What is the definition of Homocystinuria?

Homocystinuria is a genetic disorder that affects the metabolism of the amino acid methionine. Amino acids are the building blocks of life.

What are the alternative names for Homocystinuria?

Cystathionine beta-synthase deficiency; CBS deficiency; HCY

What are the causes for Homocystinuria?

Homocystinuria is inherited in families as an autosomal recessive trait. This means that the child must inherit a non-working copy of the gene from each parent to be seriously affected.

Homocystinuria has several features in common with Marfan syndrome, including skeletal and eye changes.

What are the symptoms for Homocystinuria?

Newborn infants appear healthy. Early symptoms, if present, are not obvious.

Symptoms may occur as mildly delayed development or failure to thrive. Increasing visual problems may lead to diagnosis of this condition.

Other symptoms include:

• Chest deformities (pectus carinatum, pectus excavatum)
• Flush across the cheeks
• High arches of the feet
• Intellectual disability
• Knock knees
• Long limbs
• Mental disorders
• Nearsightedness
• Spidery fingers (arachnodactyly)
• Tall, thin build

What are the current treatments for Homocystinuria?

There is no cure for homocystinuria. About half of people with the disease respond to vitamin B6 (also known as pyridoxine).

Those who do respond will need to take vitamin B6, B9 (folate), and B12 supplements for the rest of their lives. Those who do not respond to supplements will need to eat a low-methionine diet. Most will need to be treated with trimethylglycine (a medicine also known as betaine).

Neither a low-methionine diet nor medicine will improve existing intellectual disability. Medicine and diet should be closely monitored by a doctor who has experience treating homocystinuria.

What are the support groups for Homocystinuria?

These resources can provide more information about homocystinuria:

• HCU Network America -- hcunetworkamerica.org
• NIH/NLM Genetics Home Reference -- ghr.nlm.nih.gov/condition/homocystinuria

What is the outlook (prognosis) for Homocystinuria?

Although no cure exists for homocystinuria, vitamin B therapy can help about half of people affected by the condition.

If the diagnosis is made in childhood, starting a low-methionine diet quickly may prevent some intellectual disability and other complications of the disease. For this reason, some states screen for homocystinuria in all newborns.

People whose blood homocysteine levels continue to rise are at increased risk for blood clots. Clots can cause serious medical problems and shorten lifespan.

What are the possible complications for Homocystinuria?

Most serious complications occur due to blood clots. These episodes can be life threatening.

Dislocated lenses of the eyes can seriously damage vision. Lens replacement surgery may be needed.

Intellectual disability is a serious outcome of the disease. But, it can be reduced if diagnosed early.

When should I contact a medical professional for Homocystinuria?

Call your provider if you or a family member shows symptoms of this disorder, especially if you have a family history of homocystinuria.

How do I prevent Homocystinuria?

Genetic counseling is recommended for people with a family history of homocystinuria who want to have children. Prenatal diagnosis of homocystinuria is available. This involves culturing amniotic cells or chorionic villi to test for cystathionine synthase (the enzyme that is missing in homocystinuria).

If there are known gene defects in the parents or family, samples from chorionic villus sampling or amniocentesis can be used to test for these defects.

REFERENCES

Schiff M, Blom H. Homocystinuria and hyperhomocysteinemia. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier Saunders; 2020:chap 198.

Shchelochkov OA, Venditti CP. Methionine. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 103.3.