The most common congenital abnormalities of the urinary system

Three of the most common congenital abnormalities of the urinary system are horseshoe kidney, hypospadias, and polycystic kidney.

When ascending from the pelvis the kidneys are very close together, and in 1 out of 600 people they fuse across the midline, forming a single, U-shaped horseshoe kidney. This condition is usually asymptomatic, but it may be associated with other kidney abnormalities, such as obstructed drainage, that place a person at risk for frequent kidney infections.

Hypospadias, found in male infants only, is the most common congenital abnormality of urethra. It occurs when the urethral orifice is located on the ventral surface of the penis. This problem is corrected surgically when the child is around 12 months old.

Polycystic kidney disease is a group of disorders characterized by  the presence of many fluid-filled cysts in the kidneys, which interfere with renal function, ultimately leading to renal failure. These disorders can be grouped  into two general forms. The less severe form is inherited in an autosomal dominant manner and is much more common, affecting 1 in 500 people. The cysts develop so gradually that they produce no symptoms until about 40 years of age. Then both kidneys begin to enlarge as blisterlike cysts containing fluid accumulate. The damage caused by  theses cysts progresses slowly, and many victims live without problems until their 60s. Ultimately, however, the kidneys become "knobby" and grossly enlarged.

The much less common and more severe form follows an autosomal recessive pattern of inheritance. Almost half of newborns with recessive polycystic kidney disease  die just after birth, and survivors generally develop renal failure  in early childhood. Recessive  polycystic kidney disease results from a mutation in a single huge gene, but the dominan form of polycystic kidney disease is usually caused by a mutation in one of two different genes, which code for proteins involved in cell signaling. It is not yet clear how defects in these protein lead to cyst formation. As yet, the only treatments are the usual treatments for kidneys failure, renal dialysis or a kidney transplant.