Doctors understand that there are some possible causes of MCDK, though it may not always be possible to identify the cause in your baby. It is not usually caused by anything that the mother does during her pregnancy.

Multicystic dysplastic kidney: about the name

Multicystic means that the kidney has many (multiple) cysts. Dysplastic means that it is has not developed properly.

It is one type of congenital anomaly of the kidneys and urinary tract. ‘Congenital’ means that the problem is present at birth and ‘anomaly’ means different than normal.

MCDK is a severe form of renal dysplasia, in which one or both of the baby’s kidneys do not develop properly.

How common is MCDK?

It is estimated that 1 in 4,300 babies is born with unilateral MCDK. Bilateral MCDK is much rarer.

How MCDK happens

MCDK happens when part of the kidney does not develop properly in the womb.

Although there are a few known causes of MCDK most of the time we cannot identify a specific cause.

The kidneys form while a baby is growing in the womb. Normally, two tubes, which become the ureters, grow from the bladder into tissue, which becomes the kidneys. These tubes form the renal pelvis, the part of the kidney that collects urine. These tubes also form long tubes that link to the nephrons, the many tiny parts that filter blood and make urine.

In MCDK, the tubes fail to completely branch out, so that the kidney does not grow normally. The whole of what should be the kidney is a mass of cysts, which are like sacs filled with fluid (liquid).

MCDK causes: genetic mutations (inherited)

Most cases of MCDK are not inherited from the baby’s mother or father. However, some rare cases are caused by genetic mutations. These are problems in the genes (which are in each of our body’s living cells), which are passed on by the parents.

If your doctor thinks your baby has a problem that is caused by genetic mutations, you may be referred for genetic testing and counselling. Genetic testing usually involves getting a sample of blood or body tissue, which can be checked for a specific gene. Genetic counselling is a service that can give you information and guidance about conditions caused by genetic mutations.

Occasionally, the MCDK is part of a syndrome, which a collection of symptoms and signs. These children also have other problems, such as with their digestive system, nervous system, heart and blood vessels, muscles and skeleton, or other parts of their urinary system. These may be caused by genetic mutations.

MCDK causes: medicines and other drugs

A few cases of MCDK are caused by some medicines taken by the pregnant woman – including medicines for seizures (also called convulsions or fits) or high blood pressure (such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs). Speak with your doctor about the medicines that you are taking.

It may also be caused by some illicit drugs, such as cocaine.

Will it affect other family members?

Unless you have been told that your baby’s MCDK was caused by a genetic mutation, it is unlikely that a future pregnancy will result in MCDK, or other problems with the kidneys. If one of your children has MCDK, it is unlikely that another of your children or family members will get it. Speak with your doctor for more information and support.

More information

  • Renal dysplasia

    In renal dysplasia, one or both kidneys do not fully develop, and the affected kidney does not work as well as normal.

  • About the urinary system and kidneys

    If your child has a health condition that affects their kidneys or another part of the urinary system, you may wish to find out more.

  • Unilateral MCDK (one kidney)

    In unilateral multicystic dysplastic kidney (MCDK), one kidney does not develop properly while a baby is growing in the womb. Instead of a working kidney, there is a bundle of many cysts, which are like sacs filled with liquid.