A 5-Month-Old Infant Is Admitted with Vomiting and Eczema Over

A 5-month-old infant is admitted with vomiting and eczema over the lower extremities.The mother states that the infant is not developing as fast as her other children.When a diagnosis of phenylketonuria (PKU) is made,the nurse should recognize which of the following as the basic underlying defect involved?

A) absence of the enzyme hexosaminidase component A
B) absence of surfactant
C) chromosomal abnormality involving pairs 21 to 23
D) deficiency of a liver enzyme that metabolizes phenylalanine