In short: Triple-X, Triplo-X or Trisomy X is the genetical difference, when having 3 instead of 2 X chromosomes. 1 in 1.000 girls has it. Since they then have 47 chromosomes, it sometimes is also called 47, xxx.
What is a chromosome?
You are most likely familiar that we all have a DNA (desoxyribonucleic acid). Basically you can think of the DNA as of our code, that tells our body cells, what to do and what to specialize in (e.g. to become a skin cell, a brain cell, a liver cell, etc.). That code is structured in building blocks, which are called chromosomes. To keep the code analoy, you can think of chromosomes as disks or USB-sticks or SD-cards. Most people have 46 chromosomes. Most of the time the chromosomes are grouped in pairs. On pair (the 23rd one) is special because it determines our gender. In that pair you can have two X chromosomes (together both of them form an X, but it is actually made out of 2 chromosomes) which makes one female or one can have an X and an Y chromosome (together they look like a Y, which is a shorter form of the X chromosome) which makes one male.
Some people have 3 chromosomes in that 23rd pair. Mathematically one then can have the combinations of XXX, XXY and XYY. (YYY is not possible, because you get at least one chromosme from your mother and she only has XX chromosomes). XXY is also known as the Klinefelter syndrome while XYY has no special name. Here we are looking at the XXX part, which actually is quite common: every 1 in 1,000 women does have this chromosome.
If you are more interested in chromosomes, Wikipedia has a lengthly article about chromosomes.
Is it a sickness?
No, it is no sickness, it is a genetical diversity. You can’t get it like a sickness, you just have it – from the moment on one has been made. Genetic diversity is a common thing in nature and it is the foundation of evolution – basically that’s the reason why we actually became humans some hundreds of thousands of years ago.
Can it be treated?
Since it is no virus or bacteria, but an essential part of every cell in your body, you cannot treat or fix it.
How can I explain that complex thing to my daughter?
There are some good books which explains this topic in a child friendly way, e.g. Elizabeth and her Extra X – by Arlie Colvin
The Rare Chromosome Disorder Support Group (UK) has a good guide for girls and for parents. The guide for parents is extremely helpful, since it covers also issues like if and when to tell your daughter, what to consider, if and how to tell family, etc. If you find them useful, consider donating to the Rare Chromosome Disorder Support Group.
- The Rare Chromosome Disorder Support Group (UK) has prepared a 16 page documentation on XXX.
- Genetic.org KS&A has prepared a 15 page fast to read guide for parents.
- Rebecca Wilson has (et al) made a great presentation at the 2017 AXYS conference about Trisomy X.
- There are many scientific studies to go deeper into the profile of the syndrome. But we after 12 years living with the syndrome have found, that facts often repeat or grow fears because the fact that every single “Trixy” is different and has different symptoms is not present enough. And: studies are good to know, but first hand experience is key to make every day life easier.