I have psoriasis, which I have only just had diagnosed although I have had the skin problems for years. It takes a wide variety of forms according to where on the body it occurs, typically dry and scaly on the outside of joints, but raw and red on the inside of joints or in skin folds. Some chemicals, cold, damp, stress and tiredness all make it worse.
I found one study from 2005 showing a 2.7-fold increase in autism amongst the children of mothers with autoimmune conditions including psoriasis (Croen LA, Grether JK, Yoshida CK, Odouli R, Van de Water J. Maternal autoimmune diseases, asthma and allergies, and childhood autism spectrum disorders: a case-control study. Arch Pediatr Adolesc Med. 2005 Feb;159(2):151-7.), but as something of a one-off I don't think it is a significant association.
A visit to any pharmacy will confirm that these conditions are extremely common, and can be difficult to control and very distressing.