The dysfunction of these proteins is thought to be pathogenetically responsible for the manifestations of autosomal dominant polycystic kidney disease, primarily by renal ciliary dysfunction. Whether a third gene accounts for a small number of unlinked families is uncertain. Homozygous or compound heterozygous genotypes have been thought to be lethal in utero. Individuals heterozygous for PKD1 and PKD2 mutations usually survive to adulthood but have more severe renal disease.