Polycystic kidney

Generality

The polycystic kidney is a genetic disease in which the normal renal tissue is replaced by numerous cysts. There are two different forms: one affects adults, the other infants.

In patients with polycystic kidney disease, kidney damage compromises the normal function of these organs.

What is the polycystic kidney

The polycystic kidney is an inherited disorder characterized by the appearance of numerous cysts in both kidneys.

The formation of cysts compromises renal function, resulting in a pathological condition called renal failure . The medical term "renal insufficiency" indicates defects of:

• Glomerular filtration.
• Urine concentration.
• Urine excretion.

Pathological anatomy

The cysts are pockets lined with renal epithelium and containing liquid. In the case of polycystic kidney disease, their presence increases the weight and size of the organ (even three or four times compared to the normal size). The doctor may notice these anatomical alterations by palpation of the areas corresponding to the kidneys.

The size of the cysts is variable: they can measure a few tens of millimeters, or even 4-5 centimeters. They invade the areas occupied by the glomerulus and the proximal and distal tubules. This explains why they are filled with liquid, in particular pre-urine, containing:

• Urea.
• Sodium.
• Chlorine.
• Potassium.
• Phosphates.
• Creatinine.
• Glucose.

The cysts appear on both kidneys and can be several tens, even a hundred.

Classification

The polycystic kidney is a genetic disease. Based on the gene involved, two forms are distinguished:

• Autosomal dominant polycystic kidney . The English acronym is ADPKD . It is present from birth, but manifests itself with symptoms in adulthood, starting from 30-40 years.
• Autosomal recessive polycystic kidney . The English acronym is ARPKD . It occurs in the first months of life. Often the child dies after the birth, or within the first year of life. The child develops the first renal cysts already in the maternal uterus.

Epidemiology

Causes

A polycystic kidney is caused by a genetic mutation .

The dominant form, ADPKD, can be caused by two different genes: PKD 1 and PKD 2 . PKD 1 resides on chromosome 16, while PKD 2 is located on chromosome 4. Despite this, they determine the same pathology, with the same symptoms.

The recessive form, ARPKD, is caused by a single gene: PKHD 1 . PKHD 1 is located on chromosome 6.

Pathogenesis

The mechanism is very complex and involves numerous actors.

The PKD 1, PKD 2 and PKHD 1 genes encode proteins called polycystins . Polycystins make up a channel for the passage of the calcium ion through cell membranes. The calcium ion is, for the cell, an important messenger of signals. In other words, calcium, when it enters a cell, initiates numerous cellular changes. When the polycystins have mutated, the channel does not function properly and the signal induced by calcium is altered. All this translates into cyst formation.

Inheritance of the polycystic kidney

Premise: each human DNA gene is present in two copies. A copy comes from the mother, a copy from the father. These copies are called alleles .

In all the autosomal dominant hereditary diseases it is sufficient that one allele is mutated, because the gene does not work. In fact, the mutated allele has more power than the healthy one ( dominance ). For the transmission of the allele, a single parent with a mutated allele is sufficient.

Conversely, in all autosomal recessive inherited diseases both alleles must be mutated in order for the pathology to manifest. In fact, the mutated allele has less power than the healthy one and its presence in a single copy has no effect ( recession ). For the transmission of these diseases, both parents must be carriers of a mutated allele (healthy carriers).

Autosomal hereditary diseases are those in which the gene mutations reside in non-sexual chromosomes. As mentioned, the polycystic kidney is an autosomal hereditary disease, which exists in two forms, one dominant (late onset) and one recessive (more severe).

Symptoms and complications

• The dominant form ADPKD does not manifest symptoms until adulthood. Between the ages of 30 and 50, in general, the first kidney disorders appear. It is therefore a slow-moving degeneration.
• The recessive form ARPKD manifests itself shortly after birth and has a rapid and fatal course .

The different phases, initial and late, of the disease are characterized by the following symptoms:

The pain in the areas corresponding to the two kidneys is due to their enlargement, which compresses the surrounding anatomical parts.

Kidney stones occur in one person every 5 with polycystic kidney ADPKD. In some cases, they do not cause pain; in others, they block the ureter and cause acute pain (renal colic).

A late diagnosis and failure to treat these symptoms can complicate the pathological picture of the patient suffering from polycystic renal disease. The most serious complications are:

• Chronic renal failure.
• Chronic hypertension.
• Cysts in other parts of the body.
• Valvular disease.
• Brain aneurysm.
• Chronic kidney pain.
• Diverticular disease of the colon.
• Problems in pregnancy.

Kidney failure

It is the most common complication in patients with polycystic kidney disease.

In a patient with renal failure, the main functions of the kidneys are impaired.

Kidney damage can be more or less profound. In fact, the glomerular filtration assessment test allows the assessment of the stage of renal failure . Five stages have been distinguished, from the least to the most severe.

The last stage requires therapeutic treatments, such as dialysis and kidney transplantation.

Chronic hypertension

By urinary excretion, the kidneys regulate blood pressure ; their damage, on the other hand, increases their value. Hypertension is not a disease in itself, but it is a factor favoring heart diseases and stroke.

Cysts in other parts of the body

Cysts also develop in other organs, such as the liver. They do not cause liver problems but cause pain. Hepatic cysts are typical of advanced age.

