What this page covers
Practice Step 1-style biochemistry questions on BH4 deficiency hyperphenylalaninemia, including Neuro deterioration DESPITE diet, dihydropteridine reductase, with emphasis on clinical diagnosis vignette and answer-choice reasoning.
How to use this page
Review the topic and reasoning focus, then practice Step 1-style questions inside BiochemStep. The question set emphasizes mechanism-first answer-choice reasoning rather than passive content review.