What Causes Renal Agenesis

Renal agenesis refers to the complete absence of one or both kidneys in a newborn baby. The missing kidney prevents the efficient excretion of toxins and waste products from the body, eventually leading to life-threatening complications.

Read on to learn the types of renal agenesis, its causes, symptoms, and the methods for diagnosing and treating this condition.

What is renal agenesis?

Renal agenesis is a rare genetic defect that causes the failure of the development of kidneys in a newborn baby. The absence of kidneys at birth may be unilateral or bilateral.

Some babies have asymmetric renal agenesis, a subtype of bilateral renal agenesis, in which there is an absence of the kidney on one side and hypoplasia or underdevelopment of the kidney on the other side. The kidney that is underdeveloped is typically small or rudimentary and unable to function normally.

What are the types of renal agenesis?

Renal agenesis can be unilateral or bilateral.

Unilateral renal agenesis

Unilateral renal agenesis refers to the absence of one kidney. This condition is detected in roughly 1 in 1000 births, with a comparatively higher incidence in twins. There are typically no evident symptoms caused by having only one kidney. Therefore the condition is not fatal.

Most babies born with this condition are able to live normal lives. However, it is often associated with developmental anomalies in the genitals in 40% of females and 12% of males.

Bilateral renal agenesis

Bilateral renal agenesis refers to the absence of both kidneys in a newborn baby. Also called Potter syndrome, this condition occurs in approximately one in 3000 to 4500 births, with a higher incidence in boys.

Failure to develop the kidneys in the fetus results in the lack of adequate amniotic fluid. This happens because, after about 20 weeks of pregnancy, most of the amniotic fluid is made up of the baby's urine. Amniotic fluid contains several nutrients, hormones, and antibodies that contribute to the growth and development of the organs in the fetus and support the baby’s survival.

The inadequate secretion of amniotic fluids due to the absence of kidneys can hinder these processes, which reduces the unborn baby’s chances of survival.

What are the causes of renal agenesis?

The exact cause of renal agenesis is not known, although some factors have been identified to be associated with a high risk of this condition. For example, renal agenesis occurs more often in babies with other rare inherited conditions at birth. These include:

Müllerian duct, renal, and cervical vertebral defects
Cat-Eye syndrome
Rokitansky sequence
Melnick-Fraser syndrome
Fraser syndrome

Who is at risk for renal agenesis?

The risk of unilateral renal agenesis is higher in babies who inherit one copy of the abnormal gene. It is an autosomal dominant disease. A parent having specific genetic mutations responsible for this condition is 50% more likely to pass the abnormal gene to his or her child.

Unilateral renal agenesis is also associated with intrauterine growth restriction during pregnancy with multiple babies, such as twins and triplets. The presence of a two-vessel umbilical cord instead of the normal three-vessel cord can also elevate the chances of developing this anomaly.

Genetic mutation is one cause of bilateral renal agenesis, although most babies with this condition do not have a family history of renal agenesis. It is an autosomal recessive disorder, meaning the child develops this condition by inheriting the abnormal gene from both parents.

The risk of renal agenesis in future pregnancies is approximately 3 to 4% in women who have had one or more children with this condition. If the condition is associated with multiple abnormalities, the risk of it recurring in a future pregnancy increases to 8%.

What are the symptoms of renal agenesis?

The primary function of the kidneys is to facilitate the removal of toxic waste and other unwanted by-products of metabolism from the body via urine. The absence of kidneys can affect these functions leading to the accumulation of toxins in the body tissues, due to which the patient develops symptoms of kidney disease.

However, in patients with unilateral renal agenesis, one kidney is able to perform the excretory functions, meaning the child may not have any evident symptoms or visible birth defects. The remaining kidney tends to grow larger to perform the work of two kidneys. Therefore, most patients with a solitary kidney are able to live a normal life without any problems despite having only one kidney. In some cases, the absence of one kidney is not even detected until later in life.

Some common symptoms of renal agenesis include:

Kidney damage resulting in the removal of protein from the body via urine.
Backward flow of urine from the urinary bladder into ureters, and sometimes, even the kidneys
High blood pressure
Pulmonary hypoplasia
Renal failure

Children with unilateral renal agenesis only receive treatment to manage the symptoms that occur due to the failure of the other kidney to compensate.

