def dict_seq_reducer(seq, dict_key, value_keys, add_kv_dict=None):
    """
    Reduce a sequence of dicts to single dict of dicts,
    optionally adding additional k,v pairs
    """
    reduced_dict = dict()
    for element in seq:
        if len(element['REF']) > 1400 or len(element['ALT']) >= 1400:
            continue
        reduced_dict[element[dict_key]] = dict()
        for key in value_keys:
            reduced_dict[element[dict_key]][key] = element[key]
        if add_kv_dict:
            for k, v in add_kv_dict.items():
                reduced_dict[element[dict_key]][k] = v
    return reduced_dict
