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- BCKD Deficiency
- Branched-chain Ketoaciduria
- Jewish Heritage Test
- MSUD Carrier Testing, DNA
Carrier screening for Maple syrup urine disease (MSUD, OMIM 248600), an inherited recessive disease caused by deficient activity of branched-chain α-ketoacid dehydrogenase.
The diagnosis of MSUD is made by the finding of alloisoleucine in plasma. DNA testing is appropriate for carrier screening in individuals of Ashkenazi Jewish or Mennonite ancestry, confirmation of mutations in patients previously diagnosed with MSUD who belong to these ethnic groups, and prenatal diagnosis for at-risk couples who are known to carry the mutations detected by this test. This DNA test only detects the Y438N, R183P, G278S, and E372X mutations found in the Ashkenazi Jewish and Mennonite populations. This test has limited value for individuals from other ethnic groups.
Polymerase chain reaction (PCR) and primer extension
MSUD can be detected by newborn screening and effectively treated with dietary restriction.1,2 Almost all state newborn screening programs are required by statute to screen infants for MSUD.3 Untreated disease is characterized by poor feeding, brain damage, and ultimately coma and death. Even with dietary restriction of branched-chain amino acids, affected individuals may still have periodic metabolic crises due to infection or stress. Impaired intellectual development or neurological complications can occur if the initial diagnosis is delayed.2 The disease is present in all ethnic groups, but has elevated prevalence among Ashkenazi Jews and Mennonites.2,4 Parents who are each carriers of MSUD are asymptomatic, but have a 25% chance with each pregnancy to have a child with the disease. Prenatal diagnosis can be performed by molecular mutation analysis (when the mutations in the family are known) or by measurement of enzyme activity in amniocytes. Molecular testing for MSUD encompasses four mutations in two components of the branched-chain ketoacid dehydrogenase complex (BCKAD): the E1 α-subunit (BCKDHA, OMIM 608438), and the E1 β-subunit (BCKDHB, OMIM 248611). Plasma amino acid analysis can be used to diagnose affected individuals, but cannot determine carrier status. A negative result of this DNA test in an individual of Ashkenazi Jewish or Mennonite ancestry decreases the likelihood that a person is a carrier, but cannot completely eliminate the possibility. The presence of a rare mutation cannot be ruled out. DNA test results must be combined with clinical and family history information for the most accurate interpretation.
Whole blood, amniotic fluid, chorionic villus sample (CVS), or LabCorp buccal swab kit (buccal swab collection kit contains instructions for the use of a buccal swab)
7 mL whole blood, 10 mL amniotic fluid, 20 mg CVS, or LabCorp buccal swab kit
3 mL whole blood, 5 mL amniotic fluid, 10 mg CVS, or two buccal swabs
Maintain specimen at room temperature or refrigerate at 4°C.
Causes for Rejection
Frozen specimen; hemolysis; quantity not sufficient for analysis; improper container; wet buccal swab
For the diagnosis of maple syrup urine disease, order Amino Acid Profile, Quantitative, Plasma . DNA testing is appropriate for carrier screening and confirmation of mutations in individuals from specific ethnic groups (see Limitations).
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|511310||MSUD, Carrier Testing, DNA||511368||Maple Syrup Urine Disease||53039-4|
|511310||MSUD, Carrier Testing, DNA||511954||51969-4|