Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Nance-Horan syndrome ?
    ### Response:
    What causes Nance-Horan syndrome? Nance-Horan syndrome is caused by a mutation in the NHS gene, which is located on the X chromosome. Some patients have losses (deletions) of part of the chromosome X short arm (p) within the region involving the NHS gene and other genes that are located in this region.
    