Many thanks Joelf for your response.
I have got a rheumatologist, and a haematologist - amongst other "ologists". I have also got a Myeloproliferative Neoplasm - a type of blood cancer - namely Essential Thrombocytosis and Polycythaemia Rubra Vera. These were caused by a genetic mutation (JAK2 mutation).
Of interest is a paper called "MPN's as Inflammatory Diseases - the Evidence, Consequences and Perspectives" written by 2 Doctors from Copenhagen Denmark.
From reading that, it seems the genetic mutation that seems to have affected me since age 15, has led to my Scleroderma/mixed connective tissue disease (and all the other syndromes associated with it) and the blood cancer as well. It is kind of reassuring to know that I have not got multiple nasty diseases, but one overall disease caused by genetic mutation.