A condition where plasma cells make too many large protein molecules known as immunoglobulins.  MGUS is often found by chance as it can show up in routine blood tests. It does not cause any symptoms, and does not generally affect your health or need treatment. But if you have MGUS, you will be asked to see a specialist regularly for check ups, because 2 or 3 people out of every 10 (20–30%) develop myeloma.