Application of Array-based Comparative Genomic Hybridization in Diagnostic Assessment of Abnormal Prenatal Serological Screening Results of Down’s Syndrome
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摘要:目的 探讨比较基因组杂交微阵列(array-based comparative genomic hybridization,a-CGH)技术在唐氏综合征血清学筛查(简称唐筛)结果异常孕妇产前诊断中的应用。方法 选取单纯因唐筛结果异常、并行羊膜腔穿刺取羊水标本进行产前检查诊断的单胎孕妇3 578例为研究对象,将其分为3组:唐筛高风险组(2 624例)、唐筛临界风险组(662例)及唐筛单项中位数的倍数(multiples of median,MoM)值异常组(292例)。采用CGX™(8×60K)芯片对其羊水进行a-CGH检测,并采用Genoglyphix®软件进行分析。结果 3 578例羊水标本中,a-CGH分析共检出染色体异常121例,总体异常检出率为3.38%,其中非整倍体60例,占49.59%;致病性拷贝数变异51例,占42.15%;可能致病拷贝数变异10例,占8.26%。检出不明意义拷贝数变异37例,占总数的1.03%。唐筛高风险组、唐筛临界风险组及唐筛单项MoM值异常组的总体异常检出率分别为3.54%(93/2 624)、2.87%(19/662)及3.08%(9/292);致病性和可能致病拷贝数变异检出率分别为1.64%(43/2624)、1.81%(12/662)及2.05%(6/292);18-及21-三体检出率分别为1.37%(36/2624)、0.76%(5/662)及0.34%(1/292),差异均无统计学意义(P>0.05)。a-CGH漏检染色体异常1例,荧光原位杂交诊断为X(51)/XYY(49)。结论 a-CGH技术在唐筛结果异常的孕妇产前诊断中不仅可以检测非整倍体异常,还可以检出微缺失/微重复综合征等染色体拷贝数变异。
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关键词:
- 染色体微阵列分析 /
- 比较基因组杂交微阵列 /
- 拷贝数变异 /
- 血清学筛查 /
- 产前诊断
Abstract:Objective To explore the application of array-based comparative genomic hybridization (a-CGH) technology in the prenatal diagnostic assessment of abnormal serological prenatal screening results of Down’s syndrome (DS).Methods A total of 3578 amniotic fluid samples from pregnant women who underwent amniocentesis for prenatal diagnosis solely due to abnormal serological prenatal screening results were selected. The samples were categorized into 3 groups, 2624 in the high-risk group, 662 in the borderline-risk group, and 292 in the abnormal multiple of median (MoM) group. a-CGH was performed on the Agilent CGX™ (8×60K) platform and the data were analyzed by the Genoglyphix® software.Results The overall detection rate of chromosomal abnormalities was 3.38% (121/3 578). Among the chromosomal abnormalities, 49.59% (60/121) was aneuploidies, 42.15% (51/121) was pathogenic copy number variants (pCNVs), and 8.26% (10/121) was likely pathogenic CNVs (lpCNVs). The detection rate of copy number variant of uncertain significance (VUS) was 1.03% (37/3 578). In the high-risk, the borderline-risk and the abnormal MoM groups, the detection rate of chromosomal abnormalities was 3.54% (93/2 624), 2.87% (19/662) and 3.08% (9/292), respectively; the detection rate of p/lp CNVs was 1.64% (43/2 624), 1.81% (12/662) and 2.05% (6/292), respectively; the detection rate of trisomy 21 and trisomy 18 was 1.37% (36/2 624), 0.76% (5/662) and 0.34% (1/292) in the three groups, respectively. There were no significant differences in all the detection rate among these groups (P>0.05). One sample with X(51)/XYY(49) confirmed by fluorescence in situ hybridization (FISH) was misdiagnosed by a-CGH.Conclusion Prenatal diagnosis with a-CGH is of great significance for reducing birth defects in pregnancies with abnormal serological prenatal screening results of DS. It can also be used to detect CNVs of microdeletion/microduplication syndromes. -
染色体异常是最常见的遗传病,其中以唐氏综合征(Down syndrome,DS)发病率最高,新生儿发病率约1/1 000~1/800,其主要由21号染色体三体(21-三体)所致,典型的临床特征以先天性智力发育障碍和发育迟缓为主,常伴有精神障碍和多种畸形[1]。一旦DS患儿出生,往往给家庭和社会带来沉重的负担。我国目前开展的以DS为主要目标疾病的孕期血清学筛查体系对减少我国DS患儿的出生率、控制我国出生缺陷发生率有显著作用。但我国人口基数大,出生人口绝对数量多,加上技术水平的原因,现行的孕中期二联或三联血清学标志物筛查假阳性率较高(约5%~7.2%)[2-3]。因此,筛查结果只能帮助判断胎儿患有DS的机会有多大,但不能明确胎儿是否为DS,仍需要经羊膜腔穿刺取羊水标本等侵入性产前检查诊断,明确胎儿是否为21-三体等。
