It is also important to notice that different phenotypes related to the same variant may have different penetrances; i.e., while the nephronophthisis caused by homozygous NPHP1 deletion is considered to be completely penetrant, retinitis pigmentosa or Joubert syndrome affects only a minority of the patients [40, 58, 59]. This evidence concerns the gene NPHP1 and nephronophthisis.