How is trisomy 4p inherited?
Trisomy 4p can happen in two ways.
In most cases, the parent has a translocation or an inversion. This means that the short arm of chromosome 4 is found in a different place than expected. The parent does not have trisomy 4p because they have the correct amount of genetic information, even though it is a different place. The parent can pass extra chromosome 4p material onto their child in the egg or sperm.
Imagine that our genetic information is organized like a set of books on a shelf. A chromosome translocation would be like moving a chapter from one book and putting it into a different book. A chromosome inversion would be like having a chapter in one book written backwards. Both of these changes makes it more likely for someone to have a child with trisomy 4p.
The second way trisomy 4p can happen is called “de novo”. This means it is a new change in the sperm or egg. That change causes the baby to have an extra copy of chromosome 4p. The change is usually new to the child. Neither parent has trisomy 4p.
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What does it mean to have inherited a “variant” in the gene for trisomy 4p?
Genes are small parts of the larger chromosome. Chromosomes can be compared to books, and genes are the sentences in the book. There is not a specific gene or sentence that causes trisomy 4p. Rather, people with trisomy 4p have an extra short arm of chromosome 4. This is like having an extra book added to the body’s instructions, which is much different than having a change in a sentence in the book. Therefore, people with trisomy 4p do not have variants in a specific gene.
Are there forms of trisomy 4p that aren’t genetic?
All forms of trisomy 4p are genetic. Everyone with trisomy 4p has an extra chromosome 4p in the cells of the body.