Tight-skin (TSK) mouse, the experimental model for scleroderma, develops cutaneous hyperplasia and autoantibodies to scleroderma specific autoantigens. TSK syndrome is caused by a mutation on chromosome 2. Induction of cutaneous hyperplasia is due to intragenic duplication of exons 17 to 40 of fibrillin-1 gene, mapping close to TSK locus. The mutant mouse expresses a 14kb Fbn transcript in addition to 11kb wild-type transcript. Immunoprecipation analysis confirms that the mutant transcript is functional and codes for a 420kD fibrillin. The occurrence of TSK syndrome is independent of the presence of mature lymphocytes although splenic/bone marrow cells appear to be capable of transferring the disease in normal animals. Transgenic mice expressing mutant transgene develop mild skin thickness with associate biochemical changes but do not develop anti-topo I antibodies. Among the other factors that may contribute to the develop- ment of hyperplasia, collagen V seems to play an important role.