Psoriasis is an auto immune condition which can indeed run in families along with IBS, asthma, eczema and UC. DH has asthma, eczema, UC and we initially heaved a huge sigh of relief that none of our DC seemed to be affected. Spoke too soon.
Our DD (33) has Psoriatic Arthritis which is a particularly nasty aggressive form of arthritis like Rheumatoid and can necessitate joint replacements as young as your 30's or 40's.
Fortunately she was accepted on a 5 year drug trial at a major London hospital of an antibody therapy which lowers her immune system. She is 3/5 of the way through and her psoriasis disappeared almost immediately and the arthritis has gradually improved to the point where she can walk, cycle, fly long haul,without pain and it has transformed her life. The 2 big buts are that she is more susceptible to infection and it means NO BABIES. What will happen when she comes off is anybody's guess, fortunately she is closely monitored because there is also possibly a slightly increased risk of certain cancers. Before she went on to the trial she cut out wheat and dairy from her diet and gained some relief, but it was only partial. Likewise various creams helped a little, some of the time, but never made any real difference. As with all autoimmune diseases though, STRESS makes things WORSE so meditation , yoga, anything to alleviate stress can certainly do no harm.