Correlation of the response to a load of tetrahydrobiopterin (BH4) in dihydropterin reductase (DHPR) deficient patients to the type of mutation in these patients has led to the conclusion that 4 patients without mutant DHPR molecules in their cells respond to the BH4 load, whereas 3 patients with mutant DHPR in their cells do not respond. Intravenous injection of BH4 in 1 of the cases not responding to BH4 again showed no response.
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Cotton et al. (1986) studied this question.
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