Introduction: What is Pyelectasis?

Pyelectasis, also known as pelviectasis, is a condition that occurs during pregnancy, characterised by the enlargement or dilation of the baby’s renal pelvis. This is the area in the centre of the kidney where urine collects before it passes into the ureter and then to the bladder. It can affect one or both kidneys and as a result, the kidney becomes swollen due to urine buildup.

Pyelectasis occurs in only 1% of all pregnancies, and more commonly affects people assigned male at birth than people assigned female at birth. It is often detected in unborn babies during the routine 20-week ultrasound scan during pregnancy, which checks the baby’s organ development. In most cases, pyelectasis usually resolves by itself before or shortly after birth and treatment is not required, so the baby does not usually have any long-term urinary issues.

Why genetics and familial factors matter

The spontaneous nature of pyelectasis means that in most cases, it has no obvious cause. Research suggests that genetics plays a role as the condition may be passed down in families, and it may be more likely for a baby to present with pyelectasis if a parent or sibling was affected by it. This is because the development and structure of the kidneys are determined by the genes each person has. Genes contain instructions in the form of DNA, that encode proteins, which are the building blocks necessary for all bodily processes and the formation of cells. 

Some families may have a higher chance of pyelectasis due to the influence of the genes that are passed down, which control how the kidneys are formed, including their size, structure and function. Certain inherited genes responsible for kidney development may contain errors called mutations when they are being created, which can have an effect on kidney structure or size and can lead to an abnormality in their urine-draining function. 

This article seeks to explore the role of genetics in pyelectasis, to understand the origin of the condition, and how family history and genetic conditions can increase the likelihood of some infants being affected

Genetic and familial influences

What causes pyelectasis?

To understand the genetic causes of foetal pyelectasis, it is imperative to understand how the kidneys normally function and how this is altered in babies with the condition. 

The main function of the kidneys is to filter the blood and remove waste products through urine, which balances the water and electrolyte content and regulates blood pressure. Urine collects in the renal pelvis and empties into the ureter, which then drains into the bladder and out of the body through the urethra. In pyelectasis, the kidney becomes enlarged due to a buildup of urine.. Pyelectasis is diagnosed if the diameter of the renal pelvis, from front to back, is between 4mm and 10mm.¹

The two main causes of pyelectasis are blockages in the kidney and urine reflux, specifically ureteropelvic junction obstruction (UPJO) and vesicoureteral reflux (VUR), respectively.¹ Both causes often run in families and have a known genetic basis, so inheriting specific genes or random mutations occurring in these genes can make it more likely for some babies to inherit pyelectasis.

Ureteropelvic junction obstruction

UPJO occurs when there is a blockage at the junction where the ureter attaches to the kidney. Urine is retained inside the renal pelvis as a result and is not drained into the bladder, causing kidney swelling and an increased internal pressure.^1,2 This either subsides naturally as the baby matures or requires surgery to remove the blockage.

UPJO affects about 1 in 1000-1500 babies and is often caused by narrowed areas, abnormal tissue folds or harmless skin tags that block the flow of urine to the bladder.² Most cases of UPJO arise from abnormalities inside the wall of the ureter, like thickened muscle, excessive scar tissue and inflammation. 

These changes are linked to genetic factors, particularly genes like HIF1A, TGFB1, IL-6, and MCP-1, which regulate how the body responds to low oxygen, forms scar tissue, supports blood vessel growth, and manages cell signalling.² When these genes are overactive or underactive, they disrupt normal tissue development in the ureter, promoting inflammation and damage that can obstruct urine flow.² 

Vesicoureteral reflux 

VUR is an abnormal backflow of urine from the bladder into the ureter and sometimes into the kidneys, due to an abnormal valve. Urine is trapped in the kidneys, making them swell until this usually self-resolves as the baby matures. If VUR does not self-resolve, urinary tract infections can occur due to bacteria entering the kidneys and this requires treatment with antibiotics or corrective surgery to prevent pyelectasis.

