Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) nonsyndromic holoprosencephaly ?
    ### Response:
    Nonsyndromic holoprosencephaly is an abnormality of brain development that also affects the head and face. Normally, the brain divides into two halves (hemispheres) during early development. Holoprosencephaly occurs when the brain fails to divide properly into the right and left hemispheres.
    