What Is Renal Agenesis? 

Overview 

Renal Agenesis is the absence of one or both kidneys. The medical term can be broken down as follows:

• Renal refers to the kidneys. These are a pair of organs roughly the size of your fist, located on either side of your spine above the rib cage. 
• Agenesis refers to when organs fail to form completely in a foetus.

Renal agenesis is a congenital abnormality.¹ Congenital abnormalities are present at birth, so you must be born with renal agenesis to have the condition. This condition can be separated into two types: 

• Bilateral renal agenesis: This means a baby is born without any kidneys, which is not compatible with life. 
• Unilateral renal agenesis: This means a baby is born with only one kidney. Children with this condition tend to live completely normal lives.

Reading on:

It is important to understand what renal agenesis means for your baby. This article will provide information on:

• Kidney function 
• The effects of unilateral and bilateral renal agenesis
• How and when the conditions are diagnosed 
• The causes of renal agenesis 

Understanding the kidneys

To understand renal agenesis, a basic understanding of the kidneys and how they develop is helpful. 

Basic anatomy of the kidneys

The kidneys are a pair of organs around the size of your fist that sit above the rib cage on either side of the spine.  Their shape resembles a bean, and they are red/brown in colour ².  Each kidney is made up of filtering units called nephrons, which are the structural units of the organ. Around 1 million nephrons make up each kidney.³

Kidney function in the body 

Kidneys are part of the urinary system, the body's system for excreting urine. The key function of the kidneys is to filter blood. The kidneys filter blood to remove excess water and waste products from it. This allows the body to make urine and maintain the required balance of water, minerals and salts for healthy physiological function.³

Other functions of the kidneys include:³

• Controlling blood pressure is a measurement of the force that your heart pumps blood around the body.
• Making red blood cells. These are the functional cells of blood that deliver oxygen and nutrients around the body.

Kidney development 

Kidney development can start as early as three weeks into prenatal development and is typically complete between weeks 32- 34.⁴ During foetal development, the urine produced by the kidney is essential for the recycling of amniotic fluid.⁵ Amniotic fluid is a clear/ yellow liquid contained in the anatomic sac that surrounds unborn babies in the womb. Amniotic fluid has a key role in lung development. The liquid is pushed into unborn babies' developing lungs to stimulate the growth of air sacs ⁶, the spaces in your lungs for air. Therefore, kidney development is essential for the growth of foetal lungs. 

Kidneys start to make urine after 13 weeks of development ¹. No more nephrons develop after birth, but the kidneys continue to grow in size and vasculature (blood vessels)  after birth, with the most growth occurring at the start of life ^4.  It is estimated that for most people, the growth of their kidneys stops at around the age of 22 ⁴.

More on unilateral renal agenesis

In regular development, babies will be born with two functioning kidneys. Unilateral renal agenesis is a birth defect that means only one kidney develops. It is a result of one-sided failure of prenatal kidney formation. To be clear, this condition is different from being born with one or two unhealthy kidneys; it is the complete lack of development of one of your kidneys. Unilateral renal agenesis is not fatal. Babies who develop the prenatal condition will survive birth. 

Symptoms 

Life with one kidney does not tend to have a significant impact on an individual’s health, and often there are no symptoms.⁷ This is because a single kidney can grow at a faster rate and to bigger sizes compared to a pair of kidneys.⁸ This growth compensates for not having a second kidney.⁸    

Complications

Being born with unilateral renal agenesis means living with one kidney instead of two; this is referred to as a solitary kidney. Whilst one kidney's function is enough to filter your blood effectively, some children may experience complications linked to having a solitary kidney; these can occur in childhood or later in life and include:

• High blood pressure⁹
• Proteinuria (protein in urine)⁹
• The backflow of urine to the ureters⁹
• Genital abnormalities:¹⁰ these can include deviation from normal genital anatomy, pain during urination and perineal pain (pain in the region between the genitals and anus).¹¹
• Higher risk of renal injury: In one study, 50% of children with a solitary kidney experienced renal injury before adulthood.¹²
• Higher risk of kidney disease in adulthood.¹³

Treatment and management 

Not everyone born with renal agenesis will need to be treated because a lot of people will not have any related symptoms.  People who experience related high blood pressure will be offered medication to lower it ^9. However, there are some lifestyle choices that will help avoid complications: 

• Seek kidney-related medical checkups. Those with one kidney must receive regular tests for their kidney function and urine protein levels⁹
• Avoiding contact sports: Some doctors advise those with a single kidney to avoid high-contact sports like boxing and wrestling due to the enhanced risk of renal injury that is seen with having one kidney.  If this is not a choice someone wants to make, then wearing protective clothing whilst playing contact sports is very important¹⁴
• Healthy diet: Like all people, those with a single kidney should avoid consuming excessive salt and protein in their diet. Other than this, there are no drastic diet changes someone with one kidney needs to make¹⁵

