Autosomal Recessive Polycystic Kidney Disease: Genetic Counseling and Testing

What Is Autosomal Recessive Polycystic Kidney Disease (ARPKD)?

An uncommon inherited childhood illness known as autosomal recessive polycystic kidney disease (ARPKD) causes improper kidney and liver development. Kidney cysts packed with fluid can cause the kidneys of a fetus or infant with ARPKD to expand improperly. Low kidney function can result from ARPKD, even in a developing child. Due to its early diagnosis by medical professionals, ARPKD is frequently referred to as "infantile PKD."

These organs may stop working over time. Serious issues are frequently brought on by the illness shortly after birth. However, less severe cases might not show symptoms until a kid ages. Many issues can arise from ARPKD, such as:

• Inadequate lung development can lead to serious breathing problems shortly after birth.

• Elevated blood pressure or hypertension.

• Extreme thirst and urination.

• Issues with the liver's blood supply may cause severe internal bleeding.

Chronic kidney disease (CKD) is a gradual decline in kidney function. Even among family members with the illness, there can be significant differences in the onset and severity of these issues. Despite being uncommon, ARPKD is among the most prevalent kidney issues that young children face. Roughly one in 20,000 newborns are thought to have the illness. Either boys or girls are equally impacted.

Which Genes Contribute to ARPKD?

The disease known as autosomal recessive polycystic kidney disease (ARPKD) is inherited, meaning that genes are transferred from parents to their offspring. The instructions the cells require to form the organs and bodily parts are found in one’s genes. Every gene is present in two copies, one from each parent.

An anomaly in the polycystic kidney and hepatic disease 1 gene (PKHD1 gene), commonly called a mutation, causes ARPKD. The precise purpose of the protein this gene codes for is still being determined. It is believed to be in chemical signal transduction across cell membranes. The mechanism underlying gene changes that lead to multiple kidney cyst formation is unknown.

To have ARPKD, a person must have two copies of the defective gene, often one from their father and one from their mother. Typically, healthy individuals carry one flawed copy and one normal copy of the changed gene. On the other hand, there is a one-in-four probability (or 25 percent chance) that each kid born to two carrier parents would receive both copies of the defective gene and become ill.

Genetic Counseling: What Is It?

Genetic counseling aims to provide accurate information about a genetic disease to an individual or their family and support them in understanding it and the alternatives. Speaking with a genetics specialist may be beneficial because discussing genetic issues in families may be challenging.

The doctor will attempt to explain the condition's facts accurately and comprehensively. The doctor tries to explain possibilities in a way that supports one and their family members in understanding and coming to the best conclusions for them rather than being largely psychological counseling. Genetic testing may be necessary in many cases, but only in some.

When Is Genetic Testing Beneficial?

If medical professionals are already certain of the child's diagnosis, genetic testing is typically not used to confirm an ARPKD diagnosis made either before or after birth. But it can be helpful in the following circumstances:

• Genetic testing can confirm the right diagnosis if medical professionals are unclear if the child has autosomal dominant polycystic kidney disease (ADPKD) or another illness.

• Genetic testing can be done to screen the unborn child while they are still inside an individual to see if they have inherited ARPKD and if one and their partner both carry a defective PKHD1 gene and are having a child.

• Pre-implantation genetic diagnosis is a type of in vitro fertilization (IVF) that can be used in conjunction with genetic testing to choose an embryo that has not acquired ARPKD if one and their partner both possess a defective PKHD1 gene and are planning a family.

What Are the Causes of ARPKD?

• A genetic defect that impairs the normal development of the kidneys and liver is the cause of ARPKD.

• Particularly impacted are the kidneys' tiny tubes' growth and development, which leads to cysts fluid-filled sacs and bulges within them.

• The kidneys' overall function deteriorates due to the cysts' gradual enlargement and scarring (fibrosis) of the kidneys.

• Similar issues impact the bile ducts, tiny tubes that allow bile, a digestive fluid, to exit the liver.

• Cysts may form inside the bile ducts and develop improperly. Over time, the liver may also develop scars.

• The genetic mutation that causes ARPKD occurs in the PKHD1 gene, often inherited from one's parents.

• A child's likelihood of acquiring ARPKD is one in four if both parents have a defective copy of this gene.

• The inheritance pattern of autosomal dominant polycystic kidney disease (ADPKD), a more prevalent kidney illness that typically does not result in markedly impaired kidney function until maturity, differs from that of ARPKD.

