Inborn Errors of Metabolism
A group of more than 200 inherited disorders in which the body cannot metabolize food components normally. These disorders are usually caused by gene defects that cause a particular enzyme to be defective or missing. Enzymes are proteins that help the body use food, produce energy, and do work. The particular enzyme involved determines what the body cannot do and what the resulting problem may be. The likelihood of having an inborn error of metabolism is about one in 5,000 live births. Some of the more common inborn errors of metabolism are cystic fibrosis, hypothyroidism, SICKLE-CELL DISEASE, PHENYLKETONURIA (PKU), and TAY-SACHS DISEASE. Other inborn errors of metabolism include fructose intolerance, which causes a problem in the breakdown of the carbohydrate fructose; galactosemia, which causes a problem in breaking down galactose to glucose; and maple sugar urine disease, in which there is a problem with the breakdown of certain amino acids.
Symptoms
The symptoms of inborn errors of metabolism vary a great deal. A baby’s symptoms may indicate a problem by showing signs of FAILURE TO THRIVE (not gaining weight, not eating well, or having developmental delays). Vomiting and diarrhea are among other symptoms that may prompt the doctor to test for an inborn error of metabolism. Several inborn errors of metabolism cause MENTAL RETARDATION if not controlled.
Cause
The enzyme defects are caused by abnormal genes. In most cases, the child must inherit an abnormal gene from each parent in order to have the problem. Defects have been observed in almost all biological reactions, and the responsible genes are scattered among the chromosomes. The enzyme defects that lead to the inborn errors of metabolism are caused by genetic abnormalities present from the time of conception.
Parents who have had one child with an inborn error of metabolism are at risk to have other affected children. One in four pregnancies of such parents can be expected to result in an affected child.
Some inborn errors of metabolism are more often found in certain racial and ethnic groups. For example, sickle-cell anemia occurs among those of African descent, Tay-Sachs occurs more often among Ashkenazi Jewish populations, and those of northern European heritage are more likely to pass on defective genes for cystic fibrosis.
Diagnosis
Physical features such as malformations of the skeleton usually make a diagnosis obvious. A diagnosis can be 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.
Treatment
Many of the inborn errors of metabolism can be treated effectively, depending on the missing or defective enzyme and how easily the compounds involved can be eliminated or replaced. Inborn errors of metabolism often require diet changes, the type and extent of which depend on the specific metabolic error.
The diseases caused by the inborn errors may be preventable if the missing enzyme can be supplemented or a harmful buildup eliminated. For example, the disease phenylketonuria involves phenylalanine building up in the body, causing problems. When phenylalanine is eliminated from the diet, the child’s body will function normally.
Prevention
Screening programs of potential carriers of certain IEM, such as Tay-Sachs—or amniocentesis—can be performed in cases with two partners who are both carriers.
Posted in Health and Wellness
