New Method For Genetic Screening in ASDs

Researchers from the Seaver and NY Autism Center of Excellence at New York’s Mount Sinai School of Medicine have developed a new method to detect copy number variants associated with autism spectrum disorders and have also found new chromosomal duplications that can be linked to autism.The study is published in the October 16th BMC Medical Genomics.

279 child with ASDs were screened for micro-duplications and -deletions in regions of the genome that have been connected to other cognitive conditions. The researchers detected several previously known duplications associated with autism, but also some that had not previously been recognized. The approach that psychiatry researcher Joseph Buxbaum and his colleagues used is multiplex ligation-dependent probe amplification, or MLPA which, it’s underlined, is an inexpensive and “efficient method to screen or chromosomal abnormalities,” whether these are large or small duplications.

Here’s a summary of the study from Genome Web:

The researchers screened 279 unrelated children with ASD using four different MLPA panels targeted parts of the genome previously linked to cognitive impairment. The subjects, who were around 8 years old, were not pre-selected based on dysmorphism or cognitive defects, Buxbaum said.

After weeding out copy number variants that were found in healthy controls and validating micro-deletions or -duplications using fluorescence in situ hybridization, quantitative PCR, or direct sequencing, the researchers found that about one to two percent of those with ASD also had a chromosomal abnormality associated with cognitive impairment.

For instance, they found subjects with duplications in a chromosome 15 region known to be involved in Prader-Willi/Angelman syndrome, a region of chromosome 22 that’s linked to DiGeorge syndrome, and a region of the X-chromosome that’s associated with X-linked non-specific mental retardation. The team also detected subjects with a partial duplication in the ASMT gene, which is found in the pseudoautosomal region 1 of sex chromosomes and has been previously linked to ASD.

Although the approach is quick and easy, Buxbaum cautioned, MLPA can’t be used to find new, unknown mutations — a situation that may occur in autism. That means it could miss private mutations that could be caught using array CGH with a dense chip.

In contrast, array CGH is “very expensive and time consuming.”

Buxbaum notes that these findings are mostly significant for an etiological understanding of autism and to starting a child on therapy as soon as possible:

………he emphasized, it would be unrealistic and undesirable to think of applying this sort of test in a prenatal setting, particularly because the individual mutations associated with autism are often incredibly rare, often with a vast range of expressivity. In cases where there is a family-member with a known genetic condition, Buxbaum noted, genetic testing for that specific condition can sometimes be desirable.

“Every time you say genetic testing, some people automatically think of pre-natal testing,” Buxbaum said. “This is more about giving an etiological diagnosis to children with autism.”

Multiplex ligation-dependent probe amplification for genetic screening in autism
spectrum disorders: Efficient identification of known microduplications and
identification of a novel microduplication in ASMT can be read as a PDF file.