def parse_region(region_string):
    """
    Parse a region string into chrom, start, end
    :param region_string: string like "chrom:start-end"
    :type region_string: str
    :return: chrom, start, end
    """
    region_string = region_string.replace(",", "")
    sp = region_string.split(":", 1)
    chrom = sp[0]
    start = None
    end = None
    if len(sp) > 1:
        startend = sp[1].split("-", 1)
        start = int(startend[0])
        if len(startend) > 1:
            end = int(startend[1])
    return chrom, start, end