Homocystinuria due to CBS deficiency

What is the cause of homocystinuria?

Homocystinuria due to CBS deficiency is caused by mutations in the CBS gene, which lead to missing or low levels of the enzyme, cystathionine beta-synthase (CBS). When this enzyme is missing or there is not enough of it, the body cannot process homocysteine. When this happens, homocysteine and another amino acid, methionine, build up in the blood. It is not clear why this build up of homocysteine and methionine is toxic to the body.

Last updated on 05-01-20

How is homocystinuria due to CBS deficiency inherited?

Homocystinuria due to CBS deficiency is inherited in an autosomal recessive pattern. The means that both copies of the CBS gene in every cell have mutations. To have the disorder, a person must have a mutation in both copies of the responsible gene in each cell. There is nothing either parent can do, before or during a pregnancy, to cause a child to have this.

People with this disorder inherit one mutation from each of their parents. The parents, who each have one mutation, are known as carriers. Carriers of an autosomal recessive disorder typically do not have any signs or symptoms (they are unaffected). When two carriers of an autosomal recessive condition have children, each child has a:

  • 25% chance to have the disorder
  • 50% chance to be an unaffected carrier like each parent
  • 25% chance to be unaffected and not be a carrier

Last updated on 05-01-20

What is the long-term outlook for people with homocystinuria due to cystathionine beta-synthase deficiency?

When treatment is started early, children with this disorder can have normal growth and development, and can avoid the complications seen with this disorder. However, it is still possible that they could develop a dislocation of the lens of the eye or a blood clot. Sometimes the blood clots can be very serious and cause organ damage. In addition, some people may develop osteoporosis in adulthood as a result of this disorder.

Last updated on 05-01-20

How many people have homocystinuria due to CBS deficiency?

Approximately 1 in 200,000 to 1 in 300,000 people in the US has homocystinuria due to CBS deficiency. In other countries, the prevalence is higher. In Quatar, about 1 in 1800 people has this disorder and in Norway, about 1 in 6400 people has it. World-wide, it is thought that about 1 in 150,000 people has homocystinuria due to CBS deficiency.

Last updated on 05-01-20

How might homocystinuria due to CBS deficiency be treated?

People with homocystinuria due to CBS deficiency who do not respond to vitamin B6 are treated with a special, protein-restricted diet to help lower the amount of methionine and homocysteine in their bodies. In addition, they may be given supplements, such as vitamin B12, folate, and betaine. Specially trained nutritionists and dieticians work with patients to adjust the diet and protein requirements as needed. To avoid the complications seen with CBS deficiency, people with this disorder need to remain on a special diet for life.

People with the vitamin B6 responsive form of this disorder are treated with vitamin B6. In some people, diet restrictions are necessary as well.

Last updated on 05-01-20

Newborn Screening


The Newborn Screening Coding and Terminology Guide has information on the standard codes used for newborn screening tests. Using these standards helps compare data across different laboratories. This resource was created by the National Library of Medicine.

Last updated on 04-27-20

Name: Metabolic Support UK 5 Hilliards Court Sandpiper Way
Chester Business Park
Chester, CH4 9QP, United Kingdom
Phone: 0845 241 2173 Toll Free: 0800 652 3181 Email: https://www.metabolicsupportuk.org/contact-us Url: https://www.metabolicsupportuk.org
Name: Genetic Metabolic Dietitians International P.O. Box 1462
Hillsborough, NC, 27278, United States
Email: info@gdmi.org Url: http://www.gmdi.org/
Name: HCU Network America 623 Creek Lane
Flourtown, PA, 19031, United States
Phone: 630-360-2087 Email: info@hcunetworkamerica.org Url: http://hcunetworkamerica.org/
Morris AA, Kozich V, Santra S et al. Guidelines for the diagnosis and treatment of cystathionine beta-synthase deficiency J Inherit Metab Dis. 2017; 40(1). 49-74. Reference Link Homocystinuria due to cystathionine beta-synthase deficiency National Organization for Rare Disorders (NORD). 2018; Reference Link

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