What Are Inborn Errors of Metabolism?

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  • 0:05 Inborn Errors of Metabolism
  • 1:14 Inheritance
  • 2:08 Phenylketonuria
  • 4:08 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Inborn errors of metabolism are genetic disorders that affect the metabolism of food components. Many of these disorders are difficult to diagnose but must be caught early in order to be treated. Learn about a common disorder, phenylketonuria.

Inborn Errors of Metabolism

Trying to detect inborn errors of metabolism, or IEMs, in a newborn is kind of like trying to find a needle in a haystack. That's because, when considered individually, these inherited disorders that affect biochemical processes of the body are rare. They also do not show up right away. An infant may be born appearing to be perfectly healthy and then develop signs hours or even years later.

Some IEMs may not present until adulthood. This delay in the presentation of symptoms is somewhat of a hallmark of the disorders. With most IEMs there's a period of normalcy, followed by vague signs of sickness. These initial signs are non-specific and may mimic routine childhood illnesses. For example, a child with an inborn error of metabolism might present with lethargy, irritability, vomiting or respiratory distress. This illustrates the challenge in managing IEMs. Many are treatable, but only if they're identified early. If they go untreated, permanent impairment can result.


Most IEMs have autosomal recessive modes of inheritance. This means that two copies of the bad gene must be passed on to the child for the disease to develop. This adds to the difficulty in diagnosing IEMs. The parents might not know they are carrying the abnormal gene, and it's not likely that there will be a family history of the disease. However, some inborn errors of metabolism are more common in certain populations. So, if an IEM is suspected, the ethnic background of the infant's family can be important.

There are hundreds of different metabolic disorders that are classified as inborn errors of metabolism. Therefore, while individually rare, these genetic disorders are not that uncommon when considered as a group. Kind of like great white sharks may be individually rare in an ocean, but sharks, in general, are fairly common.


Since they're metabolic disorders, we see that IEMs often involve defects in the enzymes that facilitate the breakdown of foods. This leads to an accumulation of toxic compounds that harm the body. As I mentioned, there are many different IEMs. Some produce minor abnormalities, while others can be life-threatening. You may be familiar with some of the colorful names of IEMs, such as phenylketonuria, Gaucher's disease and maple sugar urine disease. Because each IEM has a unique presentation of symptoms, it would be too much to cover all of them in this lesson. Yet, we can glean some additional insights by taking a closer look at one of the more common disorders, called phenylketonuria, or PKU.

PKU is an inborn error of metabolism that can cause mental retardation if not treated early. Like many IEMs, there is a delay in the presentation of symptoms, so to catch the disorder before it does damage, babies born in the United States are screened for PKU soon after birth. A person born with PKU is unable to metabolize the amino acid phenylalanine. Because the amino acid cannot be broken down, it accumulates in the body.

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