Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Trisomy 18 ?
    ### Response:
    What causes Trisomy 18? In most cases, trisomy 18 is caused by having 3 copies of chromosome 18 in each cell in the body, instead of the usual 2 copies. The extra genetic material from the 3rd copy of the chromosome disrupts development, causing the characteristic signs and symptoms of the condition.
    