Chromosomes, upbringing or both?

Is it nature or nurture that has more influence on triggering diseases? The debate intensifies.

By
January 30, 2011 05:03
Genetics is “central in designing the brain."

DNA_311. (photo credit: (www.genome.gov))

The debate on whether certain neurological diseases result from Nurture (environment) or Nature (genes) has been going on for almost as long as the debate on what came first, the chicken or the egg? But today most researchers admit that both one’s upbringing and influences in the uterus through childhood and adolescence have as strong an influence on these disorders as the genes inherited from one’s parents.

A seminar on factors that influence the brain, from heredity and environment to creativity, parenting and medications – held recently at Jerusalem’s Shaare Zedek Medical Center in memory of the hospital’s eminent pediatric neurologist Prof. Naomi Amir – featured a lively debate on these issues.

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Dr. Adi Aran, a pediatric neurologist in the Shaare Zedek unit, said genetics is “central in designing the brain, including intelligence. The sequencing of DNA affects cognitive ability, personality, sexual orientation, and even one’s sense of humor.” But while genes are key, there is a connection between heredity and environment in the field of epigenetics, which studies how environment can influence genes and how they are expressed, he said.

Sir Francis Galton – an 18th century English anthropologist, eugenicist and statistician who coined the phrase “Nature vs Nurture” and whose book Hereditary Genius was the first social scientific attempt to study genius and greatness – conducted numerous twin studies. These compared outcomes in identical and fraternal twins after they were raised together or separated by events such as adoption. “Identical twins share 100% of their genes, as they come from one egg,” Aran noted, while fraternal twins share half of the genes inherited from their parents.

University of Minnesota psychology Prof. Thomas Bouchard also studied twins. “He examined 100 pairs of identical twins separated and adopted at infancy and found that decades later, their lives were very similar,” said Aran. He added that the journal Science published a Minnesota Twin Study showing that “70% of IQ differences are explained by genetics. Environmental influences were minimal in personality, temperament, vocation, the ways they spent their leisure time and their social approach.”

Pouring cold water on attempts by parents to boost IQ and creativity by buying Baby Mozart disks, Aran said most cognitive ability is inherited, and one could even find specific genes to explain IQ differences. “There is one defective gene that can reduce IQ and causes various syndromes. If a gene functions below capacity rather than being absent, it can also affect IQ, but sometimes differences are not significant,” said the Shaare Zedek expert. “But one single gene that affects IQ has not been found. It is much more complex than that.”

Researchers have studied the effect on IQ of breastfeeding, and it seems to raise it, but “maybe women of a certain genetic background have a greater tendency to breastfeed,” he speculated. Personality too is affected by heredity, but is not influenced by a single gene. “Openness, conscientiousness extroversion, agreeableness and neuroticism all seem to be influenced by genes, but this is difficult to investigate because it’s hard to agree on what a specific personality is.”

“What affects obesity? Genes or ice cream? Genes have a bigger effect, but we can’t weigh it exactly,” Aran suggested. Pairs of adult identical twins are similar in weight to an extent of 80%, he said, compared to only 40% in fraternal twins. “It depends on what you eat. There has been an obesity epidemic in recent years that is partly environmental. In an age of limited food, an obese person is one who has access to food. If the food supply is unlimited, whoever becomes obese has a genetic tendency to eat too much.”

If one has a good intellectual and cognitive potential, and an environment that encourages study, you will do well. If there is an environment that discourages study, genes that raise IQ will not be expressed so much, Aran continued. Nevertheless, criminals cannot blame their personal genome for making them break the law. “There is a lot of leeway to change, despite what your genes hand you,” he insisted. Sexual orientation is decided during the first two years of life, maintained Aran, “but expressed later. One can’t choose whether one is a homosexual or not, and it can’t be changed. There are pre-natal environmental influences including maternal antibodies and low levels of testosterone in the womb. It can even be viewed by comparing the length of fingers on the hand,” he said.

HIS COLLEAGUE Dr. Hilla Ben-Pazi, a champion of environmental influences, began by saying that Microsoft founder and multibillionaire Bill Gates “is no more intelligent than the average person. He was affected by the environment. In 1968, at the age of 13, he was given unlimited access to a university computer, and spent 10,000 hours programming it. If you practice anything for 10,000 hours, you will succeed.”

She compared Gates to Christopher Langan, 58, who with a tested IQ of 190 to 210 (Albert Einstein’s was 150) has been called the world’s smartest man. He spoke from the age of six months and taught himself to read by the age of four. His father died young, and the family was poor; the boy was beaten for years by his stepfather. Langen studied boxing and wrestling, and is today married to a neuropsychologist but never finished an academic degree. He worked as a construction worker, cowboy, forest service firefighter, farmhand – and for over two decades years as a “bouncer” at the entrance to a club.

