Tuesday, September 20, 2011

DNA Technology Improving for Sibling Testing

Everyone knows the stories of two families searching their child's orphanage adoption group and finding another family's child that bears an uncanny resemblance to their own child.  At times, such matches seem possible, with the two children sharing common characteristics such as birth dates and finding locations.  Sometimes it borders on the absurd, such as the adoptive mother who thought the child on the Fisher Price Little People Sonya Lee box looked just like her own daughter.

A few years ago I wrote an article on what I felt were significant weaknesses in then-current sibling DNA testing technology, cautioning adoptive families not to put to much faith in their accuracy.  The reason was simple:  Using only 27 genetic markers, the tests were possibly susceptible to "genetic drift", a problem with small, inbred populations, which many Chinese towns and villages are.  Additionally, these tests were often (usually) conducted against databases with few actual native Chinese DNA in them.  Rather, they consisted of diaspora Chinese, Korean, Japanese, and other Asian samples.  Obtaining a 95% "probability" result simply meant that the two children were more closely matched in DNA than 95% of the database.  With a database of millions of DNA samples, 5% of the DNA database's samples would produce a higher "probability". Usually, that margin of error allowed for thousands, or even tens of thousands, of possible matches ("False positives").

I remain of the opinion that many of the most well-known stories of reunited siblings in the Chinese adoption community are more than likely not really siblings at all.

Technology has improved significantly in the intervening six years, and today many DNA labs don't test only  27 markers, or even 1,000 markers, but currently a million markers or more are compared when a DNA test is done.  With so many genetic comparisons being done, previous problems of genetic drift and general uncertainty of a sibling match are eliminated.  With modern testing, the need for parental DNA to perform sibling matches is no longer needed.  When two people's DNA are compared with one million markers, the result is either a positive or negative.  The ambiguity is gone.

This is, of course, of significant importance to the adoption community, where parental DNA is usually lacking.  With current technology, one can now achieve the level of confidence one could only obtain with parental DNA five years ago.  Combined with falling testing costs, and it is now possible for every child from an orphanage to submit DNA and for sibling matches to be made across a wide number of submissions. 

One lab that employs this new technology is 23andMe.com, located in Mountain View, CA.  For $99 (plus $9 per month for 12 months) 23andMe.com will analyze over one million genetic "genomic variations" on a person's DNA.   Of interest to adoptive families, the lab will then cross-analyze the submitted DNA against the DNA from every other person in the company's database, and alert you of any sibling, half-sibling, first cousin or parental matches.  They also allow you to be alerted if a match is made in the future.  Thus, two DNA samples can be independently submitted by interested adoptive families, and 23andMe will provide information (if both parties agree) that allow matched individuals to share information. 

But 23andMe's test goes way beyond DNA matching.  As a result of their huge database of DNA samples and the results of studies done on specific genetic markers, 23andMe can provide you with ancestral information on where your child's ancestors originated -- did her ancestors originate in northern China or Southern?  Did an ancestor migrate into China from another country?  With female children, this information is only available for the maternal lines, but it is nevertheless fascinating reading.  Meikina's DNA indicates that some of her ancestors originated outside China, most likely in Vietnam.  Meigon's ancestors were the same people that migrated over the land-bridge and settled North America. 

Additionally, and perhaps the most important practical information, 23andMe's report will detail possible medical risks that may be found in one's DNA.  For example, my daughter Meigon's test indicates she has a lower than average risk of Parkinson's and type 2 diabetes, but a higher risk of high blood pressure.  Meilan's DNA suggests she may be at significantly higher risk for breast cancer.  These assessments may have important ramifications for Meigon and Meilan's futures. 

Families would be well advised to utilize the current technology in the future for any sibling testing, or to confirm previous tests conducted with the old technology.  Not only will you be given a definitive answer to your sibling suspicions, but you will be given an amazing array of useful information about your child, some of which may have important implications to their lives.

After I posted the above article, I contacted 23andMe.com to have them provide a more detailed explanation of their sibling testing.  They provided me with the following answer:

We can determine a relationship between two siblings by comparing the amount of DNA that they share. We look for segments of DNA between two people that are identical-by-descent (IBD); the more IBD segments two individuals share, and the longer those segments are, the closer their relationship. Siblings, half-siblings, cousins, parents/children all share a certain range of IBD segments. We can assign a relationship based on the segments. 

In plainer English:  When the DNA strands of the birth mother and father are separated to produce the eggs and sperm, it does not occur like a zipper, with one gene going on way, and the next one going the other.  The egg or sperm contains strands (complete sections) of original DNA.  These "gene clusters" are highly unique, and if a gene cluster appears in two individuals, it is strong evidence that the two people are related.  If two individuals possess many such gene strands in common, it is definitive proof that they are siblings.  

With modern genetic testing such as 23andMe's, population drift and other genetic anomalies are no longer a consideration.  This was the main weakness of the 27 allele tests.  But current technology is based ONLY on the two DNA samples, and are not compared to DNA databases in order to confirm a relationship.