Neural tube defects NTDs defined as "are common congenital malformations that occur when the embryonic neural tube, which ultimately forms the brain and spinal cord, fails to properly close during the first few weeks of development before most women realize that they are pregnant"(2). The most two common and severe types of (NTDs) are: Anencephaly, which is basically defined as the "absence of the brain, is regularly fatal, and results from failure of the anterior neural folds to properly elevate and fuse along the dorsal midline during early embryogenesis" (3), (15). The second type is spina bifida which is defined as" incomplete development of the posterior neural tube, and failure of fusion of one or more vertebral arches, often accompanied by protrusion of the spinal cord and its associated membranes"(3), (15). Patients with spina bifida can survive but they are more likely to develop severe disabilities later in their life the severity is determined by the intensity of the lesion. Patients with spina bifida will have walking difficulty and will require using either braces or a wheelchair, needing of hydrocephalus shunting, and they will have difficulty control bowel and bladder (4).
It has been known for years that NTDs are caused by the deficiency of the folic acid supplements, women can reduce their risk of developing NTD-affected babies by taking folic acid. Some studies showed that early pregnancy intake of drugs that are folic acid antagonists, such as trimethoprim or carbamazepine, could increase the risk of NTD-affected pregnancies. These researches also observed that taking folic acid supplementation while taking those medications will decrease the risk of developing NTD- associated folate antagonist medication(5).
However, numerous clinical and experimental studies, propose that NTDs are multifactorial in origin, having genetic, environmental, and nutritional components that contribute to their occurrence (4). It is not known specifically why a significant percentage of women who take folic acid supplements in their early pregnancies still give birth to NTD-affected offspring.
Studies have proposed that the maternal consumption of fumonisin contaminated corn-tortillas during periconceptional period has been associated with increased risk of developing NTDs especially in those who depend heavily on corn as part of their dietary (6), (7). This suggestion is based on a study concerning the mechanism of action of fumonisins which work as inhibitors of sphingolipid biosynthesis which lead to block of the folate transport, recent reports also suggests that fumonisins induce developmental abnormalities and NTDs in mouse embryos in utero (7).
Fumonisins are mycotoxins produced by the fungus Fusarium verticillioides, F. proliferatum, and more rarely, other Fusarium species. They are found in variable amounts in corn and cornâ€based foods worldwide (8). IARC (The International Agency for Research on Cancer) has listed fumonisin type (B1) as a possible human carcinogen (Group 2B) (9). Also it has been associated with high rates of esophageal cancer (10). Different studies have associated fumonisin to liver and kidney toxicity (11)
The incidence of NTDs in the regions where people consume large amounts of fumonisin- contaminated corn tortillas, is often 6-10 times higher than the average global neural tube defect rate (2), (7).
In a study relating NTDs development in women with higher consumption of fumonisin contaminated corn-tortillas during first trimester of their pregnancies, was evaluated in two direct exposure measurements: measuring the fumonisin level in the maternal blood by the sa:so ratio. And the number of tortillas the mother had consumed during her first trimester of pregnancy as she recalled (12).
Acute exposure to fumonisins is measured by the sa:so ratio, levels come back to normal when the exposure is no longer exists. when the sa:so ratio is measured 5-6 weeks after delivery, it would not reflect fumonisin levels at the time of neural tube closure (first trimester) unless contestant is exposed to fumonisins all the time of pregnancy and after delivery at a constant level. Case and control women were questioned to remember how many tortillas have they consumed over a year earlier and this may subject the results to errors (7).
Presented evidence supports that the consumption of fumonisin in early gestation has great effect in developing NTDs affected baies. However, some studies have inconsistency in their results concerning biomarker for fumonisin exposure (the serum Sa:So ratio, sphinganine: sphingosine), the highest Sa:So ratios (_0.35) were not associated with increased NTD fumonisin exposure is highly believed to be involved in the developing of NTDs (7).To explore this, an incident case-control study would be conducted to test the hypothesis that NTDs are associated to the exposure to high level of fumonisin (12).
Study design
The US incidence of NTDs is quite low, 1 per 1,000 live births (1). In this study, we examine whether or not the risk of developing NTDs in offspring is increased as maternal exposure to fumonisin in early gestation period usually 1st trimester increased. This examination, using a case-control study, represents the epidemiologic assessment of the relation between NTDs-affected pregnancies and fumonisin exposure. The study would be conducted from 2013 to 2016. To ensure an adequate sample size, we will be conducting our study in a state with a highest rate of NTDs. According to the US Census, In the United States, Texas has the highest rate especially in the southern area US / Mexico border. Department of Health reported a neural tube defect cluster among Mexicanâ€American women along the south Texas border in 1990-1991 (2.7/1000 live births) and Corn crops in the Lower Rio Grande Valley registered unusually high levels of fumonisin .
We identified study contestants through the Texas Department of Health's Neural Tube Defect Project. (13), (14). Since all cases would be obtained through hospital Medical records in the assigned Texas counties, multisource surveillance will be used to collect data from non hospitals facilities as well (midwife attended birthing centers and home birth). This would allow us to conclude mostly all NTDs cases.
