Maternal stress, preterm birth, and DNA methylation at imprint regulatory sequences in humans.

In infants exposed to maternal stress in utero, phenotypic plasticity through epigenetic events may mechanistically explain increased risk of preterm birth (PTB), which confers increased risk for neurodevelopmental disorders, cardiovascular disease, and cancers in adulthood. We examined associations between prenatal maternal stress and PTB, evaluating the role of DNA methylation at imprint regulatory regions. We enrolled women from prenatal clinics in Durham, NC. Stress was measured in 537 women at 12 weeks of gestation using the Perceived Stress Scale. DNA methylation at differentially methylated regions (DMRs) associated with H19, IGF2, MEG3, MEST, SGCE/PEG10, PEG3, NNAT, and PLAGL1 was measured from peripheral and cord blood using bisulfite pyrosequencing in a sub-sample of 79 mother-infant pairs. We examined associations between PTB and stress and evaluated differences in DNA methylation at each DMR by stress. Maternal stress was not associated with PTB (OR = 0.98; 95% CI, 0.40-2.40; P = 0.96), after adjustment for maternal body mass index (BMI), income, and raised blood pressure. However, elevated stress was associated with higher infant DNA methylation at the MEST DMR (2.8% difference, P < 0.01) after adjusting for PTB. Maternal stress may be associated with epigenetic changes at MEST, a gene relevant to maternal care and obesity. Reduced prenatal stress may support the epigenomic profile of a healthy infant.

Albinism and disease causing pathogens in Tanzania: are alleles that are associated with OCA2 being maintained by balancing selection?

Oculocutaneous albinism type 2 (OCA2) is present at significantly higher frequencies in sub-Saharan African populations compared to populations in other regions of the world. In Tanzania and other sub-Saharan countries, most OCA2 is associated with a common 2.7kb deletion allele. Leprosy is also in high prevalence in sub-Saharan African populations. The infectious agent of leprosy, Mycobacterium leprae, contains a gene, 38L, that is similar to OCA2. Hypopigmented patches of skin are early symptoms that present with infection of leprosy. In consideration of both the genetic similarity of OCA2 and the 38L gene of M. leprae and the involvement of pigmentation in both disorders, we hypothesized that the high rates of OCA2 may be due to heterozygote advantage. Hence, we hypothesized that carriers of the 2.7kb deletion allele of OCA2 may provide a protective advantage from infection with leprosy. We tested this hypothesis by determining the carrier frequency of the 2.7kb deletion allele from a sample of 240 individuals with leprosy from Tanzania. The results were inconclusive due to the small sample size; however, they enabled us to rule out a large protective effect, but perhaps not a small advantage. Mycobacterium tuberculosis is another infectious organism prevalent in sub-Saharan Africa that contains a gene, arsenic-transport integral membrane protein that is also similar to OCA2. Interestingly, chromosomal region 15q11-13, which also contains OCA2, was reported to be linked to tuberculosis susceptibility. Although variants within OCA2 were tested for association, the 2.7kb deletion allele of OCA2 was not tested. This led us to hypothesize that the deletion allele may confer resistance to susceptibility. Confirmation of our hypothesis would enable development of novel pharmocogenetic therapies for the treatment of tuberculosis, which in turn, may enable development of drugs that target other pathogens that utilize a similar infection mechanism as M. tuberculosis. From an evolutionary perspective, confirmation of our hypothesis may provide another example of heterozygote advantage.