比较基因组杂交微阵列(array-based comparative genomic hybridization,a-CGH)技术是通过在一微小的芯片表面固定大量的基因探针,待检测样品标记后与已固定的核苷酸序列进行杂交,根据检测信号的有无和强弱,确定样品中该基因或核苷酸序列的含量的一种分子检测技术[4],具有精准、快速的优点,不仅可检测到染色体非整倍体,还能提供人类全基因组亚显微水平的信息,即拷贝数变异(copy number variations,CNVs),是诊断胎儿染色体微缺失/微重复综合征的有效方法,因此称为“分子核型分析”。与传统的染色体核型分析相比,具有无需培养、所需样本量少、分辨率高、报告周期短等显著优点,不足之处是不能检出平衡易位、性染色体等比例嵌合和低比例嵌合等病例[5-6]。
本研究旨在通过对DS血清学筛查(简称唐筛)结果异常的单胎孕妇进行a-CGH检测分析,为a-CGH应用于血清学产前筛查结果异常的孕妇的产前诊断提供实验依据。
1. 对象与方法
1.1 研究对象
选取2018年12月–2019年12月在四川大学华西第二医院进行产前诊断的3 578例唐筛结果异常、要求进一步进行产前诊断的单胎孕妇为研究对象,所有孕妇均无介入性产前诊断禁忌症。本研究获得四川大学华西第二医院伦理委员会批准(批准号:20180094)。
1.2 纳入和排除标准
纳入标准:①唐筛高风险,21-三体风险值≥1/270,或18-三体风险值≥1/350;②唐筛临界风险,21-三体风险值介于1/270与1/1 000之间,或18-三体风险度介于1/350与1/1 000之间;③单项中位数的倍数(multiples of median,MoM)值异常,游离人绒毛膜促性腺激素β亚单位(free beta subunit of human chorionic gonadotropin,f-βhCG)MoM值≥2.50或≤0.25,或甲胎蛋白(AFP)MoM值≤0.40;④均知情同意并签署知情同意书。
排除标准:①双胎或多胎;②预产期年龄≥35岁;③胎儿存在超声异常,包括超声结构异常或超声软指标,如颈项透明层(NT)增厚、侧脑室增宽、脉络丛囊肿、后颅窝积液、心内点状强回声、单脐动脉、长骨短 、肠管强回声、鼻骨缺失等;④术前已明确夫妻双方存在染色体异常;⑤曾生育(或引产)过染色体异常患儿(胎儿)且未行夫妻双方染色体检测排除染色体异常的孕妇。
1.3 方法
1.3.1 相关试剂
a-CGH:采用美国AgilenTechnologies公司定制生产的PerkinElmer CGX™(8×60K)芯片,其配套试剂包括美国Agilent Technologies公司生产的DNA纯化试剂盒(PureLink™ Genomic DNA Kits)、标记试剂盒(SureTag DNA Labeling Kit,Purification Columns)和DNA杂交试剂盒(Oligo aCGH/Chip-on-Chip Hybridization Kit)。荧光定量聚合酶链式反应(quantitative fluorescence polymerase chain reactionm,QF-PCR):采用广州达瑞生物技术股份有限公司生产的染色体(13/18/21/XY)多重STR基因分型试剂盒(荧光PCR毛细管电泳法)。荧光原位杂交(fluorescence in situ hybridization,FISH):采用雅培分子有限公司(Aneu Vysion Multicolor DNA Probe Kit)试剂盒。
1.3.2 标本的采集及处理
羊水标本采集:无菌操作进行羊膜腔穿刺采集20 mL羊水,分装于4支无菌离心管中,4 ℃保存,1管用于a-CGH检测,1管用于QF-PCR检测,另2管备用;全基因组DNA提取:所有标本均采用羊水DNA提取试剂盒〔 UPure Tissue DNA Kit(M2012-A96)〕上机(Thermo King Fisher™ Flex)提取,−20 ℃储存备用。
对于离心后肉眼可见血的羊水样本,需进行羊水细胞的分离培养,收获培养的羊水细胞提取DNA进行进一步检查实验。
1.3.3 染色体微阵列分析检测
按1.3.2提取的DNA纯度达到A260/A280为1.8~2.0,A260/A230为>1.0;取200 ng/μL的待测样本DNA 13.0 μL,对照人类参照DNA稀释成相同浓度及体积,样本DNA和对照DNA用随机引物进行标记,待测DNA用Cy5标记,对照DNA用Cy3标记,标记好的产物使用纯化试剂(PureLink™ Genomic DNA Kits)纯化DNA,将待测DNA与对照DNA以1∶1比例混合,加入封闭非特异性重复序列的人类 Cot-1 DNA进行预杂交,并将预杂交好的DNA加载到芯片上,65 ℃杂交24 h。杂交结束后,洗去芯片上剩余的杂交缓冲液以及未杂交的DNA,用SureScan Dx Microarray Scanner芯片扫描仪进行扫描。
结果判断:用Genoglyphix®分析软件(https://uk.genoglyphix.com/)进行数据判读。并按照《拷贝数变异检测在产前诊断中的应用指南》[7]对CNVs进行分析。主要查询数据库包括:① Databases of Genomic Variants(DGV)(http://projects.tcag.ca/variation/);② Databases of Chromosomal Imbalance and Phenotype in Humans Using Ensembl Resurces(DECIPHER)(http://decipher.sanger.ac.uk/);③ Clinvar(http://www.ncbi.nlm.nih.gov/clinvar);④ Clinical Genome Resource(ClinGen)(https://www.ncbi.nlm.nih.gov/projects/dbvar/clingen/);⑤ Gene Reviews(https://www.ncbi.nlm.nih.gov/books/NBK1116/);⑥ Online Mendelian Inheritance in Man(OMIM)(http://www.ncbi.nlm.nih.gov/omim);⑦ PubMed(https://www.ncbi.nlm.nih.gov/pubmed)。将CNVs分为致病性CNVs(pathogenic CNVs,pCNVs)、可能致病性CNVs(like pathogenic CNVs,lpCNVs)、不明意义CNVs(uncertain clinical significance, VUS)、可能良性CNVs(likely benign CNVs)和良性CNVs(benign CNVs)五类。根据《拷贝数变异检测在产前诊断中的应用指南》中的建议,本研究对可能良性及良性CNVs不予统计报道。
1.3.4 QF-PCR检测
所有羊水样本均同时行QF-PCR检测,用于快速检测常见染色体非整倍体(13-、18-、21-三体及性染色体数目异常)及检出a-CGH分析无法检出的三倍体。实验严格按照试剂盒说明书进行。
1.3.5 FISH检测
当a-CGH分析提示性染色体异常时,进一步行FISH进行检测。实验严格按照试剂盒说明书进行。当异常细胞比例介于10%~60%时,判定为嵌合体;当异常细胞比例大于60%时,判定为该指标异常[8]。
1.3.6 染色体核型G显带分析
当a-CGH分析检出CNVs≥10 Mb,进一步行染色体核型G显带检测。实验严格按照试剂盒说明书进行,对羊水标本进行羊水细胞培养、中期染色体核型制备和G显带染色体核型分析。计数20个核型,分析3到5个,若发现嵌合体核型则进行加倍计数,分析检查结果,记录孕妇染色体异常核型结果。
1.4 统计学方法
计量资料采用t检验,计数资料采用χ2检验,P<0.05为差异有统计学意义。
2. 结果
2.1 孕妇一般情况
本次研究共纳入3 578例孕妇,年龄18~34岁,平均(27.87±3.65)岁,检查孕周17.86~31.57周,平均(20.53±1.44)周。抽取的羊水标本进行a-CGH检测时214例样本离心后肉眼可见血,经细胞培养后检测,检测成功率100%。
