FAQ: Siblingship DNA
What Tests are available?
Basically, there are three DNA tests that are available:
- Mitochrondrial DNA,
- Siblingship, and
- Twin Zygosity tests.
But names are deceiving.
The Twin Zygosity DNA Test is used to establish DNA profiles for the two children being tested IF YOU ALREADY KNOW THAT THEY ARE DEFINITELY TWINS.
In this case, if the profiles are different, then the twins are fraternal, and if the profiles are identical then a probability of being identical twins is calculated. Results are available in 5-9 days after specimens have reached the laboratory. The cost is usually $100 – $200.People have taken this test because it’s cheaper and faster, but it’s worthless to discern whether children who are adopted without note as to their twinship from the orphanage really are twins. If you receive zygosity tests results that show you have fraternal twins, you cannot be sure that they are related at all; only that they are not identical twins.
The Siblingship Test is more comprehensive. DNA samples are collected from two alleged (full or half) siblings at-home or at a DNA collection centers (a biological parent is optional, but strongly suggested). The samples are obtained using a cheek swab. After samples are sent to the laboratory, results will be available within 2-4 weeks. The cost can be anywhere from $200 to $600 depending on the lab. Siblingship testing may tell you if the children are biologically related, but may not give you highly accurate results, unless you are also testing a biological parent. Without a biological parent, you may get results that indicate a very high half-sibling chance and a lesser chance of full siblingship. This may seem inconclusive, but it may end up the best you can get.
MtDNA – Mitochondrial DNA testing. This test will only determine if the children share a maternal ancestor. Perhaps the same mother, perhaps the same grandmother, etc. This in conjunction may give you more clues as to how the children are related. Cost is similar to siblingship. You should note that recent literature shows that mtDNA may not be as conclusive as originally thought.
What should I look for in a Laboratory?
- Do they have an the appropriate ethnic Database available?
- How many genetic markers do they look at?
- Can they help you interpret the results?
- Are you accredited by American Association of Blood Banks?
- How many siblingship analyses do you run a week or month?
- Can you run additional makers if the results are inconclusive? Is there a fee?
- Do you use an ethnic database? Which Database? How large is the database?
How accurate is the DNA Siblingship test?
Not as accurate as a paternity test. Commercial DNA testing is not that specific yet. To increase the level of accuracy, a biological parent should be tested. Because international adoptees’ biological parents are usually absent, the results may not be as accurate. This is could be why some results that would indicate that the children are more likely to be half siblings. Although the siblingship test may not provide you with a conclusive answer, it may be able to provide you with an indication of whether your child is more likely to be (or not) to be the biological sibling of the other tested individual.
Why does the Lab need to use an ethnic Database?
In a siblingship test, labs generally test 16 Genetic Markers. In the interpretation of the raw data, the lab looks at how often the genetic markers at a loci matches with the suspected sibling and compares them to how often each marker/loci is found in people with the same racial background. This is why it is important to choose a laboratory that has an appropriate database available to them. Then they will do a calculation called a “siblingship index”. The higher the score of the siblingship index, the greater the possibility that the children are biological siblings.
How do I collect the DNA for testing?
Your laboratory will send you swabs (similar to large q-tips) that you will rub on the inside of your child’s cheek. Usually you will do 3 or more swabs per child to ensure that you have adequate numbers of cheek cells. This is called a buccal swab.
DNA samples are collected by simply swabbing the inside of the cheeks with a special swab like a large Q-Tip. Bacteria, or residues from food particles, toothpaste, etc will not affect the DNA collection.
How do I interpret the results?
The report should have a summary page that gives you the siblingship index with a percentage of how closely your children are related (full siblings, half siblings, etc). Also, the lab should be able to explain the results.
What does it mean when the results say that the children are more likely to be half siblings than full siblings?
Often the siblingship test will indicate that the children are more likely to be half siblings, rather than full siblings. There could be a couple of reasons for this result. First, the children may be half (not full) siblings. Second, the results are not conclusive enough because you are not testing a biological parent. It’s up to the individual families to choose how to view the results. Some may choose to believe that the children are half siblings. Some families may look at the children and/or watch the interactions between the children and decide that they believe that the children are full siblings. In any case, you can be confident that there is a biological connection.
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