Polycystic kidney disease is a genetically inherited disorder with dominant and recessive inheritance patterns. It is characterized by numerous cysts in the kidneys, causing kidney enlargement. It also affects several other organs like the liver, pancreas, spleen, etc.

What Are the Various Polycystic Kidney Diseases?

Polycystic kidney diseases are of two types, based on their inheritance pattern, which includes:

Autosomal dominant polycystic kidney disease (ADPKD).
Autosomal recessive polycystic kidney disease (ARPKD).

What Is the Difference Between Autosomal Dominant and Autosomal Recessive Polycystic Kidney Disease?

Autosomal Dominant Polycystic Kidney Disease: Autosomal dominant polycystic kidney disease happens when only a single copy of a mutated gene is present in any one of the parents or as a result of a new mutation in the affected individual. The prospect of transmitting the disease from one generation to another in each pregnancy is 50 %. It is usually diagnosed in adulthood.

Autosomal Recessive Polycystic Kidney Disease: Autosomal recessive polycystic kidney disease occurs when both parents carry abnormal genes. The chance of spreading the disease from one generation to another in each pregnancy is 25 %. It is usually diagnosed in the womb or shortly after birth.

What Is the Etiology of Polycystic Kidney Disease?

Autosomal dominant and recessive polycystic kidney show different etiologies and is discussed below:

Autosomal Dominant Polycystic Kidney Disease: It is associated with a mutation in the PKD1, which codes for polycystin 1, and PKD2 genes, which code for polycystin two, respectively. 85 % of ADPKD is caused due to PKD1 mutation, and the rest, 15 %, is due to PKD2 mutation. Few studies have reported the alteration in DNAJB11 and GANAB genes, which need further evidence to be documented.

Autosomal Recessive Polycystic Kidney Disease: It is the less common type presenting with underdeveloped kidneys, and it is caused due to mutation in the PKHD1 gene, which codes for fibrocystin.

What Is the Epidemiology of Polycystic Kidney Disease?

ADPKD is an inherited kidney disease with an incidence rate of one in 500 to one in 1000 individuals.
It is reported to be higher in men than in women, symptoms seem to be more pronounced during the fourth to fifth decades of life, and it affects over 12 million people worldwide.
Studies show that at the median age of 58 years, 70 % of patients with autosomal dominant polycystic kidney disease progress to end-stage renal disease.
ARPKD is the less common type, with an incidence rate of one in 20,000 live births, accounting for 30 % of deaths in newborns.

What Is the Pathogenesis of Polycystic Kidney Disease?

In ADPKD, mutation of PKD1 and PKD2 genes coding for polycystin 1 and 2 will cause alteration in the multiple signaling pathways associated with the normal physiological functioning of the kidneys and other organs, leading to activation of receptors and multiple cyst formation in both renal and extrarenal areas.
In the case of ARPKD, the mutation of the PKHD1 gene codes for a protein called fibrocystin and is essential for the development of fetal kidneys. Due to PKHD1 gene mutation, the development of the fetal kidneys is affected, leading to the formation of underdeveloped kidneys along with numerous cysts in the kidneys. This, in turn, causes poor kidney function resulting in the death of the babies either in vitro or soon after birth.
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What Are the Signs and Symptoms of Polycystic Kidney Disease?

Babies with autosomal recessive polycystic kidney disease have fewer survival rates due to poorly developed kidneys, and in some cases, they may be asymptomatic until adulthood.

Autosomal dominant polycystic kidney disease is a highly inconsistent multisystem disorder where the symptoms and severity vary greatly from one another. In addition, not all patients with the underlying disease show similar symptoms, or they can even be asymptomatic. The symptoms of polycystic kidney disease can be categorized as renal and extrarenal symptoms.

Renal Symptoms:

Hypertension (high blood pressure is seen in 50 % of cases).
Back pain (affecting the flank where kidneys are located).
Fatigue.
Weakness.
Change in appetite.
Edema (collection of excess fluid in the interstitial spaces).
Nausea.
Vomiting.

As the disease progresses, patients develop renal insufficiency leading to;

Nocturia (night-time urination).
Kidney stones.
Hematuria (blood in the urine).
Bulged abdomen due to enlarged kidneys.
Urinary tract infection (UTI).
Decreased glomerular filtration rate.
Elevated serum creatinine.

Extra- Renal Symptoms:

Patients may also have symptoms due to cysts developing outside the kidneys.

