Hypertension News:

Study: Proximity to Equator Dictates Presence of Gene Mutation for Hypertension

University of Chicago researchers have found genetic evidence to support a controversial 30-year-old theory that the high rate of hypertension in certain ethnic groups is partly due to an inherited tendency to retain salt.

The theory is known as the sodium-retention hypothesis. As reported in the December issue of the American Journal of Human Genetics, the study found that the closer that people live to the equator, the more likely they are to have a normal version of a gene that produces a very effective protein against salt retention. Meanwhile, populations adapted to cooler climates tend to have a mutant gene that codes for a totally dysfunctional protein.

Study author Anna Di Rienzo, Ph.D., associate human genetics professor at the University of Chicago, said the original or normal version of the gene became less and less common and the broken version more frequent as populations moved away from the tropics.

According to the researchers, humans need salt to transport nutrients, transmit nerve impulses or contract muscles, such as the beating heart. The average adult contains about 250 grams of salt, enough to fill three small saltshakers. This salt is constantly lost through sweat and urine and replaced through the diet.

Di Rienzo's team looked at the genetics of salt processing, focusing on a gene called CYP3A5, which help the body break down and eliminate a wide range of compounds, including many drugs and salt. In the kidney, CYP3A5 acts to retain salt. One version of this gene, however, a mutation known as "CYP3A5 *3," produces a truncated, non-functional protein.

The researchers looked at variations of this gene in 1,064 individuals drawn from 52 populations scattered around the world. The mutation was least common in some natives of sub-Saharan Africa, close to the equator, ranging from a low of only six percent of Yorubans in Nigeria to 31 percent among the Mandenka of Senegal.

Rates were higher among populations in East Asia, farther away from the equator, ranging from 55 percent among the Dai of China to 75 percent among Han Chinese to 77 percent among Japanese and 95 percent among the Uygur of China.

Rates in areas of Europe, relatively distant from the equator, were uniformly high, ranging from 80 to 95 percent in Italy, France and Russia. The highest rate, 96 percent, was found among the Basque, an isolated ethnic group of uncertain origins now concentrated in the Pyrenees mountains.

Source: Medical Week staff, week of November 6, 2004