Environmental Factors, Heavy
Metals, and Brain Function
All disorders have a cause. This can be purely genetic, a good example being the collapse of red blood cells due to abnormal hemoglobin in sickle cell anemia. The problem here is a mutant gene that causes production of anomalous proteins which in turn alter the shape of the red blood cells, impairing their function. Disorders can also be purely environmental – for instance, the drug thalidomide used by pregnant women to prevent morning sickness had the disastrous effect of producing severe physical deformities in the child. But, although both examples seem straightforward, they only tell part of the story.
One would expect that a gene causing faulty red blood cells would be quite rare since the sickle-shaped red blood cells do not carry oxygen and can cause blockage of small arteries. People with this gene mutation would be less healthy, leading to removal of the gene from the population. However, this mutation seems to be beneficial in malaria-infested areas – the parasite that causes malaria cannot reproduce in the altered red blood cells. People with the sickle-cell trait are protected and survive, and so carry the mutant gene into the next generation – a good example of the interaction of a genetic disorder and environmental factors.
Conversely, in the thalidomide tragedy many children of mothers taking thalidomide during the critical period showed no abnormalities. Although not well studied, one must presume that some mothers with favorable genes could degrade and detoxify the thalidomide molecule, preventing it from harming their children. And some children may not have been susceptible. Even a disorder like this, which appears to be entirely environmental, can be strongly dependent on genetic factors.