Disease Relationship
GET /api/diseases/138/relationships/combination_set?format=api
{
    "data": [
        {
            "type": "Combination",
            "id": "OLI1111"
        },
        {
            "type": "Combination",
            "id": "OLI1112"
        },
        {
            "type": "Combination",
            "id": "OLI1113"
        }
    ]
}