Unilateral Renal Agenesis - Causes, Symptoms, Diagnosis, and Treatment

Introduction:

Unilateral renal agenesis (URA) is a congenital disorder characterized by the absence of a kidney on one side. The lack of renal tissues results from a failure in kidney formation during the embryonic growth period.

What Is the Embryology of Unilateral Renal Agenesis?

Kidney formation in human beings is initiated in the fifth week of intrauterine life. It is characterized by a highly synchronous sequence of events that involves interactions between the metanephric mesenchyme and the growing bud of the mesonephric duct. As a consequence of this interaction, the ureteric bud will not form the ureter, collecting ducts, renal pelvis, and the renal mesenchyme. As a result, the nephrons are not formed, eventually leading to failure in the formation of a kidney on the corresponding side.

What Are the Causes of Unilateral Renal Agenesis?

The most common cause of unilateral renal agenesis is gene mutations. Several studies and research suggest mutations in a minimum of seven linked genes identified. The gene mutations are responsible for a defective mechanism in kidney formation in intrauterine life.

The less common causes are

• Multiple pregnancies (carrying twins, triplets, or more).

• Gestational diabetes.

• Use of teratogenic drugs in pregnancy.

What Is the Prevalence of Unilateral Renal Agenesis?

Several studies show that unilateral renal agenesis most frequently occurs in males on the left side. However, the side of occurrence was reported to be random in many cases (50 % left and 50 % right). The incidence is approximately one in 2000 to 3000 live births.

Who Are at the Risk of Unilateral Renal Agenesis?

It is an autosomal dominant disorder. If a child inherits a single copy of a mutated gene from one parent, it will develop the disease. Most frequently, children of parents affected with unilateral renal agenesis develop the disease. A parent with a gene mutation has a 50 percent probability of transferring it to their children.

How Is the Diagnosis of Unilateral Renal Agenesis Made?

• Unilateral renal agenesis is often confused with incomplete or atypical renal development, leading to a non-functioning kidney, as seen in renal aplasia or multicystic dysplastic kidney (MCDK).

• An apparent diagnosis of unilateral renal agenesis can be made by routine fetal ultrasound sonography imaging (USG) in the gestation period.

• Post-natal ultrasound imaging like renal scintigraphy and MRI (magnetic resonance imaging) can help differentiate between multicystic dysplastic kidney, renal ectopia (cross-fused kidney or pelvic kidney), or renal aplasia. However, it is essential to note that unilateral renal agenesis can be diagnosed from the involution of the multicystic dysplastic kidney.

What Are the Congenital Disorders Associated With Unilateral Renal Agenesis?

Unilateral renal agenesis is frequently associated with congenital disorders of the contralateral kidney and urinary tract, often referred to as congenital anomalies of the kidney and urinary tract (CAKUT). The anomalies are

• Pelviuretric junction obstruction (PUJO).

• Vesicoureteral reflex (VUR).

Apart from the congenital renal anomalies, patients with unilateral renal agenesis are often associated with extrarenal developmental malformations involving the cardiac, gastrointestinal, and genital systems. However, the prevalence of the associated anomalies still needs to be well established.

What Is the Importance of Assessing the Contralateral Kidney in Unilateral Renal Agenesis?

• Evaluation of the associated congenital malformations in unilateral renal agenesis will help the physician determine the renal and general prognosis. According to some earlier studies, genetic conditions are considered more or less harmless. At the same time, recent studies suggest that 40 to 50 percent of patients with unilateral renal agenesis had a need for dialysis by the age of 30. It mainly occurs due to impairment of the solitary functioning kidney.

• The impaired functioning can be explained by the hyperfiltration hypothesis described three decades back by Brenner et al. based on animal studies. The hypothesis states that the lack of one kidney will result in a considerable reduction in renal mass, leaving a solitary kidney for performing the whole filtration functions. The reduced renal mass will lead to a chain of events causing glomerular hyperfiltration as a compensatory mechanism. However, in the long run, the hyperfiltration will lead to renal injury, causing.

  1. Hypertension.

  2. Micro-albuminuria.

  3. Chronic kidney diseases.

• Apart from the renal damage from hyperfunction, the congenital anomalies of the kidney and urinary tract have a high prevalence of occurrence in solitary functioning kidneys. Therefore constant evaluation of the contralateral kidney is necessary for patients with unilateral renal agenesis.

What Are the Symptoms of Unilateral Renal Agenesis?

The typical clinical presentation of children with unilateral renal agenesis are

• An increase in blood pressure in children.

• Proteinuria: Increased excretion of protein through the urine.

• Vesicoureteral Reflux: Reversible flow of urine into the ureters.

• Clubfoot: Shapeless or twisted foot.

• Congenital heart defects like ventricular septal defects and atrial septal defects.

• Congenital Urological Anomalies: Congenital defects of the urinary and genital tract.

• Anal Atresia or Imperforate Anus: Absence of anus.

How to Manage Patients With Unilateral Renal Agenesis?

• Patients with unilateral agenesis are given medications to lower their blood pressure. A regular visit to the nephrologist should be made in frequent intervals for physical examination, imaging, urine analysis, kidney function tests, and urine protein tests.

• The patients should be advised to a kidney-friendly diet that involves reducing the sodium and sugar intake and increasing potassium and fiber.

• Avoid the use of non-steroidal anti-inflammatory drugs and painkillers.

• Actively maintain health and body weight.

• Regular examination of blood pressure.

• Avoiding physical activities like football and martial arts that have a high risk of trauma to the solitary kidney.

Can Unilateral Renal Agenesis Be Prevented?

Genetic counseling can significantly help minimize the risk of passing defective mutated genes to children in parents with gene mutations related to renal agenesis. Preimplantation genetic diagnosis helps identify embryos that do not have a mutated gene. Thereafter, invitro fertilization can be used to implant safe embryos into the female reproductive system.

Conclusion:

From the above article, it is clear that unilateral renal agenesis is a common congenital anomaly. In addition, every one in three patients have other associated genetic disorders of the kidney and urinary tract. In addition to the renal abnormalities, several patients show extrarenal malformations too. The extrarenal malformations include cardiac, gastrointestinal, and musculoskeletal defects. A definitive treatment strategy does not exist for unilateral renal agenesis. Treatment is based mainly on the presenting symptoms and an approach to safeguard the solitary functioning kidney.

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