However, babies born with bilateral renal agenesis need to be treated while still in the womb in order to improve their chances of survival. Kidney defects can prevent the formation of urine required for the amniotic fluid. The lack of enough amniotic fluid can also affect fetal growth and the development of other organs, including the lungs. It may also increase the risk of premature birth.

As a result, a child with bilateral renal agenesis may survive only a few hours or days after birth. The risk of mortality in these cases is primarily associated with poor growth and underdeveloped lungs.

How is renal agenesis diagnosed during pregnancy?

Renal agenesis can be diagnosed prenatally by ultrasound. However, it can be confirmed only after the birth of the child.

If the results of the ultrasound reveal renal agenesis, the doctor might recommend genetic testing or genetic counseling. During genetic testing, a sample of tissues obtained from the placenta or amniotic fluid is tested in a laboratory to detect the presence of specific genetic mutations. Genetic counseling provides information to parents about conditions that may occur due to abnormal genes and what to expect in terms of symptoms, complications, and treatments needed.

An ultrasound during pregnancy can also help to detect oligohydramnios, a condition characterized by the reduced production of the amniotic fluid in the womb, thus raising the suspicion of renal agenesis.

How is renal agenesis diagnosed after delivery?

The diagnosis of renal agenesis can be confirmed after the birth of the baby through routine imaging tests like prenatal ultrasounds, CT scans, or MRI (magnetic resonance imaging). An autopsy is needed to confirm the diagnosis in case of stillbirth or death.

Unilateral renal agenesis may be unnoticeable at the time of delivery if the remaining kidney is functional. In such cases, the diagnosis may occur several months or years after birth. The condition may even be left undetected throughout the life of the patient.

The diagnosis of bilateral renal agenesis is usually suspected in infants having features of Potter syndrome.

Treatment of renal agenesis

The medical treatment of renal agenesis depends on the type (unilateral or bilateral) and severity of the condition.

The standard protocol involves monitoring the child with frequent ultrasounds during pregnancy and after birth. Regular prenatal testing and planning for immediate access to medical professionals and appropriate treatments after birth is also recommended for improving the outcomes.

Treatment of unilateral renal agenesis

Most patients with unilateral renal agenesis do not have any symptoms, as the other kidney grows large enough to perform the functions of both kidneys.

However, babies with this condition may be born prematurely, have poor lung development, or develop hypertension (high blood pressure). In these cases, children may require medication to manage complications. The patient must also visit a physician or a urologist regularly for the assessment of kidney function and general health.

Treatment of bilateral renal agenesis

Bilateral renal agenesis diagnosed through a prenatal ultrasound can be addressed in utero through a series of amnioinfusions.

During this procedure, the physician administers saline solution directly into the amniotic sac to support the growth and development of the baby's lungs. Once the lungs begin to develop, the baby’s chance of survival after birth increases.

However, the child will still need specialized care and be dependent on dialysis for the excretion of waste and toxins from the body. The ability to offer dialysis depends on the birthweight, size, and gestational age of the baby. A kidney transplant can be performed at the age of 1 year or after to support the body’s excretory functions.

Renal agenesis: frequently asked questions

What are the risk factors for renal agenesis?

Some maternal factors during pregnancy can increase the risk of renal agenesis. These include:

Use of some medications
Excessive alcohol intake
Smoking
Obesity
Taking illicit drugs such as cocaine

Why would a baby not develop kidneys?

Missing kidneys at birth can occur due to genetic mutations. This means that kidney development fails to occur normally when the baby has inherited a mutated gene from the parents.

What are the complications of renal agenesis?

Unilateral Renal Agenesis — This condition can increase the risk of other abnormalities, such as premature delivery. The child may also have underdeveloped genitals and is vulnerable to developing frequent urinary infections and other renal problems later in life.
Bilateral Renal Agenesis — Most newborns with bilateral renal agenesis usually survive only a few hours or days after birth. The risk of mortality is primarily associated with complications affecting the underdeveloped lungs.

Conclusion

Renal agenesis is a rare disease marked by the absence of one or both kidneys. Genetic and ultrasound testing can help in the diagnosis of this condition in the fetus and allow the physician to plan the treatment protocol.

References: