Hyperphenylalaninemia Treatment & Management

Updated: May 18, 2017
  • Author: Eric T Rush, MD, FAAP; Chief Editor: Luis O Rohena, MD, PhD, FAAP, FACMG  more...
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Medical Care

If available, patients should be evaluated at a phenylketonuria (PKU) treatment center. The extent of the hyperphenylalaninemia determines the nature and frequency of follow-up. [4]

In one study, 54% of patients with phenylalanine levels less than 600 µmol/L (10 mg/dL) demonstrated a decline of 30% or more in plasma phenylalanine levels when sapropterin (commercial tetrahydrobiopterin cofactor) was administered at a dose of 10 mg/kg/d. [5] The percentage of patients who responded declined with increasing plasma phenylalanine levels. Response to sapropterin may improve at a dose of 20 mg/kg/d. [6]

Preliminary studies are underway for injectable phenylalanine ammonium lyase, an enzyme substitute. This shows promise in animal studies as an alternative treatment to control phenylalanine levels. [7]



If dietary treatment is necessary, refer the patient to a dietitian experienced with PKU (usually a member of a PKU treatment team).

Refer families of affected infants to a medical geneticist or genetic counselor to review the inheritance of hyperphenylalaninemia.



Determine the degree of dietary phenylalanine restriction for each patient based on untreated phenylalanine levels. For more detailed information on a phenylalanine-restricted diet, see Phenylketonuria.

Breastfeeding is usually possible and should not be stopped unless instructed by a local health official or treatment center.

Aspartame should be restricted from diet. Phenylalanine is a primary component of aspartame.

Aspartame may be present in many artificially sweetened substances, including medicines, vitamins, beverages, and foods. A pharmacist can help determine if a medication has a significant amount of aspartame.

The amount of aspartame in a children's vitamin or in a teaspoon of antibiotic may be significant for a child who can tolerate only 200 mg/d of phenylalanine, yet such a dose may be insignificant for a child who can tolerate more than 1000 mg/d.

Stringent phenylalanine-restricted diets have been reported to cause deficiencies of iron, zinc, selenium, and other nutrients and essential amino acids in patients with PKU. The diet requires careful monitoring by a professional trained in PKU management.



Do not restrict activities.



In general, patients should avoid consuming aspartame because phenylalanine is a primary component of aspartame.


Long-Term Monitoring

Phenylalanine levels determine the need for further outpatient care in patients with hyperphenylalaninemia.