Heart Health

 Test

Which of the following could also appear as a peak on this patient’s lab value chart?

A) Phenyllactate

B) Orotic Acid

C) Oxidized Tetrahydrofolate

D) Homocysteine

E) Epinephrine

Explanation:The correct answer is Choice D: Homocysteine. This patient has methylmalonic acidemia, indicative of a cobalamin/B12 deficiency. Other symptoms that prove this diagnosis are severely low hemoglobin (indicative of anemia, specifically macrocytic), encephalopathy (attributable to the patient’s secondary hyperammonemia, which is resultant of organic acids like MMA inhibiting NAG Synthase which causes an increase in free ammonia from lack of CPSI stimulation). The ataxia is attributable to neurological abnormalities due to deficiency of S-adenosylmethionine for neurotransmitter synthesis. There is therefore less epinephrine, less oxidized tetrahydrofolate (as more of it is shunted to irreversibly become reduced methyl-FH4 and remain in that state via the methyl trap), and more homocysteine (as it is unable to be converted into methionine. Orotic acid and phenyllactate (a phenylketone) are unrelated in this instance. Essentially, there are many disorders that can cause hyperammonemia (OTC Deficiency, Cirrhosis, etc.), but organic acidurias can lead to hyperammonemia via inhibition of NAGS and thus suppression of the Urea Cycle.