Evidence of an environmental contribution to the aetiology of cryptorchidism and hypospadias?

Geospatial analysis of hypospadias and cryptorchidism prevalence rates based on postal code in a Canadian province with stable population

INTRODUCTION

Hypospadias and cryptorchidism are hormone-mediated malformations that occur during male development. Prevalence rates of hypospadias and cryptorchidism are thought to be increasing worldwide. In-utero exposure to endocrine-disrupting chemicals (EDCs) may have a role in the occurrence of these malformations. Our group has reported significant clustering of hypospadias and cryptorchidism at the county level in areas of intense agricultural activity in the Canadian province of Nova Scotia (NS). Finer scale spatial analysis has shown clustering near urban centres.

OBJECTIVES

The objectives of the study were: 1) to perform a granular geospatial analysis of hypospadias and cryptorchidism prevalence, at the postal code level, of all babies born in NS over a 26-year period; and 2) to determine whether there is spatial correlation between these conditions and industries linked to toxic output.

STUDY DESIGN

Cases of hypospadias and cryptorchidism were identified based on ICD-10 codes from the Nova Scotia Atlee Perinatal Database with records of all live births in NS between 1988 and 2013. Data were geocoded and mapped based on the three first digits of the maternal postal code (Forward Sortation Area [FSA]). Regional prevalence of congenital anomalies was calculated for each of the 77 FSAs. To identify statistically significant high and low prevalence clusters for each anomaly, Local Morans I was used on the spatial data. Geospatial point data was created for industries linked to toxic output and correlation between clusters of malformations and proximity to these industries was assessed.

RESULTS

During the study period, there were 1045 cases of hypospadias and 993 cases of cryptorchidism. Both hypospadias and cryptorchidism demonstrated statistically significant areas of high prevalence clusters. There was no significant spatial correlation between the local clustering of the congenital malformations and proximity to toxic industries.

DISCUSSION AND CONCLUSION

Our study shows heterogeneity in the distribution of hypospadias and cryptorchidism, which is consistent with previously published works. In this follow-up, granular geospatial analysis of hypospadias and cryptorchidism prevalence in an area with stable population, we did not confirm the previous findings of high clustering in areas of intense agricultural activity. Furthermore, our analysis did not find high clustering of the congenital malformations in areas near toxic industries to support a clear environmental role in their development. Some of the limitations include underdiagnosis of hypospadias and cryptorchidism (as they both present with a clinical spectrum and are non-life threatening), and limited data currently available on the route of exposure to EDC industries in Nova Scotia.

Spatial analysis of hypospadias cases in northern France: taking clinical data into account

Background

Strong evidence for a causal role of environmental factors in a congenital anomaly is still difficult to produce. The collection of statistical data is crucial for gaining a better understanding of the epidemiology and pathophysiology of these anomalies. We aimed to evaluate spatial variations in hypospadias within our region and it’s association to socioeconomic and ecological factors, taking clinical data into account.

Methods

All boys with hypospadias born in northern France and seen in Lille University Medical Center (Lille, France) between 1999 and 2012 were included in the analysis. We retrospectively collected geographic data, clinical data (especially known confounding factors associated with an elevated risk of hypospadias), and demographic, socio-economic and ecological data. We analyzed the entire study population and subsequently the subset of boys lacking confounding factors.

Results

The study sample of 975 cases of hypospadias over the 13-year period resulted in an incidence of 25.4/10,000 male births, and was characterized by significant spatial heterogeneity (p < 0.005) and autocorrelation (p < 0.001). We detected two high-incidence clusters that differed with regard to their land use. After the exclusion of 221 patients with confounding factors, two high-incidence clusters with significant disease risks (1.65 and 1.75, respectively; p < 0.001) and a significant difference in land use (p < 0.001) again appeared. The first cluster contained a higher median [interquartile range] proportion of artificialized land (0.40 [0.22;0.47]) than the remaining “neutral areas” (0.19 [0.08;0.53]) did (p < 0.001). Conversely, the second cluster contained a higher median proportion of rural land (0.90 [0.78;0.96]) than the “neutral areas” (0.81 [0.47;0.92]) did (p < 0.001). The median deprivation index was significantly lower in the urban cluster (0.47 [0.42;0.55]) and significantly higher in the rural cluster (0.69 [0.56;0.73]) (p < 0.001).

