Katrina Smith Trainee Genetic Technologist Merseyside and Cheshire Regional Molecular Genetics Laboratory

Introduction  CVS received for rapid aneuploidy analysis.  Reason for referral: Exomphalus.  DNA extracted using Qiagen EZ1 robot.  CVS analysed by QF-PCR.

Molecular Genetics

Cytogenetics  Full karyotype.  Poor sample: -Bloody. -Small amount of tissue.  Cultures grown up and 2 cell lines identified.  No normal cell lines identified. 46,XX,del(18)(p11.2)[15]/46,XX,i(18)(q10)[5]

Full Karyotype: Monosomy 18p Del(18)(p11.2) Normal

Full Karyotype: isochromosome i(18)(q10) Normal

A Second Look  Looked back at QF-PCR results.  Identified an extra peak on marker D18S391.  D18S391 only marker on p arm of chromosome 18.  QF-PCR performed with chromosome 18 mulitplex on original CVS DNA.  Multiplex contains an extra p arm marker and 2 extra q arm markers.

A Second Look

Amniocentesis  Molecular received a direct prep of the amnio and DNA extracted using Instagene method.  QF-PCR using chromosome 18 multiplex.  All q arm markers diallelic: No trisomy  Extra peak on D18S391 disappears.  Both p arm markers single peaks.

QF-PCR of Amnio

Amniocentesis  Full karyotype.  2 independent cultures analysed. 46,XX,del(18)(p11.2)dn  Monosomy 18p - and no evidence of isochromosome previously seen.  Results consistent with QF-PCR.

Amnio Full Karyotype Del(18)(p11.2) Normal

Conclusion Final molecular report:  Original CVS sample was consistent with the presence of confined placental mosaicism; normal cell line being present in the placenta and a monosomy 18p cell line being present in the fetus.  In summary, the result of all molecular genetic analyses are consistent with the presence of a deletion of at least part of the short arm of one of the chromosome 18’s (monosomy 18p) in the fetus.

Monosomy 18p.  Deletion of the short arm of chromosome 18.  There is a wide range of clinical features which can vary in severity.  Clinical features include: Mental retardation Speech delay Short statue Holoprosencephaly Ptosis Behavioural disorders Dystonia

Confirmation  Pregnancy terminated.  Cord stump and placental tissue received.

Lessons Learnt  This case highlighted the fact that the QF-PCR multiplex only contained 1 marker on the chromosome 18 p arm.  This was also the case for the chromosome 21 multiplex.  This is now highlighted on the analysis spreadsheet so that any possible future cases may be investigated sooner.  It also highlights the importance cell culture artefacts can have on chromosome analysis.  This case was a good example of molecular and cytogenetics working closely together.

Acknowledgments Special thanks to: Emma McCarthy Victoria Stinton Tracy Horsedal Many thanks for everyone from the Merseyside and Cheshire Regional Molecular Genetics Laboratory.