Only in Toronto: City’s diverse population propels discovery that ethnicity may play a role in the health of children with kidney disease

Toronto-based study reveals South Asian children are more frequently affected but have less complex outcomes than those of European descent

TORONTO – From the city crowned to be the most diverse in the world, new research on ethnic differences in children with nephrotic syndrome suggests that a child’s ethnicity may influence not just the kidney disease’s incidence, but ultimately its clinical outcomes.

A new study led by The Hospital for Sick Children (SickKids) is the first to look at ethnicity’s role and the possibility of genetic influences in children with nephrotic syndrome, the most common form of kidney disease in childhood.

The study, published in the October 7 print edition of the Clinical Journal of the American Society of Nephrology, found that children with South Asian roots are more frequently diagnosed with nephrotic syndrome than their European peers. With that, children of South Asian descent had significantly less complex clinical outcomes – including more complete remissions, fewer subsequent relapses, and a longer relapse-free period after initial steroid therapy. The study also found that East/Southeast Asian children were significantly less likely to be prescribed second-line agents such as cyclophosphamide compared with European children.  

“Not only are we seeing more South Asian children with nephrotic syndrome than European children, but we found they respond differently to steroids with higher complete remission rates,” says the study’s principal investigator, Dr. Rulan Parekh, Associate Chief of Clinical Research, Staff Physician in Nephrology and Senior Scientist at SickKids. “Unravelling these ethnic differences is an important first step to determine if it’s a common mechanism among all, or if there are unique traits between groups. Down the road, this knowledge may lead to the discovery of genetic or environmental factors that can account for these differences.”

Children with nephrotic syndrome experience edema, a type of swelling in the face, belly, hands, and other extremities after an excessive amount of protein is filtered out of the blood and expelled through urine, due to the glomeruli’s inability to filter waste products and fluids properly.

The longitudinal study identified and monitored a total cohort of 711 SickKids patients ranging in age from one to 18, who were diagnosed with and treated for nephrotic syndrome from 2001 to 2011. Analyses focused on the three largest ethnic groups – South Asians (33 per cent), Europeans (23 per cent), and East/Southeast Asians (10 per cent) – with the remaining accounting for other origins (33 per cent). All study participants were from the Census Metropolitan Area (CMA) of Toronto.

Parekh notes that she decided to study ethnicity when she noticed a large incidence of nephrotic syndrome in Toronto children, something she never observed at other centres in the United States. Over a decade, the incidence changed from 1.99 to 4.71 per 100,000 children in Toronto, which she believes is because the general population’s diversity has changed.  The investigative group demonstrate that South Asian children have an incidence six times higher than those of European descent.

Recent immigration from India and China accounted for 57 per cent of all newcomers to Canada from 2006 to 2011. Immigration into a higher-income country like Canada, offering publicly funded health care, provides the capacity to study longitudinal health outcomes based on ethnicity.

“Toronto offers the perfect snapshot to study ethnic differences in health. That is the uniqueness of studying diversity in such a multicultural hub,” says Parekh, who is also Professor of Pediatrics and Medicine, Faculty of Medicine and Dalla Lana School of Public Health at the University of Toronto. “We could not do this research anywhere else.”

Study Findings

• South Asian and East/Southeast Asian children had 45 per cent and 58 per cent lower odds of developing frequent relapses of nephrotic syndrome compared to European children;
• South Asian children were 26 per cent less likely to develop a first relapse compared to European children;
• East/Southeast Asian children were 35 per cent less likely to develop a first relapse compared to European children;
• The cumulative incidence at five years for use of cyclophosphamide among European, Southeast Asian and East/Southeast Asian children was 45 per cent, 42 per cent, and 30 per cent;
• East/Southeast Asian children were 50 per cent less likely to be prescribed second-line agent cyclophosphamide compared to European children.

The study was supported by Physicians’ Services Incorporated (PSI) and SickKids Foundation.

This paper is an example of how SickKids is contributing to making Ontario Healthier, Wealthier and Smarter.