The framework
Coenzyme form → reaction class → pathway and its rate-limiting step → most dependent tissue → functional loss, ordered by turnover rate. Each arrow is a question you must answer specifically; a vague answer at any step makes the final prediction useless.
Why specificity at each step matters
A cofactor that carries electrons can serve dozens of dehydrogenases, so its deficiency is broad; a cofactor that modifies one protein residue serves a narrow set of substrates, so its deficiency is narrow. Knowing the reaction class therefore already tells you how wide the symptom set should be. Knowing the pathway tells you which organ system is at risk. Knowing the rate-limiting position tells you whether the pathway actually shuts down or merely slows.
Applying the five questions to an unfamiliar cofactor
Suppose a newly described vitamin is the precursor of a cofactor that transfers a methyl group onto a protein involved in myelin maintenance, and no other reaction uses it. Question one: the active form is a methyl-donating cofactor. Question two: one-carbon or methyl transfer. Question three: the pathway is myelin protein methylation, and because no alternative enzyme performs it, this step is rate-limiting by default. Question four: the most dependent tissue is myelinated nerve, since myelin turnover is continuous and no substitute modification exists. Question five: the predicted symptom is a progressive demyelinating neuropathy, appearing gradually rather than suddenly because myelin turns over slowly. Note what the framework did not require: any prior knowledge of this specific vitamin. It required only the reaction class and the tissue's dependence.
Where the framework stops
The framework predicts the direction and tissue of a symptom, not its severity or exact timing. Severity depends on how depleted the stores were, how long the deficiency has run, and whether a second nutrient limits the same pathway. Treat the prediction as a ranked hypothesis, not a diagnosis.