idavidi I have MGUS too, it's rare (3-5% of the population but more common as people age). The acronym means Monoclonal Gammopathy of Uncertain Significance although research is now beginning to unravel the condition and discover its significance.
The medical profession say there are no symptoms but its not difficult to find patient forums which make it clear that there are symptoms such as neuropathy, fatigue, joint pain, kidney disease. There are a number of active patient groups on Facebook from which I've learnt a lot.
MGUS progresses to multiple myeloma at the low rate of 1 per cent per year but that is cumulative, ie, 10 per cent after 10 years. It is known that all multiple myeloma sufferers have MGUS first so the diagnosis is alarming. Hence, regular monitoring - blood tests every 3 months for 2 years, after that they assume you are stable and the condition won't progress. MGUS is linked to autoimmune conditions like rheumatoid arthritis and and is a malfunction of the immune system where a protein clones itself rather than producing a normal antibody.
It's frightening to be diagnosed with something rare and the name of this condition, never mind the acronym, causes a lot of anxiety.