What is Homocystinuria?

Homocystinuria is an inherited disorder. In this disorder, the body is unable to process some of the building blocks of the body. These building blocks, called amino acids, make up proteins. Proteins perform many of the body’s functions and make up its structure. In homocystinuria, an enzyme called cystathionine beta-synthase (CBS) is needed to break down amino acids called methionine and homocysteine. When CBS is missing, these amino acids are not broken down correctly and build up in the body. High homocysteine levels can lead to health problems. Multiple forms of homocystinuria exist. They have different signs, symptoms and genetic causes. Symptoms include problems with the eyes, skeletal system, blood, and brain. Symptoms can vary and not all affected people have all of the findings. The severity of the symptoms can also vary. Some people with a mild form may not show symptoms until childhood or adulthood. People with severe forms can show symptoms as babies.

Symptoms of Homocystinuria can include:

  • Myopia (nearsightedness)
  • Ectopia lentis (lens of the eye moves to the wrong place)
  • Tall and slender body shape
  • Osteoporosis (fragile bones)
  • Curved spine
  • Chest abnormalities (Chest caved in or pointed out)
  • Blood clotting problems
  • Developmental delay (learning problems)
  • Behavior problems
  • Seizures
  • Dystonia (movement problems)

Homocystinuria is typically diagnosed by a metabolic geneticist. To find genetic services near you, ask your doctor or visit the Clinical Services Search Engine available on the American College of Medical Genetics webpage.

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Are there other names for homocystinuria?

How common is homocystinuria?

What is the usual abbreviation for homocystinuria?

What is the life expectancy of someone with homocystinuria?

Are there other names for homocystinuria?

Homocystinuria can also be called classical homocystinuria, homocystinemia, cystathionine beta-synthase deficiency, CBS deficiency, and homocystinuria caused by cystathionine beta-synthase deficiency. To find other names for homocystinuria, check a reliable website such as The National Organization for Rare Diseases.

How common is homocystinuria?

The number of people (prevalence) with homocystinuria has been estimated to be between 1 in 200,000 to 1 in 335,000. However, homocystinuria is thought to be more common than these numbers suggest. There are a few populations where homocystinuria occurs much more frequently.

  • In Qatar, the prevalence of homocystinuria is about 1 in 1,800 people.
  • In Ireland, the prevalence of homocystinuria is about 1 in 65,000 people.
  • In Germany, the prevalence of homocystinuria is about 1 in 17,800 people.
  • In Norway, the prevalence of homocystinuria is about 1 in 6,400 people.

The number of people diagnosed (new cases) with homocysinuria each year is about 1in 50,000 to 1in 100,000. For additional information on homocystinuria visit a reputable website such as Baby's First Test

What is the usual abbreviation for homocystinuria?

Homocystinuria is sometimes shortened to HCY or HCU. HCY can also be used for the amino acid homocysteine. Be sure to check for a sentence that says they are shortening homocystinuria to HCY in any document you are reading.

What is the life expectancy of someone with homocystinuria?

People with homocystinuria can live a normal life span if they are treated. However, blood clots (thromboembolism) are the major cause of early death. Blood clots can block blood flow to the body’s organs leading to a risk of death. To learn more about the risks of homocystinuria, talk to your doctor or find a genetic counselor near you using the Find a Genetic Counselor Tool on the National Society of Genetic Counselors website.

  • Jonathan D Picker, MBChB, PhD and Harvey L Levy, MDGene Reviews

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