Sunday, April 06, 2008

A father's legacy to a child's health may start before conception and last generations (?)

The idea that characteristics acquired during the lifetime can be passed on genetically is known as Lamarckism. Its best known exponent was Stalin's Trofim Lysenko and the whole idea is now generally ridiculed. Studies with rodents do however suggest that some characteristics caused by chemical exposure can be passed on to offspring even though the DNA remains unchanged. Such phenomena are now called "epigenetic" influences. I will not attempt to make any comment on the rodent studies but I think that the studies in humans mentioned below are unconvincing. The studies are epidemiological so are intrinsically capable of many explanations. Attributing the differences observed to epigenetic effects is therefore pure supposition.

The lack of insight below is in fact rather pathetic. Take this sentence: "the team found that babies of teenage fathers, but not middle-age men, had an elevated risk of still birth, low birth weight, and other birth problems". What does that tell you? It tells me that underclass people reproduce earlier and have more health problems and that they pass those problems on in the normal way. What we are seeing in the data, in other words, is simply the underclass influence. That early childbirth is to a large extent an underclass phenomenon and that lower social rank tends to go with poorer health is well established. So the idea that the differences are passed on "epigenetically" is in fact the least parsimonious explanation and so should have its throat cut by Occam's razor.

Pregnant women know the drill. Don't drink. Don't smoke. Don't eat too much fish. Take vitamins. Mothers have long shouldered the responsibility, and the blame, for their children's health. Fathers don't usually face the same scrutiny.

How a man lives, where he works, or how old he is when his children are conceived doesn't affect their long-term health, scientists used to think. But growing evidence suggests that a father's age and his exposure to chemicals can leave a medical legacy that lasts generations.

Animal studies demonstrate that drugs, alcohol, radiation, pesticides, solvents, and other chemicals can lead to effects that are handed from father to son. Human studies are less clear, but some show that fathers play a role in fetal development and the health of their children.

Teenage dads face increased risk that their babies will be born prematurely, have low birth weight, or die at birth or shortly afterward, a new study in Human Reproduction shows.

Babies of firefighters, painters, woodworkers, janitors, and men exposed to solvents and other chemicals in the workplace are more likely to be miscarried, stillborn, or to develop cancer later in life, according to a review in the February Basic & Clinical Pharmacology & Toxicology.

Fathers who smoke or are exposed at work to chemicals called polycyclic aromatic hydrocarbons put their children at risk of developing brain tumors. And, older fathers are more likely to have children with autism, schizophrenia, and Down syndrome and to have daughters who go on to develop breast cancer.

Though some of these observations are decades old, attitudes lag even further behind, says Cynthia Daniels, a political scientist at Rutgers University-New Brunswick in New Jersey. Dads aren't held accountable if something goes wrong during fetal development. Since men make new sperm every 74 days, people used to reason, the genetic slate is wiped clean every couple of months. And even if a man makes defective sperm, the "all-or-nothing" view of reproduction holds that damaged sperm don't fertilize eggs. No harm. No foul.

So no one bothers to remind men to protect themselves against environmental toxins. There are no images of "crack dads" and "crack babies" in the media like those of women who harm developing fetuses with drug and alcohol use, Daniels said in February at a meeting of the American Association for the Advancement of Science held in Boston....

Older dads also have a higher risk of fathering children with rare mutations that cause dwarfism or a premature aging disease called Hutchinson-Gilford progeria syndrome.

But sometimes aging fathers pass along traits that can't be traced to only a single mutation. Fathers 40 and older have an increased chance that their children will develop complex disorders such as autism or schizophrenia. There is growing evidence that those disorders are caused by defects in many genes and the way genes are turned off and on.

Scientists don't yet understand the changes that age induces in sperm-making germ cells, and environmental exposure presents an even bigger mystery. People come in contact with a plethora of chemicals every day. But it is no easy task to sort out exactly which ones, or which combinations, cause heritable problems. The effects chemicals and radiation may have on offspring don't always follow predictable patterns either.

And when researchers do find a clear link between a father's lifestyle and his children's health, it's not always clear what the data mean. "What we can say is that we identified a group of fathers with adverse outcomes for their fetuses, but we don't have an idea of the mechanism," says Shi Wu Wen of the University of Ottawa in Canada and one of the lead authors of the study showing that babies of teenage fathers have a greater risk of birth problems.

Wen and his colleagues examined birth records for more than 2.6 million babies born between 1995 and 2000 to married, first-time, 20-something mothers in the United States. Looking at the husbands' ages, the team found that babies of teenage fathers, but not middle-age men, had an elevated risk of still birth, low birth weight, and other birth problems. The study was published online Feb. 6 in Human Reproduction.

More here


A health characteristic is strongly genetically inherited! How revolutionary!

Blood Pressure Change and Risk of Hypertension Associated With Parental Hypertension

By Nae-Yuh Wang et al.

Background: Parental hypertension is used to classify hypertension risk in young adults, but the long-term association of parental hypertension with blood pressure (BP) change and risk of hypertension over the adult life span has not been well studied.

Methods: We examined the association of parental hypertension with BP change and hypertension risk from young adulthood through the ninth decade of life in a longitudinal cohort of 1160 male former medical students with 54 years of follow-up.

Results: In mixed-effects models using 29,867 BP measurements, mean systolic and diastolic BP readings were significantly higher at baseline among participants with parental hypertension. The rate of annual increase was slightly higher for systolic (0.03 mm Hg, P = .04), but not diastolic, BP in those with parental hypertension. After adjustment for baseline systolic and diastolic BP and time-dependent covariates-body mass index, alcohol consumption, coffee drinking, physical activity, and cigarette smoking-the hazard ratio (95% confidence interval [CI]) of hypertension development was 1.5 (1.2-2.0) for men with maternal hypertension only, 1.8 (1.4-2.4) for men with paternal hypertension only, and 2.4 (1.8-3.2) for men with hypertension in both parents compared with men whose parents never developed hypertension. Early-onset (at age ~55 years) hypertension in both parents imparted a 6.2-fold higher adjusted risk (95% CI, 3.6-10.7) for the development of hypertension throughout adult life and a 20.0-fold higher adjusted risk (95% CI, 8.4-47.9) at the age of 35 years.

Conclusion: Hypertension in both mothers and fathers has a strong independent association with elevated BP levels and incident hypertension over the course of adult life.

Arch Intern Med. 2008;168(6):643-648..

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