2.2 a-CGH总体检测结果
3 578例孕妇根据唐筛结果分为3组:唐筛高风险组(2 624例)、唐筛临界风险组(662例)和MoM值异常组(292例)。a-CGH共检出染色体异常121例,总体检出率3.38%(121/3 578),其中非整倍体60例,占49.59%;pCNVs 51例,占42.15%;lpCNVs 10例,约占8.26%。检出VUS 37例,占总数的1.03%(37/3 578)。21-三体/18-三体检出42例,占总数的1.17%。3组羊水标本a-CGH检测结果见表1,可见3组染色体异常总体检出率、染色体非整倍体检出率、pCNV/lpCNV和21-三体/18-三体检出率差异均无统计学意义。
表 1 3 578例唐氏综合征血清学产前筛查结果异常孕妇羊水a-CGH检测结果Table 1. The findings of a-CGH in 3 578 abnormal serologic prenatal screening results of DSGroup n a-CGH results/case (%) Chromosomal abnormallities Trisomy 21/trisomy 18 Aneuploidies pCNVs/lpCNVs VUS High risk 2 624 93 (3.54) 36 (1.37) 50 (1.91) 43 (1.64) 28 (1.07) Borderline risk 662 19 (2.87) 5 (0.76) 7 (1.06) 12 (1.81) 6 (0.91) Abnormal MoM 292 9 (3.08) 1 (0.34) 3 (1.03) 6 (2.05) 3 (1.03) Total 3 578 121 (3.38) 42 (1.17) 60 (1.68) 61 (1.70) 37 (1.03) P 0.663 0.163 0.210 0.849 0.935 pCNVs: Pathogenic CNVs; lpCNVs: Likely pathogenic CNVs; VUS: Variant of uncertain significance; MoM: Multiple of median. 此次检测所有QF-PCR检出染色体非整倍体与a-CGH结果均相符。
2.3 a-CGH对唐筛异常孕妇胎儿染色体非整倍体的检测结果及验证
本次检测a-CGH共检出三体综合征45例,其中包括DS 34例〔1例合并1q21.1复发性微缺失(神经发育障碍易感位点)〕、18-三体综合征8例和13-三体综合征3例。
a-CGH共检出6例性染色体异常(XXY 3例,XYY 3例)和8例染色体嵌合体(X/XY 1例、X/XX 2例、XXX/XX 1例、XYY/X/XY 2例、9-三体嵌合型 1例、21-三体嵌合型 1例),以上a-CGH检测结果与QF-PCR方法验证结果一致。
FISH验证出1例X单体与XYY的等比例嵌合体,a-CGH检测漏诊,见表2。
表 2 9例染色体嵌合体样本a-CGH检测结果及验证结果Table 2. a -CGH detection and verification results of 9 chromosomal chimeri sm samplesNo. Chimeric type a-CGH results Verification results 1
X/XY
arr[GRCh37] Xp22.33q28(2772612_154882515)x1 (152.110 Mb)arr[GRCh37] Yp11.32q12(246520_59324918)x0.91 (59.078 Mb) FISH: X(16)/XY(84)
2 X/XX arr[GRCh37] Xp22.33q28(2772612_154882515)x1.31 (152.110 Mb) FISH:X(50)/XX(50) 3 X/XX arr[GRCh37] Xp22.33q28(2772612_154882515)x1.60 (152.110 Mb) FISH: X(16)/XX(84) 4 X/XYY Missed diagnosis FISH: X(51)/XYY(49) 5 XXX/XX arr[GRCh37] Xp22.33q28(2772612_154882515)x2.09 (152.110 Mb) FISH: X(30)/XX(70) 6
XYY/X/XY
arr[GRCh37] Xp22.33q28(2772612_154882515)x1 (152.110 Mb)arr[GRCh37] Yp11.32q12(246520_59324918)x1.18 (59.078 Mb) FISH: XYY(43)/X(22)/XY(35)
7
XYY/X/XY
arr[GRCh37] Xp22.33q28(2772612_154882515)x1 (152.110 Mb)arr[GRCh37] Yp11.32q12(246520_59324918)x1.22 (59.078 Mb) FISH: XYY(31)/X(6)/XY(63)
8 Mosaic trisomy 9 Mosaic trisomy 9 (48%) FISH: Mosaic trisomy 9 (48%) 9 Mosaic trisomy 21 Mosaic trisomy 21 (40%) FISH: Mosaic trisomy 21 (44%) 2.4 唐筛异常孕妇胎儿染色体拷贝数变异检出情况
2.4.1 致病性CNVs
51例致病性CNVs结果中17例为微重复,33例为微缺失,1例为微重复+微缺失,涉及片段大小为213~96 606 kb,其中片段大于10 Mb共4例,见表3。
表 3 51例致病性CNVs结果Table 3. Pathogenic CNVs in 51 fetusesNo. a-CGH results Known syndromes Copy number Sizes of CNVs/kb OMIM gene Inherited /
or de novo1 arr[GRCh37] 1p36.31p36.23(5588468_
8898638)x1/ Loss 3 310 CAMTA1 de novo 2-4 arr[GRCh37] 1q21.1q21.2(146531538_
147384520)x11q21.1 recurrent region (BP3-BP4, distal) (includes GJA5) Loss 853 GJA5/GJA8 NA 5 arr[GRCh37] 3q29(195769570_197332975)x3 3q29 microduplication syndrome Gain 1 563 PAK2/DLG1 NA 6 arr[GRCh37] 7p14.1p12.3(42052240_
45611137)x1/ Loss 3 559 GLI3 NA 7 arr[GRCh37] 9p24.3(742688_1044097)x1 / Loss 301 DMRT1 NA 8 arr[GRCh37] 10q11.22q11.23(46980161_
50940524)x110q11.2 recurrent region (LCR-C to -D) Loss 3 960 / NA 9 arr[GRCh37] 13q32.1q34(95572054_
115091801)x1/ Loss 19 520 ZIC2/ CHAMP1 NA 10 arr[GRCh37] 15q11.2q13.1(23717628_
