Data from thirty medical records of phenylketonuric children under treatment were investigated to determine at which serum phenylalanine level (0-3.9 mg. %, 4-7.9 mg %, 8-11.9 mg. %, greater than 12 mg. %) there would be the greatest increase in intelligence. The children involved in the study were divided into the following groups according to the age dietary treatment was initiated: 0 through 5 months, 6 through 11 months, 12 through 23 months, and over 2 years of age.

Among 6 patients who were placed on the diet during the first 5 months of life, it appears that the optimal serum phenylalanine level to maintain I.Q. was between 0-3.9 mg.%. The average I.Q. at the beginning of treatment in this age group was 89, followed by a slight decrease during the next two years to 86. There were 6 children who were started on diet between the ages of 6 months through 11 months. Although it appeared that a gradual increase in I.Q. resulted even with an elevation of serum phenylalanine levels to 12 mg.%, a definite conclusion could not be made for this group since there was much missing data. The initial average I.Q. in this group was 60 and it increased to 75 after 1 1/2 years of treatment. This was an average increase of 25%.

The average initial I.Q. of the 11 patients who started on diet between 12 through 23 months of age was 51. During the following 2 years, the average I.Q. of this group increased to 65, an increase of 27%. Among this group, the greatest I.Q. increase was obtained in those patients who serum phenylalanine levels were below 4.0 mg.%. In the 7 patients who were started on the diet after the age of 24 months, the average initial I.Q. was 42 and it increased to 53 during the next 2 years, an increase of 26%. The greatest increase occurred in those patients whose serum phenylalanine levels were below 8.0 mg.%.

Since it appeared that serum phenylalanine levels below 4.0 mg.% produced the greatest increase in I.Q. in the preceding 4 groups, the phenylalanine intake of these groups were evaluated. The average phenylalanine intake was found to be comparable to that recommended by Centerwall and coworkers.

The growth study of 23 treated phenylketonuric children indicated that there was a greater percentage of patients with height growth curves below the norm as compared with their weight growth curve as ascertained by Iowa's Grid. In comparing the growth rates of those started on dietary treatment before the age of 6 months with those started after 6 months of age, it was found that greater percentages of those started on diet before 6 months of age had subnormal growth rates.

When the caloric, protein, and phenylalanine intakes of those children with normal and subnormal growth rates were compared, it was found that significantly larger amounts of all three nutrients were consumed by the children with subnormal growth rates than those with normal growth rates. In both groups, protein and calories were present in amounts greater than those recommended by the National Research Council. No definite conclusion can be made from this part of the study at this time since many factors which may influence the growth rate of a child were not considered.




Graduate School

First Advisor

Phyllis B. Acosta

Second Advisor

Robert F. Chinnock

Third Advisor

Ellin L. Lieberman

Fourth Advisor

Florence Otto

Degree Name

Master of Science (MS)

Degree Level


Year Degree Awarded


Date (Title Page)




Library of Congress/MESH Subject Headings

Phenylketonuria -- diet therapy; Phenylalanine; Intelligence



Page Count

viii; 73

Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


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