Mechanisms of non-disjunction in human female meiosis: the co-existence of two modes of malsegregation evidenced by the karyotyping of 1397 in-vitro unfertilized oocytes.
BACKGROUND
Although numerous studies have been published on the chromosomal constitution of in-vitro unfertilized human oocytes, data remain highly variable and controversial because of the size of oocyte samples, technical reservations and potential misinterpretation.


METHODS
A cytogenetic study was undertaken on 3042 unfertilized human oocytes recovered from 792 women participating in an IVF programme for various infertility problems. Both a gradual fixation technique and an R-banding procedure were used.


RESULTS
The analysis was successful in 1397 oocytes (45.9%) for which interpretable metaphases were obtained. Of the 1397 oocyte karyotypes, 1088 (77.9%) were normal (23,X). The overall frequency of chromosomal abnormality was 22.1%. No correlation was found between the rate of abnormalities and the type of infertility. Aneuploidy was observed in 151 cells (10.8%), consisting of 5.4% hypohaploidies, 4.1% hyperhaploidies, 0.8% complex aneuploidies and 0.05% extreme aneuploidies with less than 18 chromosomes. Both whole chromosome non-disjunction and chromatid predivision contributed to the formation of aneuploid oocytes, but the numerical abnormalities due to single chromatids significantly exceeded conventional non-disjunctions. Abnormalities also included 5.4% diploid oocytes, 3.8% sets of chromatids alone and 2.1% structural aberrations. Aneuploidy was found in all chromosome groups. However, groups E and G exhibited significantly higher frequencies of non-disjunction than expected, whereas groups A and B showed a significantly low incidence of aneuploidy.


CONCLUSIONS
The implication of both chromosome and chromatid abnormalities in the occurrence of non-disjunction are discussed in relation to the recent data on chromatid cohesion throughout cell division. The results were consistent with the hypothesis of an unequal occurrence of non-disjunction among the chromosome groups in female meiosis.
Pellestor
Franck
F
CNRS-UPR 1142, F-34396 Montpellier and IVF Laboratory, C.H.U. Arnaud de Villeneuve, F-34033 Montpellier, France.
Andréo
Brigitte
B
Arnal
Françioise
F
Humeau
Claude
C
Demaille
Jacques
J
D000328:Adult; D000782:Aneuploidy; D002842:Chromatids; D002869:Chromosome Aberrations; D020090:Chromosome Segregation; D020732:Cytogenetic Analysis; D004171:Diploidy; D005260:Female; D006238:Haploidy; D006801:Humans; D007247:Infertility, Female / Q000235:genetics / Q000503:physiopathology; D007621:Karyotyping; D008540:Meiosis / Q000502:physiology*; D008677:Metaphase; D008875:Middle Aged; D009865:Oocytes / Q000502:physiology*