28513165)x315q11q13 recurrent (PWS/AS) region (BP1-BP3, Class 1) Gain 4 796 / Inherited from normal mother 11 arr[GRCh37] 16p13.11(15125829_16258367)x3 16p13.11 recurrent region (includes MYH11) Gain 1 133 MYH11 NA 12 arr[GRCh37] 16p13.11(15125829_16276115)x3 16p13.11 recurrent region (includes MYH11) Gain 1 150 MYH11 NA 13 arr[GRCh37] 16p13.11(15125829_16287899)x3 16p13.11 recurrent region (includes MYH11) Gain 1162 MYH11 NA 14 arr[GRCh37] 16p13.11(15125829_16287899)x3 16p13.11 recurrent region (includes MYH11) Gain 1 162 MYH11 Inherited from normal mother 15 arr[GRCh37] 16p12.2(21950360_22428364)x1 16p12.2 recurrent deletion Loss 478 EEF2K/
CDR2NA 16 arr[GRCh37] 16p11.2(29657192_30188268)x1 16p11.2 recurrent microdeletion Loss 531 TBX6 NA 17-18 arr[GRCh37] 17p12(14104475_15420102)x1 Hereditary Liability to Pressure Palsies, HNPP Loss 1 316 PMP22 NA 19 arr[GRCh37] 17q11.2(29599688_29812361)x1 / Loss 213 NF1 NA 20 arr[GRCh37] 21q22.11q22.3(33655833_48091215)x3 / Loss 4661 TGIF1 NA arr[GRCh37] 21q22.11q22.3(33655833_48091215)x3 / Gain 14435 / NA 21-23 arr[GRCh37] 22q11.21(18919528_21417548)x3 22q11 duplication syndrome Gain 2 498 TBX1 NA 24 arr[GRCh37] 22q11.21(18919528_21417548)x3 22q11 duplication syndrome Gain 2 498 TBX1 de novo 25 arr[GRCh37] 22q11.21(18919528_21417548)x3 22q11 duplication syndrome Gain 2 498 TBX1 Inherited from normal mother 26 arr[hg19] 22q11.21(19243462_21417548)x3 22q11 duplication syndrome Gain 2 174 TBX1 NA 27 arr[GRCh37] Xp21.1(32985546_34217926)x3 / Gain 1 232 DMD Inherited from normal mother 28-31 arr[GRCh37] Xp22.31(6456777_8119328)x0 Steroid sulphatase deficiency Loss 1 663 STS NA 32 arr[GRCh37] Xp22.31(6456777_8119328)x0 Steroid sulphatase deficiency Loss 1 663 STS Inherited from normal mother 33 arr[GRCh37] Xp22.31(6522054_7974296)x0 Steroid sulphatase deficiency Loss 1 452 STS NA 34 arr[GRCh37] Xp22.31(6735844_7903465)x1 Steroid sulphatase deficiency Loss 1 168 STS NA 35-36 arr[GRCh37] Xp22.31(6456777_8119328)x1 Steroid sulphatase deficiency Loss 1 663 STS NA 37 arr[GRCh37] Xp22.31(8515091_8927293)x2 / Gain 412 KAL1 NA 38 arr[GRCh37] Xp21.1(31766614_31988723)x0 / Loss 222 DMD NA 39 arr[GRCh37] 2p25.3p24.1(36400_22973063)x3 / Gain 22 937 / NA arr[GRCh37] 5p15.33p15.32(55550_5839620)x1 Cri du Chat Syndrome (5p deletion) Loss 5 784 TERT NA 40 arr[GRCh37] 16p13.11(15049829_16287899)x1 16p13.11 recurrent microdeletion (neurocognitive disorder susceptibility locus) Loss 1 238 MYH11 NA 41 arr[GRCh37] 16p12.2(21950360_22428364)x1 Recurrent 16p12.1 microdeletion (neurodevelopmental susceptibility locus) Loss 478 EEF2K, CDR2 NA 42 arr[GRCh37] 16p13.11(15125829_16258367)x3 16p13.11 recurrent region (includes MYH11) Gain 1 133 MYH11 NA 43 arr[GRCh37] 16p11.2(29657192_30188268)x3 16p11.2 microduplication syndrome Gain 531 TBX6 NA 44 arr[GRCh37] Xp21.1(31555212_31928887)x1 / Loss 374 DMD NA 45-46 arr[GRCh37] 17p12(14104475_15420102)x1 Hereditary Liability to Pressure Palsies (HNPP) Loss 1 316 PMP22 NA 47 arr[GRCh37] 17p12(14104475_15420102)x3 Charcot-Marie-Tooth syndrome type 1A (CMT1A) Gain 1 316 / NA 48 arr[GRCh37] Xp22.31(6456777_8119328)x0 Steroid sulphatase deficiency Loss 1 663 STS NA 49 arr[GRCh37] Xp22.31(6456777_8119328)x0 Steroid sulphatase deficiency Loss 1 663 STS Inherited from normal mother 50 arr Xp22.32p22.31(5322881_8150451)x1 Steroid sulphatase deficiency Loss 2 828 STS NA 51 arr[GRCh37] Xp22.33q22.1(2772612_
99378367)x1.41/ Loss 96 606 / NA arr[GRCh37] Xq22.1q28(99460272_
