Having an understanding of our genetic make up helps in understanding the condition.
A normal genetic make up means at conception you receive 23 chromosomes from each parent 46 chromosomes in all. The chromosomes are numbered in size sequence from 1-22 with chromosome 1 the largest. The 23rd pair are the sex chromsomes either xx for girls or xy for boys.
Once the egg is fertilized by the sperm and the chromosomes have paired up cell division takes place (miosis)with the blastocyst doubling rapidly. Once this bundle of cells has travelled down the fallopian tubes to the womb and nestled in differentation takes place with organ systems. Within a very short space of time the embyro is formed.
Trisomy 18 comes in a few different forms they can each have major effects on development
In the most common form an extra chromosome18 was already present in the egg or the sperm and therefore there is three chromosomes present in all cells from then on.
In mosaic trisomy18 there is two cell lines present in the one individual. In one cell line there is a normal genetic makeup and in the other three chromosome 18 cells. It is not entirely certain why this may happen.
Partial Trisomy 18 can be full or mosaic but only part of the chromosome is duplicated three times.
Occasionally Trisomy children are born with other chromosome differences as well as their main issue of three chromosomes.
Having an extra chromosome means that defects on the third chromosome without a pair are not balanced out and therefore as the baby grows changes in development take place. It is the development in utero that will influence the babies own unique challenges and lifespan.
Trisomy18 is not something you can grow out of. There are common characteristics to children with T18 however each child is an unique individual.
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