High Rate of Neural Tube Defects Along the Texas Mexico Border

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Table of Contents

Introduction
Methods
Results
Discussion
Conclusion
Reference List

Introduction

Neural tube defects (NTD) are the commonest birth defects accounting for one in every 1000 birth defects in the USA. A neural tube defect is defined as an opening that develops early in life in the brain of the fetus (Golalipour, Mobasheri, Vakili & Keshtkar, 2007, para. 1). The condition develops between the 25^th and 28^th day after conception. There are two types of neural tube defects with the most common being the open NTDs which occur when a defect in the backbone and the skull exposes the spinal cord, particularly during birth. Spina finida, anencephaly and encephalocele are the most common types of open NTDs in the United States of America. A constellation of factors is responsible for causing neural tube defects: environmental, genetic and dietary factors. About 60% of NTDs can be prevented through supplementation of women’s diet with 0.4 mg of folic acid and water-soluble B vitamins (Duke Centre for Human Genetics).

According to Suarez et al (2000, p.1017), high prevalence rates of neural tube defects have been witnessed in the Mexican populations and subsequently in the areas along the Mexico USA border. The prevalence rates of NTDs in pregnancies during the period between 1993 and 1995 were found to be 6.4, 7.1, and 1.1 for anencephaly, spina bifida and encephalocele respectively (Hendricks, Simpson &Larsen, 1999, p.1120). The Chinese province of Shanxi has recorded the highest incidence of neural tube defects and NTD birth prevalence rate in the world. This has been blamed mainly on folic acid deficiency (Liz et al, 2006, p.238).

The prevalence of NTDs in the United States is around 1 in 1000 live births with 3.7 in 10000 for anencephaly, 1.4 in 10000 for encephalocele and 5.5 for 10000 for spina bifida (Smith and Dlugos). The states bordering Mexico have reported higher prevalence and incidences of NTDs compared to other states. This is because most of the inhabitants are of Mexican origin. According to Harris and Shaw (1995, p.163), Mexican Americans have between 50 – 200 % higher than the whites, non-Hispanic, and African Americans. Cameron County in Texas recorded 29 cases per 10000,the highest prevalence for NTD in the USA, in 1995 with the authorities confirming that the endemicity of this condition was due to the high proportion (95%) of the population being of Mexican descent (Suarez et al, 2000, p.1019). Suarez and Hendricks (2002) found that prevalence in Mexican Americans was double compared to the US-born in California, Texas Mexico border and Cameron County particularly in 1990-1995.

This study was done in Texas where epidemiological data was collected from the Texas department of health to analyze it and utilize it as a basis for policy recommendations.

Methods

Data for this study was collected from the Texas Birth Defects Epidemiology and Surveillance Branch of the Department of Health for the period 1999-2005. This branch is mandated to record and publish all data relating to neural tube defects research and surveillance and prevention in all the counties in Texas. The data was broken down in relation to maternal age, maternal race /ethnic group, infant/fetus sex, public health region and country of mother’s residence at delivery. The data were categorized into two geographical groupings; border counties and non-border counties. There are 240 non-border and 14 border counties. The 14 Texas border counties are: Cameron, Hidalgo, Starr, Zappata, Webb, Maverick, Kinney, Val Verde, Terrell, Brewster, Presidio, Jeff Davis, Hudspeth, El Paso The data sources were mainly primary (vital records) and medical records from the department of health services. Data analysis was done through use of descriptive statistics and presented in graphs and tables (Department of state health services Texas, 2009).

Results

The study delved in compiling and analysis of data on neural tube defects which was confirmed and published by the authorized agencies. The data had to be inclusive of all counties in Texas. In this case, the study considered and utilized data from 1999-2005. The findings from the health documents in the Texas Birth Defects Epidemiological And Surveillance branch yielded mixed data on the prevalence from 1999-2005 (National Birth Defects Prevention Network, 2009). Prevalence rate of encephalocele in Texas was found to be the lowest with ranges of 0.60 in 2004 and 1.07 in 2000. A decrease of 1.09 in prevalence rate was observed in anencephaly. Year to year decreases was evident with the highest rate at 3.52 (123 cases per 10000) in 1999 to the lowest rate at 2.23 (86 cases) in 1999. Persistently high rates were observed in spina bifida without anencephaly for the whole period with ranges of 3.03 (113 cases) and 4.54 (173 cases).

