The Fbn1Tsk allele contains a 30 to 40 kbp genomic tandem duplication resulting in a larger than normal in-frame transcript. Homozygotes are embryonic lethal, failing to survive past somite formation (7-8 days of gestation). Heterozygotes are viable and fertile, exhibiting excessive growth and hyperplasia of connective tissue, cartilage, tendon sheaths and bone. Skin tightness, due to hyperplasic thickening of subcutaneous loose connective tissue and abnormal organization and distribution of skin microfibrillar arrays, develops by the first week after birth. Although the size of the skeleton is increased, body weight remains normal. Mutant mice exhibit polyuria during the light cycle. Collagens and glycosaminoglycans accumulate in the skin, heart, lungs and bladder. Hypertrophy is also observed in the enlarged heart (aortic adventitia). Mutant mice have enlarged thoracic size and lungs with abnormal alveolar walls, irregular shaped alveoli, and increased lung capacity. By 1 month of age, heterozygotes develop emphysema with progressive destruction of alveolar walls and loss of elasticity. Inflammatory macrophages and neutrophils infiltrate the lower respiratory tract. The abnormal immune system characteristics exhibited by this strain also include: alveolitis, increased number of mast cells in the skin, presence of autoantibodies specific for scleroderma target antigens and anti-nuclear antibodies.
In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. This is the case for the strain above. It should be noted that the phenotype could vary from that originally described. We will modify the strain description if necessary as published results become available.

Fbn1Tsk homozygotes are embryonic lethal; heterozygotes exhibit excessive growth and hyperplasia of connective tissue, cartilage, tendon sheaths and bone. This strain is a model for Marfan Syndrome, Hereditary Pulmonary Emphysema, Stiff Skin Syndrome and Familial Progressive Scleroderma.

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