What is tetrahydrobiopterin deficiency?
Tetrahydrobiopterin deficiency is a rare disorder characterized by a shortage (deficiency) of a molecule called tetrahydrobiopterin or BH4. This condition alters the levels of several substances in the body, including phenylalanine.
What causes hyperphenylalaninemia?
Hyperphenylalaninemia is a recessive inherited metabolic condition, caused by the inability of the body to convert phenylalanine (Phe) to tyrosine, due to the total or partial absence of the enzyme phenylalanine hydroxylase. Phenylalanine is an essential amino acid found in protein-rich foods.
How is hyperphenylalaninemia treated?
Hyperphenylalaninemia may be corrected using a low phenylalanine diet or, in deficiencies of GTP cyclohydrolase, 6PTPS and pterin 4α-carbinolamine, by administration of oral BH4 (0.5–40 mg/d). BH4 is usually ineffective in DHPR deficiency.
How is BH4 deficiency treated?
Treatment of BH4 deficiencies consists of BH4 supplementation (2-20 mg/kg per day) or diet to control blood phenylalanine concentration and replacement therapy with neurotransmitters precausers (L-dopa/CarbiDOPA and 5-hydroxytryptophan), and supplements of folinic acid in DHPR deficiency.
What does hyperphenylalaninemia mean?
Hyperphenylalaninemia is broadly defined as the presence of blood phenylalanine levels that exceed the limits of the upper reference range (2 mg/dL or 120 µmol/L) without treatment but that are below the level found in patients with phenylketonuria (PKU).
How is Hyperphenylalaninemia diagnosed?
Hyperphenylalaninemia most is commonly diagnosed by newborn screening and must be distinguished from classic PKU by confirmatory testing at an experienced center. Some cases in adult women have been detected using maternal screening programs or following birth of children with birth defects.
How is Hyperphenylalaninemia inherited?
To learn more about genetic conditions, visit MedlinePlus Genetics. Non-PKU hyperphenylalaninemia is an autosomal recessive condition. Babies inherit it when each parent passes down a nonworking PAH gene to their baby. Only babies with two nonworking PAH genes—one from the mom and one from the dad—have this condition.
What is mild Hyperphenylalaninemia?
Disease definition. A rare form of phenylketonuria, an inborn error of amino acid metabolism, characterized by blood phenylalanine (Phe) concentrations of 120-600 micromol/L with or without clinical manifestations of impaired cognitive function, and behavioral and developmental disorders.
Does BH4 deficiency cause PKU?
In Taiwan, 2-30% of cases of PKU are attributed to BH4 deficiency. In Turkey, which has the highest incidence of PKU in the world with approximately 1 case per 2600 births, 15% of cases are due to BH4 deficiency. In Saudi Arabia, 66% of PKU cases are due to BH4 deficiency.
What is BH4 loading test?
The most used method is the BH4 loading test. Historically this test was performed at neonatal age, immediately after neonatal screening and aimed to distinguish hyperphenylalaninemic patients with PAH deficiency and patients with a BH4 deficiency [10, 11].
What is Alkaptonuria disease?
Alkaptonuria, or “black urine disease”, is a very rare inherited disorder that prevents the body fully breaking down two protein building blocks (amino acids) called tyrosine and phenylalanine. It results in a build-up of a chemical called homogentisic acid in the body.
