is inherited exclusively from the mother.

 

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Dr Ray Makar
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