Human Heredity 11th Edition by Michael Cummings

Exercise 20

Polybrominated diphenyl ethers (PBDEs) are flame retardants widely used in furniture, draperies, and electronics such as computers and monitors. Because PBDEs are added to products and are not chemically bonded to them, PBDEs are slowly released into the environment. They have become globally distributed contaminants and have been detected in all environments tested. Major exposure to humans comes from direct exposure (furniture), indoor air, household dust, and even some foods. Levels in human tissues (including blood) have been increasing with time, and are higher in people in North America than in Europe, where PBDEs have been widely banned.
PBDEs may disrupt thyroid hormone function and affect the development of the brain and nervous system. In addition, PBDEs are transferred across the placenta to the developing fetus and may damage the developing nervous system. Work in animal model systems has shown the neurotoxic effects of PBDEs during development of the central nervous system, raising concerns about effects on child development. Two recent studies have provided some direct evidence that prenatal exposure to PBDEs does affect motor skills as well as cognitive development and behavior in schoolchildren, and that neurodevelopmental effects are related to the concentration of PBDEs in umbilical cord blood.
In the first study, PBDE levels were measured and thyroid hormone analyses were conducted in European women near the end of their pregnancy. The children were assessed for motor skills, cognitive development, and behavior at ages 5 and 6. Results showed consistent links between thyroid hormone disruption and lowered neuropsychological functions. PBDE exposure does affect motor skills and attention spans. The second study examined the effects of prenatal PBDE exposure in U.S. children between 1 and 4 years of age and again at age 6. PBDEs were measured in umbilical cord blood at birth and in maternal blood on the day after delivery. The results showed that children with higher PBDE cord blood concentrations scored lower on tests of mental and physical development across all ages tested. Children in the highest 20% of PBDE levels had significantly lower scores than the lower 80%. Given widespread use of these compounds in the United States and the fact that environmental levels of PBDEs are four times higher in the United States than in Europe, the benefits and risks associated with flame retardants should be carefully assessed.
How do PBDEs affect the development of the nervous system? In bacterial cells and in animal models, PBDEs do not cause mutations or damage the DNA in any detectable ways. Based on the fact that these compounds are present in the environment, researchers have asked whether PBDEs might work by epigenetic mechanisms, changing the pattern of gene expression during development and maturation of the nervous system in ways that result in developmental and behavioral deficits. Exposure of rat nerve cells grown in the laboratory to PBDEs does alter the cellular pattern of DNA methylation, which is a major epigenetic pathway for changing patterns of gene expression. In addition, exposure to PBDEs caused changes in the pattern of programmed cell death, which is an important component of development in the nervous system. Further studies are needed to confirm these results and to extend them to human nerve cells.
Could epigenetic changes caused by PBDEs be passed on from parents to their children?