We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What Are the Causes of Phenylketonuria?

By H. Lo
Updated Mar 03, 2024
Our promise to you
The Health Board is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At The Health Board, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

Phenylketonuria (PKU) is an inherited disorder in which the body is unable to break down phenylalanine, an essential amino acid found in foods that contain protein such as cheese, meats and milk. There are not many different causes of phenylketonuria, as an inherited disorder means the condition runs in the family. In this sense, it can be said that one of the causes of phenylketonuria is that both parents of the affected person carry and pass the defective phenylalanine hydroxylase (PAH) gene onto their child. Generally, though, mutations in the PAH gene are what make up the causes of phenylketonuria, with different mutations determining the severity of the condition.

As an autosomal recessive disorder, phenylketonuria occurs when a child inherits a defective PAH gene from both parents. The parents of the affected person do not necessarily have the disorder because they only carry one defective copy of the gene, not two, as their child does. A person who carries the gene but does not have the disorder is referred to as a carrier. In most cases, carriers pass on the gene unknowingly. This is because carriers usually do not exhibit any symptoms of the disorder and, thus, do not realize they carry the defective gene.

Although mutations in the PAH gene are causes of phenylketonuria, different levels of these mutations are responsible for different forms of phenylketonuria. To understand this, it is best to first have some background information on the disorder itself. Essentially, the PAH gene carries instructions that enable the body to make the phenylalanine hydroxylase enzyme, which is responsible for breaking down phenylalanine and converting it into other compounds. Mutations in the PAH gene can reduce or stop altogether the production of this enzyme, which then enables phenylalanine to accumulate to excessive amounts in the body. The buildup of this amino acid is dangerous because it can harm the central nervous system and result in brain damage.

Mild forms of the disorder, such as variant phenylketonuria, occur when the gene mutation still allows some enzyme activity to persist within the body, effectively helping to break down phenylalanine. The more severe form, classic phenylketonuria, occurs when the enzyme activity is absent or so reduced to the point where buildup of the amino acid is allowed to happen. While varied mutations in the PAH gene determine the severity of an affected person’s condition, it is thought that other genes might also play a role in severity of phenylketonuria, although not much is known about this.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
The Health Board, in your inbox

Our latest articles, guides, and more, delivered daily.

The Health Board, in your inbox

Our latest articles, guides, and more, delivered daily.