Renal agenesis is a condition in which a baby is missing one or both kidneys at birth. Unilateral renal agenesis (URA) describes the absence of one kidney. Bilateral renal agenesis (BRA) is the condition in which both kidneys are missing.
According to the March of Dimes, both types of renal agenesis occur in less than one percent of births annually. Between one in 450 and one in 1,000 newborns has URA. BRA occurs in about one in 3,000 births (March of Dimes).
The kidneys perform functions that are necessary for life. In healthy individuals, the kidneys:
- produce urine, which removes urea, or liquid waste, from the blood
- keep a balance of sodium, potassium, and other chemicals in the blood
- supply the hormone erythropoietin, helping red blood cell growth
- produce the hormone renin to control blood pressure
- produce calcitriol, a hormone that supplies calcium to bones
At least one working kidney is needed. Without any kidneys, the body’s waste can’t be properly removed. This accumulation of waste can offset the balance of important chemicals in the blood and be fatal.
Both URA and BRA occur when the uretic bud (kidney bud) fails to develop at an early stage of fetal growth. It is not yet clear why this happens. This and other kidney defects are associated with gene mutations (Yalavarthy, et al., 2003). The mutations occur naturally.
Certain genetic factors can create a higher risk for URA or BRA. Babies born with a single umbilical artery and caudal regression syndrome have a higher risk of URA. Those who have a parent or sibling with either URA or BRA also have an increased chance of developing URA.
The occurrence of renal agenesis has also been linked with several prenatal factors (Parikh, et al., 2002). Risk factors associated with URA include: diabetes mellitus, black race, younger maternal age, and consumption of alcohol during pregnancy.
In addition, some drugs may contribute to defective renal development. They include: retinoids, thalidomide, arsenates, and cocaine.
Both types of renal agenesis are associated with organ abnormalities. The most commonly affected area is the respiratory system. Defects also occur in the digestive, genital, cardiac, and musculoskeletal systems.
Newborns affected with BRA typically have distinct features that include:
- widely separated eyes with skin folds over the upper eyelids
- ears that are set low
- a nose that is pressed flat and broad
- a receding chin
- limb defects
Babies born with URA may not have any symptoms at birth. Symptoms of URA may not be present until later in life. They can include:
- high blood pressure
- proteinuria, or high protein in the urine
- developmental defects in the inner ear, genital tract, head, and vertebrae
- reduced glomerular filtration rate (GFR) or the ability of the kidneys to filter waste
- swelling in the face, hands, or legs
- blood in urine
- foamy urine
Renal agenesis is typically found during routine prenatal ultrasounds. When BRA is identified, prenatal MRI can be used to confirm the complete absence of both kidneys.
BRA is not compatible with life outside the womb. The condition is typically fatal within the first few days of life. Newborns usually die from underdeveloped lungs shortly after birth.
Some newborns with BRA survive. They must have chronic peritoneal dialysis to replace their missing kidneys. Factors such as lung development, overall health, and family support determine the success of this treatment. The goal is to sustain these infants with dialysis until they grow strong enough to have a kidney transplant.
The prognosis for newborns with URA depends on the health of the solitary kidney and the presence of other abnormalities. Most individuals with URA do not experience any complications or limitations. Some physicians may recommend that children with URA refrain from playing contact sports. This is to avoid injury to the solitary kidney.
Once diagnosed, patients of any age with URA need to have their blood pressure, urine, and blood tested annually to ensure the health of the remaining kidney.
Since the exact cause of URA and BRA is not known, prevention is not possible. Genetic factors can’t be changed. Prenatal counseling can help prospective parents understand the risks of having a baby with renal agenesis.
Women can lower the risk of renal agenesis by reducing known environmental factors before and during pregnancy. These factors include use of alcohol and certain drugs that can affect kidney growth.