The genius formed a non-profit corporation called the Mega Foundation to “create and implement programs that aid in the development of extremely gifted individuals and their ideas.” But he was profiled in Malcolm Gladwell’s book Outliers: The Story of Success as an example of a person who failed to realize his potential in part because of poor social skills, possibly resulting from being raised in poverty and unpleasant circumstances. “It is the environment of one’s life that brings success or not,” concluded Ben-Pazi.

She also cited work by Johns Hopkins University researcher Dr. Karl Alexander, who examined what causes gaps in academic performance. Of 80 children who studied at the same school, differences in accomplishment depended not on IQ, he maintained, but on what they did during their summer vacation. Those who wasted it fell back compared to those who used the vacation beneficially, Ben-Pazi said.

Children raised in an orphanage with little personal attention tended to have language difficulties and inadequate concentration, as well as impulsiveness and personality problems. But when nurses studied atrisk pregnant women, made home visits during the pregnancy and during the first two years after delivery, this intervention was found to improve and enrich the children. Almost two decades later, more had completed high school and gotten jobs than those who had not had the intervention.

The best age for intervention in deprived children is between three and five years, but even teenagers who get the proper assistance can do better, insisted Ben-Pazi. Not only children born healthy can improve with intervention, but also children suffering from brain damage or other neurological conditions, she continued.

LAB STUDIES on rodents have shown that pregnant rats exposed to stress are more likely to produce offspring with problematic sociological behavior. Rats that received enrichment caught up with those whose mothers had not been exposed to stress. An improved environment such as a larger cage improved memory, learning and health of offspring, especially if their mothers groomed them. This treatment can increase the number of nerve connections, she said. “Thus, in early childhood, intervention is effective over time, especially if the brain is normal.”

The two neurologists went head-to-head on a number of disorders affecting children, and whether Nature or Nurture is the major trigger. Aran stated that “today, we know that autism is genetic, not environmental. Previously, cold ‘refrigerator’ mothers were blamed for it because they did not show emotional closeness to their child; after diagnosis, they felt a lot of guilt. Today we know that mothers’ behavior is not to blame for autism. It is a combination of genes that represents over 90% of influence compared to other triggers.”

But Ben-Pazi insisted that environmental influences such as drugs taken during pregnancy and being born with cerebral palsy can also cause autism. “There is a significant increase in the number of children diagnosed with it, now reaching one in 100. If it’s genetic, why would there be such an increase. Of course, there is improved and earlier diagnosis, but this doesn’t explain all the increase.” She suggested that women getting pregnant at older ages could also be a factor.

Depression, said Aran, has both genetic and environmental aspects. “There are six genes involved with dopamine and serotonin [neurotransmitters] that are believed to pleay a role. A study of a 2004 hurricane in Florida found that people with a certain genetic variant and a lack of social support in the aftermath were more likely to be depressed than others,” he said.

But Ben-Pazi countered that depressed mothers tend to raise depressed children. “It’s hard to separate between genes and environment, but it is known that babies born in the winter have more of a tendency to become depressed when older. If they are exposed to smoking or have poor nutrition, they are also at higher risk,” she said. “Stress is a factor. Some 140 children in Dimona were asked about depression and social support. Then a terror attack hit the town, and when they were examined later, it was found that those who had social support escaped depression, while those that had none did not.”

Ben-Pazi added that a Japanese study showed children who performed sports and had a diet high in Omega 3 fats were less likely to become depressed.

Attention-deficit hyperactivity disorder (ADHD) studies of twins, said Aran, showed that genetics are responsible for 77% of the influences that bring about the condition. But Ben-Pazi pointed out that if the mother has a chronic illness, is older, smokes or suffers stress during pregnancy, and if the delivery is longer than usual, or the baby is born late, ADHD is more likely. Even a diet rich in the preservative sodium benzoate or artificial colors can make children at high risk for ADHD, she said. “Exposure to lead, mercury and manganese and various organophosphate insecticides can cause neurological problems including ADHD.” A connection between babies who watch hours of TV at the age of one and a diagnosis of ADHD at the age of seven has been found, she concluded.

Aran stressed that one need a “suitable genetic background for ADHD. Without it, early TV viewing and chemical exposure will not cause it. It is best to avoid these dangers if there is a family history.”

Thus the best conclusion one could reach from the debate is to choose your parents carefully, avoid environmental dangers and seek help if you develop disorders.


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