Gene Symbol: TWIST1
Chromosomal Locus: 7p21
TURNAROUND TIME: 15 days
TESTING METHODOLOGY: Polymerase chain reaction (PCR) and DNA Sequencing of the entire coding region of the Twist gene.
- Collect: Prefer two 5ml whole blood EDTA (lavender top) tube.
- Min. Collection: 0.7 ml whole blood EDTA.
- Transport: Blood EDTA at Room Temp shipped next day air (No Saturday delivery; store specimen refrigerated and ship Monday).
- Stability: Ambient: up to 7 days; Refrigerated: 2 weeks. Frozen: unacceptable
- Unacceptable Conditions: Serum. Frozen or severely hemolyzed blood. Clotted blood.
- Prenatal testing: Direct: 5ml direct unspun amniotic fluid or 15mg CVS tissue with a backup flask growing. Culture: confluent T25 flask. Maternal blood sample is required for maternal cell contamination studies.
Counseling and informed consent are recommended for genetic testing. A consent form
is available as a resource but not required.
Incidence: 1 in 25,000 -50,000
Inheritance: Autosomal dominant
Classic SCS is characterized by coronal synostosis (unilateral or bilateral), facial asymmetry, ptosis, and characteristic appearance of the ear. Syndactyly of digits two and three of the hand is variably present. Intelligence is usually normal, but mild to moderate mental retardation may be present. Wide phenotypic variability and incomplete penetrance
are well documented in SCS.
Molecular Genetic Mechanism: Most cases are caused by missense/ nonsense point mutations, or small deletions or insertions. Approximately 10%-25% of cases are due to deletions of the entire gene.
Clinical Sensitivity: > 80%
Analytic Sensitivity: 99%
Test Limitations: Deletions of the entire gene or mutations outside the tested regions of the genes will not be detected. Rare diagnostic errors can occur due to primer or probe site mutations or rare polymorphisms.
INDICATIONS FOR USE:
- To determine whether Saethre-Chotzen syndrome is responsible for abnormalities in the skull, eyes, or limbs.
- To discriminate between syndromes with different but overlapping clinical symptoms in an affected individual.
- Prenatal diagnosis for Individuals at risk due to family history or ultrasound findings.