What Are Congenital Anomalies of the Kidney and Urinary Tract (CAKUT)?

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Congenital anomalies of the kidney and urinary tract (sometimes referred to as CAKUT) are problems with the urinary system that are present from birth (congenital). In someone with CAKUT, some part of the urinary system doesn’t form normally during prenatal development.

Depending on the exact issues involved, someone with CAKUT might have a condition that only causes symptoms later in life. On the other hand, a more serious problem could cause a life-threatening issue from infancy.

Although many people are more familiar with other kinds of congenital abnormalities (like congenital heart issues) congenital abnormalities of the kidney and urinary tract are the most common kind of congenital birth defect, affecting roughly 1 in 500 babies born.

Of children who have end-stage kidney disease, some type of CAKUT is the cause in roughly half. In adults with end-stage kidney disease, CAKUT accounts for about 7% of cases.

Kidney and ureters anatomy
peterschreiber.media / iStock / Getty Images

Types of CAKUT

Many different types of CAKUT exist, which can be categorized in different ways based on the specific organ affected, the type of involvement, and the different genetics involved (if known). In some cases, multiple parts of the urinary tract are affected. The issues could affect both sides of the body or only one side.

Issues can include one or more of the following:

  • Abnormally shaped or positioned kidney (e.g., a "horseshoe kidney")
  • Partial kidney duplication
  • Renal agenesis (complete failure of one or both kidneys to form)
  • Kidney dysplasia (disordered kidney development)
  • Kidney hypoplasia (small kidneys)
  • Reflux of urine into the kidneys
  • Problems with the urethra valves (such as posterior valves)
  • Extra ureter or enlarged ureter
  • Failure of the urethra to form
  • Bladder anomalies, including bladder enlargement
  • Obstruction (where the ureter connects to the kidney or the bladder)

CAKUT can also be a part of many different medical syndromes that affect multiple medical systems. These include renal-coloboma syndrome, orofaciodigital syndrome, renal cysts and diabetes syndrome, Fraser syndrome, VACTERL syndrome, and many others.

Sometimes, other heritable forms of kidney disease are grouped along with CAKUT. For example, autosomal dominant polycystic kidney disease and autosomal recessive polycystic disease are two different inherited diseases that cause fluid-filled cysts to form inside the kidneys.

These cysts eventually interrupt kidney function and cause symptoms. However, some people don’t include them when talking about CAKUT.

CAKUT Symptoms

The symptoms from CAKUT will depend somewhat on the specific type of congenital problem and its severity, as well as on the person’s age. Potential issues include:

  • Distended belly (due to bladder enlargement)
  • Difficulty feeding and poor weight gain in infants
  • Increased urinary tract infections
  • Profuse or decreased urination
  • Electrolyte disturbances
  • Delayed puberty
  • Decreased height
  • Anemia
  • High blood pressure
  • Cardiovascular disease

Additionally, some fetuses with very poor kidney function will have low amniotic fluid while in the womb (oligohydramnios). This is an issue because the fetus’ kidneys produce this fluid. This can cause other problems, like reduced growth, delayed lung maturation, limb defects, and sometimes death.

If CAKUT causes major damage to the kidneys, this can eventually cause symptoms from renal failure. In severe cases, end-stage renal disease happens in the first years of life.

If not treated with kidney transplant or hemodialysis, this can cause life-threatening problems like inability to make urine, severe electrolyte problems, neurological issues, increased tendency to bleed, and extremely high blood pressure.

Some, but not all, people with CAKUT have problems with other body systems that might lead to additional symptoms. For example, some people with congenital problems affecting the kidney and/or lower urinary tract also had problems with the development of their heart, lungs, nervous system, or other organs.

Causes

Abnormal Anatomical Development

The prenatal development of the urinary system requires a complex series of physiological steps. These must be carefully coordinated, as the different cell types develop into what will become the organs of the urinary system. When something disrupts this developmental pathway, CAKUT can happen.

Most people understand that your kidneys make urine, which is then transported through the urinary tract. It travels from the kidneys through the ureter and then into the bladder. Next, it flows through the urethra and out of the body. Through this system, your body removes certain waste products via your urine.

But the urinary system provides several other important functions. For example, your kidneys help regulate the amount of fluid in your body, as well as the amount of certain electrolytes (salts) in your blood. It also plays a key role in blood pressure control.

The kidney also is important for utilizing vitamin D and for producing a hormone needed to make new red blood cells. So the potential symptoms caused by CAKUT relate to these normal functions.

In some types of CAKUT, the urine can’t leave the body in the normal way because there is a blockage or restricted opening. In these cases, the urine can get backed up and lead to problems.

Depending on the specific problem, this can cause abnormal enlargement of the ureter, bladder, or kidney (hydronephrosis). If not corrected, this can permanently damage the kidney over time.

Genetic and Non-genetic Causes

Some kinds of CAKUT are genetic in nature. A specific mutation in a gene causes the kidney (and/or perhaps other parts of the urinary system) to not form normally.

Researchers have identified mutations in several different genes that can cause CAKUT. Two of these are PAX2 and BMP4, and researchers are still discovering new ones.