Conclusions

Our results evidenced the heterogeneous spatial distribution of cases of hypospadias in northern France. We identified two clusters with different environmental and social patterns – even after the exclusion of known confounding factors.

Hypospadias: Prevalence, birthweight and associated major congenital anomalies

The aim of this study was to determine the prevalence of hypospadias over 24 years in a Danish population and to describe the relation to birthweight and associated major congenital anomalies. It is a population-based study of all cases (live births, fetal deaths and elective terminations of pregnancy) with hypospadias born in the period 1986-2009 in Funen County and reported to the EUROCAT registry of congenital anomalies. Cases were included only if surgery for hypospadias was performed. 223 cases of hypospadias were registered during the period 1986-2009 with an overall prevalence of 16.9 per 10 000 births. The prevalence was significantly higher in 2000-2009 compared to 1986-1999 (P < 0.001). We found a three times higher occurrence of VLBW (very low birthweight) infants among cases with hypospadias. Infants with isolated hypospadias were more likely to have mild hypospadias (68%) while cases with associated major congenital anomalies were less likely to have mild hypospadias (42%) (P < 0.05). Hypospadias was associated with VLBW and the severity of the defect was related to the presence of major congenital anomalies. The prevalence of hypospadias has increased during the study period. The relation to VLBW could indicate a causal relationship for hypospadias or a shared pathogenic factor.

Geographic analysis of individual and environmental risk factors for hypospadias births

BACKGROUND

Hypospadias is a relatively common birth defect affecting the male urinary tract. We explored the etiology of hypospadias by examining its spatial distribution in North Carolina and the spatial clustering of residuals from individual and environmental risk factors.

METHODS

We used data collected by the North Carolina Birth Defects Monitoring Program from 2003 to 2005 to estimate local Moran's I statistics to identify geographic clustering of overall and severe hypospadias, using 995 overall cases and 16,013 controls. We conducted logistic regression and local Moran's I statistics on standardized residuals to consider the contribution of individual variables (maternal age, maternal race/ethnicity, maternal education, smoking, parity, and diabetes) and environmental variables (block group land cover) to this clustering.

RESULTS

Local Moran's I statistics indicated significant clustering of overall and severe hypospadias in eastern central North Carolina. Spatial clustering of hypospadias persisted when controlling for individual factors, but diminished somewhat when controlling for environmental factors. In adjusted models, maternal residence in a block group with more than 5% crop cover was associated with overall hypospadias (odds ratio = 1.22; 95% confidence interval = 1.04-1.43); that is living in a block group with greater than 5% crop cover was associated with a 22% increase in the odds of having a baby with hypospadias. Land cover was not associated with severe hypospadias.

CONCLUSION

This study illustrates the potential contribution of mapping in generating hypotheses about disease etiology. Results suggest that environmental factors including proximity to agriculture may play some role in the spatial distribution of hypospadias. Birth Defects Research (Part A) 100:887-894, 2014. © 2014 Wiley Periodicals, Inc.

A review of spatial methods in epidemiology, 2000-2010

Understanding the impact of place on health is a key element of epidemiologic investigation, and numerous tools are being employed for analysis of spatial health-related data. This review documents the huge growth in spatial epidemiology, summarizes the tools that have been employed, and provides in-depth discussion of several methods. Relevant research articles for 2000-2010 from seven epidemiology journals were included if the study utilized a spatial analysis method in primary analysis (n = 207). Results summarized frequency of spatial methods and substantive focus; graphs explored trends over time. The most common spatial methods were distance calculations, spatial aggregation, clustering, spatial smoothing and interpolation, and spatial regression. Proximity measures were predominant and were applied primarily to air quality and climate science and resource access studies. The review concludes by noting emerging areas that are likely to be important to future spatial analysis in public health.

