Stunting is a global health problem that is common in low and middle-income countries where one third of children under 5 years of age are affected6. Africa has the highest rates of stunting and is the continent that has shown the least improvement in the prevalence of stunting in recent years. Small mothers tend to give birth to small babies, but the epigenetic mechanisms that underlie this correlation are poorly understood. This study of 145 imprinted genes in placentas from 600 mothers will test the hypothesis that genetic imprinting plays a role in the inter-generational transmission of stunting. This research is innovative because it takes advantage of a prospective cohort study of a rural African population in which 1144 subjects (F1 generation) are followed from infancy, through childhood, to first parenthood. Data are also being gathered on their parents (F0 generation) and offspring (F2 generation). This study combines these longitudinal data, spanning 3 generations, with the analysis of allele-specific expression of placental genes. According to the conflict hypothesis5, growth-inhibiting genes are repressed on the paternal alleles and growth-promoting genes are repressed on the maternal alleles. The degree of imprinting varies between individuals and we hypothesize that this normal variation is the mechanism by which stunting is transmitted from one generation to the next.
Aim 1 will find out if maternal stunting and catch-up growth affect the level of imprinting in 145 placental genes.
Aim 2 will find out if loss of imprinting of placental genes leads to offspring stunting, as measured by supine length at birth and at later follow-up.
Aim 3 will test the effect of urban migration in late adolescence, and the associated improvement in nutrition, on the level of imprinting in 145 genes. The placental collections will be carried out by trained consultants who belong to the same ethnic group as the study population, namely the Dogon of central Mali. The study site is located in the District of Bandiagara and is peaceful; the principal investigator and her collaborators have been able to visit the site every year for the past five years. The research team has field-tested all the protocols and collected 77 placentas, which have already been partly analyzed in the PI's laboratory at the University of Michigan. The imprinted genes are sufficiently heterozygous to differentiate maternal from paternal alleles. A combination of PCR and deep sequencing will be used to measure loss of imprinting with high accuracy. As stunting leads to a wide array of health problems from poor cognitive function to metabolic syndrome7, it is important to understand how it is transmitted to the next generation. The proposed study is basic science that is necessary for the eventual discovery of interventions and policies that prevent stunting and its adverse effects on the quality of life.
The placenta is the organ that nourishes the fetus and that can transmit health or disease to offspring. This project will shed light on the mechanisms through which this is accomplished, especially the so- called ?epigenetic mechanisms? that contribute to problems like low birth weight and stunting that increase risk for diabetes and hypertension later in adulthood.