Liver Cysts:
- 90 % of patients with ADPKD show cysts in the liver, causing hepatomegaly.
- Pain in the lower back region.
- Early satiety.
- Dyspnea (shortness of breath).
- Jaundice (yellowing of the skin and mucous membrane). This happens if the cysts block the bile ducts.
Cysts in Pancreas:
- Usually, asymptomatic.
- In a few cases, it causes pancreatitis (pancreas inflammation).
Cysts in Arachnoid Membrane of Brain:
- It may increase the chances of subdural hematoma (blood collection between the brain's meninges).
Cysts in Seminal Vesicles:
- Seminal vesicles are the part of the male reproductive system that produces semen, cysts in this region may cause infertility.

Symptoms Related to Heart:

Cardiac manifestations of ADPKD are consequential and may include:

Mitral Valve Prolapse- It may cause a backward blood flow from the left ventricle back to the left atrium.
Dilatation of the Aorta - Widening of the walls of the heart's main artery.

How Is Polycystic Kidney Disease Diagnosed?

The steps in the diagnosis of polycystic kidney disease include:

Medical History - Proper history of the symptoms of the disorder should be collected.
Family History - The patient should obtain a family history to understand the family genetic link.
Clinical Examination - A thorough clinical examination is necessary to check for the signs of the disease, such as hypertension, edema, bulged abdomen, jaundice, respiratory rate, etc.
Ultrasonography of Kidney - Ultrasonographic kidney findings would reveal the presence of multiple cysts and the enlargement of the kidneys. In the case of ARPKD, the fetal ultrasound would reveal the enlarged, poorly developed kidneys with multiple cysts.
Computerized Tomography (CT) Scans and Magnetic Resonance Imaging (MRI) Scans - These scans would provide a much more detailed picture of the cysts and help to understand the extent of disease involvement in other organs.
Genetic Testing - Genetic testing is done to confirm the diagnosis and determine the type of inheritance pattern.

What Are the Differential Diagnosis of Polycystic Kidney Disease?

Conditions that show similar features as PKD are;

Von Hippel-Lindau Syndrome - An autosomal dominant condition characterized by multiple vascular tumors in the eyes, kidneys, brain, pancreas, etc.,
Tuberous Sclerosis - A genetic disorder that affects multiple organ systems in the body characterized by seizures and the development of various tumors in the eyes, pancreas, kidneys, etc.
Medullary Sponge Kidney - This is a disability present since birth and is characterized by the cystic dilatation of the collecting tubules of the kidney.

How Is Polycystic Kidney Disease Managed?

The management of ADPKD requires harmonized work of a team of specialists,

Nephrologist - A nephrologist is needed to treat specific kidney diseases related to polycystic kidney disease, such as kidney failure. A nephrologist is also required if one is taking Tolvaptan to manage the side effects and complications of the medication.
Urologist- An urologist is required to treat any obstruction, stones, or urinary tract infections due to polycystic kidney disease.
Nutritionist - A nutritionist can help the individual eat a balanced diet to manage high blood pressure, such as low sodium and low fat.
Radiologist - A radiologist is required to check the cysts' growth and spread across the body, such as an intracranial aneurysm.
Genetics Specialist - A genetic specialist is required to access the inheritance pattern of the condition.

Steps in Management Involves:

Tolvaptan - A V2R antagonist that helps slow down kidney function decline.
Angiotensin-Converting Enzyme (ACE) Inhibitors or Angiotensin II Receptor Blockers - To treat hypertension.
Pain - Managed using tricyclic antidepressant drugs or narcotics.
Complications of Cysts - Cysts in kidneys obstructing nearby vital structures can be removed through surgeries.
Lifestyle Changes - Patients should avoid taking acid-forming foods and foods containing caffeine and reduce their salt and protein intake.
Kidney Stones - Patients with ADPKD are advised to take plenty of water to decrease the incidence of stone formation. For patients with chronic renal stones, it is removed with lithotripsy.
Urinary Tract Infections (UTI) - Chronic UTIs should be treated with antibiotics to limit the spread of infection.
End-Stage Renal Disease - Patients with end-stage renal disease should undergo renal dialysis or kidney transplantation surgeries.

Conclusion:

Polycystic kidney disease shows two spectra of inheritance as ADPKD and ARPKD. Autosomal dominant polycystic kidney disease is a kidney disorder that progresses slowly. On the other hand, ARPKD is rare, with a poor prognosis. Therefore, patients should be educated about the signs and symptoms, the treatment modalities, and supportive care for this condition. Furthermore, treating patients at a prompt time will help limit the further progression of the disease and to improve the prognosis of the condition.