Gene clue to osteoporosis

About one in five women has a genetic variation that could increase their risk of the bone-weakening condition osteoporosis, US researchers say. A team of scientists based at the Washington University School of Medicine in St Louis have shown that a particular version of the CYP1A1 gene is linked to weak hip bones. The study, which appears in the Journal of Bone and Mineral Research, may lead to genetic tests that could help identify women at high risk of osteoporosis of the hip.

Osteoporosis affects one in three women, and one in 12 men in the UK. It is a disease of old age, in which the bones gradually become weaker and more porous (less dense). The disease often remains undetected until a patient falls and fractures their wrist, hip or spine. People with low 'bone mineral density' (BMD) are more likely to develop the disease than those with a higher BMD.

The causes of osteoporosis are a combination of genetic factors, and non-genetic influences such as diet, exercise, hormone levels and smoking. In the latest study, the researchers looked for a possible link between osteoporosis and the CYP1A1 gene, which makes a protein responsible for breaking down the hormone oestrogen in the body. This suggested that bone density might be linked to variations in the CYP1A1 gene, according to lead researcher Reina Armamaneto-Villareal.

The team looked at 156 post-menopausal women, whose average age was 63.5 years, and found that one version of the CYP1A1 gene was found in women with much lower blood oestrogen levels than normal. The women with this variant - about 19 per cent of the participants - also had much lower bone density in the upper femur, near the hip joint. 'Our study suggests that this genetic variation specifically affects the hip bones', said Armamaneto-Villareal, adding 'low density in the hip can lead to hip fractures, which can be devastating'. The team now plan to look at younger women, to see if the variant affects their bone density from birth.

Several other genes are thought to be involved in triggering osteoporosis. In 2003, Icelandic firm deCODE Genetics published a study which suggested that certain variations in a gene called BMP2 could triple the risk of the disease. The company has since launched a commercial genetic test to identify women at risk of osteoporosis.