Researchers identify cause of gastrointestinal disorder affecting Inuit

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Researchers have identified a genetic mutation that is the cause of a gastrointestinal disorder that affects as many as one in 10 Inuit people.

The condition, congenital sucrase-isomaltase deficiency (CSID), prevents the body from absorbing certain types of sugar.

Matthew Lines, a metabolic physician at the Children's Hospital of Eastern Ontario, said the practical benefit of the discovery is that children can now be diagnosed with a simple blood test instead of a biopsy of the small intestine.

"It's challenging to do an intestinal biopsy on a baby and not too pleasant for the baby, so this will be helpful," he said.

The findings in a study of Inuit people are published in Monday's edition of the Canadian Medical Association Journal.

CSID is usually diagnosed in toddlers, once they are weaned and start to consume food such as fruit, or in babies who are fed infant formula or baby food that contains sugar.

Babies who are breastfed do not have symptoms, nor do those who drink cow's milk.

CSID is a disorder that affects a person's ability to digest sucrose, a sugar found in fruit and known commonly as table sugar, and maltose, the sugar found in grains.

People who have the condition are told to follow a low-carbohydrate diet and avoid sucrose and maltose, which are common in processed foods.

"If you have CSID, a diet low in carbs is a good thing – game and fish, like a traditional Inuit diet," Dr. Lines said.

The condition is lifelong, but hits children particularly hard. The severe diarrhea and constant pain can lead to stunted growth and, in some cases, be life-threatening.

CSID was recognized in Inuit populations in Canada's Far North, Alaska and Greenland in the 1960s, when processed foods began to supplant "country foods" in the Inuit diet.

Currently, older children and adults are tested for the condition by being given a sweet drink that is loaded with sucrose and then levels of hydrogen in the gut measured. The test can cause severe intestinal pain. After the sucrase-isomaltese (SI) gene was discovered, the biopsy also became an option.

Because of the difficulty in diagnosing the condition, it is not clear how many people have CSID. Estimates range from 5 to 10 per cent of the Inuit population. Sugar intolerance also exists in much smaller numbers in people of European extraction, about one in 5,000. (It is often misdiagnosed as irritable bowel syndrome.)

The genetic mutation that causes CSID was identified after researchers isolated DNA from the blood of a child from Baffin Island. The baby suffered from severe diarrhea after consuming formula that contained sucrose.

Now that the specific mutation is known, diagnosis can be done with a blood test.

Among the Inuit who participated in the new study, 3 per cent had been diagnosed with CSID. Slightly more than 17 per cent were also found to have the genetic mutation. (The condition is inherited in an autosomal recessive pattern, meaning both parents would need to have a copy of the mutated gene for their child to develop it.)

The next question will be whether Inuit children should be routinely screened for the genetic mutation.

Dr. Lines said he is not sure if that approach will be taken. "Our next step is to ensure the test is available locally," he said.

CHEO is designated as a care centre for children from Nunavut and Baffin Island, so it treats a high number of Inuit children.

The discovery of the genetic mutation for CSID involved researchers from CHEO, Western University and the University of Washington.

The research was part of the Finding of Rare Disease Genes in Canada initiative. To date, FORGE collaborators have identified 146 genes and genetic mutations associated with rare disorders.

None of the FORGE discoveries has been patented. CHEO has launched a court challenge to the Patent Act, arguing that genes should not be patentable.