Time trends and geographic variations in the prevalence of hypospadias in China

BACKGROUND

Little is known about the main epidemiologic characteristics of hypospadias prevalence in China. We investigated the time trends and geographic variations in the prevalence of hypospadias in China from 1996 to 2008.

METHODS

Data were retrieved from the hospital-based birth defects monitoring system in China from 1996 to 2008. We used prevalence ratios (PRs) to describe the difference in prevalence of hypospadias between urban and rural areas, as well as among different regions. Poisson regression was used to explore the long time trend for the prevalence of hypospadias and its regional disparity.

RESULTS

The prevalences of hypospadias for isolated anomalies, multiple anomalies, and overall cases were 7.64, 1.39, and 9.03 per 10,000 births, respectively. The national PRs (urban vs. rural) of hypospadias for overall and isolated cases were 1.25 (95% confidence interval [CI], 1.16-1.35) and 1.27 (95% CI, 1.17-1.38), respectively. The highest prevalence (12.10 per 10,000 births) was observed in the eastern region. A positive correlation was found between the prevalence of hypospadias and maternal age (p < 0.01). The average annual increase of 7.43% (95% CI, 5.52-9.38%) was observed in the overall prevalence of hypospadias in China; it was 5.28% (95% CI, 4.16-6.43%) in urban areas, 9.79% (95% CI, 7.72-11.90%) in rural areas, 9.08% (95% CI, 6.36-11.86%) in the eastern region, 4.76% (95% CI, 2.93-6.62%) in the central region, and 6.57% (95% CI, 4.44-8.74%) in the western region.

CONCLUSION

The increasing trends and differences of hypospadias prevalence by urban-rural classification and geographical location suggest that environmental exposure and maternal age might have a critical role in the development of hypospadias.

The Generation R Study: design and cohort update 2010

The Generation R Study is a population-based prospective cohort study from fetal life until young adulthood. The study is designed to identify early environmental and genetic causes of normal and abnormal growth, development and health during fetal life, childhood and adulthood. The study focuses on four primary areas of research: (1) growth and physical development; (2) behavioural and cognitive development; (3) diseases in childhood; and (4) health and healthcare for pregnant women and children. In total, 9,778 mothers with a delivery date from April 2002 until January 2006 were enrolled in the study. General follow-up rates until the age of 4 years exceed 75%. Data collection in mothers, fathers and preschool children included questionnaires, detailed physical and ultrasound examinations, behavioural observations, and biological samples. A genome wide association screen is available in the participating children. Regular detailed hands on assessment are performed from the age of 5 years onwards. Eventually, results forthcoming from the Generation R Study have to contribute to the development of strategies for optimizing health and healthcare for pregnant women and children.

Risk of congenital anomalies around a municipal solid waste incinerator: a GIS-based case-control study

Background

Waste incineration releases into the environment toxic substances having a teratogenic potential, but little epidemiologic evidence is available on this topic. We aimed at examining the relation between exposure to the emissions from a municipal solid waste incinerator and risk of birth defects in a northern Italy community, using Geographical Information System (GIS) data to estimate exposure and a population-based case-control study design. By modelling the incinerator emissions, we defined in the GIS three areas of increasing exposure according to predicted dioxins concentrations. We mapped the 228 births and induced abortions with diagnosis of congenital anomalies observed during the 1998–2006 period, together with a corresponding series of control births matched for year and hospital of birth/abortion as well as maternal age, using maternal address in the first three months of pregnancy to geocode cases and controls.

Results

Among women residing in the areas with medium and high exposure, prevalence of anomalies in the offspring was substantially comparable to that observed in the control population, nor dose-response relations for any of the major categories of birth defects emerged. Furthermore, odds ratio for congenital anomalies did not decrease during a prolonged shut-down period of the plant.

Conclusion

Overall, these findings do not lend support to the hypothesis that the environmental contamination occurring around an incineration plant such as that examined in this study may induce major teratogenic effects.