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Nine-month-old Vivek Mehta is places on a weight scale by mother Manisha Mehta during a visit to the St. Michael's Hospital Paediatric Clinic in Toronto Feb. 14, 2012. (Tim Fraser for The Globe and Mail/Tim Fraser for The Globe and Mail)
Nine-month-old Vivek Mehta is places on a weight scale by mother Manisha Mehta during a visit to the St. Michael's Hospital Paediatric Clinic in Toronto Feb. 14, 2012. (Tim Fraser for The Globe and Mail/Tim Fraser for The Globe and Mail)

Health

Treating a medical mosaic, doctors develop a new appreciation for the role of ethnicity in disease Add to ...

Baby X is born in a Canadian hospital and her tiny, wrinkled body is placed on a scale that reads 3,061 grams, or 6 pounds and 12 ounces.

Things can go one of two ways for Baby X, whose parents are immigrants from India.

According to the standard birth-weight curves used in Canada, which are modelled after norms for Caucasian newborns, this baby could be labelled as underweight, a classification that comes with a higher risk of death and lower cognitive ability. She could be subjected to a battery of unnecessary tests and follow-ups. Her concerned mother might overfeed her in hopes of speeding up her growth.

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Or, if a new birth-weight curve developed at Toronto’s St. Michael’s Hospital – one that takes into account a wide range of ethnicities – is used, Baby X will be classified as having a perfectly normal weight and will be sent home. South Asian newborns are typically smaller than those of many other ethnicities.

It’s just one example of why there is a move in Canada and other countries to collect data on their diverse populations to deliver better patient care.

Doctors and researchers are putting greater stock in ethnicity as a variable in health outcomes. A large body of research suggests certain groups are at a higher genetic risk for particular diseases. And physiologically, what is accepted as “normal” and “healthy” varies between ethnicities.

But there are no universal standards or terms of reference used to classify ethnicity, which has made it a highly fraught subject. Some say it shouldn’t be considered a variable at all, arguing that the link between ethnicity and health is manufactured. The Canadian Institute for Health Information doesn’t collect data on ethnicity, and the Canadian Medical Association has no formal policy on the best way to classify the diverse backgrounds of Canadians.

Joel Ray, who led the St. Michael’s Hospital team that developed the new newborn birth-weight curve, is baffled that an old model developed in 1969 based on the weights of 300 Caucasian newborns in Montreal – a population unreflective of modern Canada – is still used in some parts of the country. In a study published Wednesday in the Journal of Obstetrics and Gynaecology Canada, his team analyzed 760,000 live births in Ontario and, by their measure, more than one in 10 South Asian babies was at risk of being misclassified if one of the standard Canadian birth-weight curves was used.

“They’re completely archaic – there’s no other sweet word for it,” Dr. Ray said.

Dr. Ray previously studied rates of gestational diabetes among women of various ethnic groups and found South Asians had the highest risk levels, followed by those from East Asia and the Middle East. Previous studies have lumped these three groups together under the catch-all category “Asian” – missing the heterogeneity within.

“You may as well call them human if you’re going to call someone Asian,” he said.

It seems even a breakdown by subcontinent isn’t precise enough.

In 2008, a team of New York researchers studied the rates of gestational diabetes among New York City’s population with a breakdown by country of origin. The results revealed much heterogeneity within sub-regions: While women from Bangladesh (classified as part of Southeast Asia) had a 7.1-per-cent risk of developing gestational diabetes, those in Iran (part of the same subcontinent) had only a 1.3-per-cent risk.

Sonia Anand, Canada Research Chair in ethnic diversity and cardiovascular disease at McMaster University, says the way she classifies ethnicity has greatly evolved in the last two decades. Dr. Anand runs genetic analyses on individuals she studies and asks them to list their ethnicity, as well as that of their parents and grandparents.

The wording is key: Dr. Anand asks for ancestral country of origin to allow for migration – for example, a large population of Indians has lived for generations in Trinidad.