The distribution of neural tube defects by geographical locations showed variations with slightly higher prevalence rates evident in the non-border counties. The prevalence rate for anencephaly was 3.60 in border counties and 2.51 in the non-border counties. This represented 122 and 567 cases respectively. Encephalocele had a prevalence rate of 1.00 in the border counties and 0.83 in the non-border counties representing 34 and 188 cases per 10000 live births respectively. 150 cases of spina find without anencephaly were recorded in border counties while 807 cases were reported in the non-border counties. These figures stood for prevalence rates of 4.43 and 3.58 respectively.

The prevalence rates for all types of neural tube defects were higher in border counties than non-border counties from 1999 to 2004. Anencephaly had the high prevalence of 6.2 in 1999 in bordering countries compared to 3.1 in the non-bordering counties. The average for the five years was highest in spina find without anencephaly with a rate of 4.4 in the border counties and 3.8 in the non-border counties. Encephalocele had the lowest averages with 0.8 and 1.1 for bordering and non-bordering counties correspondingly.

Female infants were more susceptible to anencephaly and encephalocele than males with prevalence rates of 2.59 and 0.90 compared to 2.21 and 0.90 respectively. However, 488 cases of spina bifida without anencephaly which translated to rate of 3.68 were reported in male infants compared to 455 cases in females in Texas

High prevalence rates were recorded among the Hispanic and white non-Hispanic races across the three types of NTDs. Generally, the Hispanic infants had prevalence rates of 3.20, 1.03 and 4.30 for anencephaly, encephalocele and spina bifida respectively for the period 1999-2005. The black non-Hispanic recorded the lowest rates of 2.06 and 2.72 in anencephaly and spina bifida without anencephaly. The white non-Hispanic has the lowest rate in encephalocele with 0.63 against 1.03 recorded in the Hispanics.

The data on prevalence rates against mothers’ age painted a dull picture on young motherhood with most cases being experienced by infants whose mothers were below 30 years for the whole period. Infants born by mothers aged 20-24 years had the highest prevalence rates of 2.75 while the lowest was in mothers aged 40 years and above for anencephaly. Prevalence rates of 1.10 (41 cases of encephalocele) were reported in infants born by mothers aged less than 20 years while rates of 0.71 were recorded in 30-34 age brackets. 24 cases of spina bifida without anencephaly which translated to rates of 5.07 were reported in infants born by mothers aged 40 years and above.

Discussion

Because Texas department of health had only partial data from 1995-1999, the study considered utilizing data from 1999 to 2005 to ensure consistency and ease in data comparison with respect to the various parameters that were in use. Health data on neural tube deaths for the years 2006 and 2007 had not been authenticated thus was left out of the study (Department of state health services Texas, 2009).

The prevalence rates for encephalocele and spina bifida without anencephaly are almost constant for six years. A marginal drop in the prevalence rates in anencephaly has been observed during this period. This is in tandem with previous researches that had noted that the prevalence rates of anencephaly and spina bifida have continued to decline in Europe, New Zealand, and North America (McDonnell et al, 1999) Overall, this represents a big drop compared to health statistics of 1993- 1995 where 14.9 per 10000 of the infants had developed the condition in the Mexican America border (Hendricks, Simpson & Larsen, 1999, p.1128). The high numbers of Mexican American mothers in Texas are responsible for the perpetuation of the NTDs cases.

Variations in the prevalence rates existed between the border and non-border counties with a much higher rate being recorded in the former. This notion is in agreement with Forester and Merz (2000) who noted that the prevalence of NTDs varies with geographical locations within or without a region. The variation can also be reflected direction wise whereby a decline is observed in the east-west or north-south directions.

The data on the prevalence for the six years shows little discrepancy with the rates changing marginally. This means that factors such as use of folic acid do not protect the infants from the condition as witnessed in other parts of America. This concurs with a study carried out by Suarez et al (2000, p.1018) where they concluded that folic acid supplements have little usefulness in the prevention of NTDs in Mexican Americans. The prevalence may also be due to the ingestion of fumonisin found in corn tortillas. A U-shaped pattern of occurrence, which is symbolic of the accumulation of NTDs to dangerous levels, is capable of causing fetal deaths (Missmer et al, 2006).

The female infants had higher prevalence rates in all types of NTDs. According to McDonnell et al (1999), the sex influences the risk whereby the females have higher tendencies to get anencephaly and spina bifida than male infants. This tendency is linked to additional birth defects and other factors such as geographic location. The variation in the process of development of males and female fetuses in the womb is a likely explanation for the tendency. The Hispanic mothers were more likely to give birth to infants with the NTDs compared to the non-Hispanic mothers. The same trend was observed by Hendricks et al (1999) where they noted that prevalence was highest in Hispanics followed by the non-Hispanic whites and African Americans. This may be due to differences in the genetic susceptibility to neural tube defects, lifestyle or cultural practices. However, insignificant differences have been noted in studies carried out in other parts of America.

