def get_study(assc, size=5):
    """
    Return most annotated genes from association dict
    """
    most_annotated = sorted(assc.keys(), key=lambda i: len(assc[i]), reverse=True)
    study = most_annotated[:size]
    study = frozenset(study)
    print(f"### Using the {size} most annotated genes as study: {','.join(study)} ")
    return study