Calendar could offer clues about disease

August 20, 2004|By Erika Niedowski | Erika Niedowski,SUN STAFF

Pisces (Feb. 19-March 20): Governed by Neptune and symbolized by the fish. Compassionate, introspective, artistic. Often dreamy and impractical. May be prone to schizophrenia, epilepsy or bipolar disorder.

It may sound like some kind of new, madcap astrology, but a number of scientists are becoming convinced that our birth month may predispose us to particular diseases later in life.

Studies have shown that schizophrenia is more common among those born in late winter or early spring. Multiple sclerosis is associated with births in April, May and June. And epilepsy occurs more frequently in those with birthdays from December to March.

The findings may seem whimsical or -- depending on which month you eat cake and unwrap presents -- alarming. But researchers hope the emerging patterns will offer clues into the origins of a range of illnesses that, despite advances in treatment, have no known cause.

"It makes you think differently about disease," said Dr. Emmanuel Mignot, professor of psychiatry and behavioral sciences at Stanford University School of Medicine, who has studied the association between birth month and narcolepsy.

"Most people tend to think that disease is really something that is determined by your genes or what happens just before the disease occurs," he said. "Maybe there are a number of things that can happen well before."

In the latest study, published in the current edition of the journal Neurology, scientists at the National Cancer Institute found that adults born in January and February had the highest risk of brain cancer. Those with birthdays in July and August had the lowest risk.

The paper's lead author, NCI epidemiologist Alina V. Brenner, says, though, that the findings could be the result of chance.

But separate studies in Britain and Norway have identified a similar correlation between birth season and risk of brain tumors in children, with a statistical "excess" of births in winter and a "deficit" in summer.

If the association turns out to be real, Brenner said, it suggests that exposures early in a child's development -- at any point from conception to the first few months after birth -- could have a hand in the genesis of the disease. Though it's not clear what those exposures are, they could include viruses, environmental toxins or even something as seemingly benign as the weather.

Seasonal birth patterns have been most firmly established in schizophrenia patients. Several years ago, a group of Danish researchers reported that the risk of developing the disorder was highest among those born in February and March and lowest among those with birthdays in August and September.

Dr. E. Fuller Torrey, research psychiatrist at the Uniformed Services University of Health Sciences in Bethesda, has ruled out the possibility that chance alone explains the findings.

"It could be chance if it were one study of 250 people, or a few dozen people here or a few dozen people there," he said. "When you're dealing with a couple hundred thousand people and 200 studies, the chances of it being chance are zero-point-zero. It's remarkably consistent."

The leading explanation implicates a seasonal infection that could be disturbing the child's normal brain development, which may help explain why other central nervous system disorders are also more common in those with winter births.

"We know that infectious agents have a seasonality -- influenza being the most striking," Torrey said. "You certainly have to think of infectious agents infecting the mother late in pregnancy or infecting the newborn in the first few months of life."

Stanford's Mignot and a group of colleagues from France published a paper in the journal Sleep last year linking birth month with another disorder: narcolepsy. Patients with that condition are seized with sleep during normal waking hours.

The researchers compared the birth dates of 886 narcoleptics being treated at sleep clinics in Montpellier, France; Montreal; and California to those of more than 35 million people in the general population.

The distribution of births was uneven, with the percentage of narcoleptics born in March (11.9 percent) significantly exceeding that expected in the general population (8.5 percent).

The researchers found a drop in narcoleptics born in September (5.6 percent) compared with the number normally expected (8.7 percent).

Mignot is among those who believe narcolepsy is an autoimmune disease, in which the body mistakenly attacks its own cells, tissues and organs as if they were foreign. Perhaps exposure to some virus early in life, Mignot said, interferes with normal immune system development.

Of course, birth month alone, for any given person, doesn't predict disease.

Said Mignot: "It's not astrology -- yet."

Birth months

Various studies have come up with the highest- and lowest-risk birth months for diseases. Some studies have confirmed only the highest-risk months.

Ailment Highest risk ............................... Lowest risk

Brain tumors February and January ........... August and July

Epilepsy December through March .... September

Narcolepsy March ........................................... September

Schizophrenia February and March ............... August and September

Multiple sclerosis April .............................................. May or June

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