Wake-up call for teen pot smokers

The finding could mean that pot users are more likely to be not too good to start with. I can think of some examples of that. But the use of siblings as controls represents a serious effort to deal with that doubt, if not a conclusive one

YOUNG adults who used marijuana as teens were more likely than those who didn't to develop schizophrenia and psychotic symptoms, a seven-year Australian study found. Those who used the drug for six or more years were twice as likely to develop a psychosis such as schizophrenia or to have delusional disorders than those who never used it.

Research involving more than 3800 young adults, released online by the Archives of General Psychiatry, found long-term users were also four times more likely to have psychotic-like experiences. The findings, by the Queensland Brain Institute at the University of Queensland, build on previous research and shows that marijuana use is not as harmless as some people think, lead study author John McGrath said yesterday in an email.

The researchers quizzed 3801 young adults who were born in Brisbane between 1981 and 1984. The participants, whose average age was about 20, were asked about marijuana use. The researchers also measured whether those in the study had psychotic symptoms. The study was the first to look at sibling pairs to discount genetic or environmental influence and still find marijuana linked to later psychosis, the authors said.

"This is the most convincing evidence yet that the earlier you use cannabis, the more likely you are to have symptoms of a psychotic illness," said Dr McGrath, a professor at the institute, in a statement. "The message for teenagers is: if they choose to use cannabis they have to understand there's a risk involved." Researchers were looking for causes of schizophrenia, Dr McGrath said.

Of the 1272 participants who had never used marijuana, 26 (2 per cent) were diagnosed with psychosis. Of the 322 people who had used marijuana for six or more years, 12 (3.7 per cent) were diagnosed with the illness. Overall, 65 people were diagnosed with psychosis, the study said. The researchers also found those who used marijuana the longest were four times more likely than those who didn't to have the highest scores derived from a list of psychotic-like experiences.

Dr McGrath said even those who used marijuana for fewer than three years still had an increased risk of scoring higher than those who had not. "Apart from the implications for policy makers and health planners, we hope our findings will encourage further clinical and animal-model research to unravel the mechanisms linking cannabis use and psychosis," the authors wrote.

Those in the study were interviewed at the ages of 14 and 21, so the symptoms emerged between those two study periods, Dr McGrath said. The study also showed that among 228 sibling pairs, those who didn't use marijuana reported fewer psychotic-like delusions compared with those who used cannabis. That difference was statistically significant and reduces the likelihood that the psychotic problems were caused by genetics or environment, the authors said.

The study was funded by the National Health and Medical Research Council of Australia.

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A gene for Alzheimer's makes you smarter

Once again, it's all in the genes -- good and bad

A GENE variant that ups your risk of developing Alzheimer's disease in old age may not be all bad. It seems that young people with the variant tend to be smarter, more educated and have better memories than their peers.

The discovery may improve the variant's negative image (see "Yes or no"). It also suggests why the variant is common despite its debilitating effects in old age. Carriers of the variant may have an advantage earlier in life, allowing them to reproduce and pass on the variant before its negative effects kick in. "From an evolutionary perspective it makes sense," says Duke Han at Rush University Medical Center in Chicago.

The "allele" in question is epsilon 4, a version of the apolipoprotein E gene (APOE). Having one copy increases the risk of developing Alzheimer's at least fourfold compared with people who have other forms of the gene. A person with two copies has up to 20 times the risk.

One big clue that epsilon 4 might be beneficial emerged several years ago, when Han's team scanned the APOE genes of 78 American soldiers. All had suffered traumatic brain injuries, many while serving in Iraq. Sixteen had at least one copy of epsilon 4. Han's team expected to find that these carriers would be in worse cognitive shape than their counterparts with different versions of APOE, given previous studies that showed elderly people with epsilon 4 fare worse after head injury. But the opposite was true: soldiers with the epsilon 4 allele had better memory and attention spans (Journal of Neurology, Neurosurgery & Psychiatry, DOI: 10.1136/jnnp.2006.108183).

It wasn't the first study to suggest that epsilon 4 may be beneficial to the young. Back in 2000, researchers showed that young women with epsilon 4 have IQs a few points higher than those with no copies of the variant and score 7 points higher on the non-verbal portion of a common intelligence test (Neuroscience Letters, vol 294, p 179). Then in the Czech Republic in 2001, researchers showed that 87 per cent of epsilon 4 carriers go on to university, compared with 55 per cent of people with another version of APOE. The last group were also more likely to drop out of school

More recently, Jenny Rusted of the University of Sussex, UK, and Natalie Marchant at the University of California, Berkeley, have uncovered still more benefits for young people carrying epsilon 4. Those aged between 18 and 30 with the gene variant excelled at tasks requiring the frontal lobe, a brain region involved in higher cognitive skills. In particular, epsilon 4 carriers did better in a card game that asked them to remember a future plan while busy with another task

Rusted suggests that epsilon 4 helps people focus on important information. But recalling something also requires you to tune out the irrelevant bits, an ability known to decline with age.

Perhaps, Rusted says, without this second capability, epsilon 4's benefits fall by the wayside. Why it has a negative effect in old age, however, is still a mystery, although a study carried out by Clare MacKay at the University of Oxford in 2009 offers a tentative, hypothesis.

Her team asked 20 to 35-year-olds to remember which pictures of animals or landscapes they had seen before, while having their brains scanned with functional MRI. It was an easy task and all performed equally well. But a brain region critical to memory lit up more strongly in epsilon 4 carriers than in the others, raising the intriguing possibility that carriers' brains get overworked in early life, only to be worn out by the time they hit old age. MacKay wouldn't go that far, but she says: "It's possible that your brain is having to work harder when it's younger and this may have consequences for later life."

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