Trisomy 20 mosaicism detected prenatally: A case report of phenotypically normal male liveborn
Mosaic trisomy through chorionic villus sampling is extraordinarily rare, but it is one of more common mosaic trisomies detected on amniocentesis. Its clinical significance remains uncertain due to rarity of live born cases with inconsistent clinical findings and short postnatal follow-up. There is a clear association between the percentage of trisomic cells detected on amniocentesis and outcome, with only 5% abnormal outcomes when <50% trisomic cells were detected. Trisomic cells are practically never confirmed in newborn blood with increasing risk for abnormal outcome in case of positive confirmation and only rarely are found in other fetal tissues samples.
We report a case of the phenotypicaly normal live born male after prenatal diagnosis of trisomy 20 mosaicism in amniocytes. This is second child in order, first child is healthy. Mother is 39 years old. Cytogenetic analysis of the amniotic fluid sample showed that mosaic tissues are consisted of two cells types, which are different in number of chromosomes: normal cells with 46 chromosomes and trisomic cells with 47 chromosomes. In trisomic cells there was a one more chromosome No 20. 31 cells of amniotic fluid were analyzed: 25 normal mitoses (46XY) and 6 trisomic mitoses (47XY) were detected. Parents were counseled that the risk of abnormalities is less than 10% and they decided to keep the pregnancy. A phenotypically normal male baby was born. He passed neonatal period, and for now, he is developing normally.
Cytogenetic analysis was performed postnatally on lymphocytes and trisomy 20 cells could not be confirmed after birth. The origin of trisomy 20 cells in amniotic fluid remained unclear.
Prenatally diagnosed trisomy 20 mosaicism required further evaluation and parental counseling. Although risk for congenital abnormalities in low level of trisomic cells is less than 10%, parents should be advised of an additional risk, such as developmental delay.
Literatur: 1.Wallerstein R, Yu MT, Neu RL, Benn P, Lee Bpwen C, Crandall B, Disteche C et al.: Common trisomy mosaicism diagnosed in amniocytes involving chromosomes 13, 16, 20 and 21 karyotype correlations. Prenat Diagn 2000; 20(2): 10-22 2.Hsu LY, Kaffe S, Perlis TE.: A revisit of trisomy 20 mosaicism in prenatal diagnosis-an overview of 103 cases. Prenat Diagn; 1991; 11 (1):7-15 3.Hsu LY, Kaffe S, Perlis TE.:Prenat Diagn 1987; 7(8):581-96 4.Aust NZJ.: Prenatal diagnosis of mosaic trsomy 20 in New Zealand. Obstet Gynecol 2002;42(5):485-9 5.Reish O, Wolach B, Amiel A, Kedar I, Dolfin T, Fejgin M.: Dilemma of trisomy 20 mosaicism detected prenatally: is it an innocent finding? Am J Med Genet. 1998;77(1):72-5 6.Micale MA, Wolff Dj, Dickerman LH, Redline R, Conroz JM, Schwartz S.: Cytogenetic and molecular genetic characterization of trisomz 20 mosaicism in fetal blood and tissues. Prenat Diagn 1996; 16(10): 893-7 7.Ensenauer RE, Shaughnessy WJ, Jalal SM, Dawson DB, Courteau LK, Ellison JW.: Trisomy 20 mosaicism caused by a maternal meiosis II error is associated with normal intellect but multiple congenital anomalies. Am J Med Genet A. 2005; 134(2):202-6 8.Tolmie JL, Ferguson-Smithj ME, Gilmore D, Ferguson Smith MA.: Normal development in two six year old bozs born after prenatal diagnosis of trisomy 20 mosaicism. Prenat Diagn 1987 (8):597-601 9.Steinberg Warren N, Soukup S, King JL, St J Dignan P.: Prenatal Diagnosis of trisomy 20 by chronic villus sampling (CVS): a case report with long-term outcome. Prenat Diagn 2001(13):1111-3
Trisomy 20 mosaicism - amniocentesis - outcome