PARENT SESSION
SLIDE SESSION 5: REGULATION OF MEIOSIS
Chairs: Stephen Downs, Sue Varmuza, Michele Calder (Trainee)
Univ Ottawa-Monpetit 202
2:30 PM-4:30 PM

DIRECT TESTING FOR AGE-RELATED CHROMOSOMAL ERRORS IN HUMAN MEIOSIS.

Verlinsky, Yury¹, Cieslak, Jeanine, Kuliev, Anver, ¹

ABSTRACT- Although it is well established that most of age-related chromosomal abnormalities originate from female meiosis I, no direct evidence has been obtained to support this phenomenon. We introduced fluorescent in situ hybridization (FISH) analysis of the first (PB1) and second polar bodies (PB2), representing by-products of the first and second meiotic divisions, which may provide an apprroach for a direct testing of the errors in meiosis I and II. A total of 5590 oocytes were obtained in 917 IVF cycles from patients of advanced maternal age (38.6 years on the average). Following a standard IVF protocol, oocytes were tested by removing and FISH analysis of PB1 and PB2, with application of commercial probes specific for five chromosomes (chromosomes 13,16, 18, 21 and 22) (Vysis). Of 4596 oocytes studied, 2077 (45.2%) were aneuploid. 1449 (36%) of 4016 oocytes with PB1 results were with errors, comparable to 1143 (29.3%) of 3895 oocytes with PB2 results. The types of abnormalities in PB1 were the following: extra chromatids in 16.3%; missing chromatids in 51.3%; missing chromosomes in 8.2%; extra chromosomes in 0.7%; and complex abnormalities, involving different types of abnormalities, in 23.5%. The proportion of abnormal oocytes with missing or extra chromatids in PB2 was 39.1% and 44.1%, respectively. PB2 of the remaining oocytes had complex abnormalities, involving missing or extra chromatids of different chromosomes (16.8%). From the total of abnormal oocytes, 44.9% had meiosis I errors, 30.2% had meiosis II errors, and 24.9% had errors from both meiotic divisions. The same chromosome was involved in more than half of these oocytes, resulting in a balance status in 36.2%. As many as 48.4% of the oocytes with errors in both meiotic divisions contained abnormalities of different chromosomes. Overall, 39.8% of the abnormal oocytes had complex errors. The data show a high (45.2%) rate of chromosomal abnormalities observed by testing for five chromosomes most commonly involved in age-related aneuploidies. Aneuploidies were demonstrated to originate mainly from chromatid errors, deriving equally in meiosis I and II, and suggesting importance for the direct testing of the outcomes of the first and second meiotic divisions in pre-selection of euploid embryos for transfer in IVF patients of advanced maternal age.

KEY WORDS: Chromosomal Abnormalities, Human Meiosis I and II, Age-related Aneuploidies, First and Second Polar Bodies