United Press International

WASHINGTON, Feb. 22 (UPI) -- Pennsylvania and New York researchers believe they have found a defective gene responsible for DiGeorge syndrome, a "blue baby" disorder that is the second leading cause of heart disease in children.

The investigators, based at the University of Pennsylvania Medical Center, Philadelphia, and the Albert Einstein College of Medicine, New York, say the discovery paves the way for better prenatal testing and treatment of newborns with the condition.

DiGeorge syndrome, which kills one in every 40,000 infants born in the United States, is a major cause of what are commonly called "blue" babies -- those infants whose lungs are so severely compressed that they slowly suffocate if they do not receive immediate medical attention.

As the journal Cell will publish Friday, Pennsylvania cardiologist Jonathan Epstein and co-authors report that an abnormality in a gene called Tbx1 causes the disease.

Tbx1 normally functions in developing blood vessels around the heart. Without two working copies of the gene, blood vessels surrounding the heart usually do not develop correctly. The condition usually requires heart surgery at birth or at a very young age.

"Up until now we have only known that the syndrome can be caused by the loss of a small portion of a particular chromosome, the so-called DiGeorge region. Now we think that we have identified the critical gene in that region," Dr. Epstein told United Press International.

The chromosome, number 22, was recently deciphered by the Human Genome Project, he explained. The portion missing in DiGeorge syndrome contains 24 genes.

The blue-baby defects manifest themselves in a number of ways, said Epstein, but usually in connections between blood vessels. Other possible effects include seizures, facial abnormalities, and the absence of thymus and parathyroid glands.

The condition is not life-threatening to the fetus, which is nourished by the mother's blood. It becomes critical at birth, and often causes a vascular ring around the newborn's trachea. This collar of swollen, oxygen-starved tissue can choke off an infant's blood supply, one cause of what is commonly called a "blue" baby.

One of the more interesting features of the study is that the researchers worked backwards. Rather than knocking out similar genes in laboratory mice until they found the defect that caused a similar disorder, they targeted the mouse gene that most closely matched the human counterpart revealed by the Human Genome Project, said Epstein.

According to Clayton Buck, professor and acting CEO of the Philadelphia' Wistar Institute, the study and others slated to appear in early March "demonstrate a phenomenal collaboration" between researchers from different countries and disciplines working together to solve the genetic basis of a life-threatening disease.