The onset of ADPKD caused by PKD1 and/or PKD2 gene mutations and the severity of their phenotypes are not only associated with gene mutations (germ cell mutations) but are also associated with somatic cell mutations or deletions in normal alleles caused by environmental factors such as toxins and infection (Feng, Watnick, Onuchic, & Germino, 1996). Here, PKD2 is linked to autosomal dominant polycystic kidney disease.