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Disorder of protein metabolism: homocystinuria

Homocystinuria is an inborn error of metabolism in which there is a disturbance in the breakdown of the amino acid methionine, causing too much of the amino acid homocysteine to enter the blood. This causes blood vessels to become damaged at a young age. This can lead to all kinds of conditions such as pulmonary embolism and thrombosis. Sometimes there is a delay in mental development. What are the symptoms of this condition and what is the life expectancy?

Amino acids homocysteine and methionine

Amino acids are the building blocks of proteins in the body. Homocysteine is an amino acid. This is produced in the body from the amino acid methionine. If something goes wrong with the conversion of this substance or with the metabolism, the level of homocysteine can become too high.

What homocystinuria means

Homocystinuria is a rare hereditary metabolic disease involving a disturbance in the breakdown of the amino acid methionine. Methionine is used in the body for protein metabolism and must be obtained from the diet. If the breakdown of methionine is disturbed, there is a lot of homocysteine in the blood and this causes the blood vessels to be damaged at an early age. It is a hereditary condition in which both parents must have the defective gene in order to pass it on to their child.


This condition involves multiple organ systems. These may include: the cardiovascular system, central nervous system, muscles and connective tissue. Because homocysteine accumulates in the blood, there is increased excretion of this substance in the urine. Children with homocystinuria appear normal and experience vague symptoms. Possible symptoms may include:

  • Long limbs
  • Blushes on the cheeks
  • Narrow physique
  • X-legs
  • Cobbler’s breast or chicken breast
  • Mental retardation
  • Eye abnormalities
  • Epilepsy
  • Psychiatric illnesses
  • Thrombosis and pulmonary embolism
  • Bone decalcification



Suspicion of this disease may arise if the above symptoms apply. Until October 2010, this was tested using the heel prick. The test turned out to be not good enough and a better test is being developed. Furthermore, homocystinuria can be diagnosed through a blood test or from the urine.


This disease cannot be cured, but it can be treated. Left untreated, the life expectancy of patients with homocystinuria is reduced. A quarter of patients die before the age of 30 as a result of thrombotic complications such as a myocardial infarction. There is no specific treatment for this condition. Patients are often given a high dose of vitamin B6, almost half of which responds to it. Patients who do not respond to this treatment should follow a diet low in methionine. This must be followed for the rest of life. In addition, treatment with trimethylglycine and additional addition of folic acid and cysteine to the diet follow. In addition, it can help to combat the symptoms.

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