What a difference a change of genes can make

Insurance companies might want to look away now. Due to recent discoveries, the notion that you can see an individual's future in their DNA is rapidly becoming last century's idea.

We now understand that environmental factors - such as illness, abnormal temperatures, poor diet, exposure to chemicals and deprivation - can induce physiological changes that get passed down the generations. These "epigenetic" changes do not correspond to any changes in the inherited DNA, but they have a significant effect.

In plants, epigenetic changes can alter the shape of flowers and the colour of fruits. In animals, epigenetics has been linked to cancer, obesity and heart disease. Naive health insurance companies that rely on tests that use only genetics might be in for severe losses.

Governments ought to take note, too. It has become clear that creating an underclass can create epigenetic legacies that extend far further than the term of political office or economic cycle.

The side effects of poverty, such as stress or parental neglect, can induce adverse epigenetic changes that last for generations. One study showed epigenetic effects in the children of Dutch women whose pregnancy coincided with a great famine at the end of the Second World War. Girls born to these women were twice as prone to developing schizophrenia.

The chief culprit for such a blighted inheritance is a process called methylation. Methyls are chemical building blocks that become attached to certain parts of the DNA molecule and determine how active the genes will be. Methyl groups turn genes on and off or delay their activity.

Under the influence

In September, researchers working at the Salk Institute in California showed that methyl groups can exert a lasting influence on thousands of DNA sites, giving them hundreds of thousands of times the influence of spontaneous mutations in DNA, once thought to be the only source of physiological variation.

Methylation is not the only cause. In June, researchers in Japan showed that chemical or environmental stress causes changes inside the chromosomes that carry the DNA within biological cells.

Normally, DNA is tightly packed in the chromosome, but certain stresses cause the DNA to unfold, activating genes that would normally remain hidden and inactive, changing the physiological development of the organism. Future generations inherit the unfolded form of DNA. If that DNA is
in an egg or sperm, every cell in the next generation will contain exposed genes, laying offspring open to potentially important changes that cascade down the generations. Clearly, lifting yourself out of the pit is harder than we thought.