def read_neighbor_graph_pickle(gname, graph_dir):
    """Read in neighbor graph for given gene.

    Parameters
    ----------
    gname : str
        name of gene
    graph_dir : str
        directory containing gene graphs

    Returns
    -------
    gene_graph : dict or None
        neighbor graph as dict for gene. Returns None if not found.
    """
    graph_path = os.path.join(graph_dir, gname+".pickle")
    if os.path.exists(graph_path):
        with open(graph_path) as handle:
            gene_graph = pickle.load(handle)
        return gene_graph
    else:
        return None