Prenatal findings and molecular cytogenetic analyses of partial trisomy 12q (12q24.32-->qter) and partial monosomy 21q (21q22.2-->qter).
OBJECTIVE
To present the prenatal findings and molecular cytogenetic analyses of partial trisomy 12q and partial monosomy 21q, and a review of the literature.


METHODS
Amniocentesis was performed at 23 gestational weeks in a 33-year-old woman because of abnormal sonographic findings. Amniocentesis revealed a derivative chromosome 21, or der(21), with a deletion on the region of 21q22.2 and an addendum of a small chromosomal segment of unknown origin. The maternal karyotype was subsequently found to be 46,XX,t(12;21)(q24.32;q22.2). Level II ultrasound showed microcephaly, micrognathia, a ventricular septal defect, and rocker-bottom feet. The pregnancy was terminated. A malformed infant was delivered without the phenotype of holoprosencephaly (HPE). Fluorescence in situ hybridization (FISH) and polymorphic DNA markers were used to investigate the involved chromosomal segments.


RESULTS
FISH study showed the absence of the signal of 21q subtelomeric probe and the presence of the signal of 12q subtelomeric probe in the der(21). The fetal karyotype was 46,XY,der(21) t(12;21)(q24.32;q22.2)mat. Genetic marker analysis showed a deletion at 21q22.2 and a breakpoint between D21S156 (present) and D21S1245 (absent). The deleted segment was measured about 4.5 Mb encompassing the HPE critical region.


CONCLUSIONS
Molecular genetic analyses help in determining the prenatally detected unbalanced cryptic translocation as well as parental balanced subtle translocation. A duplication of 12q24.32-->qter and a deletion of 21q22.2-->qter may be associated with prenatal sonographic findings of microcephaly, borderline ventriculomegaly and cerebellar hypoplasia, micrognathia, a ventricular septal defect, and rocker-bottom feet. Haploinsufficiency of the HPE critical region at 21q22.3 may not cause an HPE phenotype.
Chen
Chih-Ping
CP
Department of Obstetrics and Gynecology, Mackay Memorial Hospital, Taipei, Taiwan. cpc_mmh@yahoo.com
Chern
Schu-Rern
SR
Lin
Chyi-Chyang
CC
Wang
Tzu-Hao
TH
Li
Yueh-Chun
YC
Hsieh
Lie-Jiau
LJ
Lee
Chen-Chi
CC
Hua
Hui-Min
HM
Wang
Wayseen
W
D000328:Adult; D002872:Chromosome Deletion; D002881:Chromosomes, Human, Pair 12 / Q000235:genetics*; D002891:Chromosomes, Human, Pair 21 / Q000235:genetics*; D020732:Cytogenetic Analysis; D005260:Female; D017353:Gene Deletion; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D011247:Pregnancy; D011296:Prenatal Diagnosis; D014314:Trisomy / Q000175:diagnosis*