54 Tyrosine
Tyrosine is an amino acid that the body can make from the essential amino acid phenylalanine, and it is also obtained from protein-rich foods (dairy, meat, fish, eggs, legumes). Besides being a building block of almost all proteins, tyrosine is the starting material for the neurotransmitters dopamine, noradrenaline and adrenaline, for the thyroid hormones T4 and T3, and for the skin and hair pigment melanin. Deficiency in healthy people is rare. Blood tyrosine is measured mainly in the diagnosis and monitoring of inherited metabolic diseases.
Clinical significance
- Phenylketonuria (PKU): deficiency of phenylalanine hydroxylase; phenylalanine accumulates and tyrosine becomes low, so tyrosine becomes essential. Untreated PKU damages the developing brain; newborn screening and a low-phenylalanine diet prevent this.
- Tyrosinaemias: rare inherited defects in tyrosine breakdown with high blood tyrosine; type I causes severe liver and kidney disease and is treated with nitisinone and diet
- Transient tyrosinaemia of newborns, especially premature babies
- Liver disease raises plasma tyrosine; malnutrition and some kidney diseases lower it
- Albinism: defects in converting tyrosine to melanin
Low tyrosine has been associated with low blood pressure, low body temperature and an underactive thyroid, but this does not mean that tyrosine supplements treat these conditions; their benefit for mood or performance is not established.
Abnormal newborn screening results, developmental delay, unusual body odour, jaundice or poor growth in a child need prompt assessment by a metabolic specialist.
References
This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.
Published on 28 April 2024