def get_variant_id(variant):
    """Get a variant id on the format chrom_pos_ref_alt"""
    chrom = variant.CHROM
    if chrom.lower().startswith('chr'):
        chrom = chrom[3:]
    variant_id = '_'.join([
            str(chrom),
            str(variant.POS),
            str(variant.REF),
            str(variant.ALT[0])
        ]
    )
    return variant_id