Homocystinuria caused by CBS DEFICIENCY (classical homocystinuria)

Homocystinuria caused by cystathionine beta-synthase (CBS) deficiency is also called classical homocystinuria. CBS is an enzyme. Enzymes are proteins that regulate the body’s tissues and organs. Specifically, CBS helps convert an important amino acid—homocysteine—to another amino acid that the body needs.

When the body makes too little CBS enzyme or none at all, or it makes CBS enzyme that does not work properly, levels of homocysteine and methionine (also an important amino acid) in the blood increase. The high levels of homocysteine cause harmful symptoms to develop.

Classical homocystinuria is divided into 3 subgroups:


  • People who respond to vitamin B6 (pyridoxine)

  • People who respond partially to vitamin B6

  • People who do not respond to vitamin B6. This group may have more severe symptoms

What are the signs and symptoms of classical homocystinuria?

Classical homocystinuria can affect many parts of the body:

BRAIN

Learning problems and developmental delays, such as being slow to sit up, walk, or talk

EYES

Problems with the lenses in the eyes, such as lens dislocation; nearsightedness (often severe); quivering of the iris (the colored
part of the eye)

BONES

Tall, thin body with long arms, legs, fingers and toes; curved spine; osteoporosis (brittle or weak bones)

BLOOD

Development of blood clots

Watch this video to learn more about classical homocystinuria and common signs and symptoms.

Infants with classical homocystinuria appear to be normal at birth but, if not treated, will slowly develop symptoms.


  • Symptoms may appear for the
    first time at any age.

  • A person may have one or
    more symptoms.


  • Symptoms can range from
    mild to severe.

  • Symptoms may vary from
    person to person.

Early detection and treatment are critical to help reduce
serious health problems.

How is classical homocystinuria diagnosed?

All states screen newborns for classical homocystinuria:

  • The screening tests for high methionine levels.
  • Newborn screening is not perfect and may not catch all newborns with the condition.
  • Some newborns with the condition may not have high methionine levels so soon after birth, and some premature newborns may not be developed enough for the screening to be accurate.
  • To learn more about newborn screening, visit babysfirsttest.org.

If someone has a positive newborn screen and/or symptoms that could be signs of classical homocystinuria, the doctor will order lab tests. The following results may point to a positive diagnosis:

  • High levels of homocysteine in blood and urine
  • High levels of methionine in blood and urine
  • Reduced activity of the CBS enzyme


Once the diagnosis has been made, more tests will be done to measure response to vitamin B6. This will help determine what type of classical homocystinuria the person has and will lead to a treatment plan. Genetic testing can confirm the diagnosis.

Medical geneticists are doctors who specialize in diagnosing and treating people with classical homocystinuria.

How is classical homocystinuria treated?

The overall goal of treatment is to prevent or lessen symptoms by reducing the level of homocysteine in the blood. Treatment may include:

  • Taking vitamin B6 (pyridoxine) and additional B vitamins

  • Eating a low-protein diet

  • Taking a methionine-free amino acid formula

  • Taking CYSTADANE® (betaine anhydrous for oral solution) and other medicines

Always check with your doctor about what medicines,
vitamin supplements, and diet are right for you.

INDICATIONS AND USAGE

CYSTADANE (betaine anhydrous for oral solution) is indicated in children and adults for the treatment of homocystinuria to decrease high homocysteine blood levels. Homocystinuria is a rare genetic disorder in which there is an abnormal accumulation of the amino acid homocysteine in the blood and urine. The following are considered to be homocystinuria disorders:

  • Cystathionine beta-synthase (CBS) deficiency
  • 5,10-methylenetetrahydrofolate reductase (MTHFR) deficiency
  • Cobalamin cofactor metabolism (cbl) defect

IMPORTANT SAFETY INFORMATION

  • Hypermethioninemia in Patients with CBS Deficiency: CYSTADANE may worsen high methionine blood levels and accumulation of excess fluid in the brain has been reported. If you have been told you have CBS deficiency, your doctor will be monitoring your methionine blood levels to see if changes in your diet and dosage are necessary.
  • Most common side effects were nausea and gastrointestinal distress, based on a survey of doctors.
  • To report SUSPECTED SIDE EFFECTS, contact Recordati Rare Diseases Inc. at 1-888-575-8344, or FDA at 1‑800-FDA-1088 or www.fda.gov/medwatch.
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IMPORTANT SAFETY INFORMATION

  • Hypermethioninemia in Patients with CBS Deficiency: CYSTADANE may worsen high methionine blood levels and accumulation of excess fluid in the brain has been reported. If you have been told you have CBS deficiency, your doctor will be monitoring your methionine blood levels to see if changes in your diet and dosage are necessary.
  • Most common side effects were nausea and gastrointestinal distress, based on a survey of doctors.