Dilemma of trisomy 20 mosaicism detected prenatally: Is it an innocent finding?

Orit Reish, Baruch Wolach, Aliza Amiel, Inbal Kedar, Tzipora Dolfin, Moshe Fejgin

Research output: Contribution to journalArticlepeer-review


The clinical significance of mosaicism trisomy 20 detected prenatally following amniocentesis remains uncertain, due to the rarity of liveborn cases with inconsistent clinical findings, the short postnatal follow-up, and failure in evaluating other fetal tissues for the presence of the trisomy. We report on a 15 month-old 46,XX chromosome constitution in white blood cells, while skin fibroblasts demonstrated trisomy 20 mosaicism (54%) by fluorescence in situ hybridization (FISH) analysis. Clinical examination of the baby showed only minor phenotypic signs (bilateral epicanthal folds, delayed closure of fontanel with no other gross anomalies), but demonstrated a considerable developmental delay in gross and fine motor skills along with hypotonicity. This is the second oldest described liveborn with trisomy 20 mosaicism confirmed in skin fibrobalsts. This cytogenetic aberration along with her developmental delay suggests that the two findings are related and that aberration affects various fetal tissues and is not confined to extra- embryonic tissue as suggested previously. Yet, an undiagnosed condition may be the cause of the child's developmental delay. Based on his case and following a review of the literature we suggest that when mosaic trisomy 20 is identified in amniocytes, further evaluation is required. Cord blood should be analyzed preferably by FISH. During counseling the parents should be advised of an additional risk, such as developmental delay, even when fetal cord karyo-type and detailed ultrasonic scan are normal.

Original languageEnglish
Pages (from-to)72-75
Number of pages4
JournalAmerican Journal of Medical Genetics
Issue number1
StatePublished - 28 Apr 1998


  • Mosaicism
  • Prenatal diagnosis
  • Trisomy chromosome 20


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