Different mutations can lead to different specific types of CAKUT, with different severity and potentially different treatment options. In these cases, CAKUT can be passed down in families, although this is not always the case. 

Sometimes CAKUT comes along with a chromosomal abnormality. For example, many people are familiar with trisomy 21, also known as Down syndrome, which occurs when a person has an extra copy of chromosome 21.

Some people with Down syndrome have CAKUT, as do some people with other types of chromosomal abnormalities, like trisomy 18. For chromosomal abnormalities, CAKUT isn’t the only issue though.

Other times a person is found to have a CAKUT even though no one else in the family has ever had one, and even though no genetic cause can be found.

Some environmental factors have been shown to increase the risk of CAKUT. Two of these are diabetes in the mother and exposure to ACE inhibitors (like captopril) prenatally. However, much of the time, no cause can be found.

Diagnosis

CAKUT is now often first diagnosed prenatally. This has become more common since it became the standard of care to perform comprehensive anatomical exams (using a special kind of ultrasound) during the second trimester of pregnancy.

However, this test isn’t perfect, and sometimes a fetus diagnosed with a potential CAKUT before birth is born without any problems.

If there is a concern about CAKUT, it’s very helpful to get genetic counseling and care with a multi-disciplinary team. In some cases, genetic testing may be recommended to help get an idea of the exact nature of the problem. Your doctor can give you an idea of the potential severity of the issue.

The medical history and exam are a crucial part of the diagnostic process. Your physician will ask about any symptoms and past medical problems.

It’s important to find out if anyone else in the family has had problems with their kidneys or with urinary tract disease. This can give helpful clues about the specific cause. It’s important to realize that even if a cause is genetic, it doesn’t mean that CAKUT will show up the same way in each individual in a family.

Basic tests can play a diagnostic role. For example, standard blood tests might include a complete blood count (CBC) and blood markers used to measure kidney function. Basic urine tests are often helpful. Using some of these findings, doctors can get an estimate of how well the kidneys seem to be functioning.

Imaging tests are critical for understanding the specific anatomy involved. These might include tests like the following:

Treatment

Treatment is tailored based on the specific CAKUT and the individual clinical situation. These individuals will need ongoing monitoring care and treatment from people experienced in these conditions.

Treating Kidney Issues

Many individuals with CAKUT and kidney problems will eventually have kidney failure. That means that the kidney problem gets so severe that they are longer functioning well enough to remove wastes, leading to death if not treated. To prevent this, a person needs ongoing dialysis treatments or a kidney transplant.

A kidney transplant is preferred, but a suitable kidney might not always be available. If so, someone with severe kidney disease may need to start dialysis, at least until an appropriate donor kidney becomes available.

A kidney transplant should cure the underlying issue. However, post-surgery, the individual will need to take life-long immunosuppressive medications.

It is helpful to delay the need for dialysis or a kidney transplant for as long as possible. One important way to do this is by making sure the blood pressure doesn’t get too high.

So, one or more medications to lower the blood pressure are frequently used, often medications like ACE inhibitors (like captopril) or ARBS (like losartan). This can help delay the need for kidney replacement therapies.

Other therapies can sometimes help with some of the other complications of kidney disease, like growth hormone for decreased height or vitamin D supplements.

Treating Lower Urinary Tract Issues

For problems that affect the lower urinary tract, surgical repair may be possible, depending on the specific situation. For example, a surgery might be able to correct an abnormal urethral valve.

A procedure called a pyeloplasty might help surgically correct a kidney that had become enlarged, or a surgery might help the urine flow normally from the ureter to the bladder. Other types of surgery might be needed in specific situations.

Outlook

Unfortunately, in some cases treatment is only limited. Babies born with renal agenesis of both kidneys usually die within a few days of birth. But the prognosis is much better for most kinds of CAKUT.

For many types of CAKUT, kidney function improves for the first couple of years of life and then plateaus for a time, before kidney replacement therapy (dialysis or transplant) becomes necessary later in adolescence. Your doctor can give you a better idea of the prognosis in your situation.

Dealing with the issues of CAKUT can take a psychological toll. It’s often helpful for both patients and caregivers to get emotional and psychological support from a trained professional.

Genetics and Inheritance

It’s key to get the help of a trained geneticist when dealing with CAKUT. This can be helpful in initial diagnosis but also in estimating risks for other family members. This may involve getting specialized types of blood tests to try and find the specific gene or genes that might have been involved. It’s also helpful for family planning purposes.

Some types of CAKUT seem to be inherited in an autosomal dominant fashion. That means that someone with CAKUT would have a 50% chance of passing it down to a child (although the symptoms and issue might not be exactly the same).

Less commonly, CAKUT might be autosomal recessive, meaning that a person would need to inherit an affected gene from both their parents to be affected—not just one. But much of the time, a gene can’t be identified, so an exact risk can’t be determined.

A Word From Verywell

CAKUT represents a diverse array of problems that cause the kidney or other parts of the urinary system to not develop properly. Though individually uncommon, as a group they affect a significant number of people.

There’s a lot to learn, but your treatment team will help you understand the details of your situation. Working with an interdisciplinary healthcare team will help you make the best treatment decisions for you. 

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