Limitation of molecular karyotyping: Discordance between molecular vs. conventional cytogenetics

Shea Ming Lim, Toni Saville, Pauline Dalzell, Christopher Lucas, Joan Junio, Krystle Standen, Genevieve Temple, Louise Carey

1Molecular and Cytogenetics Unit, SEALS Pathology, Prince of Wales Hospital, Randwick

Introduction: Most laboratories are moving towards molecular based cytogenetics such as QF-PCR, CGH microarray, and MLPA as their first line of prenatal testing, therefore conventional cytogenetics is not routinely performed, and is often supplementary to molecular karyotyping.

Methods: We performed a retrospective audit of 648 fetoplacental referrals (322 prenatal chorionic villus samples and 326 product of conceptions) received in 2016 to identify cases in which cytogenetic discordance between molecular and conventional cytogenetic testing were reported. All prenatal CVS referrals received standard QF-PCR and CGH microarray testing, while the majority of POC referrals received QF-PCR and subtelomere MLPA testing. Conventional karyotype was only performed in a small number of these cases. The main indication for conventional karyotyping is to rule out Robertsonian translocation following a trisomy 13 or 21 result, or as a confirmatory test for any CNVs reported. POC referrals with 3 or more miscarriages also received a conventional karyotype in addition to a molecular karyotype.

Results: We identified 9 cases (9/648; 1.38%) where a discordance between molecular and conventional karyotype was observed.  The findings of these cases are presented in this study, with a discussion of the limitations of molecular testing over conventional cytogenetics.

Conclusion:  Conventional cytogenetics is still a useful tool in the diagnosis of prenatal cytogenetic abnormalities. However, consideration needs to be given to the resources available in each laboratory.



Graduated from Charles Sturt University, Wagga Wagga, Australia with Bachelor of Medical and Applied Biotechnology in 2007 and Bachelor of Medical Science (Pathology) in 2008. Started working for SEALS Pathology, Prince of Wales Hospital in 2009 and has been in the Molecular and Cytogenetics Unit since 2011.

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