Clin Genet 1999: 55: 20–25 Printed in Ireland. All rights resered Original Article Thalassemia carrier screening and prenatal diagnosis among the British Columbia (Canada) population of Chinese descent Yong KN, Wadsworth LD, Langlois S, Yong S-L, Wilson RD. Tha- lassemia carrier screening and prenatal diagnosis among the British Columbia (Canada) population of Chinese descent. Clin Genet 1999: 55: 20–25. © Munksgaard, 1999 The goal of thalassemia screening is the identification, prior to the conception or birth of an affected child, of couples where both partners are thalassemia carriers. When both partners are identified as carriers for alpha- or beta-thalassemia, the risk of having a fetus who is ho- mozygous or compound heterozygous for the abnormal gene is 25%. A study was performed to identify whether routine screening for tha- lassemia is indicated for the Chinese population in British Columbia (BC). In a population of 783 subjects, studied either prospectively or retrospectively, 5.0% were alpha-thalassemia carriers and 1.7% were beta-thalassemia carriers. In addition, a review of all BC cases of prenatal diagnosis for tha- lassemia over a 6-year period indicated that 26% of couples were iden- tified as alpha-thalassemia carriers because of a second or third trimester diagnosis of fetal hydrops, and 17% of couples referred for beta-thalassemia already had an affected child. The experience with prenatal diagnosis shows that a significant proportion of at-risk couples are not identified prior to or early in a pregnancy. The prevalence of carriers for thalassemia would warrant a program of education and routine screening for this condition in the BC Asian population. Karina N Yong c , Louis D Wadsworth a , Sylvie Langlois b , Siu Li Yong b and R Douglas Wilson b,c a Department of Hematopathology/Transfusion Medicine, b Department of Medical Genetics, c Department of Obstetrics and Gynecology, British Columbia Children’s and Women’s Hospital, Vancouver, British Columbia, Canada Key words: prenatal diagnosis – screening – thalassemia Corresponding author. R Douglas Wilson, Division of Maternal Fetal Medicine, British Columbia Children’s and Women’s Hospi- tal, Room 2H30-4500 Oak Street, Vancou- ver, British Columbia V6H 3N1, Canada. Tel.: +1 604 8752665; fax: +1 604 8752725; email: dwilson@wpog.childhosp.bc.ca Received 30 July 1998, revised and ac- cepted for publication 22 September 1998 Thalassemia is one of the most common single- gene diseases of the blood, occurring in individuals of all ethnic backgrounds, but particularly those of African, Asian, Central American, Mediterranean, and Middle Eastern descent (1, 2). Immigration from regions where the carrier frequency of tha- lassemia is high increases the likelihood of these recessive disorders in the Canadian population. Currently in British Columbia (BC), there are in- creasing numbers of immigrants of Chinese ethnic origin. The frequency of heterozygote carrier status among the Chinese population has been reported to vary from 5 to 15% for alpha-thalassemia and from 3 to 4% for beta-thalassemia (3). Carriers of thalassemia syndromes are usually asymptomatic, although their peripheral blood smear shows hypochromia and microcytosis. Dur- ing pregnancy, common nutritional deficiencies such as iron and folic acid deficiencies can alter the mean corpuscular volume (MCV) (2). As a result, thalassemia may be difficult to diagnose and may exclude during pregnancy. For example, individu- als with alpha-thalassemia may present with mild microcytic anemia, which can be mistaken for the microcytic anemia of iron deficiency (2, 3). In the diagnosis of thalassemia carriers, it is important to exclude iron deficiency, although iron studies may not reliably exclude this deficiency during preg- nancy. Therefore, it is best to diagnose the tha- lassemia carrier status before pregnancy (2). The most important aspect of thalassemia screening is to identify couples who are both thalassemia carri- ers, as they have a 25% risk of having a fetus/child with a serious thalassemic syndrome. Thalassemia screening programs in the Mediterranean popula- tions have been effective in identifying such carri- ers in a timely manner, in order to provide appropriate genetic counselling and offer prenatal 20