Life with Homocystinuria: Navigating Challenges & Embracing Hope

Homocystinuria (HCU) is a rare metabolic disorder that affects the body's ability to process certain amino acids. These amino acids are the building blocks of protein, and when not processed correctly, they can lead to a buildup of homocysteine in the blood. Elevated levels of homocysteine can cause various health issues, affecting various organs and […]
February 19, 2024
Dr. Ves Gitchev
Dr. Ves Gitchev MD is the Director of Global Healthcare Partnerships at Science 37. A pioneer and innovator with nearly 2 decades of experience in the research industry, Dr. Gitchev's focus is on delivering the highest quality results to drive scientific advancement.

Homocystinuria (HCU) is a rare metabolic disorder that affects the body's ability to process certain amino acids. These amino acids are the building blocks of protein, and when not processed correctly, they can lead to a buildup of homocysteine in the blood. Elevated levels of homocysteine can cause various health issues, affecting various organs and systems in the body.

HCU is usually present from birth, but symptoms may not become evident until later in infancy or childhood. The symptoms vary based on the type of HCU, often involving the eyes, vascular system, central nervous system, or skeletal systems. They include:

  • Eye-related issues like nearsightedness, dislocation of the lens in the eye, and a high risk of developing blood clots.
  • Skeletal abnormalities like bone deformities, osteoporosis, and a tendency to be taller than average.
  • Neurological problems like intellectual disability, seizures, and developmental delays.
  • Vascular system issues like blood clots that may result in pulmonary embolism or stroke.

Newborn screening programs can help identify elevated levels of methionine in the blood, prompting further diagnostic tests, such as:

  • Genetic testing
  • Amino acid screen of blood and urine
  • Skin biopsy with a fibroblast culture
  • Skeletal x-ray
  • Liver biopsy and enzyme assay
  • Homocysteine level
  • Standard ophthalmic exam

Early diagnosis is vital for initiating treatment promptly and preventing complications associated with untreated HCU.

Understanding the Genetic Basis

Homocystinuria is primarily a genetic disorder, and its occurrence is rooted in mutations that impact the body's ability to process amino acids. The most common form of homocystinuria, known as classical or CBS deficiency, is caused by mutations in the CBS gene. CBS gene provides instructions for the production of an enzyme called cystathionine beta-synthase, which plays a pivotal role in the breakdown of the amino acid methionine.

Other types of HCU are associated with mutations in different genes, like Methylene Tetrahydrofolate Reductase (MTHFR) and Methionine Synthase (MTR). Mutations in these genes hinder the proper functioning of their respective enzymes, resulting in the accumulation of homocysteine. Research studies still haven't uncovered why excess homocysteine causes the symptoms associated with homocystinuria.

How is Homocystinuria Inherited?

Homocystinuria follows an autosomal recessive inheritance pattern, meaning an individual must inherit two copies of the mutated gene (one from each parent) to manifest the disorder. Those who inherit one mutated and one normal gene are carriers of the condition but do not typically show symptoms. Carriers have a 50% chance of passing the mutated gene to their offspring.

When both parents are carriers, there's a 25% chance that the child will inherit two mutated genes with each pregnancy, leading to homocystinuria. HCU is rare; it only affects about 1 in 100,000 to 200,000 in the United States.

Some studies have found that HCU mostly affects people from the following countries:

  • Qatar
  • Norway
  • Germany
  • Ireland

Homocystinuria Treatment

While there is no cure for HCU, treatment aims to manage symptoms, prevent complications and side effects, and enhance overall well-being. Here are some strategies that help manage this rare disorder:


HCU is mostly caused by genetic mutation. However, it can also happen due to non-genetic reasons, like a severe lack of vitamin B12, vitamin B9 (folate) and vitamin B6. In this case, supplementation with these vitamins can help manage the problem.About 50% of people with HCU show improvement from taking vitamin B6 supplements. Those who don't respond well to vitamin B6 must take B12 and B9 (folic acid) supplements for the rest of their lives.

Dietary Management

In cases where supplements don't work, dietary changes become a critical component of managing homocystinuria. Dietary management focuses on controlling the intake of methionine, the amino acid central to the disorder. This means reducing the intake of foods like fish, meat, pulses, nuts, eggs, cheese, and dairy products, which are abundant methionine sources.

Baby milk also needs to be monitored and measured. Dietitians can advise on the appropriate composition of baby milk to ensure the infant receives the necessary nutrients while managing methionine levels. In some cases, they may recommend a special diet that includes vitamins, minerals, and specific amino acids to meet the growth and development needs of infants with HCU.

Early diagnosis and intervention in homocystinuria have shown positive responses, particularly when patients, including infants, switch to a low-protein diet. Catching HCU at early stages allows for timely implementation of dietary changes, leading to better symptom management and overall health outcomes.

Regular Blood Tests

To ensure effective management of HCU, patients must get regular blood tests to monitor the amount of homocysteine in their blood. These tests provide valuable insights into metabolic control and the impact of dietary management. Regular monitoring allows healthcare professionals to adjust the treatment plan and provide personalized care.

Homocystinuria Life Expectancy

The life expectancy of people with homocystinuria has significantly improved over the years due to advances in medical understanding and treatment options. With early intervention, most children with the condition can expect to live normal, healthy lives.


Since HCU happens because of genetic mutation, it is hard to prevent. But if you are expectant or planning to conceive in the future, certain steps and considerations can be taken to manage the risk of homocystinuria or its impact on future generations.

First, you can do genetic counseling to assess your risk of passing on the mutated gene and explore available options. If there is a known risk of HCU based on carrier status or family history, prenatal testing can be considered during pregnancy to determine if the developing fetus has homocystinuria. In this case, early detection enables prompt initiation of treatment, improving outcomes.

Homocystinuria Clinical Trials At Science 37

If you or a loved one has been diagnosed with classical homocystinuria, there is an opportunity to make a meaningful impact on the future of HCU research. Science 37 is actively conducting clinical trials to explore innovative solutions and therapies to improve the lives of those within the HCU community.

Your involvement has the potential to benefit not only yourself but also future generations within the HCU community. Science 37 makes it easier to participate in this research from the comfort of your home. We also offer compensation to thank you for your time and commitment. Sign up today to get started.

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