DNA dilemmas – what do ancestry DNA test results mean?

Online DNA testing kits have become popular in recent years, promising a range of insights from how your body metabolises caffeine to what type of exercise you should be doing.

Those interested in such testing should proceed with caution though, as tests conducted outside of Australia are not subject to rigorous Australian standards. This means that when you’re ordering a testing kit online, it’s difficult to know what you’re getting.

The accuracy of some of the ‘health’ claims has been called into question but one of the most popular areas for direct to consumer DNA testing is ancestry testing.

As the name suggests, ancestry DNA tests are designed to examine your DNA and determine where your ancestors were from.

Tests can be ordered online; a kit is mailed out with a test tube for collecting a saliva sample. The sample is then sent for testing and results are reported back online. The results provide an estimate of ethnic make-up broken down by percentages across different regions. The report can also include potential relatives who have been identified in the company’s database.

These tests are popular for those curious about their family tree, but how accurate are these estimates and could these findings tell a person anything about their health?

Kevin Carpenter, former President of the Human Genetics Society of Australasia helped us clear up some of the confusion.

  1. Is this a cheap way to get my whole genome sequenced?

In short, no Whole genome sequencing requires sophisticated technology that can sequence all of the 6.4 billion nucleotides that make up the human genome. It requires a higher level of analysis and interpretation by a pathologist, and takes several weeks to complete, hence the difference in cost.

The method used for ancestry DNA testing is called microarray testing and looks at single nucleotide polymorphisms (SNPs), which are points in the genome that vary between individuals.

These SNPs are spread across all the chromosomes and ancestry tests typically look at 700,000 SNPs. However, this testing is only looking for that particular variant at that point, hence microarray testing can be done more cheaply than whole genome sequencing.

  1. How can they know what the genetic makeup of someone’s ancestors was when DNA testing is such a recent invention?

This is a key misunderstanding and the cause of lots of confusion amongst people who take these tests.  The companies are steadily growing their database of SNP patterns but when they say your genetic makeup comes from a particular region, they are comparing your data with other people’s, to infer the geographical region of origin.

So, if an SNP is very common in southern European populations but rare in the rest of the world, the finding of that SNP suggests that somewhere in your family tree someone came from southern Europe. The companies offering these tests use mathematical algorithms that look at many thousands of SNPs known to have a particular geographical distribution.

It’s important, however, to know that they are comparing prevalence of that SNP in the CURRENT population of that region. They do correct for recent migrant effects (North America and Australia have largely migrant populations) by looking at SNPs that are found in older established populations, but there are lots of stories of the same SNPs giving different ethnic origins through different companies’ algorithms.

  1. Do these tests tell us anything about our health, e.g if we have genes linked to certain cancers?

Although some companies may now be offering DNA testing services for health conditions in addition to ancestry services, genetic health information is not a part of the ancestry results report.

These types of tests are not intended for medical purposes and should not be considered diagnostic.

The tools used for ancestry testing are the same as those used by researchers to try and find genetic causes of complex diseases (so called genome wide association studies or GWAS).  So, if studies have shown an association between having a particular SNP and developing a cancer for example, that could be informative. However, it would require more detailed analysis and a specific report of which SNP variants have been found and any conditions they are associated with.

It’s also important to note than in Australia there are strict guidelines for providing genetic testing. Tests must be ordered and results delivered by a medical professional. This ensures that only appropriate tests are ordered and that results can be interpreted and explained to the patient by their doctor.

A person referred for a genetic test is required to speak with a genetic counsellor before testing to discuss the test and possible results. This is essential to ensure that the person is properly informed and can make their own individual decision about testing.

  1. How is ancestry testing different to medical genetic testing for cancer risk?

Let’s say you have a family history of breast cancer.  It may be appropriate, following genetic counselling, to look for mutations in the genes BRCA1 and 2. That clinical test will look at the whole of both genes and any variants found will be classified according to the likelihood they could be disease causing.

The SNP databases show there are over 3000 known BRCA2 SNPs, but not all are disease causing and of those that are, typical ancestry DNA tests only cover about 23% of them. This is why this type of testing is offered to consumers for ancestry information rather than medical data as it does not provide the same level of detail as a specific clinical test.

Anyone who has concerns about family health history and their own risk of disease should talk to their doctor about what testing may be appropriate for them.

  1. Could this help a person find family members that they do not know about?

The short answer is yes, IF that person has had a test with the same company and they have agreed to share their information. The number of shared SNPs falls rapidly as you move back through generations or further from the parent of origin though, so you may find a second cousin but more distant relatives are much less likely.

So anyone deciding to take an ancestry DNA test should be careful about what they expect from their results and remember that this type of DNA testing sits well outside the world class genetic testing provided by Australian pathology labs for medical purposes.