Describe the causes, consequences and diagnosis of phenylketonuria (PKU).

cause: [1 max]
a genetic variation/mutation;
change in gene coding for tyrosine hydroxylase;

consequences: [1 max]
results in a failure to metabolize phenylalanine into tyrosine;
results in high levels of ketones in the blood and urine;
results in mental retardation/brain damage;

diagnosis: [1 max]
can be made by a simple blood test for the level of phenylalanine;
diagnosis can be made shortly after birth;

A3 was answered very well, with many candidates achieving full marks.