Cases would be defined as women who are Mexican-American And who are residing in one of the assigned border counties to assure participant risiding in the same area we should match his address with the medical record, who delivered a live or stillborn infant or had aborted a fetus with NTDs (anencephalus, spina bifida, or encephalocele), at all gestational ages from 2013 through 2016. To include all cases possible of NTDs we should gather all cases from both hospital and nonhospital sources (birthing centers, abortion centers, ultrasound centers, prenatal clinics, and midwives and certified nurse midwives) (15). The woman's race, ethnicity, and county of residence also be collected and recorded in the medical chart.
Controls will be defined as women from Mexican-American origin who delivered normal live births NTDs free during the same period and residents of the same area, controls should be randomly selected annually, and frequently matched to the cases by facility (hospital and non hospital) and year. To determine the participants fumonicin expoture, Maternal blood specimens should be collected and the sa:so ratio (surrogate measure of fumonisin exposure) should be correctly measured . To assure we overcome previous studies limitations we should conduct the sa:so analyses numerous times for both cases ad control throughout the study years to assure to collect the specimen at the time of neural tube closure.
To estimate fumonisin levels in tortillas, we should frequently and constantly collect tortillas' samples from participant home (homemade) and local stores throughout the study period and try to match with cases' and controls' tortillas brand and store, fumonisin levels is determined using high-pressure liquid chromatography.
Crude odds ratios with 95% confidence intervals would be calculated for the exposure measures of fumonisin. Since most cases of NTDs occur between Hispanics, ethnicity has been accepted as a confounder. To ensure all eligible cases and controls are included in the study, adjusting for ethnicity by matching should be done, matching should be also conducted between consistent by the socioeconomic status, its seen in some studies that NTDs- affected pregnancies are increased in women with lower SES than higher (low SES usually depend on homemade rather than purchased tortillas where studies showed higher level of fumonisin in homemade tortillas(16). Adjustment for BMI, date of conception, and serum B12 should also be taking into consideration.
Discussion
The planned study has a number of strengths. First, by conducting the study in a state with the highest rate of NTDs, a much higher sample size can be achieved. This is especially advantageous for the number of both cases and controls. In addition, since all the NTDs will be registered with the Texas Department of Health's Neural Tube Defect Project in our study we will capture approximately all NTDs- related pregnancy. Also, by conducting a population based study the findings are generalizable, at least to the entire state of Texas and areas of the US that bear a resemblance to Texas.
There are a number of limitations concerning this study proposal. Odds ratios were chosen as the primary measure of analyses. Concern about the possibility of having recall bias in the calculating the tortillas approximately consumed, and shortening of a true biomarker of fumonisins at the time of neural tube closure. Case and control women were questioned to remember how many tortillas have they consumed over a year earlier and this depended on the number of tortillas women recalled, which as we noted is subject to error. Although it might seem sensitive that women who had experience and had NTDs- babies are more motivated to participate and remember more events as they wanted to know some explanations for having NTD child more than controls women.
Temporality when to collect the blood sample is also an important issue. Acute exposure to fumonisins is measured by the sa:so ratio, levels come back to normal when the exposure is no longer exists. when the sa:so ratio was measured 5-6 weeks after delivery, it would not reflect levels at neural tube closure (first trimester) unless contestant were exposed to fumonisins all the time of pregnancy and after delivery at a constant level.
To estimate fumonisin amount in the consumed corn tortillas, tortillas were collected from local supermarket or from homes ( homemade), this sample will may not represent what was really consumed by each cases and control. In addition, the sample of tortillas may not be systematic, and the samples may not proportionately representative of brand, region, or season.
Implications
The evidence that the development of NTDs due to fumonisins contaminated corn tortillas is slowly being gathered. epidemiological studies have documented that a population (women) who consume large amounts of fumonisin contaminated corn products (tortillas) have higher chances to develop NTDs affected offspring. In addition, studies also confirmed that the amount of fumonisins in corn used to make tortillas especially the homemade one may be high.
It was also demonstrated with laboratory data that, women with high sa:so ratios (a measurement for fumonisin exposure) are more likely to develop NTD-affected pregnancy, independent of known NTD risk factors (as we know that there are so many factors that lead to develop NTDs folate, B12, obesity, and other covariates. risk factors included in the adjusted model for fumonisin exposure.
Recent laboratory experiments supported these epidemiologic findings by explaining the mechanism of action of fumonisins in which has the possibility of increasing the risk for NTDs. Fumonisins biologically inhibit the biosynthesis of sphingolipids , which obstructs the uptake of 5-methyltetrahydrofolate and decreases total folate binding (Stevens and Tang 1997). Moreover, in animal studies mice embryos exposed to fumonisin have developed NTDs in vitro . Administration of folate reverses this effect. These epidemiologic and biologic findings support the hypothesis that consumption of fumonisin contaminated corn tortillas poses women of the risk of developinf NTDs affected pregnency, by impacting sphingolipid and folate metabolism.
