@staticmethod
def _get_disease(dct, rel, dst):
    """Get disease associated with a pathway."""
    assert dst['schemaClass'] == 'Disease'
    assert dst['databaseName'] == 'DOID'
    assert rel['stoichiometry'] == 1
    if 'disease' not in dct:
        dct['disease'] = [dst['displayName']]
    else:
        dct['disease'].append(dst['displayName'])
