Copper is a Jekyll-and-Hyde element in the human body - in small quantities it has an essential and benign role in normal development and metabolism, but in excess or deficiency, it can be a killer.

Copper is a toxic heavy metal - it reacts with oxygen, creating oxygen free radicals that can inactivate vital enzymes and damage DNA.

Professor Julian Mercer, a molecular geneticist with Deakin University's School of Biological and Chemical Sciences, says about one in 200,000 males is born with a devastating genetic disorder called Menke's disease. Its symptoms include profound mental retardation, and connective tissue (collagen) abnormalities that result in soft bones and cartilage and weakened artery walls. Few baby boys with the disease survive beyond the age of three.

In patients with Menkes disease, deletions of large segments of the gene, or a so-called frameshift mutations that grossly distort its DNA-encoded instructions, completely abolishes the activity of the MNK protein.

Certain point mutations - changes in a single "letter" of the gene's DNA code - can cause a mild form of Menkes disease, resulting in only slight mental retardation and impairment of physical coordination.

Other point mutations produce a condition called occipital horn syndrome, which results in mild mental retardation, and collagen abnormalities that cause loose joints and weak artery walls that may rupture - the latter symptoms parallel severe Menkes disease.

Why do different mutations in this one gene produce such different diseases? Since the MNK gene was cloned, Professor Mercer and long-time co-worker, Melbourne University geneticist Associate Professor Jim Camakaris, have been trying to find out.

Their studies of the MNK protein's structure and function have shown that it functions as a finely tuned molecular pump that maintains a safe concentration of copper ions inside cells.

Professor Mercer's and Dr Camakaris's research groups have deliberately induced mutations in the MNK gene that subtly change the MNK protein's "recipe", to establish which regions of the molecule are essential to its normal activity.

They grew cell lines from several Menke's patients in tissue culture, after assessing their ability to accumulate copper. They then used a technique called lipofection to introduce a healthy MNK gene through the cell membrane - it involves encapsulating the DNA in small lipid "bubbles".

The transfected cells began to accumulate normal levels of copper, and exported it when grown in a copper-rich medium, showing that, in vitro at least, defective cells can be repaired.

They also introduced a different copper-metabolism gene into the Menke's cells - a gene that, in mutant form, causes another rare disorder of copper metabolism called Wilson's disease. They were exploring the possibility that the Wilson's gene, which is normal in Menke's patients, could be manipulated to act as a surrogate for the defective Menke's gene.

Professor Mercer says the two genes are structurally similar, and probably share a common ancestor. But whereas the Menke's gene is expressed in tissues like skin-building fibroblasts, the kidneys, the placenta, the brain, the gut and the vascular system, the Wilson's gene is expressed mainly in the liver, and individuals with the disorder accumulate toxic concentrations of copper in the liver.

Another of Professor Mercer's colleagues at Deakin University, Dr Leigh Ackland, has found that Menke's and Wilson's genes are both expressed in breast tissue and the proteins are probably involved in supplying copper to breast milk. Adequate supplies of copper in breast milk are essential for normal growth of the infant. Interestingly, during lactation the distribution of the proteins in the cells of breast tissue change in the same way as cells exposed to copper.

The result hints that another, more fundamental physiological mechanism may regulate traffic in the Menke's and the Wilson's proteins - if this mechanism could be identified, it might be possible to harness it to force the Wilson's protein to export copper in Menke's patients.

Professor Mercer and his colleagues are developing DNA-based tests to look for mutations in the Menke's gene Menkes disease is caused by recessive variants of the gene - females are protected against Menke's disease because they possess a normal, dominant gene on their second X-chromosome - males have only one X-chromosome, so if their lone Menke's gene is defective, they inevitably develop Menkes disease or occipital horn disorder.

About one mother in 100,000 carries a defective Menke's gene, and on average, will transmit it to 50 per cent of her sons - hence the rarity of the disorder.

About one person in 100 - both males and females - carries a defective Wilson's gene. The odds that two carriers will meet and have children is thus one in 10,000 couples, but only one in four of their children is likely to inherit two defective Wilson's genes, so only one in 40,000 babies is born with Wilson's disease.

But the presence of so many carriers of recessive, mutant variants of the Menke's and Wilson's genes in the general population raises another interesting question, according to Professor Mercer: could these outwardly normal individuals have an increased sensitivity to copper toxicity?