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Gout is a common rheumatic disease caused by elevated serum concentrations of uric acid, and affects more than 5 million men and women in the US (1). The risk of developing gout is dependent on a number of factors, including sex, age, ethnicity, and environment, although the interplay of these factors has not been well defined. Moreover, genetic factors play a significant role in the pathogenesis of gout, with both serum uric acid concentrations and renal uric acid clearance having been shown to have significant heritability (2, 3). Despite the difficulties in estimation of gout prevalence due to heterogeneous methodology, gout among different Western countries has progressively increased in the recent decade (4).
Over the past 90 years, serum uric acid concentrations have shown a significant increase from 3.5 mg/dl to 6–6.5 mg/dl in the general US male population (5, 6). In addition to the development of gouty arthritis, hyperuricemia has been associated with several conditions, such as the metabolic syndrome, hypertension, and chronic kidney disease (7, 8), although the relative importance of these associations has not been fully established (8–10).
An increased prevalence of gout is noted among indigenous, native populations concurrently with the adoption of a more Western lifestyle (11–13). A group of newly arrived Americans, the Hmong, initiated immigration following the conclusion of the Vietnam conflict in 1975. This ethnically distinct population of Laotian refugees has been observed to be uniquely susceptible to uric acid kidney calculi (14). As such, we sought to define the prevalence of gout among the Hmong of Minneapolis/St. Paul (MSP), Minnesota, and determine their status as a novel gouty population.
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- MATERIALS AND METHODS
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In this study, we investigated the prevalence of gout in the MSP Hmong population by 2 methods. Self-reported gout was surveyed in Hmong individuals attending cultural events on 2 occasions, generating consistent results. Physician-reported gout was estimated from the billing data of a large primary care clinic system. Both self-reported and physician-reported gout in the Hmong population was found to be significantly more prevalent than in the non-Hmong comparison groups.
Hmong refer to gout as mob ko taw vwm (crazy foot pain), a term not far removed from the classic term podagra. Although to our knowledge no published data are available, Hmong elders relate that gout was an affliction in Laos, but that it is more prominent in the US. The Hmong have undergone a massive and abrupt geographic and cultural translocation. Modernization of other underdeveloped societies, most notably New Zealand Maoris and Taiwanese aborigines, has been associated with the emergence of widespread gout (11–13, 17–19). The prevalence of gout in these groups far exceeds that of Western industrialized populations, yet gout was not recognized until their adoption of Western habits. A comparison of gout prevalence in these cultures and the US is shown in Table 2. The higher prevalence of gout in some of these populations is likely related to dietary influences and the presence of other comorbid conditions. The Maori are exposed to all major risk factors, including high purine intake, alcohol consumption, obesity, glucose intolerance, and hypertension (17, 19, 20). Similarly, alcohol, central obesity, diabetes mellitus, and hypertension have been identified as significant risk factors for hyperuricemia and gout in Taiwanese aborigines (12, 13, 18, 21–23). Conversely, the prevalence of gout in a Vietnamese urban community was reported as being much lower, at 0.14% (24). However, it is noteworthy to mention that the genetic backgrounds of the Vietnamese and Laotian Hmong populations are distinctly different.
Table 2. Cultural comparison of gout prevalence*
|Author, year (ref.)||Study population||Criteria||Age, years||Prevalence of gout among adults, %|
|Klemp et al, 1997 (11)||Maori||≥6 ACR survey setting criteria (40)||≥15||6.4||13.9||1.9|
|Prior et al, 1966 (19)||Maori||History of podagra and SUA level >7 mg/100 ml (men) or 6 mg/100 ml (women)||≥20||5.8||10.2||1.6|
|Chou and Lai, 1998 (12)||Taiwanese aborigines||MSU crystals, tophi, or Wallace criteria||18–40||9.0||20.3||0.0|
| || || ||>40||13.5||30.2||1.6|
| || || ||≥18||11.7||26.2||1.0|
|Chang et al, 2001 (18)||Taiwan aboriginal region||Self-report of physician-diagnosed gout||≥19||–||15.3||2.2|
|Chang et al, 1997 (13)||Taiwanese aborigines||Self-report of physician-diagnosed gout||>40||–||15.2||4.8|
|Current study, 2007||MSP Hmong||Self-report of gout||18–40||1.9||2.8||0.8|
| || || ||>40||10.0||19.9||2.5|
| || || ||≥18||6.5||11.5||1.9|
| || ||Clinic diagnosis coding||18–40||1.5||4.5||0.0|
| || || ||>40||6.5||9.6||0.8|
| || || ||≥18||2.8||6.1||3.6|
|Freedman et al (NHANES-III), 2002 (5)||US||Self-report of physician-diagnosed gout||18–40||0.4||0.6||0.2|
| || || ||>40||4.8||6.8||3.1|
| || || ||≥18||2.9||4.1||1.9|
|Kramer and Curhan, 2002 (1)||US||Self-report of physician-diagnosed gout||≥20||2.7||3.8||1.6|
Knowledge of risk factors and biomarkers in the Hmong is limited. Immigration has provided an improved supply of meat, fish, and poultry (25, 26), and a dramatic increase in the intake of these protein sources has been noted. Alcohol is consumed by men on social occasions, but women usually do not drink (25, 26). Patterns consistent with a high prevalence of obesity and hypertension have been observed among American-born Hmong youth (27, 28). While recognized in the Hmong community as a “new” condition, diabetes mellitus is prevalent in adult Hmong (29). Although societal modernization is consistent with the presentation of other gouty populations, the Hmong experience was uniquely accelerated. Whereas other populations adopted Western habits in response to improved social and economic conditions in their native “homeland,” the Hmong immigrated en masse to the US as a sequela of the Vietnam conflict (16). The recency of the resettlement (the final group of refugees arrived in the second half of 2004) places this emerging, novel gouty population at the forefront of any discussion of pathophysiology and treatment.