154882516)x1/ Loss 55 422 / NA CNVs: Copy number variants; OMIM: Online mendelian inheritance in man; CAMTA1: Calmodulin-binding transcription activator; GJA5: Gap junction protein alpha-5; PAK2: P21-activated kinase; DLG1: Discs large homolog 1; GLI3: Greig cephalopolysyndactyly syndrome; DMRT1: Doublesex and mab-3 related transcription factor; ZIC2: Zic family member 2; CHAMP1: Chromosome alignment maintaining phosphoprotein 1; MYH11: Myosin, heavy chain 11, smooth muscle; EEF2K: Eukaryotic elongation factor 2 kinase; CDR2: Cerebellar degeneration-related autoantigen 2; TBX6: T-box transcription factor 6; PMP22: Peripheral myelin protein 22; NF1: Neurofibromin 1; TGIF1:TGEB-induced factor homeobox 1; TBX1: Congenital heart disease associated protein 1; DMD: Duchenne muscular dystrophy; STS: Steroid sulphatase deficiency; KAL1: Kallmann syndrome 1 sequence; TERT: Telomerase reverse transcriptase. 2例片段大于10 Mb样本同时行染色体核型G显带分析,G显带核型分析均检出异常:1例核型确诊遗传自无表型平衡易位母亲,核型结果为:46, XN, der(18), t(18:21)(p11.3:q22) mat(表3:No. 20);1例核型确诊异常嵌合核型:45, X[24]/46, X, psu idic(X)(q22.1)[6](表3:No. 51)。
2.4.2 可能致病CNVs
10例可能致病CNVs结果中8例为微重复,2例为微缺失,涉及片段大小为412~5 854 kb。2例微缺失/微重复综合征的部分区域:1q21.1复发性微重复(神经认知障碍易感位点)1例,16p13.11复发性微重复(神经认知障碍易感位点)1例。见表4。
表 4 10例可能致病性CNVs结果Table 4. Likely pathogenic CNVs in 10 fetusesNo. a-CGH results Known syndromes Copy number Sizes of CNVs/kb OMIM gene Inherited /or de novo 52 arr[GRCh37] 1q21.2(147277739_147712417)x3 1q21.1 recurrent microduplication (possible susceptibility locus for neurodevelopmental disorders) 32.2% Gain 435 / de novo 53 arr[GRCh37] 2p16.1p15(60320492_61592578)x3 2p15p16.1 region (includes BCL11A) 38.0% Gain 1 272 BCL11A de novo 54 arr[GRCh37] 2q13(111398336_113058889)x3 2q13 recurrent region (includes BCL2L11) Gain 1 661 / de novo 55 arr[hg19] 4q13.3q21.1(71176988_77031108)x1 / Loss 5 854 / de novo 56 arr[GRCh37] 15q13.2q13.3(31140606_32427978)x3 15q13.3 recurrent region (BP4-BP5) (includes CHRNA7) Gain 1 287 CHRNA7 de novo 57 arr[GRCh37] 15q13.3(31361538_32438943)x3 15q13.3 recurrent region (BP4-BP5) (includes CHRNA7) Gain 1 077 / de novo 58 arr[GRCh37] 16p13.11(15512480_16246473)x3 16p13.11 recurrent region (includes MYH11) Gain 734 / de novo 59 arr[GRCh37] 16p13.11(15125829_16282387)x3 16p13.11 recurrent microduplication (neurocognitive disorder susceptibility locus) 77.1% Gain 1 157 MYH11 de novo 60 arr[GRCh37] 22q11.1q11.21(17528442_
17940650)x322q11.21 recurrent (Cat eye syndrome) region (includes CECR2) 34.4% Gain 412 / de novo 61 arr[GRCh37] 22q11.21q11.22(21798705_
23326623)x322q11.2 recurrent region (distal type I, D-E or D-F) 81.4% Gain 1 528 / de novo CNVs: Copy number variants; OMIM: Online mendelian inheritance in man; BCL11A: B-cell CLL/lymphoma 11A; CHRNA7: Cholinergic receptor, nicotinic, alpha 7; MYH11: Myosin heavy chain 11, smooth muscle. 3. 讨论
唐氏综合征血清学产前筛查具有“安全、无创、方法简单、经济”等优点,是产前筛查的常用检查方法。通过对孕妇进行血清学筛查,可检测母体PAPP-A、f β-hCG、AFP、inhibin-A、uE3等,结合孕妇年龄、孕周、体质量、病史等进行综合风险评估,可得出患儿患唐氏综合征及18-三体综合征的风险度,中孕期血清学筛查还可评估胎儿神经管缺陷风险度,对降低胎儿出生缺陷率及预测不良妊娠结局具有重要意义[9]。然而血清学筛查受多种因素影响,准确率、敏感度、特异度不高等原因容易造成漏诊和假阳性等不良后果,因此需对筛查结果异常人群进行羊水穿刺等有创性检查进行最终诊断。
既往针对唐筛的传统确诊方法是染色体核型G显带分析和常见染色体非整倍体快速检测(如QF-PCR、FISH等)。染色体核型分析虽然可发现染色体数目异常和结构异常,但需要进行细胞培养、检测周期长,同时分辨率较低,仅可检出显微结构的染色体异常(通常>5~10 Mb),对于亚显微结构的染色体异常无法检出;QF-PCR、FISH检测技术虽然检测快速、灵敏性高、特异性强,但仅针对目标染色体数目进行检测,无法检出目标染色体以外的染色体异常[10],在临床应用存在一定的局限性。本研究共检出p/lp CNVs 61例,且片段绝大多数是传统染色体G显带核型分析无法检出。检出的p/lp CNVs片段大小>5 Mb的共5例,>10 Mb的共4例,若用传统的染色体核型G显带分析,能检出约1.79%(64/3578)~1.82%(65/3 578)的异常,而a-CGH能检出约3.38%的异常,因此与传统的染色体G显带核型分析相比,a-CGH可显著提高唐筛异常孕妇胎儿染色体异常的检出率1.56%~1.59%。对唐筛异常孕妇可能会存在其他染色体异常,特别是微缺失/微重复综合征,需要采用能针对CNVs进行检测的方法,a-CGH可满足上述要求。
