For example, the strategy in treating phenylketonuria is to withhold phenylalanine from the diet. Another way to prevent the diseases caused by the inborn errors of metabolism is family planning. A couple who know that they are both carriers of a gene responsible for an inborn error may choose to modify their family planning. They might choose not to have children at all. They also might choose to make use of one of the recent advances in assisted pregnancy or prenatal diagnosis.
Genetic counseling can be very helpful.
Physical features such as malformations of the skeleton or abnormal hair usually suggest the presence of an inborn error of metabolism. Whether or not the physical features are obvious, diagnosis is confirmed by checking the blood or urine for one or more of the compounds involved. Tests for urine amino acids can be helpful. There may be too much of a compound, not enough of another, or abnormalities among others. The compounds may also be studied in tissue from biopsies .