Prenatal detection and characterization of a psu idic(8)(p23.3) which likely derived from nonallelic homologous recombination between two MYOM2-repeats

The embryo battle against adverse genomes: Are de novo terminal deletions the rescue of unfavorable zygotic imbalances?

De novo distal deletions are structural variants considered to be already present in the zygote. However, investigations especially in the prenatal setting have documented that they are often in mosaic with cell lines in which the same deleted chromosome shows different types of aberrations such as: 1) neutral copy variants with loss of heterozygosity that replace the deleted region with equivalent portions of the homologous chromosome and create distal uniparental disomy (UPD); 2) derivative chromosomes where the deleted one ends with the distal region of another chromosome or has the shape of a ring; 3) U-type mirror dicentric or inv-dup del rearrangements. Unstable dicentrics had already been entailed as causative of terminal deletions even when no trace of the reciprocal inv-dup del had been detected. To clarify the mechanism of origin of distal deletions, we examined PubMed using as keywords: complex/mosaic chromosomal deletions, distal UPD, U-type dicentrics, inv-dup del chromosomes, excluding the recurrent inv-dup del(8p)s which are known to originate by NAHR at the maternal meiosis. The literature has shown that U-type dicentrics leading to nearly complete trisomy and therefore incompatible with zygotic survival underlie many types of de novo unbalanced rearrangements, including terminal deletions. In the early embryo, the position of the postzygotic breaks of the dicentric, the different ways of acquiring telomeres by the broken portions and the selection of the most favorable cell lines in the different tissues determine the prevalence of one or the other rearrangement. Multiple lines with simple terminal deletions, inv-dup dels, unbalanced translocations and segmental UPDs can coexist in various mosaic combinations although it is rare to identify them all in the blood. Regarding the origin of the dicentric, among the 30 cases of non-recurrent inv-dup del with sufficient genotyping information, paternal origin was markedly prevalent with consistently identical polymorphisms within the duplication region, regardless of parental origin. The non-random parental origin made any postzygotic origin unlikely and suggested the occurrence of these dicentrics mainly in spermatogenesis. This study strengthens the evidence that non-recurrent de novo structural rearrangements are often secondary to the rescue of a zygotic genome incompatible with embryo survival.

Complication rates after chorionic villus sampling and midtrimester amniocentesis: A 7-year national registry study

PURPOSE

To assess the complication rates following chorionic villus sampling (CVS) and midtrimester amniocentesis in Taiwan.

METHODS

This is a national registry-based cohort study from Taiwan. We included all women with singleton pregnancies who received either CVS (n = 1409) or midtrimester amniocentesis (n = 250,566) during 2006-2012. We assessed preterm premature rupture of membranes (PPROM), intrauterine fetal demise (IUFD), infection and spontaneous abortion (SA) that occurred within fourteen days after the procedures. We also assessed the risks of preterm delivery and miscarriage before 24 gestational weeks after amniocentesis. These complications were collected from the Genetic Disease Database of the Ministry of Health and Welfare, Taiwan National Birth Certificate Registry, and the Taiwan National Health Insurance Database. Pearson χ² tests were used to compare the distributions between groups.

RESULTS

For patients who underwent midtrimester amniocentesis, the rates of PPROM, IUFD, infection and SA within fourteen days were 0.24%, 0.11%, 0.05%, and 0.05%, respectively. Women with a normal fetal karyotype had a preterm birth rate (<37 gestational weeks) of 9.38%. The miscarriage rate (<24 gestational weeks) was 0.68%, which was 0.22% higher than those who did not receive the invasive procedures (p < 0.0001). After CVS, the IUFD rate was 1.68%, and the SA rate within fourteen days was 0.77%.

CONCLUSION

The use of our large cohort demonstrated that the procedure-related complication rates were comparable to recent review or meta-analysis. This dataset might facilitate counselling in women who consider invasive genetic diagnostic procedures.