Âge maternel et anomalies chromosomiques dans les ovocytes humains

Tetrasomy 9p, a Prenatal Challenge: Two Novel Cases

Tetrasomy 9p is a chromosomal disorder characterized by the presence of a supernumerary chromosome. This rare abnormality exhibits a broad phenotypic variability and is not clearly distinguishable from other more frequent aneuploidies in the prenatal setting. We present two prenatal cases with dissimilar phenotypes, one with solely increased fetal nuchal translucency and one with multiple congenital anomalies, and discuss prior studies. These cases illustrate the difficulty of prenatally diagnosing this condition based on phenotypic information alone. We conclude that invasive prenatal diagnosis with (molecular) karyotyping is the best choice for the prenatal detection of tetrasomy 9p.

Molecular turnover, the H3.3 dilemma and organismal aging (hypothesis)

The H3.3 histone variant has been a subject of increasing interest in the field of chromatin studies due to its two distinguishing features. First, its incorporation into chromatin is replication independent unlike the replication-coupled deposition of its canonical counterparts H3.1/2. Second, H3.3 has been consistently associated with an active state of chromatin. In accordance, this histone variant should be expected to be causally involved in the regulation of gene expression, or more generally, its incorporation should have downstream consequences for the structure and function of chromatin. This, however, leads to an apparent paradox: In cells that slowly replicate in the organism, H3.3 will accumulate with time, opening the way to aberrant effects on heterochromatin. Here, we review the indications that H3.3 is expected both to be incorporated in the heterochromatin of slowly replicating cells and to retain its functional downstream effects. Implications for organismal aging are discussed.

Follicular fluid protein content (FSH, LH, PG4, E2 and AMH) and polar body aneuploidy

PURPOSE

Our objective was to identify a marker for oocyte aneuploidy in follicular fluid (FF) in women with an increased risk of oocyte aneuploidy after controlled ovarian hyperstimulation.

MATERIALS AND METHODS

Three groups of oocytes were constituted for polar body screening by FISH (chromosomes 13, 16, 18, 21 and 22): Group 1, advanced maternal age (n = 156); Group 2, implantation failure (i.e. no pregnancy after the transfer of more than 10 embryos; n = 101) and Group 3, implantation failure and advanced maternal age (n = 56). FSH and other proteins were assayed in the corresponding FF samples.

RESULTS

Of the 313 oocytes assessed, 35.78 % were abnormal. We found a significant difference between the follicular FSH levels in normal oocytes and abnormal oocytes (4.85 ± 1.75 IU/L vs. 5.41 ± 2.47 IU/L, respectively; p = 0.021). We found that the greater the number of chromosomal abnormalities per oocyte (between 0 and 3), the higher the follicular FSH level.

CONCLUSION

High FF FSH levels were associated with oocyte aneuploidy in women having undergone controlled ovarian hyperstimulation.

Monozygotic twins discordant for trisomy 21 and maternal 21q inheritance: a complex series of events

We report on a monochorionic/diamniotic twin pregnancy discordant for trisomy 21. Amniocentesis (at 13(5/7) weeks) was performed following ultrasound signs of hydrops and cystic hygroma in twin 1 (T1). Prenatal karyotype showed non-mosaic trisomy 21 in T1 (47,XX,+21[7]), and low-grade mosaic trisomy 21 in twin 2 (T2) (47,XX,+21[2]/46,XX[19]). Post mortem examination of fetal skin, kidneys and lungs confirmed trisomy 21 in T1 (47,XX,+21[548]) and the placenta (47,XX,+21[200]). T2 had a normal karyotype (46,XX[648]). Analysis of microsatellite polymorphisms in multiple samples from the placenta, hand, lungs, kidneys and the umbilical cords of both twins confirmed monozygosity for all loci tested, and trisomy 21 in T1. Unexpectedly, T1 and T2 inherited different maternal alleles for markers of the most distal 4 Mbp of 21q. At least four successive events are needed to explain the genetic status of both twins and include maternal MI premature chromatids separation or maternal II meiotic nondisjunction and post-zygotic events such as, chromosome rescue, nondisjunction, an/or recombination.

Oxidative stress and tumor necrosis factor–α–induced alterations in metaphase II mouse oocyte spindle structure

OBJECTIVE(S)

To examine the effect of exogenous exposure to hydrogen peroxide (H(2)O(2)) and tumor necrosis factor (TNF)-alpha on mouse metaphase II (MII) oocyte spindle structure and to examine the potential benefits of supplementing the culture media with vitamin C.

DESIGN

Prospective study.

SETTING

Research laboratory in a tertiary hospital.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Microtubule changes and alterations in chromosomal alignment.

RESULT(S)

Both concentration- and time-dependent alterations were seen in spindle structure after exposure to H(2)O(2). An H(2)O(2) concentration as low as 12.5 microM increased the odds of an oocyte with altered microtubule and chromosome alignment (score >or=3) by 93%. Significantly increased damage was seen with increasing period of incubation. Higher scores were seen after exposure to both TNF-alpha alone and in combination with H(2)O(2) compared with controls. Changes in chromosomal alignment were comparable among the three groups. Oocytes coincubated with H(2)O(2) and vitamin C at 200 microM demonstrated less damage compared with those with H(2)O(2) alone.

CONCLUSION(S)

Oxidative stress results in concentration and time-dependent alterations in the spindle structure and augments the effects induced by TNF-alpha. Proper oocyte handling in vitro may help reduce oxidative insult, thus improving the oocyte quality. Antioxidants may have a protective effect and need to be further evaluated.