Genetic factors may also contribute significantly to the overall disease burden of gout in the Hmong population, although the relative contribution of genetics to the pathogenesis of gout in this ethnic group is difficult to estimate at this time. The Hmong population may be an ideal candidate for this genetic exploration because the Hmong have a high cultural identity and a low marriage rate outside of their ethnic group. This cultural habit has been maintained from first-generation Hmong refugees. Furthermore, the young median age of the Hmong compared with the total US population (30) may allow exploration of the contribution of genetic factors as independent confounders in the pathogenesis of primary gout (31).
The higher prevalence of gout in the Hmong was particularly observed among men. This finding may result from a differential exposure of Hmong men to environmental factors (such as alcohol or dietary protein intake). Alternatively, genetic polymorphisms unique to the Hmong could influence serum uric acid concentrations with pronounced sex-specific effects (32). Interestingly, postmenopausal Hmong women exhibited a greater prevalence of gout than premenopausal women (Figure 2). This is likely a reflection of the reduced exposure to estrogen, which enhances renal clearance of uric acid (33). Another potential factor that could lead to a greater prevalence of gout in this subgroup is the use of diuretics, which are known to lower uric acid clearance and consequently increase serum uric acid levels.
The cross-sectional community surveys of the present study were subject to several limitations. First, the use of convenience samples limits the generalizability of the present data to the larger Hmong population. Second, the surveyors' interactions with the sample population were not parallel between the 2 events. In one case, all of the attendees who had approached a health education booth were solicited, whereas in the other, interviewers using a fixed selection procedure actively approached attendees. Third, to our knowledge, the validity of self-reported gout has never been examined against medical records. Relative to physician-reported medical history, self-reported use of gout medication has shown low sensitivity (68%) and high specificity (98%), suggesting that data reported in the current study may be an underestimation (34). Finally, the comparison of the present data with the general US population is open to critique due to differences between the NHANES-III survey and our self-report evaluation tools. In addition to wording differences, evaluation technique may have played a role in the results. Bergmann et al have observed that personal interviews were nearly twice as likely to detect a history of gout when compared with self-administered surveys, suggesting that observed differences in the present study may be the result of technique (35).
Our investigation of clinic data was also not without limitations. One obvious limitation is the validity of gouty diagnosis using medical record review, which may overestimate the incidence and prevalence of gout (36, 37). Additionally, we did not extract information on risk factors associated with gout (such as hypertension, type 2 diabetes mellitus, or obesity) or on medications used for the treatment of gout (allopurinol or colchicines). The use of billing records to identify the prevalence of gout is also complicated by a lack of health insurance coverage among immigrants. It is estimated that the foreign-born population is nearly 3 times more likely than native-born Americans to be without health insurance (38). As such, the Hmong could conceivably be less likely to seek care while being at a relatively higher risk of gout. The use of surname in defining ethnicity can also be tenuous in a multicultural society such as that of the US. Fortunately, most Hmong clan names are not common in non-Hmong populations. In addition, most Hmong people living in St. Paul, Minnesota, are first- or second-generation immigrants, and therefore it is assumed that surnames have not changed greatly due to marriage.
Current data strongly suggest that the Hmong American population of MSP has a unique predisposition to gout. Possible long-term consequences of this susceptibility include an increased risk for chronic kidney disease and cardiovascular disease (5, 6, 39). Although the adoption of a westernized lifestyle may have played a key role in the high incidence of gout in this population, further investigation is important to elucidate the relative roles of inherent and acquired risk factors. Increased understanding of gout pathophysiology and its potential genetic basis may result in improved care of both the Hmong and the general population at large.
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- MATERIALS AND METHODS
- AUTHOR CONTRIBUTIONS
All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be submitted for publication. Dr. Portis had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study conception and design. Portis, Laliberte, Tatman, Moua, Culhane-Pera, Sakhaee.
Acquisition of data. Portis, Moua, Culhane-Pera.
Analysis and interpretation of data. Portis, Laliberte, Tatman, Moua, Culhane-Pera, Maalouf, Sakhaee.