Tamaki Yuko, Katagiri Yukiko, Umemura Nahomi, Takeshita Naoki, Morita Mineto
Department of Obstetrics and Gynecology, Toho University Omori Medical Center, Japan.
Department of Obstetrics and Gynecology, Toho University Sakura Medical Center, Japan.
Case Rep Womens Health. 2020 Jun 25;27:e00236. doi: 10.1016/j.crwh.2020.e00236. eCollection 2020 Jul.
Tetrasomy 18p syndrome (Online Mendelian Inheritance in Man 614290) is a rare chromosomal disorder that is seen in approximately 1 in every 180,000 live births. It is caused by the presence of isochromosome 18p, which is a supernumerary marker composed of two copies of the short arms of chromosome 18. Isochromosome 18p is one of the most commonly observed isochromosomes. We report tetrasomy 18p syndrome diagnosed prenatally after noninvasive prenatal testing (NIPT) was positive for trisomy 18. Tetrasomy 18p was finally diagnosed by G-banding and fluorescence hybridization of chromosome 18p, before invasive confirmatory testing the karyotype findings by NIPT showed an increase in the DNA fragments from chromosome 18p, indicating duplication of chromosome 18p. NIPT can detect not only trisomy 13, 18, and 21, but also structural chromosomal anomalies, such as deletions and duplications. An NIPT report "positive for trisomy 18" indicates the possibility of tetrasomy 18p, and detailed analysis of NIPT data can reveal subchromosomal copy number variations, to a certain extent, before definitive diagnostic testing.
18号染色体短臂四体综合征（《人类孟德尔遗传在线》614290）是一种罕见的染色体疾病，每18万例活产中约有1例。它由18号染色体短臂等臂染色体引起，这是一种由两条18号染色体短臂组成的额外标记物。18号染色体短臂等臂染色体是最常观察到的等臂染色体之一。我们报告了1例在无创产前检测（NIPT）提示18三体阳性后产前诊断的18号染色体短臂四体综合征。在进行侵入性确诊检测之前，通过G显带和18号染色体短臂荧光杂交最终确诊为18号染色体短臂四体综合征，NIPT的核型分析结果显示18号染色体短臂的DNA片段增加，提示18号染色体短臂重复。NIPT不仅可以检测13、18和21三体，还可以检测染色体结构异常，如缺失和重复。一份NIPT报告“18三体阳性”提示18号染色体短臂四体的可能性，在进行确定性诊断检测之前，对NIPT数据的详细分析在一定程度上可以揭示亚染色体拷贝数变异。
