White Coat Notes

Popular? Maybe it's in your genes

February 2, 2009
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Excerpts from the Globe's blog on the Boston-area medical community.

Social butterflies at the center of attention and wallflowers on the social fringes may have their genes to thank, new research suggests.

Dr. Nicholas A. Christakis of Harvard and James H. Fowler of the University of California, San Diego - the same researchers who explored social networks to explain how obesity, smoking, and happiness spread among groups - have turned their attention to the connections made in social groups.

They conclude that people inherit not only a tendency to be shy or gregarious, but also a likelihood to have tightly knit or diffuse groups of friends.

"This paper is the first paper to show a genetic basis for human social network structure," Christakis said in an interview. "Where someone is positioned in a social network, and how interconnected their friends are, depends significantly on their genes."

The researchers studied 1,110 twins from a sample of more than 90,000 high school students. They compared identical twins, whose genes are the same, with fraternal twins, who share 50 percent of their DNA. The researchers tracked how many students named a particular student as a friend, how many friends the particular student listed, and whether the friends named by the student were also friends with one another.

Identical twins were significantly more likely to show the same patterns of social ties than fraternal twins, the researchers concluded.

"We have genes that make us popular and genes that make us act like yentas, making friendship matches among people we know," Christakis said. The research was reported in the Proceedings of the National Academy of Sciences.

Prematurity linked to signs of autism

Babies who are born more than three months early are up to three times more likely than other children to show symptoms of autism when screened using a standard checklist, Boston researchers report. The higher rate persisted even after excluding visual, motor, and cognitive impairments that are common in premature babies.

The 988 children in the study had not been diagnosed with autism, but they showed signs of the disorder according to a screening tool used by pediatricians for children who are 16 months to 30 months old. The checklist asks whether a child points at an object to show interest, for example, or how good their hearing is.

Among the general population children, the rate of positive scores is 5.7 percent. Among children in the study, who were born after less than 28 weeks, the rate was 21 percent. After children with disabilities were removed from the analysis, the rate was 16 percent.

"We're not implying that it's prematurity that causes autism," lead author Dr. Karl Kuban, chief of pediatric neurology at Boston Medical Center, emphasized in an interview. "They may hare a common risk that leads to both, but it's not that one causes the other."

Pediatricians should be aware that children who have handicaps may score positive on the autism checklist without having autism, he said. Autism is diagnosed after a more rigorous evaluation, but because early detection helps children get treatment, screenings are recommended.

About 0.6 percent of children are diagnosed with autism, about one-tenth the number who score positive on the checklist.

The study appears in the Journal of Pediatrics. Follow-up studies of the children in the study are needed, Kuban said.

"If it turns out these children do go on to have autism much more often than we would expect, it does beg the question of why that should be and it offers us an avenue of study," he said.


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