Simplify the following text for a Grade 6 native English-speaking person.
Original: Trisomy 18 ( T18 ) ( also known as Trisomy E or Edwards syndrome ) is a genetic disorder caused by the presence of all or part of an extra 18th chromosome .
Simplified: Trisomy 18 , also known as Trisomy E and Edwards syndrome is a trisomy . It is a genetic disorder .