def _label_tuple_to_text(label, diff, genes=None):
    """
    Converts the variant label tuple to a string.

    Parameters
    ----------
    label : tuple(str)
        A tuple of (chrom, pos, ref, alt).
    diff : float
        The max difference score across some or all features in the model.
    genes : list(str) or None, optional
        Default is None. If the closest protein-coding `genes` are specified,
        will display them in the label text.

    Returns
    -------
    str
        The label text.

    """
    chrom, pos, ref, alt = label
    if genes is not None:
        if len(genes) == 0:
            genes_str = 'none found'
        else:
            genes_str = ', '.join(genes)
        text = (
            'max diff score: {0}<br />{1} {2}, {3}/{4}<br />closest protein-coding gene(s): {5}'
            .format(diff, chrom, pos, ref, alt, genes_str))
    else:
        text = 'max diff score: {0}<br />{1} {2}, {3}/{4}'.format(diff,
            chrom, pos, ref, alt)
    return text
