However, uPA/SCID mice have the following disadvantages as hosts for chimeric mice: 1) the h-heps replacement index (RI) in mouse liver is decreased, even in homozygotes used in long-term studies, 2) the tendency to develop kidney disorders is increased, 3) body size is decreased [13], and 4) hemizygotes cannot be used as hosts [1]. This evidence concerns the gene PLAU and kidney disorder.