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Alternative names
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Cystathionine β-synthase (CBS) deficiency
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About the condition
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Classical homocystinuria is an amino acid disorder. It is a hereditary disease that is caused by a missing enzyme (cystathionine β-synthase) that is required to metabolise methionine and homocysteine. These are amino acids found in protein.
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Inheritance
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Autosomal recessive
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| Year screening started in WA |
2005 |
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Incidence in Australia
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Approximately 1 in 100,000 births
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Enzyme defect
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Disorder of the methionine trans-sulphuration pathway.
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Symptoms if untreated
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- Mild to moderate intellectual disability
- Seizures, psychiatric disturbances
- Skeletal problems, including osteoporosis
- Ocular problems, including dislocation of the lens of the eye
- Thromboembolism
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Metabolites on bloodspot screening
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- Increased methionine
- Increased homocysteine (second-tier test)
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Diagnostic tests
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- Plasma total homocysteine
- Plasma amino acids
- Urine amino and organic acids
- CBS gene analysis
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Treatment
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- Methionine-restricted diet with supplements
- Betaine supplementation
- Vitamin B6 may benefit some forms
- Additional vitamin B12
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Screening issues
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The vitamin B6-responsive form of CBS deficiency may be missed as methionine may not be increased in the first weeks of life.
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