Other cysts may appear in the pancreas, the seminal bladder and the arachnoid membrane.

Brain aneurysm

The term aneurysm indicates the dilation of a portion of the blood vessel. One in 10 people with ADPKD polycystic kidney develop an aneurysm in a cerebral artery. Usually this condition does not create any disturbance to the patient, but the risk that the aneurysm may break should not be underestimated. The rupture of the affected vessel, in fact, determines bleeding, with invasion of the surrounding areas to the point of leakage (see further information on cerebral hemorrhage). Particular attention should be paid to those with ADPKD who also have a family history of aneurysm. Indeed, the aneurysm is very often hereditary.

valvulopathy

Mitral valve prolapse occurs in one out of 5 patients with ADPKD.

Chronic pain

The polycystic kidney can also present a hundred cysts. In such conditions, the kidney is also 3 or 4 times larger than normal and pushes on the surrounding areas. This leads to chronic pain.

Pregnancy

Pregnant women with ADKPD may develop preeclampsia (toxemia gravidarum). This is a remote possibility, but still verifiable.

Diagnosis

The medical history is a good investigation tool. In fact, knowing an individual's family history can be useful for an early diagnosis, even in the absence of obvious symptoms.

Palpation of the two areas corresponding to the kidneys is another reliable test: an irregular surface of both is indicative of the disease.

For a complete and safe diagnosis, the following tests can be performed:

• Ultrasound of the kidneys.
• TAC.
• Nuclear magnetic resonance.
• Urinalysis.
• Blood tests.

Ultrasound

It is the exam of choice. It is not invasive, shows the increase in kidney volume and the presence of liquid-containing cysts.

TAC and nuclear magnetic resonance

They provide more details on the condition of the kidneys. Ultrasound is often sufficient. Furthermore, the TAC is a (slightly) invasive examination, since it uses ionizing radiation.

Urinalysis

It is an important test for testing kidney function. The presence of blood and protein in the urine is typical of the polycystic kidney.

Blood tests

They are useful for measuring the concentration of erythropoietin (EPO), produced by the kidneys. Renal failure, due to polycystic kidney disease, causes a decline in EPO production; as a result, the patient suffers from anemia.

Therapy

Today, there are still no specific treatments to stop cyst formation and growth.

Furthermore, doctors agree that surgery is dangerous. Both kidney transplantation and cyst emptying are delicate, risky and not always resolutive operations. They are used in extreme cases.

However, there are several therapeutic approaches useful in alleviating certain symptoms, or slowing down the inevitable progression. The disorders that require treatment are:

• Hypertension.
• Kidney failure.
• Lumbar and abdominal pain.
• Urinary and renal infections.
• Cysts scattered in other organs.

Treatment of hypertension

Maintaining blood pressure within normal values ​​is essential to not worsen the patient's health and the condition of the kidneys. In fact, hypertension is a risk factor for many other diseases, such as stroke and cardiovascular diseases .

The recommended drugs are:

• ACE-inhibitors.
• Angiotensin receptor blockers, ARB.

Furthermore, a low-sodium diet is recommended.

Diuretics are to be avoided. In fact, their intake increases the amount of pre-urine passing through the glomerulus and the renal tubules. This preurine, in patients with polycystic kidney rather than being excreted, appears to be accumulated in cysts. Therefore, cysts would increase even more.

Treatment of renal failure

Renal failure, as we have seen, is synonymous with more or less deep kidney damage. Moreover, like hypertension, it is fertile ground for cardiovascular diseases.

Since there is no specific therapy for polycystic kidney disease, it can only slow down renal degeneration with a healthier lifestyle :

• Low-fat diet to lower cholesterol levels.
• Not smoking.
• Do regular physical activity.
• Reduce or avoid alcohol consumption.

Patients in old age, or with highly compromised kidney function, need:

• Dialysis.
• Kidney transplantation.

Other treatments

• The treatment of urinary and renal infections is based on taking antibiotics .
• Analgesic drug therapy is performed against abdominal and lumbar pain due to enlarged kidneys. The most widely used anti-pain medication is paracetamol.
• Finally, if cysts are present in other organs, such as the liver, their drainage is useful to remove them.

Prevention

Premise: not all those who suffer from polycystic kidney disease ADPKD are aware of being sick, since the pathology remains asymptomatic up to 30-40 years of life.

When do you suspect polycystic kidney disease?

Those with a family history of polycystic kidney disease should undergo the necessary checks. In younger people, cysts are not yet evident on ultrasound examination; therefore, it is advisable to carry out a particular genetic test, to know if the PKD gene for polycystin has changed or not.

Preventive measures

Until the first symptoms appear, individuals with polycystic kidney disease do not need treatment.

However, to better face future kidney damage, periodic checks should be performed. It is recommended, in fact, to perform once a year:

• An ultrasound examination of the kidneys.
• Blood pressure measurement.
• Blood tests.
• A check on kidney functions.

It is equally important, moreover:

• Do not practice contact sports, such as rugby or boxing. There is a risk, in fact, of breaking renal cysts and creating internal bleeding.
• Consult your doctor before taking certain medications. Prolonged intakes may have side effects on the kidneys.

These countermeasures should not be neglected, as they lengthen and improve the quality of life of patients with polycystic kidney disease.