WASHINGTON (Reuters) - A rare genetic mutation may help explain why some people get hit with a triple whammy of high blood pressure, cholesterol and a tendency to gain weight easily, U.S. researchers reported on Friday.

The mutation is seen in one gene found in mitochondrial DNA - handed down virtually unchanged from mother to child. Mitochondrial DNA affects basic cell functions and while the mutation itself is rare, it may help explain so-called metabolic syndrome or syndrome X, in which people are prone to diabetes, heart disease and obesity.

"This finding raises the possibility that all features of the metabolic syndrome may be attributable to altered mitochondrial function," said Dr. Richard Lifton, a geneticist at Connecticut's Yale medical school who led the study.

This in turn could help explain why people are more prone to heart disease as they age -- because mitochondria work less efficiently as people get older, Lifton and colleagues wrote in Friday's issue of the journal Science.

Lifton and colleagues studied 142 people in four generations of a family whose members frequently had high blood pressure, cholesterol and another, less well-known disorder in which their blood carried low levels of magnesium.

It was this rare disorder that first put them onto the case, said Lifton, whose work is funded by the Howard Hughes Medical Institute. Colleagues at the State University of New York treated a woman with a rare condition causing her to have low magnesium levels.

"She said, 'Gosh I think several of my other family members have the same problem'," Lifton said in a telephone interview.

"That led us to suspect that this might be a new disease."

The family also tended to have high blood pressure and cholesterol.

"That's when the real saga began," said Lifton. "The family was extraordinarily cooperative, and we eventually studied 142 relatives. When we looked at the pattern of these pathologies, we found there was a whopping excess of affected individuals on the maternal lineage."

That points to mitochondrial DNA.

Genetic tests showed that everyone in the family had a certain mutation in the mitochondria, although they did not all have high cholesterol, for instance, or high blood pressure. The mutation affected each family member differently.

Lifton said many studies have shown that people prone to high cholesterol often have high blood pressure too, or other symptoms such as diabetes or even low magnesium.

"Not everybody who has any one of these traits has all of the others. The pattern of inheritance is complicated, and there hasn't been a clear understanding of what's driving this relationship."

Now it will be worth studying mitochondrial DNA to see just what its role is in heart disease - the no. 1 killer in the United States and much of the developed world - and diabetes - the sixth leading cause of death.

Clearly, other genes will play a role, Lifton said. Genes found in the nucleus regulate mitochondrial DNA and as with everything in human biology, its gets complicated quickly.

What the finding does not provide is a quick answer. The woman's family members are treated for symptoms such as high blood pressure or cholesterol but there is no cure for their overall condition.

Lifton said the finding provides no easy out for people with metabolic syndrome, either. All the symptoms can be helped with regular exercise, a diet rich in whole grains, fruits and vegetables and reduced fat.

SOURCE: Science, October 22, 2004.

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