PKU (eLAB) Flashcards
Name 3 clinical features of PKU
Fair skin
Profound and irreversible mental disability
Elevated Phe
What is the most common cause of PKU?
Autosomal recessive loss of function mutation in the PAH gene leading to a deficiency in phenylalanine hydroxylase.
What is the normal function of phenylalanine hydroxylase?
Normally converts phenylalanine into tyrosine. Tyrosine is involved in the biochemical pathway for melanin (pigment) and dopamine (neurotransmitter).
How does the mutation cause the clinical features of PKU?
Deficient PAH –> reduced tyrosine –> reduced melanin (= pale skin) and reduced dopamine (neurological abnormalities)
What is the rare cause of PKU?
Deficiency in dihydropteridine reductase (DHPR) which results in reduced tetrahydrobiopterin (a co factor for phenylalanine hydroxylase)
A person is tested for PKU. The results show high Phe levels and normal DHPR. What does this tell you?
The individual has PKU caused by a mutation in the PAH gene. Rules out the possibility of PKU caused by deficiency in DHPR.
Why can’t PAH activity be measured directly in material from a blood sample?
PAH acts in the liver
How is PKU managed?
Low protein diet (limit foods with phenylalanine)
People who follow the PKU diet are able to get enough essential nutrients from food. T/F?
False. Phenylalanine is an essential amino acid and they can not get this from their diet.
Why do people with PKU need to avoid the sweetner aspartame?
When aspartame is digested, one of the components produced is phenylalanine.
What are the potential consequences of poorly controlled maternal hyperphenylalanaemia for the unborn foetus?
Low birth weight Microcephaly Mental retardation Behaviour problems etc
How is PKU tested for?
Heel prick test as a part of newborn screening in Australia and many other countries.
