Public Release: 

March of Dimes awards $250,000 prize to pioneering scientist

Discovery of genetic control of X chromosome was one of the first great insights of the 20th century

March of Dimes Foundation

SAN FRANCISCO, MAY 3, 2004 - One of the 20th century's most influential female scientists, Mary F. Lyon, Ph.D., whose discovery of the process of X-chromosome inactivation unlocked a central mystery underlying many inherited birth defects and diseases, has been awarded the 2004 March of Dimes Prize in Developmental Biology.

"Dr. Lyon's recognition in 1961 of X-chromosome inactivation, which is still referred to as 'Lyonization,' was one of the first great insights into genetic control mechanisms of the 20th century," said Dr. Jennifer L. Howse, president of the March of Dimes. "This was the key to understanding the inheritance pattern of X-linked disorders such as hemophilia, Duchenne muscular dystrophy, fragile X syndrome, and certain types of cancer. As a result of Dr. Lyon's work, it became possible to provide accurate tests and genetic counseling for families affected by these disorders and to begin the research into potential treatments that continues today."

"In addition, Dr. Lyon's pioneering work became a model for the study of gene regulation and has had an enormous influence on the work of many other scientists for the past 40 years," Dr. Howse said.

The Prize is a cash award of $250,000 and a silver medal in the design of the Roosevelt dime, in honor of President Franklin Delano Roosevelt, who founded the March of Dimes.

The human genome consists of 23 pairs of chromosomes, the string-like structures in the nuclei of our cells that contain the genes. Twenty-two of these pairs are known as autosomes and are identical in males and females. Inheriting an excess number of an autosome can result in the death of an embryo or drastic health consequences.

The remaining pair of chromosomes, known as the sex chromosomes, are designated by the letters X and Y. Males have one X chromosome and one Y chromosome, while females have two X chromosomes.

More than 95 percent of the genes on the Y chromosome are "male-specific," that is, involved in determining maleness and fertility in an embryo. The X chromosome, on the other hand, contains many genes needed for growth and development by both males and females. These include genes that are necessary for normal blood clotting as well as genes for normal muscle and brain function.

Geneticists puzzled over the mysteries posed by the double female X chromosomes for many years. Why, they asked, do females thrive despite having a double dose of the genes located on the X chromosome? And why is it that most females who inherit an X chromosome with a mutated gene do not show signs of the disorder associated with that mutation?

For example, the bleeding disorder hemophilia is caused by mutations in clotting factor genes that are located on the X chromosome. The disease occurs in about 1 in 5,000 males -- but rarely occurs in females.

Dr. Lyon's groundbreaking hypothesis explained that, very early in embryonic development, females compensate for the double dose of X chromosomes by randomly switching off one of the X chromosomes in each cell. The inactivation of one X chromosome gives females only one working copy of the genes located on the X chromosome. Fortunately for females, this random inactivation means they usually will be left with enough healthy copies of the X chromosome in operation.

Dr. Lyon also suggested that the inactive X is reactivated in female egg cells and that, during the early cell division that follows conception, the process begins all over again in the next generation. X-inactivation has since been shown to be unique to mammals.

The study of X-inactivation continues to excite researchers today, with much attention focused on breaking down the many steps involved in the process.

The March of Dimes Prize in Developmental Biology has been awarded annually since 1996 to investigators whose research has profoundly advanced the science that underlies the understanding of birth defects. The March of Dimes created the Prize as a tribute to Dr. Jonas Salk shortly before his death in 1995.

The March of Dimes Prize will be awarded to Dr. Lyon at a black tie dinner and ceremony on May 3 at the Ritz-Carlton, San Francisco. Greg Gumbel, the lead play-by-play broadcaster for CBS Sports' coverage of the National Football League, and a member of the March of Dimes National Board of Trustees, will host the ceremony.


Dr. Lyon also will deliver the ninth annual March of Dimes Prize Lecture on May 3 during the 2004 Annual Meeting of the Pediatric Academic Societies.

The March of Dimes is a national voluntary health agency whose mission is to improve the health of babies by preventing birth defects and infant mortality. Founded in 1938, the March of Dimes funds programs of research, community services, education, and advocacy to save babies and in 2003 launched a five-year campaign to address the increasing rate of premature birth. For more information, visit the March of Dimes Web site at or its Spanish Web site at

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