| Phenylketonuria | |||||
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- What is phenylketonuria?
- Symptoms of phenylketonuria
- Causes of phenylketonuria
- Treatment of phenylketonuria
- Important phenylketonuria facts
Pphenylketonuria (also known as PKU) is a genetic condition that affects the body's ability to metabolise the amino acid phenylalanine.
In people with phenylketonuria, the enzyme that breaks down phenylalanine for absorption is either missing or in too level level to work effectively. The amino acid normally converts phenylalanine into tyrosine, a non-essential amino acid. Without this enzyme, phenylalanine and the other substances accummulate in the blood supply and body tissues causing problems.
Most people with phenylketonuria need to be on a special diet for life, but there are some individuals seem to have a "transient" or temporary form of phenylketonuria, which means they may not have the condition for life.
Babies with phenylketonuria appear generally normal at birth, but may have lighter hair and eyes than either of their parents.
Around half of the babies born with phenylketonuria have the following early symptoms:
- Eczema-like rash
- Increased muscles tendon reflexes
- Increased muscle tone
- Irritability
- Odd-smelling urine
- Vomiting
Later symptoms:
- Mental retardation
- Seizures
Children who do not get treated for phenylketonuria often have the following symptoms:
- Decreased body growth
- Poor tooth enamel development
- Prominent cheek and upper jaw bones
- Small head (microcephaly)
- Widely spaced teeth
Phenylketonuria is caused by a gene that needs to be inherited from both parents (who need to be carriers of this disorder).
People who are carriers of phenylketonuria do not have any symptoms of the disorder.
Fever and illness can cause an increase of phenylketonuria in the body and an exacerbation of symptoms. A doctor or nutritionist can advise on the dietary changes required during illness to maintain proper phenylalanine levels during illness or fever.
Diagnosis and testing
Newbown babies are screened for levels of phenylalanine while still in hospital, wth a simple blood test by pricking the heel of the foot.
If the test shows abnormal levels of phenylalanine, other tests are needed to confirm it.
Conventional treatment
A special diet is required to reduce levels of phenylalanine to between about 2-10mg per dl of blood. This requires a diet that has some phenylalanine but in much lower amounts than normal.
Certain foods need to be avoided (or severely restricted):
- Cheese
- Dried beans
- Eggs
- Fish
- Meat
- Milk
- Peas
- Poultry
Basically all foods high in protein need to be avoided or limited.
Foods that can be eaten:
- Cereals
- Fruits
- Low protein milk substitutes
- Phenylalanine-free baby formula (for babies)
- Starches
- Vegetables
Most people with phenylketonuria need to be on a special diet for life, but there are some individuals seem to have a "transient" or temporary form of phenylketonuria, which means they may not have the condition for life. This is difficult to determine without trying a phenylalanine challenge which should only ever be done under strict medical supervision.
The current advice is to be on a low-phenylalanine diet for life to treat phenylketonuria.
Alternative / complementary treatment
Alternative / complementary treatment is the same as conventional treatment - a special diet to reduce levels of phenylalanine, plus supplementation of the following (based on medical advice):
- Vitamin B6 - studies show that adults with phenylketonuria may have lowered intake of vitamin B6 (pyridoxine) due to a lower dietary intake of animal products
- Vitamin B12 - studies show that adults with phenylketonuria may have an increased risk of deficiency of vitamin B12 (cobalamin) due to a lower dietary intake of animal products
Important phenylketonuria facts
- The incidence of phenylketonuria in men and women occurs in equal propertions
- Phenylketonuria occurs in about 1 in every 10,000 to 20,000 Caucasian and Asian babies
- Screening newbown babies allows early identification and better managment of phenylalanine
- Women with phenylketonuria need to strictly follow a low phenylalanine diet otherwise they risk abortion of the foetus or congental defects in the baby when it is born
references
- Aoki K, Ohwada M, Kitagawa T. Long-term follow-up study of patients with phenylketonuria detected by the newborn screening programme in Japan. J Inherit Metab Dis. 2007 Aug;30(4):608
- Bodamer OA, Hoffmann GF, Lindner M. Expanded newborn screening in Europe 2007. J Inherit Metab Dis. 2007 Aug;30(4):439-44.
- Burton BK, et al. The response of patients with phenylketonuria and elevated serum phenylalanine to treatment with oral sapropterin dihydrochloride (6R-tetrahydrobiopterin): a phase II, multicentre, open-label, screening study. J Inherit Metab Dis. 2007 Sep 12
- Hvas AM, Nexo E, Nielsen JB. Vitamin B12 and vitamin B6 supplementation is needed among adults with phenylketonuria (PKU). J Inherit Metab Dis. 2006 Feb;29(1):47-53
- Kanufre VC, Starling AL, Leão E, Aguiar MJ, Santos JS, Soares RD, Silveira AM. Breastfeeding in the treatment of children with phenylketonuria. J Pediatr (Rio J). 2007 Aug 3;83(5)
- Michals, K, and others: Return to Diet Therapy in Patients with Phenylketonuria. The Journal of Pediatrics, 106:933-939
- NCBI. Genes and Diseases - PDF. Accessed 21 September 2007
- Therrell BL, Adams J. Newborn screening in North America. J Inherit Metab Dis. 2007 Aug;30(4):447-65. Epub 2007 Jul 23
- Weigel C, Rauh M, Kiener C, Rascher W, Knerr I. Effects of various dietary amino acid preparations for phenylketonuric patients on the metabolic profiles along with postprandial insulin and ghrelin responses. Ann Nutr Metab. 2007;51(4):352-8. Epub 2007 Aug 28
To learn more, go to the following web sites:
- Genetic Reference - Phenylketonuria (USA)
- National PKU News (USA)
- National Society for Phenylketonuria
- Princess Margaret Hospital for Children (Australia)
- Tests for Phenylketonuria (NSW Government, Australia)
