"If DNA doesn’t add up, array CGH steps in"
DNA Samples (PDF document 1,431 K)
What does array CGH look like to a practicing medical geneticist?
"From a clinical geneticist’s perspective, microarray analysis allows
us to identify children with subtle chromosomal abnormalities that are
not detected by available standard techniques—karyotyping or FISH
analysis," says Mira Irons, MD, FACMG, interim chief in the Division
of Genetics at Children’s Hospital, Boston, who sends occasional samples
for array CGH. Among patients seen by a clinical geneticist, approximately
40 percent to 50 percent don’t have a diagnosis. No chromosomal abnormality
or metabolic condition can be identified and no syndrome can be diagnosed
based on how the child looks. In these patients, Dr. Irons says, array
CGH provides an additional tool. She estimates that it can identify an
underlying chromosomal abnormality in a few percent of kids being sent
to a geneticist for evaluation.
"In my own personal practice, having microarray analysis has allowed
me to diagnose a few kids that I have been following with mental retardation
of unknown etiology or multiple congenital anomalies of unknown etiology
or growth retardation," Dr. Irons says.
She suggests that, as array CGH covers larger sections of the genome,
it may replace standard karyotyping. "Clearly it is not there yet,"
she says. "Doing initial karyotyping is still a geneticist’s first-line
test. Depending on the clinical presentation, I might then go to FISH
As for cost, she considers array CGH to be like any other expensive test.
"You have to weigh the cost of doing the test against the chance
of getting a diagnosis and its benefits," she says. The cost of array
CGH must also be balanced against the cost of doing many FISH probes or
many metabolic tests. "There is no cookbook approach to evaluating
children with mental retardation or congenital anomalies or growth problems,"
Dr. Irons says. "You have to determine the best testing path for
William Check, PhD