How genes help -- and hurt -- us

Our genes create a formula that makes us unique. But recent research on just how much genes affect health, longevity, mental health and other outcomes over a lifetime offers some surprises.

To start with, no one seems exempt from the lottery of bad genetic variants.

British researchers reported earlier this month that a normal, healthy person carries, on average, about 400 potentially damaging DNA variants, with two known to be associated directly with disease traits.

In studying the genomic sequences of 179 individuals, they found that one in 10 could be expected to develop a genetic disease.

Of course, these estimates are based only on knowledge of gene mutations for a relatively small number of diseases and conditions gained over the past two decades. The numbers thus are likely to increase as that understanding grows.

Gene mutations typically cause disease only when two copies of the gene -- one in each chromosome -- are present. The exception comes with so-called dominant genetic variants, which can produce a disease trait even with just a single copy of the gene.

“In the majority of people we found to have a potential disease-causing mutation, the condition is actually quite mild, or would only become apparent in the later decades of life,’’ the study’s lead author, David Cooper of Cardiff University, said in a statement. “We now know that normal healthy people can possess many damaged or even completely inactivated proteins without any noticeable impact on their health.”

The researchers, who published their work online in the American Journal of Human Genetics, noted the presence of so many genetic flaws in everyone underscores the challenge of broad genetic screening: It may identify mutations that don’t pose significant health risks to an individual.

Scientists are also finding more ways that some genetic mix-ups produce both tremendous evolutionary advantages but also raise the odds of disease.

Researchers at the University of Edinburgh recently traced back a surge in the number of copies of brain genes 500 million years to simple invertebrate animals that ultimately set the stage for higher intelligence in humans and other mammals.

The genes are part of a family of proteins that help make key building blocks of synapse -- the connections between nerve cells in the brain. Comparing mice and human genetic codes, they found that the genes that control higher mental function also can impair mental function -- can cause mental illness -- if they’re damaged or have mutated, they reported in the journal Nature Neuroscience in early December.

While the genetic code inside each cell is the same, the chemical signals that regulate genetic functions vary among each tissue and organ.

Two studies sponsored by the National Institutes of Health found that the signals passed along from various brain regions often differ even for the same genes, and over specific periods. The journal Nature published the results in October.

Gene activity is high in a fetus, slowing after birth and declining particularly after adolescence before leveling off in middle age. The activity surges again in old age, as the brain adjusts to mental decline and rearranges functions to maintain mental capacity.

Understanding how these messenger chemicals work across different parts of the brain at different times is essential to mapping and possibly treating different brain disorders.

Another study looked at how regulatory signals of white blood cells behaved in people of different ages. Spanish researchers published their results last summer in the Proceedings of the National Academy of Sciences.

They found the signals given by infants and a 103-year-old were much different, even though the genes involved were not any different over the lifespan. While the regulation of the immune cells was strong in the youngsters, many switches were gone or distorted in advanced age, causing them to deactivate some protective genes.

It might be possible to restore youthful patterns through diet or drugs, the researchers said, and so reduce the incidence of infections and boost longevity.

(Contact Lee Bowman, Scripps health and science writer, at bowmanl@shns.com)