本次研究我们对3 578例单纯因为唐筛结果异常要求进行羊水染色体检测的孕妇进行了a-CGH的检测,共检出染色体异常121例,总体检出率3.38%。其中非整倍体60例,约占49.59%;p/lp CNVs 61例,约占50.41%。本研究p/lp CNVs的检出率约为1.70%,与文献报道的人群CNVs携带率1.7%[11-13]一致。3个分组总体检出率、p/lp CNV检出率、非整倍体、21-/18-三体检出率差异均无统计学意义,但胎儿染色体非整倍体检出率及针对唐筛目标疾病21-三体及18-三体的检出率可以看出,唐筛高风险的检出率高于唐筛临界风险及唐筛MoM值异常,这可能与本研究中唐筛临界风险及唐筛MoM值异常组样本量较少有关,在以后的研究中,希望通过样本量的累积,再次评估异常检出率。另外,本研究额外检出了3例DMD,这些孕妇无家族史,a-CGH用于产前诊断的偶然发现,有助于发现并避免因DMD基因外显子缺失或重复所致的患儿的出生,可在一定程度上提高该类疾病诊断率[14]。因此对因唐筛异常需要或要求进行介入性产前诊断的孕妇,可以用a-CGH替代核型。
本次研究检出的60例非整倍体中共有9例染色体嵌合体,其中1例为X(51)/XYY(49)(表2:No. 4),a-CGH检测漏诊,FISH检测偶然发现。对于染色体净平衡,a-CGH可能会漏诊,虽然发生率极低,但漏诊有可能影响妊娠结局,导致出生缺陷的发生。本次研究还检出1例复杂的性染色体异常胎儿(表3:No. 51),a-CGH结果提示X染色体短臂及部分长臂缺失嵌合型(嵌合比例约59%)及X染色体长臂末端缺失;FISH结果提示可能为X(35)/XXX(18)/XX(47)嵌合体。两种方法结果不一致提示该胎儿的性染色体可能存在更加复杂的结构变异,a-CGH无法明确其结构表现。进一步行核型G显带分析,可从显微结构了解其真实表现,结果为45,X[24]/46,X,psu idic(X)(q22.1)[6],为X单体与X染色体长臂假双着丝粒两种核型嵌合。由于Xq假双着丝粒染色体替代了一条正常的X染色体,因此出现了a-CGH与FISH两种结果不一致的情况。对于难以解释的a-CGH结果,需要其他的诊断方法进行相互验证。FISH对于诊断染色体数目异常的嵌合体优越性高于其他方法,而染色体核型分析能够定位染色体并明确其真实表现,对于诊断染色体的结构异常的诊断仍然是无法用其他方法进行替代的。因此,a-CGH结果复杂难以解释时,建议结合FISH、染色体G显带分析等方法,提供科学准确的信息,并结合B超等影像学检测结果,对避免严重的染色体病患儿的出生,减少不必要的正常胎儿丢失,对减轻孕妇和家属的精神及经济负担,提高人口素质有重要意义[15]。
在本次研究中,a-CGH技术还检出了37例不明意义的拷贝数变异,检出率为1.03%。VUS结果不仅目前一直是困扰临床医师的一大难题,而且VUS结果的检出给孕妇造成了很大的心理负担。对于不明意义拷贝数变异,建议进一步对胎儿生物学父母进行比对,以便明确CNVs来源,帮助判断CNVs致病性,也有助于评估夫妇下次妊娠胎儿的再发风险,决定再次妊娠方式及进行后续产前诊断。
综上所述,对于因单纯唐筛结果异常而接受了有创产前诊断的孕妇,a-CGH技术不仅能检出染色体非整倍体异常,还能检测出传统核型无法检出的微缺失/微重复综合征,具有更高的检出率,可以作为一线产前诊断检测技术应用于上述人群中。但对于染色体复杂的结构变异或嵌合体净平衡等情况,a-CGH应结合FISH、染色体G显带分析等其他检测方法,从而提高胎儿染色体病检出率,减少出生缺陷的发生,有利于提高出生人口质量。
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表 1 3 578例唐氏综合征血清学产前筛查结果异常孕妇羊水a-CGH检测结果
Table 1 The findings of a-CGH in 3 578 abnormal serologic prenatal screening results of DS
Group n a-CGH results/case (%) Chromosomal abnormallities Trisomy 21/trisomy 18 Aneuploidies pCNVs/lpCNVs VUS High risk 2 624 93 (3.54) 36 (1.37) 50 (1.91) 43 (1.64) 28 (1.07) Borderline risk 662 19 (2.87) 5 (0.76) 7 (1.06) 12 (1.81) 6 (0.91) Abnormal MoM 292 9 (3.08) 1 (0.34) 3 (1.03) 6 (2.05) 3 (1.03) Total 3 578 121 (3.38) 42 (1.17) 60 (1.68) 61 (1.70) 37 (1.03) P 0.663 0.163 0.210 0.849 0.935 pCNVs: Pathogenic CNVs; lpCNVs: Likely pathogenic CNVs; VUS: Variant of uncertain significance; MoM: Multiple of median. 表 2 9例染色体嵌合体样本a-CGH检测结果及验证结果
Table 2 a -CGH detection and verification results of 9 chromosomal chimeri sm samples
No. Chimeric type a-CGH results Verification results 1
X/XY
arr[GRCh37] Xp22.33q28(2772612_154882515)x1 (152.110 Mb)arr[GRCh37] Yp11.32q12(246520_59324918)x0.91 (59.078 Mb) FISH: X(16)/XY(84)
2 X/XX arr[GRCh37] Xp22.33q28(2772612_154882515)x1.31 (152.110 Mb) FISH:X(50)/XX(50) 3 X/XX arr[GRCh37] Xp22.33q28(2772612_154882515)x1.60 (152.110 Mb) FISH: X(16)/XX(84) 4 X/XYY Missed diagnosis FISH: X(51)/XYY(49) 5 XXX/XX arr[GRCh37] Xp22.33q28(2772612_154882515)x2.09 (152.110 Mb) FISH: X(30)/XX(70) 6
XYY/X/XY
arr[GRCh37] Xp22.33q28(2772612_154882515)x1 (152.110 Mb)arr[GRCh37] Yp11.32q12(246520_59324918)x1.18 (59.078 Mb) FISH: XYY(43)/X(22)/XY(35)
7
XYY/X/XY
arr[GRCh37] Xp22.33q28(2772612_154882515)x1 (152.110 Mb)arr[GRCh37] Yp11.32q12(246520_59324918)x1.22 (59.078 Mb) FISH: XYY(31)/X(6)/XY(63)
8 Mosaic trisomy 9 Mosaic trisomy 9 (48%) FISH: Mosaic trisomy 9 (48%) 9 Mosaic trisomy 21 Mosaic trisomy 21 (40%) FISH: Mosaic trisomy 21 (44%) 表 3 51例致病性CNVs结果
