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Homocystinuria due to Cystathionine β-Synthase Deficiency
CBS gene
Homocystinuria due to cystathionine β-synthase (CBS) deficiency is the most common inborn error of methionine metabolism, characterized by involvement of the eye (ectopia lentis and/or severe myopia), skeletal system (marfanoid habitus, osteoporosis, scoliosis, pectus excavatum, genu valgum), vascular system (premature artherosclerosis and thromboembolism), and central nervous system (developmental delay/mental retardation, seizures, psychiatric problems). Any or all of these systems may be involved. There is variable expressivity even among patients within the same family. Ectopia lentis may be the only presenting feature in some patients, other individuals can present with a thromboembolic event as an adult. About half of all CBS deficient patients respond to pharmacologic doses of pyridoxine (vitamin B6). Pyridoxine-responsiveness is constant within sibships. It has been estimated that newborn screening for elevated methionine levels detects only about one-third of patients. Homocystinuria due to CBS deficiency is caused by mutations in the CBS gene. Mutation analysis is expected to identify a sequence variant in greater than 95% of patients with deficiency of the CBS enzyme.
Using genomic DNA, bi-directional sequence of the coding region and splice junctions of the CBS gene is analyzed. If sequencing identifies a mutation on only one allele of the CBS gene, and if clinically indicated, reflex deletion/duplication testing (ExonArrayDx) will be performed at no additional charge to evaluate for a deletion/duplication of one or more exons of this gene. Carrier testing and prenatal diagnosis is available once the mutation in the family has been defined.
Information Sheet, including prices and CPT codes
Consent Document
Genetic Test Sample Submission Form (Test Requisition Form) including Payment Options
Cystathionine Beta-Synthase Deficiency, CBS deficiency, cystathionine, cysteine, homocystine, methionine
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