Chen Chih-Ping, Chern Schu-Rern, Lee Chen-Chi, Chen Li-Feng, Chin Daniel T H, Tzen Chin-Yuan, Wang Wayseen
Department of Obstetrics and Gynecology, Mackay Memorial Hospital, Taipei, Taiwan, Republic of China.
Prenat Diagn. 2003 Sep;23(9):758-61. doi: 10.1002/pd.684.
To present the perinatal findings and molecular cytogenetic analysis of concomitant trisomy 18p (18p11.2-->pter) and distal 21q22.3 deletion.
A 29-year-old woman, gravida 2 para 1, underwent amniocentesis at 17 weeks' gestation because she was a carrier of a balanced reciprocal translocation, 46,XX,t(18;21)(p11.2;q22.3). Cytogenetic analysis of the cultured amniocytes revealed a karyotype of 46,XX,der(21)t(18;21)(p11.2;q22.3). The fetus had a derivative chromosome 21 with an extra short arm of chromosome 18 attached to the terminal region of the long arm of chromosome 21. Level II sonograms did not find prominent structural anomalies. The pregnancy was terminated subsequently. At autopsy, the proband displayed a mild phenotype of hypertelorism, a small mouth, micrognathia, a narrowly arched palate, low-set ears, and clinodactyly. The brain and other organs were unremarkable. Genetic marker analysis showed a distal deletion at 21q22.3 and a breakpoint between D21S53 (present) and D21S212 (absent), centromeric to the known holoprosencephaly (HPE) minimal critical region D21S113-21qter.
Genetic marker analysis helps in delineating the region of deletion in prenatally detected unbalanced cryptic translocation. Fetuses with concomitant trisomy 18p and distal 21q22.3 deletion may manifest inapparent phenotypic abnormalities in utero. Haploinsufficiency of the HPE critical region at 21q22.3 may not cause an HPE phenotype.
呈现18号染色体短臂三体（18p11.2→pter）与21号染色体长臂远端22.3缺失并存的围产期发现及分子细胞遗传学分析。
一名29岁女性，孕2产1，因是平衡易位携带者，46,XX,t(18;21)(p11.2;q22.3)，于孕17周接受羊膜穿刺术。对培养的羊水细胞进行细胞遗传学分析显示核型为46,XX,der(21)t(18;21)(p11.2;q22.3)。胎儿有一条衍生的21号染色体，其上附着有一条额外的18号染色体短臂，位于21号染色体长臂末端区域。二级超声检查未发现明显结构异常。随后终止妊娠。尸检时，先证者表现出轻度的眼距增宽、小嘴、小颌、腭弓狭窄、耳低位及小指内弯等表型。脑和其他器官未见明显异常。基因标记分析显示21q22.3存在远端缺失，断点位于D21S53（存在）和D21S212（缺失）之间，在已知的全前脑畸形（HPE）最小关键区域D21S113 - 21qter的着丝粒侧。
基因标记分析有助于在产前检测到的不平衡隐匿易位中界定缺失区域。18号染色体短臂三体与21号染色体长臂远端22.3缺失并存的胎儿在子宫内可能表现出不明显的表型异常。21q22.3处HPE关键区域的单倍剂量不足可能不会导致HPE表型。
