Over the past 30 years and since the first trial to treat phenylketonuria (PKU) by Horst
Bickel and his coworkers, the dietary treatment of PKU has produced a generation of adult women
with PKU who have minimal cognitive deficits and are now of child-bearing age. If PKU is detected
early enough in infancy, mental retardation can be prevented by giving a diet containing a restricted
amount of phenylalanine. The principle of therapy is that all newborn babies with phenylalanine
concentration of 360 µmol or above are to be treated as early as possible to achieve a higher mental
function in terms of intelligence quotient, blood phenylalanine levels should be maintained in the
range of 120 - 360 µmol/l. Subnormal as well as high phenylalanine levels are to be avoided. In the
last few years there are increasing published articles on late treated PKU patients. In these patients,
the mean IQ was 57. For those treated after 2 months of age, recent studies have suggested that
approx. 23% of those children have normal IQ. In our hospital most of our cases were late treated (15
patients out of 22), the age at which treatment was started ranges from 2 weeks to 9 years. It is noted
that those patients who were diagnosed before 2 years of age (6 children) and were on strict
phenylalanine low diet with a phenylalanine maintained less than 4mg/dl have a normal IQ (75 or
above) (6 patients), one child has difficulty in speech, 2 children had border line IQ (above 70 and
less than 75), two children had moderate learning difficulties (IQ above 35 and below 50), 4 children
had severe learning difficulties (IQ above 20 and less than 35 of which two of them diagnosed before
2 years of age.