Table 3 Pathogenic CNVs in 51 fetuses
No. a-CGH results Known syndromes Copy number Sizes of CNVs/kb OMIM gene Inherited /
or de novo1 arr[GRCh37] 1p36.31p36.23(5588468_
8898638)x1/ Loss 3 310 CAMTA1 de novo 2-4 arr[GRCh37] 1q21.1q21.2(146531538_
147384520)x11q21.1 recurrent region (BP3-BP4, distal) (includes GJA5) Loss 853 GJA5/GJA8 NA 5 arr[GRCh37] 3q29(195769570_197332975)x3 3q29 microduplication syndrome Gain 1 563 PAK2/DLG1 NA 6 arr[GRCh37] 7p14.1p12.3(42052240_
45611137)x1/ Loss 3 559 GLI3 NA 7 arr[GRCh37] 9p24.3(742688_1044097)x1 / Loss 301 DMRT1 NA 8 arr[GRCh37] 10q11.22q11.23(46980161_
50940524)x110q11.2 recurrent region (LCR-C to -D) Loss 3 960 / NA 9 arr[GRCh37] 13q32.1q34(95572054_
115091801)x1/ Loss 19 520 ZIC2/ CHAMP1 NA 10 arr[GRCh37] 15q11.2q13.1(23717628_
28513165)x315q11q13 recurrent (PWS/AS) region (BP1-BP3, Class 1) Gain 4 796 / Inherited from normal mother 11 arr[GRCh37] 16p13.11(15125829_16258367)x3 16p13.11 recurrent region (includes MYH11) Gain 1 133 MYH11 NA 12 arr[GRCh37] 16p13.11(15125829_16276115)x3 16p13.11 recurrent region (includes MYH11) Gain 1 150 MYH11 NA 13 arr[GRCh37] 16p13.11(15125829_16287899)x3 16p13.11 recurrent region (includes MYH11) Gain 1162 MYH11 NA 14 arr[GRCh37] 16p13.11(15125829_16287899)x3 16p13.11 recurrent region (includes MYH11) Gain 1 162 MYH11 Inherited from normal mother 15 arr[GRCh37] 16p12.2(21950360_22428364)x1 16p12.2 recurrent deletion Loss 478 EEF2K/
CDR2NA 16 arr[GRCh37] 16p11.2(29657192_30188268)x1 16p11.2 recurrent microdeletion Loss 531 TBX6 NA 17-18 arr[GRCh37] 17p12(14104475_15420102)x1 Hereditary Liability to Pressure Palsies, HNPP Loss 1 316 PMP22 NA 19 arr[GRCh37] 17q11.2(29599688_29812361)x1 / Loss 213 NF1 NA 20 arr[GRCh37] 21q22.11q22.3(33655833_48091215)x3 / Loss 4661 TGIF1 NA arr[GRCh37] 21q22.11q22.3(33655833_48091215)x3 / Gain 14435 / NA 21-23 arr[GRCh37] 22q11.21(18919528_21417548)x3 22q11 duplication syndrome Gain 2 498 TBX1 NA 24 arr[GRCh37] 22q11.21(18919528_21417548)x3 22q11 duplication syndrome Gain 2 498 TBX1 de novo 25 arr[GRCh37] 22q11.21(18919528_21417548)x3 22q11 duplication syndrome Gain 2 498 TBX1 Inherited from normal mother 26 arr[hg19] 22q11.21(19243462_21417548)x3 22q11 duplication syndrome Gain 2 174 TBX1 NA 27 arr[GRCh37] Xp21.1(32985546_34217926)x3 / Gain 1 232 DMD Inherited from normal mother 28-31 arr[GRCh37] Xp22.31(6456777_8119328)x0 Steroid sulphatase deficiency Loss 1 663 STS NA 32 arr[GRCh37] Xp22.31(6456777_8119328)x0 Steroid sulphatase deficiency Loss 1 663 STS Inherited from normal mother 33 arr[GRCh37] Xp22.31(6522054_7974296)x0 Steroid sulphatase deficiency Loss 1 452 STS NA 34 arr[GRCh37] Xp22.31(6735844_7903465)x1 Steroid sulphatase deficiency Loss 1 168 STS NA 35-36 arr[GRCh37] Xp22.31(6456777_8119328)x1 Steroid sulphatase deficiency Loss 1 663 STS NA 37 arr[GRCh37] Xp22.31(8515091_8927293)x2 / Gain 412 KAL1 NA 38 arr[GRCh37] Xp21.1(31766614_31988723)x0 / Loss 222 DMD NA 39 arr[GRCh37] 2p25.3p24.1(36400_22973063)x3 / Gain 22 937 / NA arr[GRCh37] 5p15.33p15.32(55550_5839620)x1 Cri du Chat Syndrome (5p deletion) Loss 5 784 TERT NA 40 arr[GRCh37] 16p13.11(15049829_16287899)x1 16p13.11 recurrent microdeletion (neurocognitive disorder susceptibility locus) Loss 1 238 MYH11 NA 41 arr[GRCh37] 16p12.2(21950360_22428364)x1 Recurrent 16p12.1 microdeletion (neurodevelopmental susceptibility locus) Loss 478 EEF2K, CDR2 NA 42 arr[GRCh37] 