Ulcerative colitis in the Chinese population of Vancouver , British Columbia

The clinical records of 22 Chinese patients with ulcerative colitis (UC) seen in Vancouver, British Columbia from 1975 to 1989 were reviewed. There was a predominance of males, with a male to female ratio of 1.75:1. The age range at diagnosis was 14 to 67 years (mean 38.9). Eighteen of the 22 patients were immigrants, and one was a visitor from Hong Kong. The age at diagnosis of the three Canadian-born patients (14, 26 and 26 years old) was less than the mean age at diagnosis of the immigrant group. The immigrants had resided in Canada for a mean of 9.3 years before developing symptoms of UC. Despite the rarity of UC in Hong Kong, 59% of the Chinese patients in this series were Hong Kong immigrants. This study demonstrates that UC is not as uncommon a disease in Chinese as had been previously perceived. Adequate time is apparently necessary for exposure to environmental factors in the pathogenesis of UC. The opportunity for continued study of defined ethnic immigrant populations in North America may yield useful information related to environmental factors that may be important in the etiology and pathogenesis of UC.

erally assumed to be uncommon in the Chinese.This is suggested by a number of publications.A report from Singapore in 1971 (1) wa probably the first literature de cription of UC in the Chinese.UC was found in only 18 Chinese patients in Hong Kong from 1951 to 1980 (2).There was another review of 23 cases of UC occurring in Hong Kong Chinese between 1986 and 1991 (3 ).The annual incidence rate of UC in Hong Kong from 1966 to 1980 wa estimated to be around 1 per 1,000,000 (2).There were two Chinese among 10 Malaysian patients with UC in Kuala Lumpur during a 10-year period to 1977 ( 4).Five of 23 cases of UC in the same city from 1982 to 1987 were Chinese (5 ); at that time, 53% of the population of Kuala Lumpur were Chinese.UC also appears to be rare in Singapore, with an estimated incidence of 0.02 per 100,000 and prevalence of 2 per 100,000 in 1971 (1), and a possible prevalence of 8.6 per 100,000 in 1992 (6).In 1974, the population in Singapore wa about 2,000,000 of whom 7 5% were Chinese (7).Sixty-nine per cent of 61 cases of UC in Singapore seen between 1971 and 1986 were Chinese (8), and 28 of 40 patients (70%) in the same city seen between 1981 and 1990 were Chinese (6).UC has been observed in China (9).In the United States, Mendeloff noted seven cases of inflammatory bowel disease in Chinese CJ IAU AND FREEMA Hong-Kong.Cette etude demontre que la CU n'est pas une maladie si rare dam la population chinoise, conttairement ace que l'on avait pen e jusqu'alors.II faut apparemment uffisamment de temps d'exposition a des facteurs environnemcntaux avant d'ob.erver la pathogene e de la CU.La possibilite de poursuivre l'etude de cette population immigrante nord-americaine bien circonscrite pourrait etre une source de renseignements utiles sur Jes facteurs environnementaux, possiblement incrimines dans l'ctiologie et la pathogene •e de la CU.

PATIENTS AND METHODS
Medical records were •ought retro pectively of all patients of Chine c extraction with an establi •hed diagnosis of UC seen in the office from 1975 to 1989, and in three teaching hospitals and two community ho pitals in Vancouver from 1979 to 1989.The records were then reviewed.The diagnosis of UC was based on a compatible history and characteri •tic sigmoidoscopic, histological and, when available, banum enema and/or colono-•copic findings.In all patients, extensive investigations had been undertaken to exclude intestinal bacterial and parasiti infections.

RESULTS
Twenty-two patients of Chinese extraction ( 14 males and eight females) were diagnosed with U in Vancouver between 197 5 and 1989.The age range at diagno•i was 14 to 67 years (mean 3 .9).Table 1 shows epidemiological data for all 22 patients.Ten patients were born in hina, nine in Hong Kong and three in anada.Thirteen patient had lived in Hong Kong before emigrating to anada, two in China, and one in each of Taiwan, England and India; one patient was a visitor from Hong Kong.The three Canadianborn patients had never resided in a fore ign country.The 18 immigrants had lived in Canada for a mean of 9.3 years before they developed ymptoms ofuc.
The clinical features of the 22 patients are sh wn in Table 2.In 16 patients observed for one to 13 years, the course of the disea e wa similar to that of Caucasian patient .The di ease was limited to the rectum or rectosigmoid region in 13 patients.One patient had segmental resection for a igmoid carcinoma; none of the patients had colectomy for U .Of the cxtraintestinal manifestations of the disease, three patients had arthralgias, one had po • ible arthralgias and iritis, one had ankylosing spondyliti and one had erythema nodo um.

