Renal agenesis is a condition in which a newborn is missing one or both kidneys. Unilateral renal agenesis (URA) is the absence of one kidney. Bilateral renal agenesis (BRA) is the absence of both kidneys.
Both types of renal agenesis occur in fewer than 1 percent of births annually, according to the March of Dimes. Fewer than 1 in every 1,000 newborns has URA. BRA is much rarer, occurring in about 1 in every 3,000 births.
The kidneys perform functions that are necessary for life. In healthy people, the kidneys:
- produce urine, which removes urea, or liquid waste, from the blood
- keep a balance of sodium, potassium, and other electrolytes in the blood
- supply the hormone erythropoietin, helping red blood cell growth
- produce the hormone renin to help regulate blood pressure
- produce calcitriol, also known as Vitamin D, which helps the body absorb calcium and phosphate from the GI tract
Everyone needs at least part of one kidney to survive. Without either kidney, the body cannot remove waste or water properly. This accumulation of waste and fluid can offset the balance of important chemicals in the blood, and leads to death without treatment.
Both types of renal agenesis are associated with other birth defects, such as problems with the:
- genitals and urinary tract
- stomach and intestines
- muscles and bones
- eyes and ears
Babies born with URA may have signs and symptoms at birth, in childhood, or not until later in life. Symptoms can include:
- high blood pressure
- poorly working kidney
- urine with protein or blood
- swelling in the face, hands, or legs
Babies born with BRA are very sick and do not usually live. They typically have distinct physical features that include:
- widely separated eyes with skin folds over the eyelids
- ears that are set low
- a nose that is pressed flat and broad
- a small chin
- defects of the arms and legs
This group of defects is known as Potter Syndrome. It occurs as a result of reduced or absent urine production from the fetal kidneys. The urine makes up a large part of the amniotic fluid that surrounds and protects the fetus.
Risk factors for renal agenesis in newborns appears to be multi-factorial. This means that genetic, environmental, and lifestyle factors combine to create a person’s risk.
For example, some early studies have linked maternal diabetes, young maternal age, and alcohol use during pregnancy to renal agenesis. More recently, studies have shown prepregnancy obesity, alcohol use, and smoking to be linked to renal agenesis. Binge drinking, or having more than 4 drinks over 2 hours, during the second month of pregnancy also increases risk.
Environmental factors may also result in kidney defects like renal agenesis. For example, maternal medication use, illegal drug use, or exposure to toxins or poisons during pregnancy may be factors.
Both URA and BRA occur when the uretic bud, also called the kidney bud, fails to develop at an early stage of fetal growth.
The exact cause of renal agenesis in newborns is not known. Most cases of renal agenesis are not inherited from the parents, nor do they result from any behavior by the mother. Some cases, however, are caused by genetic mutations. These mutations are passed on from parents who either have the disorder or are carriers of the mutated gene. Prenatal testing can often help determine if these mutations are present.
Renal agenesis is typically found during routine prenatal ultrasounds. If your doctor identifies BRA in your child, they can use a prenatal MRI to confirm the absence of both kidneys.
Treatment and Outlook
Most newborns with URA have few limitations and live normally. The outlook depends on the health of the remaining kidney and the presence of other abnormalities. To avoid injuring the remaining kidney, they may need to avoid contact sports when they’re older. Once diagnosed, patients of any age with URA need to have their blood pressure, urine, and blood tested annually to check kidney function.
BRA is typically fatal within the first few days of a newborn’s life. Newborns usually die from underdeveloped lungs shortly after birth. However, some newborns with BRA survive. They must have long-term dialysis to do the work of their missing kidneys. Dialysis is a treatment that filters and purifies the blood using a machine. This helps keep your body in balance when the kidneys can’t do their job.
Factors such as lung development and overall health determine the success of this treatment. The goal is to keep these infants alive with dialysis and other treatments until they grow strong enough to have kidney transplants.
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 exposure to possible environmental factors before and during pregnancy. These include use of alcohol and certain medications that can affect kidney development.
The cause of renal agenesis is not known. This birth defect is sometimes caused by mutated genes passed from the parents to the baby. If you have a family history of renal agenesis, consider prenatal genetic testing to determine your baby’s risk. Babies born with one kidney usually survive and live a relatively normal life, with medical attention and treatment. Babies born without kidneys usually don’t survive. Those who do survive will need long-term dialysis.