Autosomal recessive polycystic kidney disease

This is a rare inherited condition that begins long before birth. The tiny tubules the kidney is built from develop abnormally: they widen and turn into large numbers of fluid-filled spaces. The bile ducts of the liver form with the same defect, which is why the disease always involves two organs rather than one. About one baby in 20,000 is born with it, and boys and girls are affected equally. It is usually shortened to ARPKD.

What actually goes wrong in the kidneys and the liver

The shape of the tubules depends on a protein called fibrocystin, and a single gene builds it: PKHD1. When both copies of that gene work poorly, the tubules stop being smooth channels and become elongated sacs. Large surface cysts are rarely the picture here; instead the kidneys become uniformly firm and enlarged, and in a newborn they can fill half the abdomen. Working tissue is then gradually replaced by scar tissue, and it is this fibrosis, rather than the cavities themselves, that takes away the kidney's ability to filter blood and hold on to water.

In the liver the damage falls on the bile ducts: they form already widened, dense tissue grows around them, and blood struggles to pass through the organ. Meanwhile the liver itself keeps working well for years and blood tests stay normal, even though pressure inside its vessels is already raised. That mismatch is why the liver side of the disease is so often noticed late.

Why it runs in families, and how it differs from adult polycystic disease

For a child to be affected, a faulty copy of the gene has to arrive from the mother and from the father. Someone carrying a single copy is entirely healthy and usually has no idea; roughly one person in seventy is a carrier. If both parents carry it, each of their children has a one-in-four chance of having the disease.

Hence something that surprises families: the condition turns up where nobody has ever heard of it, because healthy parents pass it on invisibly. The reverse is true too — two brothers with the very same fault can be affected to completely different degrees, one needing help from the first hour of life while the other reaches school age without serious trouble.

Adult polycystic kidney disease is a different illness with a similar name: there a single faulty copy from one parent is enough, and the kidneys usually only begin to fail in middle age. If a family already has a child with ARPKD, seeing a geneticist before the next pregnancy is worth the appointment.

What shows up before birth and in the first days

The first sign is usually a routine scan in the second half of pregnancy: the baby's kidneys look enlarged and unusually bright, and there is less amniotic fluid than there should be. Fluid is short because its main source is the baby's own urine, and damaged kidneys barely produce any.

The shortage of fluid is not dangerous in itself. Without it the lungs cannot expand and stay underdeveloped, while the wall of the womb presses on the baby and distorts the face, feet and hands. What decides the outcome of the first weeks is that immature lung, not the state of the kidneys: around a third of babies with the severe form do not survive the first month because they cannot breathe.

After birth the pointers are breathing difficulty from the very first minutes, a swollen firm abdomen and very little urine. Intensive care and mechanical breathing support are needed, sometimes surfactant. If hugely enlarged kidneys push up against the diaphragm, removing one of them is occasionally discussed. For babies who get through that first month the outlook improves considerably: about nine in ten reach the age of five.

Blood pressure, thirst and weight: life for older children

• High blood pressure. Most children develop it, sometimes within the first months. It is treated continuously rather than in courses, the aim being to protect the heart, the blood vessels and whatever kidney function remains. Treatment usually starts with the drug groups that act on the kidney's own vessels.
• Passing a lot of urine and constant thirst. Damaged tubules cannot concentrate urine, so the child loses too much water in it: frequent trips to the toilet, waking at night, sometimes a return to bedwetting. Drinking should be free and on demand — restricting fluids here is not an option.
• Dehydration comes on quickly. A stomach bug, a fever or hot weather throw such a child off balance far faster than a peer. Ask the kidney specialist in advance which rehydration solutions suit your child: the standard ones from the pharmacy are not always right.
• Feeding and growth. Enlarged kidneys take up room in the abdomen, so the child eats little and brings feeds back. If weight is not going on, a dietitian and high-calorie feeds are brought in, sometimes tube feeding. Where growth is delayed, the doctor may suggest growth hormone.

Liver and spleen: the most underestimated part of the disease

This is the part people know least about and the part that threatens most, especially in children whose kidneys are holding up well.

Scar tissue raises the pressure in the vessels carrying blood to the liver. The blood looks for a way round and diverts through veins in the oesophagus and stomach that were never built for that flow. Those veins swell, their walls are thin, and they can rupture: the bleeding then starts suddenly and can be heavy. At the same time the spleen enlarges and removes too many platelets from the blood, which makes bleeding harder to stop.

The second danger is an ascending infection of the bile ducts. Bile stagnates in malformed ducts and bacteria travel up them into the liver. This causes a high fever with shivering, pain under the right ribs and yellowing of the skin or the whites of the eyes, and it needs hospital admission and intravenous antibiotics without delay. Any unexplained fever in a child with ARPKD is investigated with this possibility first in mind.

That is why follow-up is not run by the kidney specialist alone: the liver, the size of the spleen and the platelet count are checked regularly, and swollen veins in the oesophagus are looked for in advance, before any first bleed, because they can be banded endoscopically.

When to seek help urgently

Call an ambulance rather than waiting until morning if your child has:

• vomiting of blood, or black tarry stools;
• sudden pallor, cold hands and feet, listlessness, a racing heartbeat;
• a high fever with shivering, particularly alongside pain under the right ribs or yellow skin and eyes;
• laboured or very fast breathing, a bluish tinge around the mouth;
• severe pain in the side or abdomen after a blow, a fall or a knock during play;
• almost no urine, refusal to drink, sunken eyes, dry lips, difficulty waking;
• a seizure or confusion.

What treatment can offer today

There is still no medicine that removes the cause: a faulty gene cannot be repaired. Every consequence of the disease, however, can be treated, and that is why survival has improved so markedly. Several fronts are worked on at once: blood pressure control, iron and drugs that stimulate red cell production for anaemia, phosphate binders to protect the bones, and monitoring of the liver.

When the kidneys can no longer cope, there are two ways of replacing them. Dialysis takes over the filtering of the blood. A kidney transplant gives a better quality of life and allows a living donor, since one kidney is enough for a person. Where the liver is severely damaged, a liver transplant is considered too, and the two operations are sometimes combined.

Everyday precautions matter as well. Enlarged kidneys are vulnerable to impact, so contact sports are not advised, while swimming and cycling fit in well. Painkillers from the non-steroidal anti-inflammatory group are harmful to damaged kidneys, and any new medicine, including anything bought over the counter, is worth checking with the doctor first.

Online consultation

In an online consultation the doctor goes through the scans and blood results, explains what the blood pressure, creatinine and platelet numbers mean, helps put together a follow-up plan that makes sense, and advises which specialists to involve. If the condition has already occurred in the family, this is the place to discuss which tests are worth doing before the next pregnancy.

This material is for information only and does not replace medical advice.