PALM SPRINGS, CALIF. -- Routine DNA-based screening of newborns is not far off, and it will probably be used initially to detect three conditions: cystic fibrosis, congenital adrenal hyperplasia, and deafness.
That was the prediction of Dr. Edward R. McCabe, who serves as chairman of the Advisory Committee on Genetic Testing of the Secretary of Health and Human Services.
DNA technology is evolving rapidly, Dr. McCabe noted at a meeting that was sponsored by the American College of Medical Genetics.
In a short time, he predicted, physicians will have the ability to test for many conditions concurrently and to receive the results in less than an hour.
Some cystic fibrosis screening programs already use a DNA test as a second-tier test for confirmation when an immunoreactive trypsin assay is positive. Other cystic fibrosis screening programs also are moving in that direction, he said.
The advantage of using the two tests together is that it allows the lab to lower the threshold of the trypsinogen test without having to worry about false positives. Therefore, more patients can be picked up, said Dr. McCabe, who is physician-in-chief at Mattel Children's Hospital, University of California, Los Angeles.
DNA testing in congenital adrenal hyperplasia permits a better assessment of prognosis than measurement of 17-hydroxyprogesterone alone, he said.
There are very few mutations that cause congenital adrenal hyperplasia, and each one appears to be specifically associated with a mild or severe phenotype. DNA analysis therefore allows early identification of those patients who are at risk for an adrenal crisis that could be prevented with glucocorticoid replacement, Dr. McCabe explained.
In cases of congenital adrenal hyperplasia in which the child is born with ambiguous genitalia, the DNA test can make sure that the proper sex assignment is given to the child, he said.
DNA testing for mutations that are associated with connexin 26 deafness would help identify a high-risk group of infants among those whose initial hearing evaluation indicates a problem, Dr. McCabe said.
Connexin 26 deafness may account for 40% of all childhood deafness, and 60% of those with the connexin 26 phenotype will have severe to profound deafness, he noted.
Identification of these children will allow for early language intervention, which has been demonstrated to be crucial for the proper development of language faculties, Dr. McCabe said.
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