200.The answer is e.(Kumar, pp 487–488. Kasper, pp 371, 376, 2332–2334.)
In patients with phenylketonuria (PKU), there is a diffuse pigmentary dilution
due to elevated levels of L-phenylalanine resulting from a deficiency in the
enzyme L-phenylalanine hydroxylase that converts L-phenylalanine to L-
tyrosine. The high levels of phenylalanine provide competitive inhibition for
tyrosinase (answers c and d).The characteristic blonde hair of PKU can
undergo darkening when the patient is on a low phenylalanine diet. The num-
ber of melanocytes that differentiate from the neural crest would be normal
(answer a).Melanocytes do not proliferate (answer b).
Integumentary System Answers 311