Blood Test Identifies Genetic Mutation Responsible for CSID

A common mutation for congenital sucrose-isomaltase deficiency has been identified in the Inuit population where the condition is highly prevalent.

Congenital sucrose-isomaltase deficiency (CSID) is a rare hereditary cause of chronic diarrhea in children and people with this condition lack the intestinal brush-border enzyme required for digestion of di- and oligosaccharides, including sucrose and isomaltose, leading to malabsorption.

Scientists at the University of Ottawa (Canada) and their colleagues isolated DNA from the blood of a child from Baffin Island in Nunavut, Canada's largest territory, in whom severe chronic diarrhea developed while taking sucrose-containing infant formula. They then sequenced the sucrose-isomaltase (SI) gene in this child to identify the specific genetic mutation responsible for the disorder.

The team then genotyped and sequenced 128 anonymized samples from Inuit controls from a range of Canadian Arctic locales on an ABI 3730 DNA Analyzer (Applied Biosystems; Foster City, CA, USA). Sequencing of the SI gene identified a novel homozygous frameshift mutation in the proband NM_001041.3:c.273_274delAG (p.Gly92Leufs*8). From the 128 anonymized samples from Inuit controls they identified a further two homozygous and 40 heterozygous individuals. The observed allele frequency of this mutation in the sample was 17.2% (44 of 256 total alleles).

Matthew A. Lines, MD, the senior author of the study, said, “People with CSID may remain asymptomatic unless they consume sucrose, which is why persons consuming a Western diet are more likely to become ill. Timely recognition of this condition and initiation of appropriate therapy is paramount. Our study should prompt physicians to consider CSID and to review the sucrose content of a patient's diet, and specifically that of infant formula if applicable”. Dr. Lines added that as result of the team's findings CSID, which formerly required an intestinal biopsy for diagnosis, can now be diagnosed with a simple blood test. The study was published on December 1, 2014, in the Canadian Medical Association Journal.

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University of Ottawa
Applied Biosystems