HPA and PKU
Hyperphenylalaninemia (HPA)
Phenylalanine (Phe) is an essential amino acid provided by various proteins consumed in a regular diet. Hyperphenylalaninemia (HPA) is defined as a chronic, abnormal elevation in blood Phe levels.
HPA generally occurs as a result of two inborn errors of metabolism: phenylketonuria (PKU) or tetrahydrobiopterin (BH4) deficiency.
PKU is a hereditary metabolic disorder caused by a genetic mutation leading to a deficiency of the enzyme phenylalanine hydroxylase (PAH). PAH is required for the metabolism of Phe, an essential amino acid found in all protein-containing foods. If the active enzyme is not present in sufficient quantities, Phe accumulates to abnormally high levels in the blood and brain, resulting in a variety of complications including several mental retardation and brain damage, mental illness, seizures and tremors, and cognitive problems.
Although it is a rare disease, PKU is one of the most common genetic metabolism disorders. Approximately one in 8,000 children in Europe is born with PKU1, although this ratio varies among countries.
BH4 deficiency is a very rare inborn error of metabolism, estimated to account for less than 2% of HPA2. BH4 is the natural cofactor for the PAH enzyme (a cofactor is a non-protein compound that is essential for enzyme function).
If left untreated, the neurological damage caused by HPA can result in serious brain damage and, if insufficiently controlled, HPA can cause transient to lasting impairments in children and adults.
HPA/PKU is currently managed with a strict, life-long diet aimed at maintaining blood Phe levels as low as possible within target ranges based on age group. A typical low-Phe diet consists of vegan-vegetarian food (no red meat, chicken, fish or eggs) as well as synthetic, Phe-free formula and special low-Phe foods to provide essential amino acids, vitamins, fats, trace elements and minerals that are deficient due to dietary restrictions.
¹ Loeber JG. Neonatal screening in Europe: the situation in 2004. J Inherit Metab Dis 2007; 30: 430–438.
² de Baulny HO, Abadie V, Feillet F, de Parscau L. Management of phenylketonuria and hyperphenylalaninemia. J Nutr 2007; 137: 1561S-1563S; discussion 1573S–1575S.
² de Baulny HO, Abadie V, Feillet F, de Parscau L. Management of phenylketonuria and hyperphenylalaninemia. J Nutr 2007; 137: 1561S-1563S; discussion 1573S–1575S.
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