Some researchers also use surname databases to determine ethnicity, but that’s an imprecise system, Dr. Ray points out. “Lee” can be a Chinese name, but also an Anglo one. “De Souza” is a common surname for both the Portuguese and Goan Indians.

Although Dr. Anand and Dr. Ray believe they’ve zeroed in on relatively accurate systems for classification, both acknowledge that the growing ranks of mixed-ethnicity individuals in the Western world present significant challenges.

Many geneticists believe mixed-ethnicity breeding could be one of the keys to reducing risk levels for genetic diseases that plague particular groups – just as purebred dogs are more susceptible to disease than their mixed-breed counterparts.

“People go, ‘How dare you compare?’ But if you want to look at the anatomy of a dog, pig or human, like it or not, we’re not that different,” Dr. Ray said.

According to the World Health Organization, one in every 27 Ashkenazi Jews carries the gene for Tay-Sachs disease, a fatal disorder. A child with two Ashkenazi Jew parents would have a much higher risk for developing Tay-Sachs versus a child with one parent of that background.

Jim Wilson, a senior lecturer at the University of Edinburgh’s Centre of Population Science, has spent the last seven years researching whether an individual’s genetic relationship with his parents determines risk level for developing conditions such as hypertension, diabetes and heart disease.

The need for answers is in high demand in Britain, where the fastest-growing population is of mixed ethnicity. Ethnic classification, he says, is becoming even more complex.

“What you’re really going to need is proper genetic testing,” he said. “Self-identified ethnicity isn’t going to reflect genetic reality.”

But some see this rush to modernize classification systems in keeping with rapidly diversifying Western populations as a wasted effort.

Linda Hunt, a professor of anthropology at Michigan State University, says ethnicity is a “highly ambiguous” variable. In a published survey of 30 human geneticists in Canada and the United States, she found various issues in methodology: There was no consistency in the categories used; self-identification was unreliable, and genetic testing pointed to greater genetic diversity within ethnic groups than between them.

As for links between certain groups and diseases – that’s to do with geographic distribution rather than genetics, Dr. Hunt says. In contrast to many geneticists, who say sickle-cell anemia predominantly affects those of African ancestry, Dr. Hunt says the disease is overrepresented in that population because it’s present in areas where malaria is also present.

“It has nothing to do with whether people are black or white – it has to do with people living in a terrain where this parasite is prevalent.”

“The appropriate level of analysis would be to do some sort of family history. To use the shortcut of racial identity or ethnic identity or religious identity is a false shortcut,” Dr. Hunt said.

Dr. Anand, who has devoted her career to studying how both behaviour and genetics contribute to heart disease risk in various ethnic populations, says it’s challenging to “parse out what component of a disease is due to environmental factors versus genetics,” but she says there’s a huge value in using ethnicity as a variable.

“People recognize that a given ethnic population may be high risk for various health outcomes and ethnic-specific programs of prevention, diagnosis and treatment can be set up for that ethnic group as opposed to one-size-fits-all.”



Risk and ethnicity

Tay-Sachs

A genetic disorder in which a fatty substance builds up in the brain. It can lead to paralysis, dementia, blindness, psychosis and death.

Who’s at heightened risk: Ashkenazi Jews and Québécois

Cystic fibrosis

A respiratory disorder in which thick mucus builds up in the lungs. It can cause digestive and reproductive problems as well as fatal lung infections.

Who’s at heightened risk: Those with European ancestry

Sickle cell anemia

A disorder that causes blood cells to change shape. The cells can cause blockages that prevent the flow of blood to other parts of the body.

Who’s at heightened risk: Those of African and South American ancestry

Gaucher’s disease

A disease in which an individual is without the glucocerebrosidase enzyme. Lack of this enzyme prevents cells and organs from functioning properly and can lead to the buildup of harmful substances in the liver, spleen, bones and bone marrow.

Who’s at heightened risk: Ashkenazi Jews

Sources: World Health Organization, U.S. National Center for Biotechnology Information

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