<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 9-month-old infant presents to your office for a check-up. Exam reveals mental retardation, microcephaly, and a mousy odor to his breath. You should be concerned that the infant may have which of the following?? A: Deficit of phenylalanine hydroxylase activity, B: Deficit of porphobilinogen deaminase activity, C: Deficit of tyrosine hydroxylase activity, D: Excess tetrahydrobiopterin cofactor, E: Excess phenylalanine hydroxylase activity,  <response>: This is a clinical vignette describing a 9-month-old infant with findings of mental retardation, microcephaly, and musty odor on the breath. This presentation is classic for phenylketonuria PKU. PKU is caused by a deficiency in the enzyme phenylalanine hydroxylase, which converts phenylalanine to tyrosine. The lack of this enzyme leads to a buildup of phenylalanine and its metabolites, which are toxic to the developing brain and cause the findings described. Choice A describes a deficit of phenylalanine hydroxylase, which is the underlying cause of PKU. The other choices describe enzyme deficiencies or excesses unrelated to the clinical findings described.A: Deficit of phenylalanine hydroxylase activity 