Epidemiology of Rheumatic disorders in the Pacific with particular emphasis on hyperuricaemia and gout

Epidemiology of gout and hyperuricemia in New Caledonia

OBJECTIVES

New Caledonia is a Pacific island of 270,000 inhabitants with mixed ethnicities, including Polynesians (10.2%), people from European ancestry (27.2%), and Melanesians (39.1%),. This study aimed at determining the prevalence of gout and hyperuricemia in the general population and the various ethnicities of New Caledonia.

METHODS

A 3-degree random sample of the population aged 18 to 60 years was adjusted according to the 2014 New Caledonia census. Face-to-face planned interviews and physical measurements were performed by trained nurses. All consenting participants underwent capillary measurement of creatinine; all consenting men and only women older than 40 years underwent point-of-care uricemia testing. Gout was defined by a validated algorithm. Two definitions of hyperuricemia were used: capillary level equivalent to plasma uric acid level>360μmol/l (6mg/dl) and>420μmol/l (7mg/dl) and/or urate-lowering drug treatment for both thresholds.

RESULTS

We included 1144 participants (adjusted mean age 37.7±12.0 years; adjusted sex ratio 50.4% men). The adjusted prevalence of gout was 3.3% (95% confidence interval 2.2-4.9). Prevalence was 6.7% (2.5-16.8), 4.1% (1.8-8.9), and 2.6% (1.4-4.7) for Polynesians, Europeans and Melanesians, respectively, and 1.9% (0.5-6.6) for other ethnicities. Prevalence of hyperuricemia, determined in 658 participants, was 67.0% (61.9-71.6) and 37.0% (32.3-42.0) for the 360- and 420-μmol/l thresholds, respectively, and was significantly greater for Polynesians and Melanesians than Europeans for both thresholds.

CONCLUSIONS

The prevalence of gout and hyperuricemia in New Caledonia was high, including in patients of European descent.

Gout: an Asia-Pacific update

Even though, Hippocrates recognized gout as an affection of older men and a product of high living long back in 5th century BC, this painful condition promises to accompany humanity to the 21st century. The incidence is progressively rising and females are also affected in the modern era. There are also regional and ethnic variations in the incidence, the genetics of which is being studied. The recommended best therapy for the acute attacks and long term prophylaxis has improved remarkably in the recent years. However, patients are often treated inadequately and risk factors for their disease are not well explored in daily practice. Although well designed long term studies of current and newer treatment are welcomed, educating doctors especially the primary care physicians who manage majority of gout cases, in optimizing the currently available management options would improve the present care.

Pacific Populations, Metabolic Disease and 'Just-So Stories': A Critique of the 'Thrifty Genotype' Hypothesis in Oceania

Pacific populations have long been observed to suffer a high burden of metabolic disease, including obesity, type 2 diabetes and gout. The 'Thrifty Genotype' hypothesis has frequently been used to explain this high prevalence of disease. Here, the 'Thrifty Genotype' hypothesis and the evolutionary background of Pacific populations are examined. We question its relevance not only in the Pacific region but more generally. Not only has the hypothesis not been explicitly tested, but most archaeological and anthropological data from the Pacific fundamentally do not support its application.

Hyperuricaemia in the Pacific: why the elevated serum urate levels?

Pacific Island populations, particularly those of Polynesian descent, have a high prevalence of hyperuricaemia and gout. This is due to an inherently higher urate level among these populations with a demonstrated genetic predisposition. While an excess of urate can cause pathology, urate is also important for human health. It has been implicated as an antioxidant, has a neuroprotective role and is involved in innate immune responses. This paper provides a brief review of urate levels worldwide, with a particular focus on island Southeast Asia and the Pacific. We then present possible evolutionary explanations for the elevated serum urate levels among Pacific populations in the context of the physiological importance of urate and of the settlement history of the region. Finally, we propose that ancestry may play a significant role in hyperuricaemia in these populations and that exposure to malaria prior to population expansion into the wider Pacific may have driven genetic selection for variants contributing to high serum urate.

Systematic review of the prevalence of gout and hyperuricaemia in Australia

AIMS

Gout is a growing health problem worldwide especially in affluent countries, such as Australia. Gout and hyperuricaemia are associated with the metabolic syndrome, diabetes mellitus, obesity and hypertension. More importantly, Australia has a growing prevalence of these important health problems. The aim of this study was to systematically review published information regarding the prevalence of gout and hyperuricaemia in Australia.

