Chronic kidney disease (CKD) is a major global health challenge, affecting more than 3 million people in the UK, and can lead to kidney failure. Once someone reaches kidney failure, they may need dialysis or a kidney transplant. Dialysis in particular can be very expensive, with the NHS spending more than £1 billion on dialysis treatment in 2023, and can significantly reduce someone’s quality of life. The most common causes of CKD are diabetes and high blood pressure. Rare kidney diseases are defined as affecting less than 5 in 10 000 people.

Less than 1 in 10 people living with CKD have a rare kidney condition, however 1 in 4 people with kidney failure have a rare disease. The reason why there is a much higher proportion of people with rare kidney diseases in the CKD group compared to the kidney failure group is not well understood.

Additionally, it is often hard to find accurate up-to-date information on rare diseases because they affect so few patients. Doctors may only treat a few patients with a rare disease in their whole career. It is often unclear how a rare disease might progress, leaving patients and their families with a lot of uncertainty.

The National Registry of Rare Kidney Diseases (RaDaR) has collected information from patients with more than 30 different types of rare kidney diseases for 15 years to answer some of these questions. It is the largest rare kidney disease registry in the world.

In this paper we compared >27,000 people living with rare kidney diseases in RaDaR to people living with CKD caused by other, more common kidney conditions. We found that patients with rare kidney diseases were more likely to develop kidney failure that those with more common kidney conditions, and were much less likely to die before and after starting dialysis.

This finding suggests that, whilst patients can live long and healthy lives with a successful kidney transplant, investing in treatments for rare kidney diseases to prevent kidney failure in the first place might have a big effect on reducing the burden of kidney failure for patients and the NHS.

We also described in detail how 28 different rare kidney diseases affected patients over time, including what average age someone with each rare kidney disease reaches kidney failure. We hope this data will help patient and their families to understand their condition, plan their lives and make joint decisions with their medical teams.

Rare kidney diseases affect less than 5 in 10,000 people in the population. Studying rare kidney diseases can be challenging due to small numbers of patients. This can lead to delays in patients receiving their diagnosis and a lack of reliable information once they are diagnosed.

RaDaR (The National Registry of Rare Kidney Diseases) was set up in 2010 to collect information of people living with rare kidney diseases across the whole of the UK, who choose to participate.

In this study we describe 23,946 adults and 1,934 children with rare kidney diseases who have agreed to join RaDaR. This is the largest description of people living with rare kidney diseases worldwide. The most common rare disease group in adults is Autosomal Dominant Polycystic Kidney Disease, and Idiopathic Nephrotic Syndrome in children. We found that children in

RaDaR were more likely to be from more deprived areas compared to adults in RaDaR, and compared to other children living in the UK. This suggests that families with children with rare kidney diseases may experience more social deprivation and may require increased support.

IgA nephropathy is a rare kidney disease which can lead to kidney failure. Most patients are diagnosed before 40 years old. Previous studies in IgA nephropathy have looked at how patients do over relatively short periods of time. Little is therefore known about how likely someone living with IgA nephropathy is to develop kidney failure over their whole lifetime.

This study found that people living with IgA nephropathy who agreed to join RaDaR had a high risk of reaching kidney failure in their lifetime. The risk of reaching kidney failure was higher for patients with higher levels of protein in their urine (proteinuria). These findings suggest more needs to be done to diagnose and treat patients with IgA nephropathy earlier, and to reduce proteinuria levels, to stop them progressing to kidney failure.

C3 Glomerulopathy and Immune Complex Membranoproliferative Glomerulonephritis are both rare conditions that affect the kidneys, causing protein leak into the urine (proteinuria) and often lead to kidney failure.

This study looked at early changes in kidney function and proteinuria at the time patients are diagnosed. We found that reducing protein levels in the urine by 20-50% in the year after diagnosis strongly reduced the risk of kidney failure. Reducing protein levels in the urine to <100mg/mmol in the first year reduced the risk of patients developing kidney failure by 85%.