How to read and understand common DNA test results

Written by Craig Macpherson
April 11, 2019

We all know what DNA is, but our genetic makeup can often be quite an abstract concept to get our heads around.

Home DNA testing kits have never been more popular, with researchers estimating that the market is on track to reach $10.04 billion by 2022. Though people are keen to see what interesting information can be unveiled through their genes, absorbing the scientific facts and figures is a daunting prospect for many of us.

Luckily, whether you’re considering taking a DNA test or awaiting the results of one, our helpful guide for common DNA test results is here to help you read and understand them.

How to read autosomal ancestry DNA results

Most DNA tests for ancestry reveal where in the world your genes originate from in the form of an ethnic breakdown – this is calculated according to your autosomal DNA. This will normally take the form of a list of ethnicity percentages corresponding to particular regions. For example, the list could reveal 87.5% of your genes hail from Northern and Western Europe, 7.8% derive from Eastern Europe, and 4.7% come from ‘various’ or ‘unknown’ regions. Some providers will break down larger regions (e.g. Western Europe) by country, and others, such as Living DNA, specialize in breaking down small regions (e.g. Britain) almost by county!

The regions that are included depend on the public and private reference populations that ancestry DNA providers use to calculate the origins of your genes. This means that some of the regions presented to you will be very large and vague (e.g. the Middle East) where fewer population groups have been analysed, and some will be very specific (e.g. Finland) where rich genetic information has been documented for that group.

Results are also based on data generated from each provider’s previous customers, so as ancestry DNA testing in North America and Europe is very popular, your Anglo-Saxon and European lineages will be more accurately reported; as there’s plenty of data available from people of these ethnicities. On the other hand, providers tend to have far fewer customers (and so a much smaller genealogical pool) of Asian and Hispanic descent, so results for these regions are likely to be far less specific.

In addition to the ethnicity percentages you’re given, there will often be an interactive map divided into various regions with color-coded sections highlighting where your DNA originates from. These maps often come with more information about regional history, and details of your ancestor’s migratory routes going back tens of thousands of years.

Many test results will also provide a ‘range’ of accuracy. For example, when you read AncestryDNA results, each region will be accompanied by a percentage range which shows your minimum and maximum reported ancestry for the region. This feature can often be surprising. Though the results may illustrate approximately 28% Western European ancestry, for example, the margin of error could potentially be anywhere between 0% and 57%.

How to read genetic predisposition results from health DNA tests

Certain health DNA tests will report on your genetic predisposition to a number of things; the diseases you’re most or least susceptible to, whether you’re a carrier for certain genetic conditions, and/or which medications you’re likely to respond positively or negatively to.

For example, 23andMe divide their report into:

• Health risks
• Inherited conditions
• Traits
• Drug response

Their health risks section lists conditions such as coronary heart disease and lupus, alongside percentages illustrating your risk compared to the average risk. When looking at any genetic predisposition report, it’s important to make sure you understand whether the risks you’re being shown are a comparison of your risk to the average risk (e.g. you have a 20% chance of suffering with Type 2 Diabetes vs. the average risk of 15%), your ‘lifetime risk’ regardless of the average risk (e.g. you have a 20% chance of suffering with Type 2 Diabetes), or your ‘increased risk’ compared to the average risk (e.g. you are 33% more likely to suffer with Type 2 Diabetes than the average person).

Some providers will also present your ‘genetic risk’ vs. the ‘environmental risk’ for a given condition; to help you understand how much your genes may contribute to your risk vs. non-genetic factors. For example, breast cancer is understood to be strongly associated to your DNA, but Type 2 Diabetes is much more strongly associated to your lifestyle than to your DNA.

23andMe’s report also details whether you have a ‘typical’ or ‘reduced’ response to particular drugs – your ‘drug response’. Some of the most commonly prescribed drugs are blood thinners, and it’s important to note that the effectiveness of these medications (and many others) are dependent on the genetic variants you possess.

Once you receive a drug response report from a DNA testing provider, you may be able to take it to your physician to help them tailor any medications you’re taking. However, it’s important to bear in mind that many physicians have not specialized in genetics and the report may not be meaningful to them. Sometimes, your physician may take your drug response report as a prompt to commission additional genetic testing from their trusted partners, so that meaningful action can be taken.

When considering any type of genetic predisposition result from a health DNA test, if you’d like reassurance, we advise you check the scientific references that the DNA testing provider has used. Try to identify:

• How many people participated in the study(s) that produced the research? Over 1,000 participants is recommended for meaningful research of this type.
• Were participants of your gender and ethnicity included? If the answer is ‘yes’, then this also adds to the meaningfulness of the research.

There are many other ways for you to investigate your genetic predisposition result, so if researching the above doesn’t reassure you, or you’re not the researching type!, you should reach out to the DNA testing provider who has a responsibility to provide you with ‘genetic counselling’ support. You’ll be able to discuss your result over the phone, face to face, or by web meeting; and the counselor will be able to answer your questions and explain why the result is meaningful.

How to read family tree DNA results

Many people take ancestry DNA tests for the ‘family finder’ feature; this is what allows individuals to find distant family members based on their DNA, providing those family members have also taken an ancestry DNA test with the same company you take yours with. Once the results are in, the DNA testing provider will give you access to a list of distant relatives who you’ll be able to contact, up to and including your 9th cousins!

Providers such as Family Tree DNA and MyHeritage also provide a ‘family tree builder’ as part of their service, which lets you build a family tree using the relatives you know about, and add those distant relatives who’ve been discovered by the DNA test. Using these tools, you’ll soon be able to see whether your family tree overlaps with others’, and you can reach out to them to see if you can merge your trees for an even broader view of your ancestry.

To go into more detail, your familial relationship with other people in these DNA testing providers’ DNA databases is measured in centimorgans (cM), which refers to how many sections of DNA you share with a possible relative aka match. Reports, such as those by MyHeritage, highlight all your matches and include the number of shared DNA segments, the length of the largest shared segment in cM, and the overall percentage of shared DNA. This information allows the provider to estimate the familial relationship between you and your match. MyHeritage also provides a ‘chromosome browser’ which demonstrates the exact locations of the DNA you share with a particular match.