By Dr Ananya Mandal, MD
There is no specific cure for phenylketonuria. The condition results from the overloading of phenylalanine that the body is unable to metabolize due to lack of enzyme Phenylalanine hydroxylase.
This build-up may lead to severe brain and cognitive damage. The condition is often detected in babies and children.
Therapy or interventions should begin immediately to prevent further damage.
Management of PKU (1, 2, 3) –
There are several ways to manage PKU. The main way is by controlling the diet.
Avoidance of protein in the diet
Primary intervention or therapy is avoidance of protein in diet. Phenylalanine is obtained from diet.
Protein rich foods like meat must be avoided. Safer proteins or specially formulated substitutes need to be started.
Diet of the growing child with PKU needs to be strictly monitored and controlled preferably with the help of a dietician.
Phenylalanine is found in eggs, meat, milk, artificial sweetener (aspartame) etc.
Babies with PKU may need special infant formula with low Phenylalanine content.
Sufferers of PKU may also be prescribed fish oil supplements to replace the long chain fatty acids that are missed in the phenylalanine-free diet. This additionally helps in neurologic development and fine motor activities.
Patients may also need supplementation with carnitine, Calcium, vitamin D and iron.
The generally accepted goal of therapy for the hyperphenylalaninemias is normalization of the concentrations of phenylalanine and tyrosine in blood.
Target levels are 120-360 µmol/L (2-6 mg/dL) for phenylalanine.
The diet is begun as soon as the condition is detected and continued at least till the teenage years.
Pregnant women should be advised of this diet to prevent the exposure of their unborn babies.
If the babies are exposed to high phenylalanine in the mother’s diet, they may be at risk of abortions, birth defects, brain damage, small heads (microcephaly) and skin changes even if they do not acquire PKU themselves from the mother.
Special infant formula for newborns
In newborns formula free from phenylalanine is initiated as soon as diagnosis is made.
Breast feeding is given along with the formula under guidance of a nutritionist.
The formula intake is spread over the whole day to prevent blood level fluctuations.
Total amino acid intake of at least 3 g/kg/day including 25 mg tyrosine/kg/day is recommended in children below two years of age.
Blood levels of phenylalanine need to be monitored once or twice weekly.
Diet for children over two years of age
These children need 2 g/kg/day amino acids including 25 mg tyrosine/kg/day.
They also need biweekly monitoring until seven years of age and thereafter a monthly monitoring is recommended.
Diet for adolescents and adults
Some recommend phenylalanine free diet for life.
Some recommend relaxation after 12 years of age.
Diet needs to be reinstated during pregnancy and if symptoms appear in adulthood.
Treatment of other conditions
The treatment of associated conditions like epilepsy is also important especially when the disease is manifested.
Behavioral therapy, counselling and other psychosocial management is essential in children who develop cognitive delays due to PKU.
The team of therapist consists of nutritionists, genetic counsellors, social workers, nurses along with physicians and psychologists.
Some studies have shown supplementation of diet with 6R-BH4 stereoisomer in less than 20 mg/kg daily in several divided oral doses may help patients with PKU.
Those with mild or moderate PKU may respond to this therapy. The drug is said to improve phenylalanine hydroxylation and thus reduces levels of plasma phenylalanine and improves dietary tolerance of phenylalanine. (3)
Potential gene therapies for PKU
There are clinical trials and research on the use of gene therapies in order to modify the faulty genes to prevent and treat PKU.
However, none of these have been put to wide clinical use as yet and diet remains one of the only methods for management of this condition.
Edited by April Cashin-Garbutt, BA Hons (Cantab)
What is Phenylketonuria (PKU)?
Last Updated: Jun 7, 2012