VUR affects approximately 1 in 100 babies and carries a high familial risk, as 27-50% of siblings or children of affected parents can inherit the condition. Research shows that VUR can be caused by faulty gene functions, specifically mutations in a gene called SPRY1. This gene plays a role in kidney development by regulating signals from a protein called GDNF (glial cell line-derived neurotrophic factor). A mutation in SPRY1 can cause it to function incorrectly and create high sensitivity to GDNF, causing ectopic ureters (where the ureter from the kidney doesn’t connect to the bladder properly).³

Other genes called FOXC, SLIT2 and ROBO2 are responsible for keeping the protein GDNF active in the correct areas during the baby’s early development. Mutations in these genes can activate GDNF in the wrong areas within the kidney, increasing the risk of extra ureters being formed.³ A combination of different genetic factors, rather than errors in a single gene, can cause VUR, and research is still being conducted to determine precisely which genetic errors cause VUR and subsequently pyelectasis.³

Down syndrome and pyelectasis

Research focusing on how genetic conditions can give rise to pyelectasis has shown that the condition is often a marker for Down syndrome.^4,5 This means that pyelectasis being detected during ultrasound scans can imply an increased likelihood of the baby having Down syndrome; however, not all babies with pyelectasis have Down syndrome. This means that doctors often consider further genetic testing when pyelectasis is found along with other markers in Down syndrome.

Trisomy 21 is a chromosomal abnormality where babies are born with an extra chromosome, specifically chromosome 21, and is present in almost all cases of Down syndrome. This extra chromosome affects how different organs and tissues can develop, including the kidneys and the urinary system. The altered kidney function in babies with Down syndrome can prevent urine from draining from the kidney to the bladder smoothly, causing urine to temporarily build up and the kidney to swell. 

Pyelectasis is found in 25% of babies with Down syndrome compared to about 2-3% of babies with normal chromosomes.⁴ However, research has not yet determined exactly how pyelectasis is linked to Down syndrome and further studies are needed to explore this link.

Diagnosis and monitoring

When a baby presents with pyelectasis that does not resolve on its own, doctors conduct investigations and blood tests to analyse DNA and check for a possible genetic cause of the condition. This includes kidney ultrasound scans and urine analysis, to monitor babies with UPJO and VUR and checking for any continued swelling after birth. The risk for Down syndrome can be assessed using prenatal screening tests and ultrasound scans, testing the amniotic fluid that surrounds the baby during pregnancy, as well as taking samples from the placenta to check for any suspected genetic conditions.

The monitoring of babies that present with pyelectasis should include a tailored, thorough approach that checks for possible genetic risks and associated conditions. Using diagnostic and screening methods is key in determining whether the kidneys show any signs of development into long-term urine build-up, known as hydronephrosis.

FAQs

Does pyelectasis show any signs or symptoms? 

Pyelectasis usually does not present with any symptoms and, in most cases, is found in babies during ultrasound scans. However, it can sometimes cause pain in the back or side of the body, blood in your urine, a weak urine stream, or lack of urine, and associated symptoms of a bacterial infection in the urinary tract, such as frequent, painful urination and feeling tired.

What is the difference between pyelectasis and hydronephrosis?

Pyelectasis refers to the swelling within the kidneys due to urine build-up and is mostly self-resolving. In rare cases, the baby’s kidney may show a large buildup of urine and the blockage in the kidney deteriorates to become obstructive, resulting in kidney ballooning and becoming a condition known as fetal hydronephrosis. You can read more about the difference here. 

Can pyelectasis be treated?

Pyelectasis usually resolves and goes away on its own and doesn’t require treatment. The cause of kidney damage or blockage, especially due to an underlying condition like UPJO and VUR, can be corrected by surgery. Surgery that is done to remove any blockage or narrowing of the point that connects the ureter and kidney is called pyeloplasty. In some rare cases, corrective surgery may be required in the unborn baby if hydronephrosis occurs and there is a risk of kidney damage. It is important to consult a specialist doctor if you are worried about your baby’s pyelectasis worsening or not self-resolving, so that their kidneys can be examined and the risk is assessed.

Summary

Pyelectasis is a condition that presents with swelling of the kidneys, specifically in the renal pelvis, and can have a significant impact on kidney health if it is left undiagnosed and untreated. Pyelectasis is linked to underlying genetic causes and a family history of certain conditions that increase the chances of the condition occurring in babies and possibly further complications. It is crucial to understand the associated risk factors and causes of pyelectasis so that appropriate monitoring strategies and timely treatment methods can be implemented to protect kidney function and allow for a healthy life.