def _combine_variants(in_vcfs, out_file, ref_file, config):
    in_vcfs.sort()
    wrote_header = False
    with open(out_file, "w") as out_handle:
        for in_vcf in (x[-1] for x in in_vcfs):
            with open(in_vcf) as in_handle:
                header = list(itertools.takewhile(lambda x: x.startswith("
                                                  in_handle))
                if not header[0].startswith("
                    raise ValueError("Unexpected VCF file: %s" % in_vcf)
                for line in in_handle:
                    if not wrote_header:
                        wrote_header = True
                        out_handle.write("".join(header))
                    out_handle.write(line)
        if not wrote_header:
            out_handle.write("".join(header))
    return out_file