Personal Genome

Roughly one in eight women faces breast cancer at some point in her life and nearly everyone has a mother, sister or friend who’s been diagnosed with it. These statistics are staggering and really demonstrate that breast cancer touches everyone.

As a genetics company, 23andMe is invested in understanding how genetics influences the development of cancer and how people respond to treatment (see bottom of post). But we’re motivated most of all by the stories we hear from people whose lives are impacted by the diseases we study. Below are two stories from women affected by breast cancer.

Jill

Jill’s 23andMe results came back in 2010 reporting a mutation in the BRCA1 gene, which can significantly raise a person’s lifetime odds of developing breast cancer. She and her husband then met with a genetic counselor and had the test redone by another genetic testing company only to get the same result.

This knowledge combined with her family history of cancer prompted Jill to meet with specialists and see what could be done to avoid developing the disease. Jill elected to have a double mastectomy, which decreases the odds of developing breast cancer. Said Jill, “the decision to have the double mastectomy, although it was scary, was actually pretty easy to make…Once I found out I was BRCA positive I felt I was in a lucky position to fight cancer before I ever got cancer.”

Joy

Joy is a breast cancer survivor who also lost both her mother and a sister to breast cancer. In order to find out if she had passed a genetic risk for the disease to her children she purchased 23andMe’s Personal Genome Service. She also paid the more than $3,000 it costs for complete BRCA screening. “I was two or three months into treatment and I figured I must be carrying the (variant),” Joy said.

It turned out that neither test pulled up a mutation in either the BRCA1 or BRCA2 genes. Although BRCA mutations account for most but not all inherited breast cancers in women, they still only explain a small fraction of total breast cancer cases. Non-genetic factors and mutations in other genes can also influence risk (see sidebar for more information). Still, for Joy, it was a relief to know that she isn’t passing one of the BRCA mutations to her children. “It was a revelation in that I assumed I had the (variant),” she said.

Jennie Cole, c.1895

As the series Finding Your Roots with Henry Louis Gates, Jr. begins its 10-week run on PBS, The Spittoon will feature posts from 23andMe’s Ancestry Ambassadors featuring their own stories about using DNA to dig into ancestry.

By CeCe Moore

I have always felt a special affinity for Jewish people and their heritage. Throughout my life I have had many Jewish friends.

I have even been mistaken for a Jewish person despite having no known Jewish ancestors.

As a result, I was especially intrigued when, after 23andMe’s Ancestry Finder launched in 2010, I found that a number of people with segments of DNA that matched mine were self-identified as Ashkenazi Jews. The Ancestry Finder lab seeks to graphically illustrate the country of origin for certain segments of your DNA by locating stretches that match those of people from specific geographic regions. Ancestry Finder also identifies matching segments for Ashkenazi Jewish ancestry.

My Ancestry Finder chart showing matches with people who have three Ashkenazi grandparents

In particular, in my Ancestry Finder results I noticed a cluster on my seventh chromosome that appeared to contain a significant number of matches with self-declared Ashkenazi ancestry. When I examined the downloaded spreadsheet of Ancestry Finder matches, I discovered that on Chromosome 7 between the positions 51,500,000 and 146,700,000, I had no less than 47 matches with people who self-identify as, at least, partially Jewish. These matches all appeared to be rather small and concentrated on that one spot, but it did cause me to ponder the possibility that I could have distant Jewish ancestors.

Investigating further, I found that my mother had no matches associated with Ashkenazi Jewish ancestry on her Ancestry Finder lab. Since my father is deceased, I asked my paternal uncle to test in his place. When I received his results, there it was clear as day, that same Ashkenazi cluster on his seventh chromosome!

In fact, his Jewish connection appeared to be even more substantial than mine, with 69 self-described “Ashkenazi” matches on Chromosome 7 between positions 39,400,000 and 103,400,000 found in the Ancestry Finder match download.

Paternal Uncle’s matches with people who have three Ashkenazi grandparents.

Notably, my paternal uncle’s results also included a number of Public Matches in 23andMe’s Relative Finder who list their ancestry as Jewish. Most of these are predicted as “Distant Cousins”, which probably explains why they don’t show up in my Relative Finder. In this case, testing just one generation further back in time revealed very useful information.

While this Ashkenazi ancestry is fairly distant, it certainly appears to be authentic. With approximately 70% of my uncle’s chromosomes covered in Ancestry Finder, 3.6% – 7.8% is declared Ashkenazi. With this in mind, I would guess that he and my father have a 2^nd great-grandparent of primarily Jewish descent or several ancestors with lesser amounts of Jewish ancestry.

Paternal Uncle’s matches with people who have one Ashkenazi grandparent.

Since the majority of the matches cluster in the same area, the most likely conclusion is that this DNA is inherited from a single ancestor. My paternal family tree is fairly complete and so far without an obvious suspect, but since my father’s great-grandmother Jennie Cole’s father is unknown, this scenario is certainly a viable possibility. In order to focus in on this prospect, I would need to test more of Jennie’s descendants to isolate her DNA and determine if there is evidence of Jewish ancestry in the portions of the DNA that each of them inherited from Jennie. Since the paternity of Jennie has long been an enigma to me, this is a very intriguing new avenue of exploration for my genealogy research.

Before testing at 23andMe, I never would have imagined that I had Jewish ancestry. Now that I have discovered this tantalizing fact, I am on the hunt to learn more about this illusive ancestor!

CeCe Moore is a genetic genealogist specializing in the use of autosomal DNA for genealogy. She writes the popular blog Your Genetic Genealogist and works as a television producer with StudioINTV.  CeCe is the Southern California Regional Coordinator of the International Society of Genetic Genealogy (ISOGG), serves on the Advisory Board of the Mixed Roots Foundation and is a member of Mensa.  Her favorite genetic experiment is her seven-year old son, Nicolas.