inborn errors of metabolism

Inborn errors of metabolism are inherited disorders that are caused by a defect in a single gene. There are many inborn errors of metabolism. Some produce relatively unimportant physical features or skeletal abnormalities. Others produce serious disease and even death.

 

The gene defect can cause a particular enzyme to be defective or missing. Because the enzyme fails to do what it is supposed to do for the body, a variety of health conditions may result.

 

Enzymes help the body by stimulating biological reactions inside cells, thus making it possible for the body to use food, produce energy, and do work. When a particular enzyme is defective or missing, then the body is unable to do something that it should do to maintain health. The enzyme involved determines what the body cannot do and what the resulting physical features are. Inborn errors of metabolism affect about 1 in every 5,000 babies born. Some of the more familiar inborn errors of metabolism are phenylketonuria (PKU), sickle cell anemia, and Hunter Syndrome.

 

The symptoms of inborn errors of metabolism vary greatly. Each one must be reviewed separately to know what the physical features are. Often, an infant will show signs of failure to thrive by failing to gain weight, not eating well, and generally showing developmental delay. Vomiting and diarrhea are among other symptoms that may signal the healthcare professional to test for an inborn error of metabolism.

 

The enzyme defects that lead to the inborn errors of metabolism are caused by abnormal genes. In most cases, the abnormal gene is autosomal recessive in character. Autosomal means that the gene is on one of the twenty-two non-sex chromosomes. Recessive means that there must be two copies of the gene, one inherited from each parent, in order for the enzyme defect to exist.

The enzyme defects that lead to the inborn errors of metabolism are caused by genetic abnormalities present from the time of conception. Therefore, nothing can be done to prevent them. The diseases caused by the inborn errors, however, may be preventable in some cases. A familiar example of this is PKU, in which the toxic buildup of phenylalanine in the body, occurring because of the missing enzyme, can be averted by withholding phenylalanine from the diet.

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. DNA tests may also confirm the diagnosis.