Microarray analysis ‘best test for prenatal diagnosis’

Chromosomal microarray analysis is able to identify significantly more clinically relevant information for prenatal diagnosis than is karyotyping, and is equally able to highlight aneuploidies and unbalanced rearrangements, US study findings suggest.

Lead researcher Ronald Wapner, from Columbia University Medical Center, in New York, told the press: "Based on our findings, we believe that microarray will and should replace karyotyping as the standard for evaluating chromosomal abnormalities in fetuses. These chromosomal micro-deletions and duplications found with microarray are often associated with significant clinical problems."

He added: "We hope that in the future - when microarray can be done non-invasively - every woman who wishes will be offered microarray, so that she can have as complete information as possible about her pregnancy."

The researchers studied samples from 2275 women with a singleton gestation who underwent chorionic-villus sampling and 2131 who underwent amniocentesis at 29 prenatal diagnostic centers. Indications for prenatal diagnosis were advanced maternal age in 46.6% of cases, abnormal Down's syndrome screening result in 18.8%, structural anomalies on ultrasonography in 25.2%, and other indications in 9.4% of cases.

Microarray analysis of DNA was successful in 98.8% of cases, the team reports in the New England Journal of Medicine. Of the 4282 samples included in the primary analysis, 7.4% had common autosomal and 1.3% had sex-chromosome aneuploidies on standard karyotyping.

All of these were identified with microarray analysis. Eight of these cases were mosaic on the microarray and could represent mosaicisms not detected on karyotyping. In addition, microarray analysis identified all 22 unbalanced rearrangements, one as a mosaic.

As expected, none of the apparently balanced rearrangements identified on karyotyping were detected on microarray analysis. Two of the three marker chromosomes detected on karyotyping were detected on microarray. None of the 17 triploid samples were identified on microarray.

Clinically significant, segmental aneuploidies were revealed on microarray analysis that were not spotted with karyotyping. In all, 1399 samples were identified as having copy-number variants, of which 1234 were classified as common and benign and 35 were on the predetermined list of pathogenic variants. Of the remaining 94 copy-number variants, 61 were deemed to be clinically significant.

In cases with normal karyotypes, 6.0% had clinically relevant findings on microarray, including 1.7% of women tested due to advanced maternal age and 1.6% of those tested due to abnormal Down's syndrome screening test.

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