About FSGS

Focal segmental glomerulosclerosis (FSGS) is a rare disease that affects the kidneys. In particular, FSGS scars parts of the filters in the kidney, which are called glomeruli. Let's break it down:

Focal = some
Segmental = sections
Glomerulo = of kidney filters
Sclerosis = are scarred

The glomeruli's job is to filter the blood and remove water and some toxins, making urine and leaving the protein behind. When the glomeruli become scarred, they can't properly do their job and protein may leak into the urine instead of remaining in the blood, where it belongs. The leaking protein is a condition called proteinuria. Proteinuria causes fluid to build up in the body. If the protein leaks for too long, your kidneys can become damaged or even stop working.

What are the symptoms of FSGS?

FSGS causes the kidney filters to not work properly, which can cause the following problems:

  • Proteinuria (leaking of protein into the urine)
  • Edema (swelling, especially in the hands, feet, and ankles, and around the eyes, that is caused by extra fluid in the body)
  • High blood pressure
  • High cholesterol
  • Low blood protein

What causes FSGS?

The scarring of the kidneys may be caused by an infection (like HIV) or a disease such as diabetes, sickle cell anemia, or lupus. This type of FSGS is called secondary FSGS. In some cases, the cause of FSGS is not known. This is called primary FSGS. The DUET study is for patients with primary FSGS.

How is FSGS treated?

There is currently no treatment for FSGS approved by the Food and Drug Administration. Many doctors prescribe steroids and other medications to try to decrease the proteinuria. Doctors also often prescribe medications to lower high blood pressure, lower high cholesterol, remove the extra fluid from the body, or suppress your immune system.

If FSGS is not treated properly, it can lead to nephrotic syndrome, which means that too much protein is going into the urine. This is a sign that the disease is getting worse.

Additional resources

The following sites provide more information about this study, FSGS, and other chronic kidney diseases.

NephCure Foundation

National Institutes of Health

National Kidney and Urologic Diseases Information Clearinghouse

National Kidney Foundation


About Clinical Research

Clinical research studies (also called clinical trials) are done to test investigational treatments for diseases and conditions. Studies determine if treatments are safe to use and work to improve the health of people. Before a medication, therapy, or medical device can be made available to the general public, it has to go through several phases of clinical research. All prescription medications that are sold and used today have been tested in clinical studies.

Why do people participate in studies?

Clinical study participation is completely voluntary. People participate in clinical research studies for a variety of reasons. Some volunteer to participate in studies because they want to learn more about their disease. Others volunteer because they want to help researchers learn more about a disease so that it may help others in the future. Participating in a study is an important personal decision that should be made after talking with your doctor and family members.

Are clinical studies safe?

Clinical research studies follow a specific set of standards and are closely regulated. Precautions are put in place to protect people who participate in clinical research. Studies follow a written plan that is called a protocol. The protocol describes the goals of the study, how the study is organized, and what doctors and participants will have to do during the study. Protocols and studies are reviewed by independent groups to evaluate whether the trials are safe and ethical.

What if I have questions during the study?

You can ask questions of the study team at any point before, during, and after the study. Before agreeing to participation, please make sure that you understand the responsibilities of study participants. If you have any concerns about participating in the study, you should feel comfortable discussing them with a member of the study team at any time.

Can I leave the study once I have agreed to participate?

Study participation is completely voluntary, and you can end your participation at any time, for any reason. If you decide you no longer wish to participate in the study, the study doctor may ask you to return to the study site for a final visit. If you decide to leave the study early, there will be no negative impact on the care you receive.

Can I see other doctors during the study?

During the study, you can still see your regular doctor for non-study-related care. You should tell the study doctor if you start taking any other study medications. You should tell your regular doctor that you are participating in a clinical research study.

About the Study

What is the purpose of the study?

The purpose of the DUET study is to evaluate the safety and effectiveness of an investigational medication in patients with focal segmental glomerulosclerosis (FSGS). The goal is to learn whether the investigational medication may change the amount of protein in the urine and decrease proteinuria.

What is the investigational study medication?

The investigational study medication is called RE-021 or sparsentan. In this study, sparsentan will be compared to a drug called irbesartan, which is approved to treat high blood pressure and kidney disease caused by diabetes. Irbesartan is also commonly prescribed for patients with proteinuria.

How long will the study last?

Study participation may last up to approximately 39 months and include up to 18 study visits to the study site. You will have tests and evaluations to monitor your health at the study visits.

Who can participate?

You may be eligible to participate in the DUET study if you:

  • Are 8 to 75 years of age
  • Have a confirmed diagnosis of primary FSGS
  • Do not have a history of heart disease, diabetes, hepatitis, HIV, or organ transplant

What will happen during the study?

Screening Period (Up to 4 weeks)

  • You will have your health checked to see if you are eligible to participate in the study.
  • You may need to stop taking other medications before you can begin participating in the study.

Treatment Period (8 weeks)

  • You will be randomly assigned to receive either the investigational medication or irbesartan.
  • You have a 75 percent chance of receiving the investigational medication.
  • Both the investigational medication and irbesartan are taken as pills at the same time every morning.

Open-label Period

Following the eight-week treatment period, you may be able to continue taking the investigational medication for 136 more weeks.

What are the potential risks and benefits?

The study doctor will explain all of the potential risks and benefits of participating in the study. Before choosing to take part in the study, read all the information the study doctor provides and ask questions about the study. The study doctor can answer any questions you may have about study procedures or potential risks and benefits of study participation.

Does it cost anything to participate?

The investigational study medication and study-related tests and evaluations will be provided at no cost.