Molecular Genetic Diagnostics of Prader-Willi Syndrome:a Validation of Linkage Analysis for the Chinese Population

Prader-Willi Syndrome （PWS） is a genetic disorder that is difficult to detect, particularly at an early age. PWS is caused by disruption of normal, epigenetically controlled gene function in the chromosome 15q11-q13 region. Clinical symptoms are difficult to diagnose in infants and only become clearer at later ages as the patients develop hyperphagia and morbid obesity. Molecular genetic tests are able to definitively diagnose PWS and allow early diagnosis of the syndrome. High resolution cytogenetic testing, methylation-specific PCR （MS-PCR）, and linkage analysis are routinely used to diagnose PWS. To establish a linkage analysis method for Chinese patients, this study identified a useful set of STR markers in the typical PWS deletion and adjacent area, for linkage analysis in two Chinese families with PWS offspring. Using this method, the authors confn＇rned that one patient had a paternal deletion in chromosome 15q 11-q 13 and the other patient had maternal uniparental heterodisomy of chromosome 15. MS -PCR and high resolution chromosome G-banding also confirmed this diagnosis. This linkage analysis method can detect both deletion and uniparental disomy, thus providing valuable information for genetic counseling and the opportunity to analyze the relationship between the genotype and phenotype of PWS.

单亲二倍体染色体异常的研究进展

单亲二倍体(UPD)是指同源染色体或染色体上的部分片段均来源于双亲中的一方,其发病率较低,但可继发隐性基因纯合突变或基因印迹障碍,从而导致各种各样的临床表型。临床上常用的检测技术,如染色体核型分析、无创产前筛查以及染色体拷贝数目变异等都难以发现UPD的存在。在临床工作中,可能会因对UPD的认识不足或者检测技术有限而导致医者对该类疾病的误诊。通过全面搜集与单亲二倍体相关的研究报道,系统地对其形成机制、致病机制、临床检测技术以及预防和治疗手段进行综述,以便更好地指导基础研究和临床诊治。

Single Nucleotide Polymorphism-Based Chromosomal Microarray Evaluation of Hydatidiform Moles: A US National Reference Laboratory Experience

Objectives: This retrospective study evaluated 1) benefits of single nucleotide polymorphism (SNP)-based chromosomal microarrays (CMAs) in the diagnosis of complete hydatidiform mole (CHM) and partial HM (PHM) in products of conception (POC) and amniotic fluid (AF) specimens, and 2) frequency of whole-genome uniparental disomy (wgUPD) and triploidy in POC and AF specimens received at a US national reference laboratory. Methods: We reviewed consecutive 2138 POC and 3230 AF specimens and identified the cases with wgUPD and triploidy which are associated with molar pregnancy. Results: Of 2138 consecutive POC specimens tested, SNP-based CMA detected wgUPD in 10 (0.47%) and triploidy in 84 (3.93%). Of the 10 wgUPD cases, 9 (90%) were confirmed as CHM. Of 3230 consecutive AF specimens, the array detected wgUPD in 1 case (0.03%) and triploidy in 11 (0.34%). Conclusions: SNP-based microarray allows detection of wgUPD in POC and AF specimens at a US national reference laboratory. Correctly diagnosing HM and differentiating CHM from PHM are important for clinical management. The effective SNP-based CMA detection of wgUPD in CHM may enable physicians to monitor patients at risk for gestational trophoblastic disease and neoplasm. Conventional chromosome analysis of POC has a high failure rate, cannot be performed on formalin-fixed paraffin embedded samples, and cannot detect wgUPD. Further multi-institutional collaborative assessmen on accuracy, cost-effectiveness, and adequate access to SNP-based CMA, may lead this testing platform to be considered as the first-tier analysis tool for POC specimens, including those showing PHM or CHM.

