August 03, 1999
Dr. Paul Adams
519-685-8500, ext. 33513
519-685-8500, ext. 35947
Hemochromatosis study indicates population screening may be beneficial and that genetic testing may be falsely positive in many cases
(LONDON, Ontario) Hemochromatosis is a very common genetic disease in which iron overload in the body leads to damage of the liver, heart, pancreas and endocrine organs (ie: pancreas and thryroid). The condition is often not diagnosed until damage has already been done. The condition is autosomal recessive, meaning both parents must carry the gene and an affected person has two copies of the gene. The disease is most common in people of Northern European ancestry (Ireland, England, Wales, France, Germany, and Scandinavia). The disease is easily treated by the weekly removal of 500 mL of blood to decrease iron in the body.
The gene for hemochromatosis was discovered in 1996 and a diagnostic blood test became available. Initially, more than 90 per cent of typical hemochromatosis patients tested positive on the genetic test, indicating that hemochromatosis was, by far, the most common genetic disease in Canada.
Given that the condition is so common and often undiagnosed, and since it is so easily treated, London Health Sciences Centre, under the leadership of gastroenterologist, Dr. Paul Adams, set out to study the prevalence of the disease more thoroughly.
"We approached 5,211 voluntary blood donors who were young, healthy and already presenting to give a blood sample. With their consent, they had genetic testing for hemochromatosis. Initial results suggested that one in 168 were positive for the genetic test," says Dr. Adams. Many of the positive results, however, had no evidence of iron overload, leading Dr. Adams to further investigate. "We sequenced a small region of the hemochromatosis gene and found that in many cases the person was actually a carrier of the gene (one copy of the gene) but did not have the two copies of the gene needed to cause the disease. A new variation in the gene was found during this study (5569A polymorphism of the HFE gene) that led to a carrier erroneously appearing as a true hemochromatosis patient on the original test. This new variation was common, affecting 20 per cent of normal cases tested. By changing the conditions of the genetic test, the problem of erroneous results can be avoided," says Dr. Adams.
When the improved genetic test was used, it was found that one in 327 blood donors were discovered with hemochromatosis. The study findings are to published in the August issue of the prestigious medical journal, Nature Genetics.
"Since the disease is very common, can be detected by simple blood tests and has an effective and inexpensive treatment, population screening should be considered," concludes Dr. Adams.
In Ontario, all children are screened for congenital hypothyroidism which affects one in 5,000. Children in Ontario are also screened for phenylketonuria (PKU) - a genetic disorder that prevents the normal use of protein in food - which affects one in 10,000.