THE US Food and Drug Administration has cleared a first-of-a-kind blood test that can help diagnose mental disabilities in babies by analysing their genetic code.
The laboratory test from Affymetrix detects variations in patients' chromosomes that are linked to Down syndrome, DiGeorge syndrome and other developmental disorders. About 2 to 3 per cent of US children have some sort of intellectual disability, according to the National Institutes of Health.
The test, known as the CytoScan Dx Assay, is designed to help doctors diagnose children's disabilities earlier and get them appropriate care and support. It is not intended for prenatal screening or for predicting other genetically acquired diseases and conditions, such as cancer.
While there are already genetic tests used to detect conditions like Down syndrome, doctors usually have to order them individually and they can take several days to develop.
Pediatricians said that Affymetrix's test should offer a faster, more comprehensive screening approach. Dr Annemarie Stroustrup stressed that such tests are generally only used after children exhibit certain physical or behavioural signs that suggest a disorder.
"When there's something about the child that strikes us as unusual or pointing to a potential genetic disease, that's when we would use this testing," said Stroustrup, an assistant professor of pediatrics at Mount Sinai Hospital in New York.
"This is not a screening test to be done on all newborns to predict how they are going to do in school when they are 5."
The technology behind Affymetrix's test has already been used for several years to screen fetuses for potentially debilitating diseases. Known as microarray analysis, the technique involves a high-powered computer scanning a gene chip of the patient's DNA for slight chromosome imbalances. Older techniques involve scientists looking at chromosomes under a microscope for major irregularities.
The FDA said it approved the new test based on studies showing it accurately analyses a patient's entire genome and can accurately spot variations associated with intellectual disabilities.
Hospitals in all 50 states are now required to screen newborns for at least 29 disorders that can be detected though laboratory testing, including sickle cell anaemia and cystic fibrosis. Generally those tests pick up irregularities in metabolism, not genetic variations.
The mandatory screening program, begun a half-century ago, is considered one of the nation's most successful public health programs.
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