Young and old mothers were more likely to give birth to infants who have NTDs. Higher prevalence rates were reported in mothers in age bracket 20-24, below 20 and 40 and above compared to the middle age brackets. This was mainly observed in anencephaly and encephalocele. This is in tandem with Golalipour and colleagues’ (2007) study which noted the same trend among its respondents.

Conclusion

Neural tube defects are known to cause many deaths in infants particularly in the United States. Texas is among the few states which have high prevalence rates for neural tube defects. This is mainly due to the large proportion of the population being Mexican Americans and its location at the border with Mexico. The preponderance is mostly influenced by the sex of the infant, maternal age, maternal race or ethnicity and lifestyle. There is a slight variation in the prevalence rates in Texas with higher rates recorded in the border counties than in the non-border counties. This is mainly due to the composition of the population in the two regions.

The findings in this paper concur with other earlier studies and publications made by the Department of Human and Health Services. It is vital for the relevant state agencies to utilize this paper and earlier publications to come up with policies that will advocate for prevention programs in the state. This is to cover the Hispanic and Mexican Americans who can’t benefit from the utilization of folic acid as prevention program.

There is need to carry out more research on the association between the increased incidences in specific age groups and the exposure to fumonisin. This is in tandem with the recommendations made by the Food Drug Administration that there was a need for an evaluation on this relationship with regard to the potential health risks be carried out (2001). The impact of the association on the development and the outcome of the embryo should also be assessed. Mothers in specific risk groups should be advised to avoid having children early or late in their lives since this is one of the major risk factors. The Mexican and Hispanic populations must be educated on the proper lifestyles such as dietary intakes to lower their vulnerability to the NTDs.

Reference List

Department of state health services Texas. (2009). Selected Health Facts 2005. Centre for Health Statistics, 512, 458-726. Web.

Duke Centre for Human Genetics. Neural tube defects. 2010. Web.

Forrester, M., and Merz, R. (2000). Descriptive epidemiology of limb reduction deformities in Hawaii, 1986-2000. Hawaii Medical Journal, 62, 11, 242-7.

Harris, J. and Shaw, G. (1995). Neural tube defects–why are rates high among Populations of Mexican descent?. Environmental Health Perspective, 103, 6, 163–4.

Hendricks, K., Simpson, J., and Larsen, R. (1999). Neural tube defects along the Texas-Mexico border, 1993-1995.Amertican Journal of Epidemiology, 149, 1119-27.

Golalipour, M. J., Mobasheri, E., Vakili, M. A., & Keshtkar, A. A. 2007. Epidemiology of neural tube defects in northern Iran, 1998-2003. Health Journal, 13(3).

Li, Z., Ren, A., Zhang, L., Ye, R., Li, S., Zheng, J., Hong, S., Wang, T., Li Z. (2006). Extremely high Prevalence of neural tube defects in a 4-county area in Shanxi Province, China. Birth Defects Research. A Clinical and molecular teratology, 76, 4, 237-40.

McDonnell, R., Johnson Z, Delaney, V. and Dack, P. (1999). East Ireland 1980–1994: epidemiology of neural tube defects. Epidemiology and community health, 53, 12, 782–8.

Missmer S.A., Suarez L., Felkner M., Wang E., Merrill A.H. Jr., Rothman K.J., Hendricks K.A. (2006). Exposure to fumonisins and the occurrence of neural tube defects along the Texas-Mexico border. Environmental Health Perspect, 114, 237–241.

National Birth Defects Prevention Network. (2009). Population-Based Birth Defects Data. Birth Defects Research, 85, 939-1004.

Smith, S.E., & Dlugos, D. (2008). Neural Tube Defects: The 5-Minute Pediatric Consult (Fourth Ed). New York: Lippincott Williams & Wilkins

Suarez, L., Hendricks, K., Cooper, S., Sweeney, A., Hardy, R. and Larsen, R. (2000). Neural tube defects among Mexican Americans living on the US Mexico Border: Effects of folic acid and dietary folate. American Journal of Epidemiology, 152, 1017-23.

U.S. FDA. (2001). Background Paper in Support of Fumonisin Levels in Corn and Corn Products Intended for Human Consumption. Washington, DC: U.S, Food and Drug Administration. Web.

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