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Understanding Health Risk Reports

December 2013 – Pending an FDA decision, 23andMe no longer offers new customers access to health reports. Customers who received their health information prior to November 22, 2013 will still be able to see their health reports, but those who purchased after that time will only receive their ancestry information as well as access to their uninterpreted raw data.

In the Health Risks section, you will find information about how your genetics influences risk for complex diseases like type 2 diabetes and colorectal cancer. For reports designated as Established Research, we provide an estimate of your risk, using the 23andMe Odds Calculator, based on one or more SNPs associated with the disease as well as measures of the disease incidence in specific ethnic groups. These estimates do NOT take into account personal or family history or your lifestyle or environment. There may also be additional genetic factors, yet unidentified or unavailable to our technology, that also contribute to risk for these conditions.

How does the 23andMe Odds Calculator work?

The 23andMe Odds Calculator provides an estimate of incidence for a disease or condition based on specific genetic factors. We incorporate the latest available data in the biomedical literature to make this estimate. Such data include the contribution of SNPs to disease risk, differences in these contributions among ethnic groups, and measurements of the incidence and prevalence of diseases in different populations. This data may change over time as our understanding of disease, genetics, and epidemiology improves.  

In epidemiology, incidence is a measure of how often people in a population are diagnosed with a particular condition in a given period of time. The 23andMe Odds Calculator estimates incidence in two different contexts: average incidence, and incidence for people with a particular genotype. 

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Incidence may also be thought of as an individual's chance of being diagnosed with a condition during a given period of time (assuming that he or she did not have the condition to begin with). Saying that "25 people out of 100" will be diagnosed with a condition is another way to describe a 25% chance of developing the condition. 

The "genotype-specific" incidence is an estimate of how many individuals in a population composed of people with your genotype are likely to be diagnosed with a condition over a given age range.

In order to estimate genotype-specific incidence, we do the following:

  1. Find genetic association studies detailing risk associated with those SNPs;
  2. Decide which associations are most likely to be real based on our vetting criteria;
  3. Retrieve your genotype at the relevant SNPs that are also available to our technology;
  4. Combine your genotype-specific risk from all relevant, available SNPs; and
  5. Plug your combined genotype-specific risk and data about disease incidence into the 23andMe Odds Calculator to estimate disease incidence for people with your genotype.

The 23andMe Odds Calculator reports genotype-specific incidence for people who share your genotype and the selected ethnicity and age range. The estimate is based on the current state of biomedical literature and is related only to your particular genotype, but not to your personal or family history, or your environment (although we do take into account age and ethnicity). It is only an estimate.

The incidence values we obtain from the literature were generally measured in U.S. samples. They may differ from estimates of incidence in other populations.

Also note that genetics may contribute only a small amount to one's overall risk for a disease. Smoking, for example, increases risk for lung cancer far more than any single SNP. 

What does the Marker Effects display in Established Health Reports show?

The bar chart shows the amount of decreased or increased risk the SNPs in various genes contribute to estimated incidence of disease for people with your genotype.

The horizontal line represents the average person's risk of disease. If we knew nothing about your genotype at all, we would estimate that you had the average risk for your ethnicity and age.

 

Each bar represents the contribution of a single SNP to risk. (Note that there may be other, as yet unidentified SNPs or associations that contribute to your risk for a particular disease.)

You can mouse over a bar to learn more about the associated marker and/or gene:

 

Depending on your genotype for a known SNP, people with your genotype may have risk that is higher than average (above the line and red), lower than average (below the line and green), or close to average (at or near the line). The size of the bar is related to the change in risk due to your genotype at the SNP, whether increased or decreased.

The light gray bars show you the full range of contributions to risk made by a given SNP. You might have a genotype that doesn’t change your risk much from the average (i.e., the red or green bar is close to the line). But other people have genotypes that increase or decrease risk by the amount shown by the light gray bar.

What does NA/NC/NG mean in the marker effects bar chart included in Established Health reports?

In some cases, the bar chart will not be able to display data for a user. A circle will appear with one of three codes: NA, NC, or NG.

NA: Not Applicable. Many association studies have been confirmed in samples from specific ethnic groups. Until the association is repeated in other ethnic groups, 23andMedoes not assume that the data holds for all ethnic groups. This is quite common when selecting "Asian" or "African" for ethnicity, for reasons outside of our control. If an association has been shown NOT to hold in another population, the bar chart will also show “NA” for that SNP.

NC: No Call. Occasionally, a user's data may not allow us to determine his or her genotype at a SNP or marker with confidence. It is possible that future review will allow us to call the genotype, but until that time, the 23andMe Odds Calculator does not include the ambiguous data in estimates of disease incidence.

NG: Not Genotyped. If the user has been genotyped on an older version of our technology platform, there may be some SNPs or markers for which the user has no data at all. 

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