PKD1 and Complex Cyst of Kidney: Finally, zebrafish contains two Pkd1 paralogs with distinct expression patterns and the single knock-out of Pkd1a, or the simultaneous knock-out of Pkd1a and b, induces kidney cysts only in a small fraction of embryos (not exceeding 20%) and even though signs of kidney failure like severe edema are observed more frequently, a hydrocephalus and jaw defects seem to be the primary developmental phenotype caused by the knock-out of these genes [22].