Homocystinuria (HCU) includes several related metabolic disorders that affect how the body processes certain amino acids, especially methionine. In many forms of HCU, homocysteine builds up in the body. If HCU is not recognized and managed, elevated homocysteine can affect multiple systems over time.

 

Important: HCU is not one single condition. Treatment and monitoring depend on the specific subtype (for example CBS deficiency - often called classical HCU - and certain remethylation disorders that affect homocysteine metabolism). Your metabolic clinic will confirm the subtype and guide a plan.

 

Jump to: What is HCU? | Why early detection matters | Living with HCU | Tools | Where to go next

 

 

HCU is a genetic condition a person is born with. It is often inherited in an autosomal recessive pattern, meaning a child inherits a non-working copy of a gene from each parent. The most commonly discussed form is classical HCU, usually caused by reduced activity of the CBS enzyme (CBS deficiency), but there are also other subtypes that affect homocysteine metabolism.

 

In plain language, the body has trouble moving homocysteine through the pathway it normally follows. When homocysteine stays too high, it can increase health risks over time.

 

Common terms:
• HCU - Homocystinuria
• CBS - Cystathionine beta-synthase (commonly involved in classical HCU)
• tHcy - Total homocysteine (a lab measure commonly used in follow-up)
• B6 - Vitamin B6 (pyridoxine), sometimes discussed in “B6-responsive” management

 

Key ideas:
• Homocysteine can build up and may affect blood vessels and connective tissue.
• Methionine may also be elevated in some subtypes (especially classical HCU).
• Symptoms and severity can vary between individuals and between subtypes.

 

 

Babies with HCU often appear healthy at birth. Early identification can reduce the chance of serious complications later in childhood, adolescence, or adulthood by allowing families and care teams to begin management before symptoms develop.

 

In Canada, newborn screening for HCU is not consistent across provinces and territories. Some people are diagnosed later, after symptoms appear. If you have concerns or a family history of HCU, your metabolic clinic or healthcare team can guide next steps.

 

Want to learn more? Newborn Screening Ontario provides a family-friendly overview: Homocystinuria information.

 

 

Lifelong condition:
HCU is a genetic condition, and many people manage it over their lifetime with support from a metabolic clinic and a multidisciplinary care team. Plans can change with age, growth, pregnancy, or health events.

 

What clinics monitor:
Clinics often track total homocysteine (tHcy) and may also monitor methionine and nutritional markers. Monitoring helps the care team understand how the body is responding and adjust a plan as needed.

 

Why management matters:
Management focuses on lowering homocysteine and supporting overall health. This can help reduce the risk of complications, including blood clots (thrombosis), eye issues (including lens dislocation), skeletal differences, and learning or development concerns.

 

Important: HCU management can look different from person to person. Some individuals respond to vitamin therapy (such as B6), while others require different approaches. Always follow your clinic’s plan and ask if you are unsure.

 

 

For condition-specific targets and monitoring details, visit your disorder page: HCU. For practical nutrition support, visit Nourish.

 

 

 

If you are looking for treatment options used in Canada, start here:

Therapies for HCU HCU Studies & Trials

Or explore practical food and nutrition support:

Nourish Flourish Life Stages