METHODS

A systematic search was undertaken of the MEDLINE, EMBASE and Web of Science databases, as well as relevant websites for journal articles and reports relating to the prevalence of hyperuricaemia and gout in Australia.

RESULTS

Twenty-five journal articles and five reports were included in the review. Data collected in a standardised way show gout increased in prevalence from 0.5% population prevalence to 1.7% population prevalence from 1968 to 1995/1996. There has been a significant rise in the prevalence of gout in the Australian Aboriginal population from 0% in 1965 to 9.7% in men and 2.9% in women in 2002. Consistent with the rise in gout prevalence, serum uric acid in blood donors has increased from 1959 to 1980 (17% in 30- to 40-year-old men).

CONCLUSIONS

The rate of gout and hyperuricaemia in Australia is high in relation to comparable countries and is increasing. The prevalence of gout in elderly male Australians is second only to New Zealand, which has the highest reported rate in the world. Further research on Aboriginal and Torres Strait Islander gout and hyperuricaemia is required as a result of the lack of contemporary data.

The genetic basis of hyperuricaemia and gout

Gout results from elevated urate concentrations in the blood (hyperuricaemia). When super-saturation of urate is reached, monosodium urate crystals form within the joint. In some individuals, these crystals elicit a painful self-limiting inflammatory response that is characteristic of acute gouty arthritis. The most important cause of hyperuricaemia is reduced excretion of uric acid in the urine. Uric acid excretion is coordinated by a suite of urate transport molecules expressed in the renal collecting tubules, and is a key physiological checkpoint in gout. Other checkpoints in gout are hepatic production of urate, monosodium urate crystal formation, and initiation of the acute inflammatory response. Genome-wide association scans for genes regulating serum urate concentrations have identified two major regulators of hyperuricaemia- the renal urate transporters SLC2A9 and ABCG2. The risk variants at each gene approximately double the risk for gout in people of Caucasian ancestry, with SLC2A9 also resulting in higher risk for gout in people of Polynesian ancestry, a diverse population characterized by a high prevalence of gout. Ongoing genetic association studies are identifying and confirming other genes controlling serum urate concentrations; although genome-wide association studies in gout per se await recruitment of suitable case sample sets.

Genetics and experimental models of crystal-induced arthritis. Lessons learned from mice and men: is it crystal clear?

PURPOSE OF REVIEW

We examine the major genes in mice and humans involved in the pathogenesis of monosodium urate, calcium pyrophosphate dihydrate and hydroxyapatite crystal-induced arthritis.

RECENT FINDINGS

Several genetic causes of renal disease associated with hyperuricemia and gout provide insight into genes involved in renal urate handling. Mutations or polymorphisms in exons 4 and 5 and intron 4 of urate transporter 1 may be independent genetic markers of hyperuricemia and gout. Genetic analysis supports the role of ANKH mutations in calcium pyrophosphate dihydrate-induced arthritis. ANKH gain-of-function mutations were confirmed by functional studies; however, the crystals formed in ATD5 cells were basic calcium phosphate, not calcium pyrophosphate dihydrate, underlying the significance of chondrocyte differentiation state and the factors regulating normal and pathological mineralization. Animal models have implicated a general model of crystal-induced inflammation involving innate immunity through the NALP3 (Natch domain, leucine-rich repeat, and PYD-containing protein 3) inflammasome signaling through the interleukin-1 receptor and its signaling protein myeloid differentiation primary response protein 88.

SUMMARY

Genetic analysis has elucidated genes responsible for crystal formation and animal models have unveiled mechanisms in the development of crystal-induced arthritis. Future studies will hasten understanding of the pathology of crystal-induced arthritis and provide new therapies.

New developments in the epidemiology and genetics of gout

The prevalence of gout appears to be rapidly increasing worldwide and is no longer a disorder suffered primarily by over-fed alcohol consumers. Emerging risk factors include longevity, metabolic syndrome, and new classes of pharmacologic agents. In some ethnic populations, no obvious risk factors can explain the high incidence of hyperuricemia and gout, suggesting a genetic liability. Studies to identify genes associated with gout have included families with defects in purine metabolism, as well as families in whom the occurrence of gout is secondary to renal disorders such as juvenile hyperuricemic nephropathy and medullary cystic kidney disease. Case-control studies of isolated aboriginal cohorts suffering from primary gout have revealed several chromosomal loci that may harbor genes that are important to the development and/or progression of gout.

Community-based study in Taiwan aborigines concerning renal dysfunction in gout patients

OBJECTIVE

To reveal the factors associated with renal dysfunction among gout patients in Taiwan aborigines.

