Neural tube defects (NTDs) are one of the most common malformations in humans with 1 in 1,000 pregnancies affected in the United States each year. NTDs include all malformations involving lack of closure of the spinal cord during embryogenesis. Most NTDs are one of two types: anencephaly, lack of closure in the region of the head leading to death soon after birth, and spina bifida (SB), lack of closure in the region of the back, often with associated brain malformations. These two types of NTDs occur in approximately equal frequencies at birth. NTDs are common complex birth defects caused by a combination of genetic and environmental influences. The objective of this competing continuation is to evaluate genetic and environmental factors involved in the etiology of SB. We are focusing on two ethnic groups: Hispanics of Mexican descent and North American Caucasians of European descent. Of the major ethnic groups in the US, Mexican Americans have the highest risk for having an NTD affected child (9- 16/10,000 births) and Mexico has one of the highest rates worldwide (36/10,000 births). Our targeted sample size is 550 parent-child trios distributed with 300 Mexican and 250 Caucasian families. To date, we have enrolled approximately 150 Mexican and 150 Caucasian trios. We have also identified and enrolled 150 Hispanic and 80 Caucasian (mother-child or father-child) duos. To attain our goal of 550 trios (Specific Aim I), we will recruit new trios and complete the duo families. Two new recruitment sites (one in the Rio Grande Valley of Texas along the Texas-Mexico border and the other in Galveston, Texas) have been identified. To assess environmental influences, we will conduct a two-part survey of all newly and previously enrolled mothers (Specific Aim II). Part one of the survey will assess socio-demographic/epidemiologic and environmental factors that have been identified as potentially important in NTD risk. Part one includes questions concerning socio-demographic/epidemiologic factors [socioeconomic status, maternal and paternal ages and occupations, maternal reproductive history, place of conception (US v. Mexico), parental birthplaces] and environmental factors [maternal glucose status (i.e. calculations of BMI and presence/absence of diabetes), maternal hyperthermia (illness/hot tub use), maternal medication and recreational drug use]. Part two is a detailed dietary questionnaire that will estimate folate status, alcohol use and status of other micronutrients. We will estimate the level of admixture (Specific Aim III) in the Hispanic patients and compare the level to the general US population as well as specifically selected controls. Our genetic studies will focus on candidate genes in two metabolic pathways that relate to the environmental information gathered: folate/homocysteine (Specific Aim IV) and glucose metabolism (Specific Aim V). We will also specifically test the hypothesis that variants in genes of the folate/homocysteine and glucose metabolism pathways are important in causing the cognitive and structural brain features observed in the SB phenotype (Specific Aim VI). We will use a multi-pronged approach to the analysis including both transmission/disequilibrium tests (TDT) and case-cohort methodologies. The data set will be analyzed as a whole as well as by ethnicity. As we have demonstrated for the physical phenotype (i.e. level of spinal defect), we expect that clinical markers accounted for by genetic heterogeneity will have a role in accounting for the variability of the cognitive/behavioral and neural phenotypes of SB.
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