Sotos综合征的研究进展

Sotos综合征(MIM#117550)是一种以儿童期过度生长现象为特征的遗传病,主要表现为巨头畸形、特殊面容、骨龄提前以及不同程度的发育迟缓.目前已有数百名病例报道,具体发病率不详.约75%的病例是由NSD1基因内点突变或5q35微缺失所导致,欧裔患者多由5q35微缺失引起,而约50%日本患者主要由基因内点突变引起,仍有约25%病例未检测出NSDI基因异常,其具体致病机制尚不完全清楚.NSD1基因定位于染色体5q35,此基因编码一种组蛋白甲基化酶,该酶与转录调节过程有关.通过FISH(fluorescent in situ hybridization)分析、MLPA(multiplex ligation-dependent probe amplification)及实时定量荧光PCR反应等技术可以检测NSD1基因整体或部分缺失,直接测序可以检测出NSD1基因点突变.绝大部分NSD1基因异常为新生突变,多数为散发病例,但也发现数例家族性遗传病例.本病鉴别诊断主要为以生长过度为特征的疾病,包括Weaver综合征,Beckwith-Wiedeman综合征,脆性X染色体综合征等.目前本病尚无理想疗法,主要为对症治疗.出生后第一年内儿科随访对于本病临床并发症如脊柱侧弯及热性癫痫发作的治疗和预防监测有重要意义.     

Sotos综合征的研究进展

Sotos综合征(MIM#117550)是一种以儿童期过度生长现象为特征的遗传病,主要表现为巨头畸形、特殊面容、骨龄提前以及不同程度的发育迟缓.目前已有数百名病例报道,具体发病率不详.约75%的病例是由NSD1基因内点突变或5q35微缺失所导致,欧裔患者多由5q35微缺失引起,而约50%日本患者主要由基因内点突变引起,仍有约25%病例未检测出NSDI基因异常,其具体致病机制尚不完全清楚.NSD1基因定位于染色体5q35,此基因编码一种组蛋白甲基化酶,该酶与转录调节过程有关.通过FISH(fluorescent in situ hybridization)分析、MLPA(multiplex ligation-dependent probe amplification)及实时定量荧光PCR反应等技术可以检测NSD1基因整体或部分缺失,直接测序可以检测出NSD1基因点突变.绝大部分NSD1基因异常为新生突变,多数为散发病例,但也发现数例家族性遗传病例.本病鉴别诊断主要为以生长过度为特征的疾病,包括Weaver综合征,Beckwith-Wiedeman综合征,脆性X染色体综合征等.目前本病尚无理想疗法,主要为对症治疗.出生后第一年内儿科随访对于本病临床并发症如脊柱侧弯及热性癫痫发作的治疗和预防监测有重要意义.     

一例主动脉狭窄伴拇指缺如患儿的遗传学诊断CSCD

目的分析1例主动脉狭窄伴拇指缺如患儿的发病机制,为遗传咨询提供依据。方法用常规G显带分析患儿及其父母的外周血染色体核型,用微阵列比较基因组杂交（array comparative genomic hybridization,aCGH）技术对患儿及其父母进行染色体片段重复／缺失的分析。结果G显带分析结果显示患儿及其父母染色体核型未见异常。aCGH检测结果显示患儿2q22．3-q23．3区存在5．86Mb的杂合缺失,其父母未检测到染色体微重复／微缺失。结论患儿2q22．3-q23．3缺失为新发突变,诊断为2q23．1微缺失综合征,MBD5基因可能是该综合征的关键基因。     

荧光原位杂交在产前诊断胎儿先心病22q11微缺失中的应用

目的应用荧光原位杂交（FISH）技术检测胎儿染色体22q11微缺失,以探讨该技术在胎儿先天性心脏病病因检测中的临床应用。方法对41例产前诊断有各类心脏畸形、且染色体核型分析结果未见明显异常的胎儿以及1例先证者进行FISH检测,检测探针位于22q11微缺失综合征微缺失关键区域22q11的TUPLE1基因,与22q末端ARSA基因。结果 41例胎儿FISH检测均成功,所有胎儿22q11两位点均未发现微缺失;一胎儿家庭的1名先证者经检测确证为22q11微缺失综合征患者。结论胎儿心脏畸形有多种病因,常规染色体检查仅能检出其中一部分染色体数目异常,对于各种微缺失综合征,仍然需要FISH、芯片等更高分辨率的技术手段应用,对相关可能的致病位点进行针对性检测或筛检,以提高病因检出率,防止心脏畸形患儿出生。     