METHODS

Social demographic data, alcohol consumption data, anthropometric measurements, blood samples, and 24-h urine samples were collected from 128 aboriginals (101 men, 27 women) suffering from gout.

RESULTS

The men displayed higher mean creatinine clearance (Ccr) values than women. Twenty-two post-menopausal women had significantly lower Ccr values compared to the five pre-menopausal women [probability (p)<0.001]. The males displayed higher 24-h urinary creatinine value than females (8.60+/-5.39 versus 5.58+/-2.14 mmol/L; p<0.05), and showed a significantly higher positive relationship between 24-h urinary creatinine and uric acid excretion [correlation coefficient (r)=0.7304; p<0.001], whereas the females did not (r=0.1144; p=0.5691). Overall, those who were older members of the Tsou tribe, or had excreted less uric acid from urine in 24 h tended to suffer renal dysfunction.

CONCLUSIONS

Gout patients displayed diversity in renal function. An exogenous source of creatinine in men was more likely than in women.

Genomewide scan for gout in taiwanese aborigines reveals linkage to chromosome 4q25

Gout is a disorder of uric-acid metabolism. The Pacific Austronesian population, including Taiwanese aborigines, has a remarkably high prevalence of hyperuricemia and gout, which suggests a founder effect across the Pacific region. We report here a genomewide linkage study of 21 multiplex pedigrees with gout from an aboriginal tribe in Taiwan. From observations of familial clustering, early onset of gout, and clinically severe manifestations, we hypothesized that a major gene plays a role in this trait. Using 382 random polymorphic markers spread across 22 autosomes, we demonstrated a highly significant linkage for gout at marker D4S2623 on chromosome 4q25 (P=.0002 by nonparametric linkage [the NPL(all) statistic]; empirical P=.0006; LOD=4.3, P=4.4x10-6 by logistic regression). When alcohol consumption was included as a covariate in the model, the LOD score increased to 5.66 (P=1.3x10-6). Quantitative traits, including serum uric acid and creatinine, also showed a moderate linkage to this region. To our knowledge, this is the first genome-scan report to identify a genetic locus harboring a gout-susceptibility gene.

Migration and gout: the Tokelau Island migrant study

The prevalence and 14 year incidence of clinical gout and its precursors were investigated in the Polynesian population of Tokelauans living in the Pacific basin, non-migrant Tokelauans living in their isolated atoll homeland being compared with migrant Tokelauans living in urban New Zealand. The age standardised prevalence of gout in Tokelauan men in New Zealand was higher than that in non-migrant Tokelauan men, being 21.0 and 19.5/1000 subjects at the beginning of the study and 51.0 and 14.6/1000 at the end of study, respectively. Migrant men in New Zealand aged under 55 had higher mean serum uric acid concentrations than non-migrant men of the same age. The prevalence of gout was low in women in both environments. The age standardised relative risk of developing gout between 1968 and 1982 was 9.0 times higher in the migrant men than in the non-migrant men. Age, serum uric acid concentration, serum cholesterol concentration, and self reported alcohol consumption at entry to the study were the best set of predictors of gout in men. Preventive strategies to change body mass, diet, and patterns of alcohol use need to be developed in this population.

Rheumatic complaints in Tokelau. I. Migrants resident in New Zealand. The Tokelau Island migrant study

The three Tokelau atolls are 8 degrees south of the equator. In 1966 the islands were involved in a severe hurricane which drew attention to overcrowding and led to resettlement of more than half the population in New Zealand. One thousand three hundred and eighty one migrants over 15 years old were examined in New Zealand in 1980 and 1981 for rheumatic complaints as part of a continuing assessment. Clinical criteria for osteoarthritis (COA), including crepitus in any joint and in the knee, showed an increase in prevalence with age and weight in both sexes. Partial correlation coefficient analysis showed an association of the number of affected joints or the severity of knee COA (COAK) with both age and weight. Stepwise regression showed that age was the best predictor of both COA and COAK scores. Weight had predictive value only for COAK and only in women. Using the tracking method, previous high and/or increasing weight was related to COAK observed at this assessment. Heberden nodes increased with age and were more prevalent in women but were not associated with weight. Low back, dorsal and neck pain showed no association with age or sex. Low back pain was associated with weight. Joint pain following injury occurred in 15.4% of men. Gout, more common in men, was the only frequent inflammatory arthritis found. Two definite cases of rheumatoid arthritis (RA) were identified and four had criteria 1 and 2 for the New York criteria.