Homocystinuria is a rare metabolic disorder with a lifelong impact on patients and their families.

CBS (cystathionine beta synthase) deficiency, also known as Classical Homocystinuria is a serious, progressive disorder characterized by elevated levels of total homocysteine. A genetic mutation in the CBS gene, leads to low levels or absence of an enzyme called CBS (cystathionine beta synthase). The result of CBS being absent or not working correctly is the build-up of homocysteine and other toxic chemicals in the blood and urine.

The accumulation of homocysteine may lead to complications including thromboembolic vascular events, skeletal abnormalities (including severe osteoporosis), developmental delay, intellectual disability, lens dislocation and severe near-sightedness.

Homocystinuria is an autosomal recessive disorder, meaning both parents must pass one copy of the mutated gene to their child in order for the child to be affected. Current treatment options include significant dietary restrictions, betaine and vitamin B6.

Diet & Nutrition
Current treatment for Homocystinuria includes dietary protein restrictions to limit the amount of methionine in their diet. While protein restriction is effective, it is limited in its ability to reduce homocysteine levels to the normal range.

The normal range of protein intake amount varies by age and weight. If a protein-restricted diet is needed, consider working with a dietitian for guidance.

Managing a low-protein diet can be challenging, particularly for children. You can learn more about low-protein diet options, including recipes and meal planning resources, on our Diet & Nutrition page.

Ongoing Clinical Trials
We are conducting a Phase 1/2 clinical trial to study the impact of investigational drug pegtarviliase as a treatment for Homocystinuria. The trial will enroll 16-20 people with Homocystinuria in the United States, United Kingdom and Australia. More information about the trial can be found on ClinicalTrials.com (NCT05154890).

If you wish to learn more about how clinical trials work, visit our Clinical Trials FAQs page.

Homocystinuria Advocacy Organizations
While Homocystinuria is a rare condition, patients and families do not have to face this disorder alone. There is an established community of patients, caregivers, doctors, nurses, genetic counselors and dieticians who are ready to lend help and support.


Meet the patients and caregivers living with Homocystinuria and inspiring us each day. They are true heroes!

Elliott’s Story


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Read Elliott’s story in Spanish – Lea la historia de Elliott en español.

Four-year-old Elliott is living with Homocystinuria. Elliott was diagnosed when he was two years old after being on a family vacation at the beach. His family returned home and could tell something was wrong.

He was taken to the hospital where it was determined that he was having seizures pretty much around the clock due to clotting throughout his brain. During the hospital stay the doctors found that Elliott’s homocysteine level was extremely high, and he was diagnosed with Homocystinuria. That was the first time his parents had ever heard this word.

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People with Homocystinuria, like Elliott, lack the ability to break down certain amino acids and proteins in food and without being able to process these things, levels build up and can cause catastrophic events to occur.

Since the diagnosis, Elliott and his family have to constantly be mindful of how much protein he eats each day. Elliott’s mom, Liz, lives with a never-ending stress, which causes a lot of worry for the whole family. In particular, Liz worries about the unknown and what could happen if Elliott experiences more seizures or other complications from the disease.

As Elliott gets older and is able to make some of his own life choices, Liz is concerned he may make mistakes with his diet. Because if he doesn’t stay regimented, it could result in another catastrophic event.

If Liz had one wish for people living with Homocystinuria, it would be that there are products developed and advancements made medically so that they can live the most normal life possible.

While there is always worry and stress, life does get easier. For Liz, there was a huge learning curve involved after being thrown into a situation that she never expected. But she and her family developed a new normal and Liz knows Elliott is going to do great things in his life. Maybe even change the world!

Alex’s Story


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Read Alex’s story in Spanish – Lea la historia de Alex en español.

Alex was diagnosed with Classical Homocystinuria through newborn screening in 1987. Now an adult, Alex relies on a complex regimen of low protein diet, medical formula, and vitamins to manage his disease, but still often worries about the potential negative effects of the disease. Along with physical complications, Alex believes that the psychological side effects of having a rare disease can be equally devastating.

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Through music and art, Alex has found a creative outlet that allows him to turn something that seemed to be an obstacle into a superpower. Alex has found great success as a singer/songwriter, and his songs Homocystinuria Part I and Homocystinuria Part II chronicle his experiences growing up with this rare disorder.

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