 Prevalence and incidence  

• Unilateral renal agenesis occurs in roughly 1 in 2000 live births. 
• Renal agenesis is more common in multiple pregnancies, so it is more prevalent in twins, triplets, etc.¹
• Genital abnormalities associated with unilateral renal agenesis are more common in individuals assigned female at birth ( 37-60% ) than individuals assigned male at birth (12%)¹⁶

More on bilateral renal agenesis 

Bilateral Renal Agenesis is a defect where both kidneys fail to develop in a foetus. This condition is not compatible with life.¹ 40% of foetuses with bilateral renal agenesis will be stillborn. This is when a baby is born dead after at least 24 weeks of pregnancy.  Babies with bilateral agenesis who do survive birth will die shortly after due to respiratory complications. This is because, without any developing kidneys, the lungs will not be able to grow properly.¹⁷ This is because the recycling of amniotic fluid by the kidney is essential for foetal lung development.⁶

Symptoms 

Newborn babies with the condition will present certain physical characteristics, such as:

• Wide eyes
• Loose skin 
• Sharp nose   
• Folded inner eye corners¹ 

Treatment 

Unfortunately, there is no treatment or cure for this condition ^17. 

Prevalence and incidence 

This is a rare condition occurring in 1 in 5000 live births in the UK, which equates to 0.02%. 

Diagnosis of renal agenesis

Prenatal 

Bilateral and unilateral renal agenesis can first be detected between weeks 18 to 22 of pregnancy.¹⁸ Foetal ultrasound scans can detect if the kidneys are missing and detect low amniotic fluid, a sign that there is an issue with kidney development.¹⁷ Foetal magnetic resonance imaging (MRI) scans can be used to confirm a diagnosis.¹⁷

Postnatal 

Imaging scans such as MRI’s or autopsies can confirm bilateral renal agenesis after birth.¹⁹ Unilateral renal agenesis diagnosis can also be confirmed by an MRI.¹⁹ If unilateral renal agenesis was missed in prenatal scans, it may not be diagnosed till later in the child's life. This is because the condition may not cause any symptoms. Often it is confirmed when X-rays have been taken for another medical concern.¹

Causes of renal agenesis

Renal agenesis is caused by a developmental defect, where two embryonic structures that are meant to fuse do not, therefore, a kidney is not formed.²⁰ In unilateral renal agenesis, this failure is one-sided; in bilateral, it occurs on both sides of the spine.  No single cause of this failure has been identified.  However, research has found some possible causes: 

Genetic factors

Genes contain all the information for the development and function of the human body and are contained in sequences in DNA, the molecule in our body that carries all genetic information. Mutations change gene  DNA sequences; this happens all the time, but most do not have any impact on our health.²¹ Some gene mutations do, however, lead to disease, research has linked several mutated genes to unilateral and bilateral renal agenesis.²² These changes to DNA are linked to interference with normal kidney development in the first trimester of pregnancy.⁹ Genetic factors have been estimated to cause the condition in 20-36% of cases. 

Familial history

Genetic mutations can be passed on from parents to offspring. Unilateral renal agenesis can be classed as autosomal dominant; this means inheriting a single copy of a mutated gene from a parent can cause the disease.⁹ A parent with the condition has a 50% chance of passing it on to their child. Bilateral mutations are autosomal recessive; this means the same mutated gene must be passed on from both parents to the foetus for the condition to arise.⁹

Environmental 

Environmental factors concerning birth givers have also been linked to renal agenesis. Environmental risk factors include: 

• Smoking and drinking alcohol during pregnancy ²²
• Gestational siabetes mellitus ²² . This is the onset of intolerance to glucose (the main sugar in the blood) in pregnancy that tends to end after giving birth. 

Summary 

In summary, renal agenesis is a birth defect that results in the absence of one (unilateral) or both (bilateral) kidneys. Whilst bilateral renal agenesis is a fatal condition not compatible with life, babies born with unilateral renal agenesis often live healthy lives. There are still some complications related to being born with a single kidney, so it is important to monitor kidney health more frequently than someone with two healthy kidneys. There is no current treatment for bilateral renal agenesis, but there is ongoing research and clinical trials into treating the defect pre- and postnatally to look out for in the future ^23.

FAQs 

What support will I be offered after receiving a bilateral renal agenesis diagnosis for my baby? 

Receiving a diagnosis is difficult. The team at your hospital will offer you support and go over your options, which include ending or continuing your pregnancy. There are several charities that offer support to parents who are making decisions about continuing their pregnancy after a diagnosis like this, and there are support groups for people affected by baby loss^18. 

Are there signs to look out for renal agenesis during pregnancy? 

No. There are typically no specific symptoms seen in pregnant people who receive a renal agenesis diagnosis for their baby. 

Should a renal agenesis diagnosis prevent me from having future pregnancies? 

Unless your doctor has diagnosed an inherited genetic mutation as the cause of your baby's renal agenesis, you should not worry. It is highly unlikely that this condition will affect future pregnancies. If a genetic test does confirm that the condition was inherited from parent to offspring, you may be offered genetic counselling to discuss your options.²⁴