Kidney problems in children - tubular disorders

This page explains about the causes, symptoms and treatment of kidney problems in children, from Great Ormond Street Hospital (GOSH).

The kidneys clean our blood. The first step in this cleaning process is filtration, which happens in tiny little filters, called glomeruli, designed to hold back large proteins and blood cells.

The filtered fluid then enters elongated narrow tubes, which are called tubules.

But a number of different problems can affect the tubules – which in turn can affect the ability of the kidney to carry out its work.

The tubules have two jobs. They act as transport ducts, carrying filtered fluid from the glomeruli to the kidney pelvis where it is stored.

But their main job is to ensure that along the way, filtered water, salts, amino acids and sugars pass back into the body – rather than being excreted in urine.

Having the right concentration of salts and acids in the body ensures that our brain, heart and other organs work properly. One salt, sodium, is also crucial in how the kidneys regulate our blood pressure.

Retention of salt by the kidneys expands the fluid volume in our blood vessels, thus increasing the pressure. For that reason, people with high blood pressure typically are advised to maintain a low-salt diet.

A newborn baby’s kidneys will filter approximately 15 litres of blood per day, a toddler’s filter around 80 litres a day and a teenager’s kidneys filter around 150 litres a day – as much as an adult. This amount of blood contains the equivalent of more than one kilogram of cooking salt.

Thus, without the work of the tubules, we would have to drink an awful lot of water and eat massive amounts of salt in order to compensate for losses in the urine.

A number of problems can affect the tubules. They can be very specific disorders – for instance affecting only one function of the tubule such as the regulation of water, acid, or of a substance that can form stones. Or the tubules can be affected more generally with several abnormalities combined.

Most of these conditions are inherited, in other words passed on from either or both parents, but some can be acquired during childhood.

Some conditions can be caused by side-effects of medications, most commonly cancer drugs, or some antibiotics.

Damage to tubules can lead to abnormalities in the level of salts in the blood. It can also affect the amount of acids and water circulating in the bloodstream. This can often lead to secondary complications, such as rickets or kidney stones.

For a child, early symptoms might include increased amounts of urine, in contrast to glomerular disorders where urine volume is typically diminished.

Disorders of the tubule can also affect blood pressure. If too much sodium is excreted, a child will have low blood pressure. On the other hand if too much sodium passes into the urine, a child can suffer from high blood pressure.

There are several different conditions that can affect the way that the tubules work. The most common in children who come to Great Ormond Street Hospital are:

• Hypophosphataemic rickets

• Bartter syndrome

• Gitelman syndrome

• Diabetes insipidus

This is a rare, inherited condition involving a particular salt called phosphate. Rather than being reabsorbed into the body as it passes through the tubules, as it should be, phosphates are excreted in the urine.

This leads to high levels of phosphate in the urine, and low levels of phosphate in the body.

Because phosphate, together with calcium, is a main constituent of bones, loss of phosphate results in a slow growth rate and rickets. Older children may suffer from dental problems such as abscesses.

This is a rare, inherited problem affecting one particular portion of the tubule. It involves loss of sodium with low blood pressure and a tendency for dehydration, low potassium levels in the body, and the blood is less acidic than usual.

This is another disorder of salt loss in the kidney, and is a rare, inherited defect affecting a specific part of the tubule.

It means that sodium, magnesium, chloride and potassium pass into the urine rather than being reabsorbed into the bloodstream.

This condition is characterised by an inability of the kidney to concentrate the urine. Patients pass large amounts of very diluted urine and therefore experience excessive thirst and are prone to dehydration.

One type, known as nephrogenic diabetes insipidus, affects the kidneys. Usually, a hormone called vasopressin or anti-diuretic hormone (ADH) acts on the walls of the kidney tubules, increasing their permeability. This allows water to pass through the walls of the tubules and be reabsorbed into the body, which in turn concentrates the urine.

But in nephrogenic diabetes insipidus, the tubules seem to be insensitive to this hormone. Water is not reabsorbed into the bloodstream, and the urine is very diluted.

The diagnosis of these disorders is made by kidney specialists and relies mostly on biochemical analysis of blood and urine.

The treatment is specific for the individual disorder and relies mostly on the supplementation of the substance(s) lost in the urine.

In cases of retention of salts, medications can be given to promote their excretion.

Some of the tubular disorders have associated problems with weight gain and growth and may need the help of the dietitian to maximise caloric intake, occasionally with the help of a feeding tube.

The outlook depends on the individual disorder. Some are relatively easy to treat just with supplementation, and these children have an excellent prognosis.

Others are more difficult, may necessitate frequent hospital admissions and can mean a child has associated problems in other organs.

Most of these disorders, however, are easier to manage once the child gets older and can self-regulate access to water and salts. In fact, these children often develop an appetite for certain foods that contain the salts lost in the urine.