早孕期自然流产的遗传学病因:815例分析

目的分析早孕期自然流产的遗传学病因。方法本研究为回顾性研究。研究对象为2021年1月至2022年12月在青岛大学附属妇女儿童医院因孕6~13周自然流产自愿检测早孕期流产胚胎的患者815例。采用高通量测序技术对流产组织进行检测,利用生物信息学方法分析结果。采用χ^(2)检验进行统计学分析。结果(1)815例研究对象中检出染色体异常525例(64.4%),包括染色体数目异常479例(91.2%,包括非整倍体异常421例和三倍体58例),结构异常(拷贝数变异,copy number variation,CNV)44例(8.4%),单亲二体2例(0.4%)。(2)染色体数目异常以染色体非整倍体最常见(87.9%,421/479),涉及除1号染色体的所有染色体,以16-三体最多(17.5%,84/479),其次为X染色体单体(13.4%,64/479)和22-三体(11.3%,54/479)。27例(5.6%)存在多种染色体异常。在9例常染色体单体中,21号染色体单体7例,18和4号染色体单体各1例。(3)44例结构异常中,发现62个致病性或可能致病性CNV,片段长度为19.58 Mb(1.08~103.81 Mb)。涉及8号染色体的CNV最多,为16个(25.8%,16/62),其次为4号和18号染色体[各6个(9.7%,6/62)]。62个CNV中的10个(16.1%)片段大小≤5 Mb,包括3例微缺失综合征。(4)对低深度全基因组CNV测序(low-depth copy number variation sequencing,CNV-seq)结果未提示常染色体数目异常的胚胎进行荧光定量聚合酶链反应验证,检出2例全染色体组单亲二体,均为父源性单亲二体,为完全性葡萄胎。(5)CNV-seq结果提示胚胎存在CNV的44例中,32例孕妇及其配偶选择进行外周血染色体核型分析,其中一方为染色体平衡易位携带者9例(28.1%)。这9例样本均涉及2条染色体变异,且均位于染色体末端。对于片段大小≤5 Mb的CNV,有2例进行了CytoScan 750K芯片检测,结果与CNV-seq测序结果基本一致。(6)32对进行了外周血染色体核型分析的夫妻中,9对(28.1%)进行了染色体相关区域的荧光原位杂交检测,其中正常6例,异常3例。荧光原位杂交异常区域与染色体核型结果一致。(7)年龄≥35岁的孕妇胚胎染色体异常率,以及胚胎染色体数目异常率明显高于年龄<35岁者[75.8%(182/240)与59.6%(343/575),χ^(2)=23.37;73.3%(176/240)与53.2%(306/575),χ^(2)=19.34;P值均<0.001]。2组孕妇的胚胎染色体结构异常率差异无统计学意义。结论染色体数目异常是早孕期自然流产的主要原因,在流产年龄≥35岁的孕妇中表现更为明显。CNV-seq可能更适用于早孕期自然流产胚胎的检测。

遗传性痉挛性截瘫5A型一个家系的临床表型及遗传学分析

目的探讨1个遗传性痉挛性截瘫5A型(SPG5A)家系的临床表型及遗传学特点。方法选取2022年8月15日在河南省儿童医院疑诊为遗传性痉挛性截瘫(HSP)的1个家系作为研究对象。收集该家系的临床资料,采集家系成员的外周血样,提取基因组DNA,进行家系全基因组测序(trio-WGS),对可疑致病性变异进行Sanger测序验证。结果该家系患儿为1岁男性,主要表现为小头畸形,颜面部、四肢远端及躯干背侧多毛,智力和运动发育落后,双下肢肌张力高,双侧膝腱反射亢进,病理征阳性;其父母及姐姐表型均未见明显异常。Trio-WGS检测发现患儿携带CYP7B1基因c.1250G>A(p.Arg417His)纯合变异,其母亲携带杂合变异,父亲和姐姐均为野生型,变异来源分析为8号染色体(chr8)母源单亲二倍体(UPD),Sanger测序与trio-WGS结果一致。既往未见chr8母源UPD导致SPG5A的报道。结论上述SPG5A患儿为复杂型HSP,chr8 CYP7B1基因c.1250G>A母源UPD可能是其遗传学病因。

四例Prader-Willi综合征患儿的分子遗传缺陷分析

目的 观察Prader Willi综合征 (PWS)患者的分子遗传基础及临床筛查策略 ,为进一步的遗传咨询提供信息。方法 应用甲基化特异性PCR(MSPCR)及荧光原位杂交 (FISH)技术对 4例临床诊断PWS患者进行基因分析研究。结果 4例患者MSPCR结果均显示缺乏父源的相关片段 ,而仅为母源DNA ,即第 1 5号染色体母源单亲二体 (matUPD1 5) ;FISH检测发现 2例 1 5q近端SNRPN基因片段的微小缺失。结论 父源 1 5q1 1 1 3特异区带缺失及matUPD1 5亦与我国PWS患者致病的分子病理缺陷有关。临床开展相关的细胞分子遗传学实验诊断对PWS临床诊断及遗传咨询。

一例11p嵌合单亲二倍体患者的遗传学分析

目的分析1例11p嵌合型单亲二倍体(uniparental disomy,UPD)患者的临床表型及基因组异常,探讨其致病原因.方法常规G显带技术和单核苷酸多态性微阵列芯片对患者进行全基因组水平的检测.结果患者常规染色体检查未见异常,芯片检测显示患者染色体11p15.5p12区存在42.7Mb的嵌合性UPD([hg19]chr11:491333-43189376).结论患者11p15.5p12区嵌合性UPD可能是导致其心脏室间隔缺损、左侧乳头发育畸形的主要原因.