You’ve likely never heard of Trisomy 13 or you’re unclear what the medical jargon means. This is a very basic explanation of trisomy, trisomy 13, and a few of it’s common variations. Think of it as the far less famous sister of Down Syndrome. I will also explain Liam’s rare variation, which is called Complete Isodicentric Trisomy 13 Mosaicism or Complete Isodicentric Mosaic Trisomy 13.
An Easy Guide to Understanding Trisomy + Trisomy 13 in simple terms. #TrisomyAwareness #Trisomy13 Click To TweetTrisomy 13 (Patau Syndrome)
People have 23 pairs of chromosomes. Tri-somy means three-chromosomes. Trisomy 13 means there’s an extra chromosome kickin’ it with chromosome pair 13. Down Syndrome is Trisomy 21- extra chromosome on pair 21. Make sense? Trisomy 13 is also known as Patau Syndrome (named after the dude who first ascertained T13).
Trisomy 13 is common in occurrence but rare in prevalence.
There’s a common misconception that Trisomy 13 is rare. It is not. However, you don’t see or hear of it often. Trisomy 13 is common in occurrence but rare in prevalence. In other words, trisomy 13 happens often, but typically results in miscarriage, stillborn, or death. For that reason, Trisomy 13 is medically labeled incompatible with life, although that is clearly bullshit. Despite trisomy 13 not being rare, those who are thriving are. With better education resulting in greater medical care, Trisomy 13/Patau Syndrome will be synonymous with life.
Mosaic means some cells have a well organized 23 pairs and some cells didn’t get their shit together.
Variations of Trisomy:
Complete + Partial (chromosome)
The terms, complete and partial, characterize the extra chromosome. Complete refers to an entire chromosome being copied. Partial refers to some of the chromosome being copied.
Full + Mosaic (cell)
The terms, full and mosaic, characterize the cell but are different in many ways. Full means every cell in the body has trisomy (an extra chromosome) regardless of whether it’s complete or partial and occurs at fertilization.
Mosaic means some cells have a well organized 23 pairs and some cells didn’t get their shit together and there’s a tag along (extra), also regardless of whether it’s complete or partial and occurs after fertilization.
A person with mosaicism can have all the features of full trisomy, none of the features, or snuggle somewhere in between; meaning mosaicism does not dictate the severity of the expression.
A different number of trisomy cells can be present in different parts of the body, making mosaic trisomy complicated to understand. However, it’s safe to assume, anywhere there is a defect or anomaly, there is a higher number of trisomy cells.
Being mosaic means a person has two different genetic makeups. Because mosaicism varies so much within one person, another person with the exact same trisomy mosaicism cannot be compared because it varies so greatly and so does its expression. In fact, a person with mosaicism can have all the features of full trisomy, none of the features, or snuggle somewhere in between; meaning mosaicism does not dictate the severity of the expression.
Isodicentric (arrangement)
Isodicentric is a rare variation, which characterizes the arrangement of the extra chromosome. In this instance, the extra chromosome is mirror imaged and stuck to its pair. It’s a copycat with attachment issues.
Complete Isodicentric Trisomy 13 Mosaicism
Liam has an extra, complete, #13 chromosome, mirror imaged on pair 13 in most of his cells. His tests showed over 80% of his blood has Trisomy 13 cells and he has several anomalies. To our knowledge, Liam is the only known case of Isodicentric Trisomy 13. (See images above).
This is the absolute most basic and simple way to explain Trisomy 13, which is still a LOT of info. Genetics is crazy complex and there is SO MUCH MORE to it than what is above (but I’m trying to not overwhelm you). If you have any questions about something above, Liam, or about genetics in general, let me know and I will clarify or do my very best to point you in the right direction.
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[…] Liam’s Mom.” It turns out, Liam has a rare arrangement that is best described as Complete Isodicentric Trisomy 13 Mosaicism affecting over 80% of his blood […]