Stable dicentric duplication-deficiency chromosome 14 resulting from crossing-over within a maternal paracentric inversion

Chromosomal Aberrations in 224 Couples with Recurrent Pregnancy Loss

Background

Recurrent pregnancy loss (RPL) is a major reproductive health issue, affecting 2%-5% of couples. Genetic factors, mainly chromosomal abnormalities, are the most common cause of early miscarriage accounting for 50%-60% of first trimester abortion.

Aim

To estimate the prevalence and nature of chromosomal anomalies in couples with recurrent miscarriage.

Patients and Methods

This study included 224 couples with a history of 2 or more abortions. Both partners were karyotyped as part of the primary investigation. Cytogenetic analysis was carried out using the standard method.

Results

A total of 224 couples with a history of two or more recurrent abortions were enrolled in this study. Chromosomal abnormalities were detected in 26 couples (11.6%) and 28 individuals (6.25%). We found a structural chromosome abnormality in 17/28 patients (60.7%); 12 patients had a reciprocal translocation (42.9%) including one patient with an additional inversion of the Y chromosome, 4 (14.3%) had a Robertsonian translocation, and one patient (3.6%) carried a paracentric inversion of chromosome 2. Numerical chromosome aberrations were detected in 5 patients; three patients (10.7%) with sex chromosome abnormalities and two (7.1%) with a marker chromosome. Six patients (21.4%) showed a heteromorphic variant involving chromosome 9.

Conclusion

The prevalence of chromosomal abnormalities in couples with RPL is within the range reported worldwide. Cytogenetic analysis should become an integral part of the investigations of couples with at least two pregnancy losses of undetermined etiology.

Breakpoint mapping and complete analysis of meiotic segregation patterns in three men heterozygous for paracentric inversions

Paracentric inversions (PAIs) are structural chromosomal rearrangements generally considered to be harmless. To date, only a few studies have been performed concerning the meiotic segregation of these rearrangements, using either the human-hamster fertilization system or fluorescence in situ hybridization (FISH) with centromeric or telomeric DNA probes. To improve the assessment of imbalances in PAI, we present a new strategy based on FISH assay using multiple bacterial artificial chromosome probes, which allow a precise localization of chromosome break points and the identification of all meiotic products in human sperm. Sperm samples of three cases with PAI were investigated: an inv(5)(q13.2q33.1), an inv(9)(q21.2q34.13) and an inv(14)(q23.2q32.13). The frequencies of spermatozoa with inverted chromosomes were 44.7% in inv(5), 42.7% in inv(9) and 46.7% in inv(14). The global incidences of unbalanced complements were 9.7, 12.6 and 3.7% in inv(5), inv(9) and inv(14), respectively. This report is the first study providing a detailed description of meiotic segregation patterns in human sperm by using a sperm FISH approach. This study demonstrates that the detailed analysis of segregation in PAI may provide important data for both genetic analysis and counseling of inversion carriers.

Suppressed recombination on mouse chromosome 15 defined regions of chromosomal inversions associated with koala (koa) and hairy ears (eh) mutations

Koala (Koa) and hairy ears (Eh) mutations of mice are associated with chromosomal inversions in the distal half of chromosome 15. Since these two mutant mice show some common phenotypic features including extra hair on pinna and craniofacial dysmorphogenesis and have similar inverted regions, we determined the inverted regions of these two chromosomal inversions to examine whether a common gene is responsible for the phenotypes of these two mutants. The inverted regions were identified as the recombination-suppressed regions by linkage analysis. The length of the recombination-suppressed regions of Koa and Eh were approximately 52 and 47 Mb, respectively, and these inverted regions were not the same. These results indicate that the phenotypes of Koa and Eh mutant mice are likely to be caused by different genes.

Sperm studies in heterozygote inversion carriers: a review

The risk of producing unbalanced gametes in heterozygous inversion carriers mostly depends on the occurrence of recombination events within the inverted segment. Recombination determines the possibility of producing chromosomes with duplications/deficiencies (pericentric inversions) or with duplications/deficiencies which furthermore appear as dicentric and acentric fragments (paracentric inversions). In this work, a general description of the close relationship between the occurrence of crossovers in pericentric and paracentric inversions and the final segregation outcome is presented. After this introduction, a compilation of inversion segregation data and interchromosomal effect results from previously published sperm studies have been reviewed. Segregation results indicate a great heterogeneity in the percentage of unbalanced gametes, from 0 to 37.38%. The size of the inverted segments and their proportion in the chromosome are two parameters closely related with the incidence of recombination (P < 0.0001; using a quadratic model and Pearson's correlation test). These results suggest that the production of a significant level of unbalanced gametes would require a minimum inversion size of 100 Mbp and the inversion of at least 50% of the chromosome. Interchromosomal effects are seldom observed in chromosomal inversions. Finally, implications of the meiotic behavior of the inversions in the progeny of the carriers and the incorporation of sperm FISH segregation analysis for reproductive genetic counseling are discussed.