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What is Phenylketonuria (PKU)? - Definition, Symptoms & Treatment

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Instructor: Amanda Robb

Amanda has taught high school science for over 10 years. They have a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. They also are certified in secondary special education, biology, and physics in Massachusetts.

Phenylketonuria, or PKU, is a rare disease that prevents people from being able to break down certain amino acids. Define PKU, then look at its symptoms, treatment, and how it is inherited. Updated: 11/24/2021

What Is PKU?

High-protein diets are all the rage right now. Diets high in protein and low in carbohydrates will help you get strong and lean, right? Well, not for some people! For some individuals with a rare metabolic disorder, protein is toxic and should be nearly eliminated from their diet. Want to know more about this disease, where carbohydrates have become an ally? Keep reading!

The disease is called phenylketonuria, or PKU. In this disease, people have a rare metabolic defect in which they cannot break down the amino acid phenylalanine. Amino acids make up proteins, which are in foods we eat such as meat, eggs, or diary.

Since those with PKU cannot break down phenylalanine, it starts to build up in their blood. Eventually, this amino acid starts to cause brain damage. If not treated, the damage may be irreversible. Imagine if you had a factory where you broke down boxes into pieces of cardboard and then recycled them. If one of the machines that takes apart the boxes broke, the boxes that were just entering the factory would build up. Eventually, the factory would get so backed up that things would break down. This is what's going on in the brains of people with PKU. The phenylalanine starts to build up, and the person's brain stops functioning correctly.

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  • 0:02 What is PKU?
  • 1:22 How Is PKU Inherited?
  • 1:42 Symptoms
  • 2:04 Is PKU Treatable?
  • 2:48 Lesson Summary
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How Is PKU inherited?

PKU is a genetic disorder, meaning it is inherited from one's parents. The disease is autosomal recessive, meaning the person must inherit one defective copy from each parent to get the disease. If one parent has the mutation, or defective gene, and the other doesn't, the child is safe from inheriting PKU.

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