16p13.11(15125829_16258367)x3 16p13.11 recurrent region (includes MYH11) Gain 1 133 MYH11 NA 43 arr[GRCh37] 16p11.2(29657192_30188268)x3 16p11.2 microduplication syndrome Gain 531 TBX6 NA 44 arr[GRCh37] Xp21.1(31555212_31928887)x1 / Loss 374 DMD NA 45-46 arr[GRCh37] 17p12(14104475_15420102)x1 Hereditary Liability to Pressure Palsies (HNPP) Loss 1 316 PMP22 NA 47 arr[GRCh37] 17p12(14104475_15420102)x3 Charcot-Marie-Tooth syndrome type 1A (CMT1A) Gain 1 316 / NA 48 arr[GRCh37] Xp22.31(6456777_8119328)x0 Steroid sulphatase deficiency Loss 1 663 STS NA 49 arr[GRCh37] Xp22.31(6456777_8119328)x0 Steroid sulphatase deficiency Loss 1 663 STS Inherited from normal mother 50 arr Xp22.32p22.31(5322881_8150451)x1 Steroid sulphatase deficiency Loss 2 828 STS NA 51 arr[GRCh37] Xp22.33q22.1(2772612_
99378367)x1.41/ Loss 96 606 / NA arr[GRCh37] Xq22.1q28(99460272_
154882516)x1/ Loss 55 422 / NA CNVs: Copy number variants; OMIM: Online mendelian inheritance in man; CAMTA1: Calmodulin-binding transcription activator; GJA5: Gap junction protein alpha-5; PAK2: P21-activated kinase; DLG1: Discs large homolog 1; GLI3: Greig cephalopolysyndactyly syndrome; DMRT1: Doublesex and mab-3 related transcription factor; ZIC2: Zic family member 2; CHAMP1: Chromosome alignment maintaining phosphoprotein 1; MYH11: Myosin, heavy chain 11, smooth muscle; EEF2K: Eukaryotic elongation factor 2 kinase; CDR2: Cerebellar degeneration-related autoantigen 2; TBX6: T-box transcription factor 6; PMP22: Peripheral myelin protein 22; NF1: Neurofibromin 1; TGIF1:TGEB-induced factor homeobox 1; TBX1: Congenital heart disease associated protein 1; DMD: Duchenne muscular dystrophy; STS: Steroid sulphatase deficiency; KAL1: Kallmann syndrome 1 sequence; TERT: Telomerase reverse transcriptase. 表 4 10例可能致病性CNVs结果
Table 4 Likely pathogenic CNVs in 10 fetuses
No. a-CGH results Known syndromes Copy number Sizes of CNVs/kb OMIM gene Inherited /or de novo 52 arr[GRCh37] 1q21.2(147277739_147712417)x3 1q21.1 recurrent microduplication (possible susceptibility locus for neurodevelopmental disorders) 32.2% Gain 435 / de novo 53 arr[GRCh37] 2p16.1p15(60320492_61592578)x3 2p15p16.1 region (includes BCL11A) 38.0% Gain 1 272 BCL11A de novo 54 arr[GRCh37] 2q13(111398336_113058889)x3 2q13 recurrent region (includes BCL2L11) Gain 1 661 / de novo 55 arr[hg19] 4q13.3q21.1(71176988_77031108)x1 / Loss 5 854 / de novo 56 arr[GRCh37] 15q13.2q13.3(31140606_32427978)x3 15q13.3 recurrent region (BP4-BP5) (includes CHRNA7) Gain 1 287 CHRNA7 de novo 57 arr[GRCh37] 15q13.3(31361538_32438943)x3 15q13.3 recurrent region (BP4-BP5) (includes CHRNA7) Gain 1 077 / de novo 58 arr[GRCh37] 16p13.11(15512480_16246473)x3 16p13.11 recurrent region (includes MYH11) Gain 734 / de novo 59 arr[GRCh37] 16p13.11(15125829_16282387)x3 16p13.11 recurrent microduplication (neurocognitive disorder susceptibility locus) 77.1% Gain 1 157 MYH11 de novo 60 arr[GRCh37] 22q11.1q11.21(17528442_
17940650)x322q11.21 recurrent (Cat eye syndrome) region (includes CECR2) 34.4% Gain 412 / de novo 61 arr[GRCh37] 22q11.21q11.22(21798705_
23326623)x322q11.2 recurrent region (distal type I, D-E or D-F) 81.4% Gain 1 528 / de novo CNVs: Copy number variants; OMIM: Online mendelian inheritance in man; BCL11A: B-cell CLL/lymphoma 11A; CHRNA7: Cholinergic receptor, nicotinic, alpha 7; MYH11: Myosin heavy chain 11, smooth muscle. -
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