Trisomy 2 due to a 3:1 segregation in an abortion studied by QF-PCR and CGH

Double trisomy in spontaneous miscarriages: cytogenetic and molecular approach

BACKGROUND

Although single trisomy is the most common chromosomal abnormality observed within first trimester spontaneous abortions (SA) (>50%), double trisomy (DT) ranges from 0.21 to 2.8% in the literature. Since little is known about mechanisms underlying DT, we report the results of our experience with 517 SA, establishing parental origin and cell stage of non-disjunction when possible in DT cases, and making a revision of those previously reported.

METHODS

Cytogenetic analysis was performed in all aborted specimens. Quantitative fluorescent PCR (QF-PCR) and multiplex ligation-dependent probe amplification (MLPA) were performed in DT cases in order to assess parental origin and stage of error of aneuploidy in addition to its reliability in detecting aneuploidies.

RESULTS

Karyotyping was successful in 321 miscarriages; the rate of DT was 2.18%. Among the seven DT cases reported, three new combinations were found. Maternal origin was established for all DT SA analysed. Meiotic stage of error was presumed meiosis I (MI) for 48,XX+15+22 and 48,XX+8+21, meiosis II (MII) for 48,XXX+18, and MII and MI respectively for 48,XY+18+22. Molecular results agreed with cytogenetic results.

CONCLUSIONS

Similar maternal age-related mechanisms could be implicated in both single and double trisomy. Molecular techniques could be useful in diagnosing not only single but multiple aneuploidy and determining its origin. This will improve our knowledge about mechanisms underlying human aneuploidy, and enable appropriate genetic counselling.

Application of quantitative fluorescent PCR with short tandem repeat markers to the study of aneuploidies in spontaneous miscarriages

BACKGROUND

Aneuploidies involve approximately 80% of chromosomal anomalies found in spontaneous miscarriages. Since cytogenetic studies show high rates of failure, we have incorporated the quantitative fluorescent polymerase chain reaction (QF-PCR) technique to the study of numerical chromosome anomalies in miscarriages.

METHODS

Multiplex and simple QF-PCR assays have been performed on 160 miscarriage and 34 parental DNA samples analysing specific short tandem repeat (STR) markers for chromosomes 2, 7, 13, 15, 16, 18, 21, 22 and X. Cases successfully karyotyped were used as controls in our study.

RESULTS

While maternal contamination could be detected in such cases, a molecular result was obtained for 94% of miscarriages without a cytogenetic one. Thirty-six per cent of them were diagnosed with numerical chromosome anomalies. Parental origin of the extra chromosome and the error stage of meiosis could be also determined.

CONCLUSIONS

QF-PCR represents a useful and reliable tool to diagnose aneuploidies in spontaneous miscarriages. It provides information about parental and meiotic origin of anomaly, allowing an appropriate genetic counselling.