Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Anencephaly ?
    ### Response:
    What causes anencephaly? The underlying cause of anencephaly is not fully understood. Like other forms of neural tube defects (NTDs), anencephaly is likely caused by the interaction of multiple genes and environmental factors, many of which remain unknown. Variations in many genes may influence the risk of developing anencephaly.
    