What is ARPKD?
Autosomal recessive polycystic kidney disease (ARPKD) is a rare genetic disease affecting about 1 in every 20,000 babies born.
How is ARPKD inherited?
ARPKD is almost always inherited by faulty (mutated) genes being passed from both parents to their child. Although we each inherit about 20,000 genes from our parents, only one gene is linked to ARPKD. It’s called PKHD1.
ARPKD occurs when a child inherits a faulty PKHD1 gene (dark green in the diagram) from both their mum and dad.
Parents of children with ARPKD usually don’t have the disease themselves. This is because you can carry one faulty PKHD1 gene without having ARPKD, provided the second copy you have is normal (shown in light green). This is known as being a carrier.
Most people have two normal copies of the PKHD1 gene. It’s unusual for two parents to be carriers, but this can happen by chance. If two carriers have a baby, there is a 1 in 4 chance the baby will inherited two faulty PKHD1 genes and therefore have ARPKD.
How is ARPKD diagnosed?
ARPKD is usually diagnosed by an ultrasound scan during pregnancy or soon after birth. This uses sound waves to make an image of the inside of the baby’s body, which can show up cysts in the kidneys. Other types of scan can be used too.
Genetic tests of a blood sample can be used to look for faults in the PKHD1 gene linked to ARPKD. This can help to confirm ARPKD and is useful for future family planning.
What damage does ARPKD cause to the kidney?
Healthy kidneys are about 5 cm long in newborns, growing to 10–12 cm in adults. They’re found either side of the mid back. The kidneys filter out waste products and excess water (making urine).
During pregnancy, fluid-filled cysts form in the kidneys. Over time, more and more cysts appear and increase in size, making the kidneys much larger than normal and leaving less healthy kidney tissue to filter the blood. Unfortunately, some babies do not survive pregnancy.
Babies born with ARPKD often have poorly functioning kidneys. By age 10, about 6 in every 10 children with ARPKD need dialysis or a kidney transplant to survive.
What other problems does ARPKD cause?
ARPKD can mean that a baby’s lungs do not develop fully in the womb. Not all babies with ARPKD have under-developed lungs, but those with severe disease usually do. This can be life-threatening, because it makes breathing difficult. A ventilator is used to help newborns with under-developed lungs to breathe.
Our kidneys regulate our blood pressure. Damage to the kidneys by ARPKD can lead to high blood pressure. This can increase the risk of heart or circulation problems later in life. High blood pressure can be treated with medication.
During childhood, ARPKD can cause scarring (fibrosis) in the liver. This can cause other problems, such as bile duct infections and bleeding in the oesophagus (gullet) or stomach. About 1 in 10 children need a liver transplant by the age of 10 years.
ARPKD can make the kidneys and liver much larger than normal, leaving little room for other organs. Some babies and children have difficulty eating, because the stomach cannot expand easily to hold food. This can be helped with an artificial feeding tube, or surgery to remove a kidney.
Changes to the kidney make children with ARPKD more likely to get a urinary tract infection (an infection of the bladder, kidneys, or connecting tubes). This can be treated with a course of antibiotics.
Can children survive with ARPKD?
Yes, most children with ARPKD survive. However, the outlook differs from child to child.
In general, ARPKD is a very severe disease, yet about 8 out of 10 babies with ARPKD survive beyond the first year of life. Many children need treatment for their kidney disease by the age of 5. Encouragingly, most children now survive into adulthood and can live full and productive lives.
Is there a cure for ADPKD?
There is currently no cure for ARPKD. Potential new treatments for diseases similar to ARPKD are being studied in clinical trials. There is hope that these might help children with ARPKD too.