Zygosity
It is the responsibility of the ordering physician to ensure that informed consent has been obtained from the patient/legal guardian before ordering genetic testing. Please review the following Pre-Test Counselling Information with your patient before requesting any of our genetic tests.
Indications for Testing
- Multiples of the same sex for whom determination of zygosity is required to:
- aid in understanding of whether different clinical presentations could be explained by dizygosity or;
- assess risk in asymptomatic multiple(s), in the context of a genetic condition of variable expressivity having been confirmed in one of the multiples.
Contraindications
Testing is only performed for the indications listed above. If the motivation is to pursue testing for other reasons, private genetic testing companies will perform this analysis for a fee.
Description of this Assay
The AmpFlSTR® Identifiler™ kit is used to compare multiples (twins, triplets, etc) at highly polymorphic short tandem repeats across the autosomes. Monozygotic (identical) multiples share identical alleles at all markers. Dizygotic/Trizygotic/etc (fraternal) multiples will typically have non-identical alleles at more than one locus.
Sensitivity and Limitations
Since DNA fingerprinting does not attempt to match the entire genome of the children, there is a small probability that multiples are dizygotic, despite matching at all DNA markers used in the fingerprinting analysis.
Turnaround Time
Routine
6 weeks
Specimen Requirements
Blood: 4 mL EDTA is optimal (Minimum: 1 mL EDTA)
DNA: 100 μL at 200 ng/μL is optimal (Minimum: 30 μL at 200 ng/μL)
Label each sample with three patient identifiers; preferably patient name, PHN, and date of birth and ship to the address below. Samples should be shipped at room temperature with a completed MGL Requisition to arrive Monday to Friday (not on Canadian statutory holidays).
Test Price and Billing
Testing is only available to residents of Canada, except in very specific circumstances where testing is urgent or emergent. This test is only available to individuals who are insured by Health Insurance BC (administered through the BC Medical Services Plan (MSP)) and who meet test utilization guidelines or policy. For those without this coverage, contact the laboratory to discuss.
Cautions
Molecular genetic testing is limited by the current understanding of the genome and the genetics of a particular disease, as well as by the method of detection used.
Rare single nucleotide variants or polymorphisms could lead to false-negative or false-positive results. If results obtained do not match the clinical findings, consult the on-service Molecular Geneticist.
A previous bone marrow transplant from an allogenic donor will result in molecular data that reflects the donor genotype rather than the recipient (patient) genotype. Consult the on-service Molecular Geneticist for approach to testing in such individuals.
Transfusions performed with packed red blood cells will generally not affect the outcome of molecular genetic testing. However, if there is no clinical urgency, the cautious approach is to wait one week post packed red cell transfusion before collecting a sample for genetic testing. Consult the on-service Molecular Geneticist as needed.
Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in our interpretation of results may occur if information given is inaccurate or incomplete.