Homocystinuria (HCU)

Homocystinuria (HCU)

What is Homocystinuria (HCU)?

Homocystinuria is a disease in which an enzyme called cystathionine beta synthase (CBS) is not working properly leading to very high levels of homocysteine and low levels of cysteine. If untreated, there is a elevated risk of thrombotic events such as strokes and heart attacks, ocular issue including myopia, fragile bones and osteoporosis, cognitive issues such as executive functioning deficits, and even severe mental retardation.

What are the symptoms?

Symptoms may include, but are not limited to:

  • Strokes
  • Seizures
  • Nearsightedness
  • Dislocation of the lenses of the eyes
  • Developmental delays and learning disabilities
  • Behavioral problems
  • Osteoporosis, weak bones
  • Marfanoid appearance: long and thin arms and legs
  • Chest deformities
  • Scoliosis
  • Pale skin and hair
Homocystinuria, if untreated or undertreated, can effect the ocular, skeletal, vascular, and central nervous systems.

How is HCU diagnosed?

Homocystinuria is diagnosed by a blood test. Newborn screening testing for elevated methionine levels can capture some classical HCY patients that have significant biochemical CBS deficits. However, patients are frequently diagnosed later in life due to development delays in adolescence or in conjunction with medical emergencies in early adulthood.

Current treatments

Current treatment for HCU involves following to a very low protein diet supplemented with some or all of the following: vitamin B6, betaine anhydrous powder, and medical foods. The special diet reduces the amount of methionine a patient eats and therefore the amount of homocysteine that is produced. However, patients still must eat enough methionine to support normal protein production that the body needs to be healthy and grow. Methionine is also critical for countless biological processes such as biosynthesis of hormones, neurotransmitters, phospholipids, and methylation of DNA and RNA. Methionine is present in almost all foods and therefore compliance with the HCU diet is extremely difficult.