Immunologic Responsiveness in Phenylketonuria

Recent studies have demonstrated that administration of the amino acid phenylalanine (L-phenylalanine) to experimental animals will result in partial suppression of antibody responses to diptheria toxoid and sheep red blood cells and will also cause partial suppression of homograft rejection.^1,2 Since patients with phenylketonuria may have markedly elevated serum phenylalanine levels, the present study was undertaken to determine if immunologic responsiveness is impaired in humans with this disorder. Antibody responses following immunization with diphtheria toxoid and Escherichia coli Vi antigen, the development of delayed hypersensitivity following administration of BCG vaccine, and serum immunoglobulin levels were studied in phenylketonuric children on normal diets and on standard low-phenylalanine diets. Similar studies were performed in nonphenylketonuric controls.

Materials and Methods 

Subjects.—  Four groups of subjects (Table 1) were used for this study:

Group A.—  Children with phenylketonuria (PKU currently on a standard low-phenylalanine diet with biochemical controls.

Group B.—  Control