• Rarely, ADPKD can occur when a defective gene is solely inherited from one parent.

What Are the Early Symptoms of ARPKD?

Early life and in the womb are common times for ARPKD symptoms to manifest. Early symptoms of ARPKD in the fetus can create major health complications. Prenatal care should, therefore, be sought as soon as a woman becomes pregnant if she is in danger of passing on PKD to her offspring.

• Enlarged kidney.

• Lack of growth.

• Low amniotic fluid level.

Some individuals with ARPKD may not exhibit any symptoms or indicators until much later in infancy or even into adulthood.

If an ARPKD baby survives delivery, their breathing may be hampered by kidney and liver issues. These difficulties might be aided by collaborating with a healthcare team as soon as feasible.

• Breathing issues.

• Renal failure.

• Liver issues.

• Elevated blood pressure.

How Are Genetic Tests Carried Out?

Any source of DNA can be utilized for the test; often, white blood cells taken from a blood sample are employed. Placenta or amniotic fluid cells can be used to test an unborn kid. The liquid that envelops the developing embryo in the womb is called amniotic fluid. The embryo can be checked if an advanced form of in vitro fertilization (IVF) is utilized (see more on family planning below).

Genes are just character codes. After the cells' DNA has been removed, the lab personnel can look for any errors in the ARPKD gene. The results of the initial test in a baby or person with ARPKD may not be known for several months or more, making the interpretation of the data time-consuming.

If defects are discovered in both copies of the defective gene, subsequent children's DNA samples can also be examined during IVF or pregnancy. Because the lab employees already know precisely what defective DNA code they are looking for, this process goes much more quickly. Typically, this testing phase takes two weeks.

What Might the Genetic Test’s Findings Be?

The polycystic kidney and hepatic disease 1 gene (PKHD1 gene) can have various mutations that could lead to ARPKD. If the newborn has the disorder, there is roughly a 75 in 100 (75 percent likelihood) chance that the gene defects causing ARPKD will be discovered by genetic testing. Still, there is a potential that the culpable flaws go undiscovered.

If the child develops ARPKD, a genetic test could reveal the following:

• The PKHD1 gene carries genetic errors in both copies, which explains why the child has ARPKD.

• One copy is faulty, but the other is not.

• There is no malfunctioning DNA coding that accounts for the baby's ARPKD.

• Although one or both PKHD1 genes have a flaw or unique coding segment, genetic experts are unsure if this is the reason behind the baby's ARPKD.

It may still be feasible for someone to test embryos in the future or to become pregnant if they have a child with ARPKD, but no defective code is discovered in either their or the PKHD1 genes. In that instance, the lab will compare the DNA samples from the embryo and unborn child.

Even if a mutation is known, it would not be common to give testing to the extended family, such as siblings and sisters, to find out if they were carriers. A defective copy of the PKHD1 gene must be inherited by the infant with ARPKD from both parents. Testing a general public member to determine whether or not they are a carrier is not feasible. It is extremely unlikely for someone without a family history to be a carrier.

How Can One With ARPKD Start a Family?

Prenatal genetic testing can be done if both parents are known carriers of a PKHD1 mutation. This entails examining the fetus to determine whether or not the child has the altered gene and, hence, ARPKD.

Together with ultrasound images, it entails examining tiny samples of placental tissue or amniotic fluid. As the genetic test requires specialized laboratories to conduct, it is preferable to have these discussions before getting pregnant. Requesting a referral to the neighborhood genetic clinic could be beneficial if one wants more details and guidance on organizing the family.

Parents should also consider pre-implantation genetic diagnosis (PGD). To do this, in vitro fertilization (IVF) embryos are genetically tested for the two PKHD1 mutations. A kid born from that IVF cycle will not have ARPKD since only embryos lacking two copies of the mutant gene are put into the mother.

Conclusion:

ARPKD arises from a genetic anomaly, sometimes called a mutation, in the PKHD1 gene. The instructions for this gene produce a protein, but the precise purpose is unknown. It is believed to play a role in the passage of chemical signals via cell membranes. The mechanism by which many kidney cysts develop is unknown due to changes in the gene. A referral from a general practitioner or kidney specialist is required to receive genetic counseling. Many centers have outreach clinics at nearby hospitals or health centers since they serve wide geographic areas. A genetic counselor, clinical geneticist, or specialized genetic nurse may be consulted.