Identification of minor chromosomal defects causing abnormal foetus and spontaneous abortions

Chromosomal abnormalities are the most common cause of recurrent abortions and miscarriages (RAM), but micro-variations on chromosomes causing RAM have never been previously studied. Single nucleotide polymorphisms (SNPs) are the single nucleotide variations frequently present at genome with the density of at least one common (>20% allele frequency) SNP per kilobase pair. It has already been reported that SNP array examination for chromosomal abnormalities has better performance than the conventional cytogenetic karyotyping.

We applied SNP array to detect the chromosomal defects in 80 placental villi and foetal tissues of abnormal foetus and spontaneous abortions.

The analyses of data revealed that total 52.5% (42/80) cases were found to have chromosomal abnormalities. The trisomies were most commonly found 26/42 (61.9%) in current samples. Total 8/42 (19.1%) cases were found to have other structural aberrations including translocations in 2/8 (25%), duplications and deletions in 3/8 (37.5%) cases, respectively. SNP analysis also successfully detected triploidy 69,XXX and tetraploidy 92,XXXY. Total 12/80 cases were performed by cytogenetic karyotyping and results were compared with SNP data. Total 5/12 (41.7%) cases were found to have same findings with SNP data while results of 2/12 (16.7%) cases had partial similarity between both techniques. Four cases were declared as karyotypically normal (46,XY or 46,XX) by cytogenetic examination, but later on these four cases were found to have small chromosomal variation which could be the cause of RAM in women.

Therefore, we conclude that use of a high-density SNP platform in diagnosis can give better understanding of molecular causes of pregnancy loss and foetal abnormalities.