DISCUSSION
In a previous report, we detailed our experience with Crohn's disease in the h inese population of Vancouver ( 14 ).
Thi report further describes our experience with inflammatory bowel disea e in hine e patients from Vancouver, pecifically with U .Some feature of our Chine e patients and their di ea e were intriguing.First, the predominance of male reported here is compatible with chat of a previous study of Chinese patients in I long Kong (2).This contra ts   both northern and southern Alberta, prevalence rates of UC were similar in males and females (15,16).Our observations in this Oriental population also contrasts with patients of Anglo-Saxon descent worldwide where the disease has a female preponderance ( 10).Second, a limited form of colitis was generally een in our Chinese patients.
In 13 of the 22 patients (59%) surveyed in this study, the disease was localized to the rectum or extended to the distal few centimetres of the sigmoid colon.Although the duration of the follow-up in our report is less than 10 years in most of the patients, this limited form of disease appears to be more common in the Chinese than that usually re-  ( 19,20), even allowing for the difficulties in diagnosis due to a scarcity of medical resources and possible confusion with the infective dysenteries that are prevalent in underdeveloped regions (22).Nevertheless, there have been reports of UC in several Asian populations (1-6,8,9,23-27).There have also been reports of inflammatory bowel disease occurring in Asian immigrant populations in Canada (11,14, 28) and Great Britain (29)(30)(31).However, apart from our initial presentation ( 11 ) there has been no other report of UC in the Chinese populations of North America and Europe, areas with the highest incidence rates of the disease in the world.
The variability in the incidence of UC among different ethnic groups from the same geographical regions suggests a genetic predisposition to the disease.UC is three to five times more common in Jewish people compared with Anglo-Saxon populations living in western communities (18).UC is rare in the Black population in South Africa (32) and in the Maoris in New Zealand (33 ), in contrast to the Caucasian populations residing in those countries.In Israel, the incidence and prevalence in the Arab population were markedly lower than those in the Jewish population (34,35).In India, UC occurs more frequently in Hindus than in Muslims, Christians or Parsees (21).In Malaysia, Indians (especially Sikhs) appeared to be more prone to the disease than Chinese and Malays (5).Similarly, in Vancouver, the disease seems to be more common in Asian Indians than Chinese (28).
As in the series of patients with Crohn's disease (14), the majority of patients (14 of 22) in this study immigrated from Hong Kong.In the 1986 national population census from Statistics Canada ( 13), Hong Kong was listed as the birthplace among 22,275 Chinese living in Vancouver.This represented 22% of the total Chinese population of 100,340 in metropolitan Vancouver.The high proportion of Hong Kong immigrants in the present series of patients suggests that, within the Vancouver Chinese community, there is an apparently increased predisposition to develop UC.The reason for this susceptibility is unknown.It is also of interest that in the Vancouver Chinese population, our previously reported experience with Crohn's disease (14) is similar to that with UC.
There are epidemiological data of UC in Canada reported from northern and southern Alberta (15,16,36) (15) and in southern Alberta was 21. 7 per 100,000 (16).Although precise data for British Columbia are not available, these data from Alberta compare with the estimated prevalence rate of 22 per 100,000 in our Chinese population and indicate that UC is not as rare in Chinese as had been previously perceived.
Three of the 22 patients in the present study were born and raised in Canada.Their age at diagnosis of UC was distinctly younger than the mean age at diagnosis of the immigrant group.Immigrants had lived in Canada for a mean of 9.3 years before first developing symptoms of the disease.One patient was a visitor from Hong Kong and was not included in this group.These observations suggest that a time factor may be important in the exposure to one or more exogenous risk factors that could influence the pathogenesis of UC.Moreover, the disparity between the prevalence of UC in the Chinese in Hong Kong and Vancouver strongly supports the influential role of environmental determinants in the pathogenesis of UC.
In the past decade, there has been substantial migration of Chinese people from Hong Kong, Taiwan and China to North America, particularly Vancouver.This offers a continuing opportunity to explore possible environmental factors, such as dietary habits (37) and other life patterns, in a defined ethnic immigrant population that may provide clues to the etiology and pathogenesis of UC.

Ulce rative colitis in Chinese
with the Canadian experience in nearby Alberta (since no data arc available in British Columbia); in 304 CAN J GASTROENTEROL VOL 8 NO 5 EPTEMBER/0CTOBER 1994

TABLE 2 Clinical features Apparent Course of Extraintesti nal Other c linical features Years
'Apparent maximum extent of disease from anal verge but the incidence and prevalence of the disease in British Columbia have not Chronic inflammatory bowel yet been determined.The mean prevalence rate of UC in northern Alberta was 37.2 per 100,000 6. Tan CC, Kang JY, Guan R, Yap I, Tay HH.Inflammatory bowel disease: An uncommon problem in Singapore.J Gastroenterol Hepatol 1992;7:360-2.7. Lee SK.Crohn's disease in Singapore.Med) Aust 1974;1:266-9.8. Ng HS.