Prenatal diagnosis of mosaic trisomy 20 in New Zealand.
OBJECTIVE
Mosaic trisomy 20 is not an uncommon finding on amniocentesis or CVS. Unlike other mosaic aneuploidies it is a relatively benign abnormality which, along with a lack of long-term follow-up of cases, has led to uncertainty when counselling parents. We aimed to identify known mosaic trisomy 20 pregnancies in New Zealand in the last 10 years and document their outcome.


METHODS
Retrospective database review with prospective clinical follow-up.


METHODS
Cases were identified from the databases of the two clinical genetic services, as well as the four regional cytogenetics laboratories. Medical records were reviewed and where patients were available they were offered follow-up.


RESULTS
Fourteen cases were identified (13 on amniocentesis, one on CVS), all with low levels of mosaicism (8-50%). In 12 cases, the children were physically and developmentally normal, with the longest follow-up being 10 years. Minor anomalies were noted in two cases. There were no major malformations noted in any of the cases and where repeat karyotypes were performed on blood or urine cytology these were normal.


CONCLUSIONS
This series confirms a much lower incidence of phenotypic abnormalities associated with mosaic trisomy 20 compared to other forms of mosaic aneuploidy. Attempts to predict which of these pregnancies will have poor outcomes have not proven to be reliable. We recommend that, if a detailed anatomy scan is normal, parents be counselled that the risk of abnormality is less than 10%. Further tests should be performed only on the basis of a clinical indication.
James
Paul A
PA
Northern Regional Genetic Service, Auckland Hospital, Auckland, New Zealand.
Gibson
Kate
K
McGaughran
Julie
J
D000328:Adult; D000649:Amniocentesis; D015193:Chorionic Villi Sampling; D002890:Chromosomes, Human, Pair 20 / Q000235:genetics*; D005260:Female; D005315:Fetal Diseases / Q000175:diagnosis* / Q000453:epidemiology; D006801:Humans; D009030:Mosaicism / Q000175:diagnosis / Q000235:genetics; D009520:New Zealand; D017063:Outcome Assessment, Health Care; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D012189:Retrospective Studies; D014314:Trisomy / Q000175:diagnosis*