Basic feature of human anatomy is such that it has two sets of chromosome 18 in each of the somatic cells
. However people suffering from Trisomy 18 have three such somatic cell copies. Extra chromosome affects both health as well as development of the body. In result the signs of the genetic disorder like trisomy 18. It is rare that tirsomy 18 is present in only some body cells but not in other. This only happens with few lucky people who are suffering from not full but partial trisomy. Such disease may not be fatal.