New Mexico is known as the Land of Enchantment, but did you know we’re also the land of a genetic disorder called recombinant 8 syndrome?
Recombinant 8 (Rec8) syndrome is a rare change in chromosome 8 where there is extra material from one end, called the q arm, also known as the long arm, and missing information from the other end, called the p arm, also known as the short arm. Chromosomes are the containers for all of our genes in our cells. It is critical for typical development that we have the right number of chromosomes, but also that they are in a certain order.
So how does Rec8 syndrome come about? First, a large section of the 8th chromosome, including the center point between the p arm and q arm, known as the centromere, is flipped. As a result, the ends of the chromosome are essentially on backwards (see image below). Carriers of this change, called an inversion, do not have any health problems themselves. However, when a parent with this inversion has children there is a small chance they will pass on a new version of chromosome 8. The second step is a process called recombination, meaning two copies of the same chromosome will line up and exchange pieces. So, for an inversion carrier, since the ends of one chromosome 8 are flipped, the new recombinant chromosome 8 for their child will contain a duplication and deletion of genetic information (see image below). These changes to chromosome 8 can unfortunately result in complex birth defects and intellectual disabilities; some people with Rec8 syndrome even pass away at a young age.
Interestingly, researchers have traced the inherited inversion back to a common Hispanic ancestor in the San Luis Valley in northern New Mexico and southern Colorado. As a result, people also refer to Rec8 syndrome as San Luis Valley syndrome. Of course, because people have moved away over time, Rec8 syndrome may be found in other areas of the world too. Rec8 syndrome is a rare condition with its exact incidence being unknown.
If you have a family history of Rec8 syndrome or your ancestors are from the San Luis Valley, you may want to consider genetic testing. Testing to see if you could be a carrier for the inherited chromosome 8 inversion involves a genetic blood test called a karyotype. A karyotype takes a picture of a person’s chromosomes and looks at their structure to see if any pieces are extra, missing, or in the wrong place. This testing gives people the best information about whether they could have a child with Rec8 syndrome. If you are interested in learning more about Rec8 syndrome, including if testing is right for you, talk to a genetic counselor!
– Michelle Maxedon, MS, Licensed Genetic Counselor & Ruthann Schmiege, BA, Genetic Counseling Student
Sources:
- https://onlinelibrary.wiley.com/doi/10.1002/ajmg.a.34104
- https://omim.org/entry/179613
- https://rarechromo.org/media/information/Chromosome%20%208/8q%20duplications%20FTNW.pdf
- https://www.cell.com/ajhg/fulltext/S0002-9297%2807%2964034-8
- https://medlineplus.gov/genetics/condition/recombinant-8-syndrome/#frequency