22q11.2微缺失综合征产前临床表型的分析

目的探讨产前诊断的22q11.2微缺失综合征病例的不同临床表型,进一步提高对该疾病的认识。方法收集2016年1月至2018年12本院医学遗传中心因产前筛查高风险而就诊,应用染色体微阵列技术确诊的22q11.2微缺失综合征病例,分析其临床表现。结果14651例产前筛查高风险病例中22例(1.5‰)确诊为22q11.2微缺失综合征,其中心脏超声结构异常13例(59.09%),心脏结构异常合并腭裂1例(4.55%),足内翻4例(18.18%),肾脏超声异常3例(13.64%),胎儿发育迟缓并唐氏筛查高风险1例(4.55%);22例22q11.2微缺失综合征中经典型19例(66.36%),非经典型3例(13.64%)。结论本组22q11.2微缺失综合征病例以足内翻为突出临床表现,仅次于心脏结构异常,应予以重视。     

一例Williams-Beuren综合征患儿的遗传学诊断与分析

目的对1例疑似Williams-Beuren综合征的先天性心脏病患儿进行遗传学诊断,分析其可能的分子病因,为临床遗传咨询提供依据。方法用常规G-显带分析了患儿及其双亲的外周血染色体核型,并用微阵列比较基因组杂交(array comparative genomic hybridization,aCGH)技术检测患儿及其双亲可能存在的染色体微重复/微缺失异常。结果G-显带分析结果显示,未见患儿及其父母外周血染色体核型的异常。aCGH检测结果发现,患儿第7号染色体的7q11.23区存在1个1.41 Mb长度的杂合性缺失,而其双亲不存在此染色体微缺失异常。结论患儿的7q11.23杂合性缺失为新发突变(de novo mutation),可确诊为Williams-Beuren综合征。     

一例软骨发育异常胎儿的遗传学分析

目的对1例软骨发育异常的胎儿进行遗传学分析,为产前诊断及评估其家庭的再发风险提供依据。方法对1例软骨发育异常的胎儿行G显带染色体核型分析、单核苷酸多态性微阵列(single nucleotide polymorphism-based arrays,SNP-Array)检测、荧光原位杂交(fluorescence in situ hybridization,FISH)及FGFR3基因突变检测。胎儿父母行外周血染色体核型分析、SNP-Array及FISH检测,以明确胎儿基因组变异的来源。结果胎儿脐血染色体核型为46,XY。脐血SNP-Array结果显示染色体Xp22.33区段存在3.7Mb微缺失,8q24.12区段存在538.4kb微重复,其缺失区段包含SHOX和ARSE等软骨发育相关基因;FGFR3基因未发生c.1138GA/C突变。根据胎儿及其父母SNP-array检测和FISH验证,胎儿携带的8q24.12微重复遗传自母亲,Xp22.33微缺失为新发突变。结论 Xp22.33微缺失是造成胎儿软骨发育异常的遗传学因素,因其为新发突变,在其家庭复发风险低。     

17q12微缺失综合征的产前超声表现和遗传学分析

目的 分析产前孕中晚期17q12微缺失胎儿的超声发现、染色体微阵列分析（CMA）结果、妊娠结局和跟踪随访，探索17q12微缺失综合征的基因组与临床表型的相关性，为产前咨询与诊断提供理论依据。方法 对16例因超声提示胎儿肾脏实质性回声增强或结构异常行侵入性产前诊断羊水或脐带血穿刺，CMA检测结果为17q12微缺失的胎儿进行回顾性研究分析。结果 16例17q12微缺失病例的缺失片段大小在1.42～1.94 Mb，区域内均包含HNF1B、LHX1等相关致病基因。14例为新发突变，2例遗传自母亲。15例肾脏双侧或单侧高回声，1例除肾脏结构畸形外还伴有心脏和肺部结构畸形。5例遗传咨询后选择终止妊娠，11例选择继续妊娠。结论 产前胎儿17q12微缺失综合征的临床表型差异大，超声肾脏回声增强与其存在密切相关性。产前胎儿肾脏高回声行CMA检测，可准确诊断该综合征并明确其基因组学信息，为孕妇妊娠选择提供指导性建议。     

微滴数字PCR技术检测先天性心脏病患儿染色体22q11．2区段微缺失CSCD

目的探索一种检测22qii．2微缺失综合征的新方法。方法针对22q11．2微缺失综合征特异缺失区内的TBX1基因和内参基因RPP30设计引物和探针,采用微滴数字PCR（dropletdigitalPCR,ddPCR）的方法计算TBX1／RPP30的比值,检测22q11．2区段微缺失。结果通过数字PCR方法计算TBX1／尺PP30的比值检测22q11．2微缺失综合征,检出3例微阵列比较基因组杂交检测结果为22q11．2微缺失综合征阳性的样本。在14例临床诊断为先天性心脏病的患儿中检测出2例22q11．2微缺失阳性样本。结论微滴数字PCR可以准确检测出22q11．2区段微缺失,可提供一种快速、经济的检测先天性心脏病相关染色体22q11．2微缺失综合征的方法。     

三例22号染色体异常胎儿的产前遗传学分析

目的应用超声以及多种遗传学检测技术对3例产前筛查提示染色体可能异常的胎儿进行分析,为遗传咨询提供依据。方法对3例孕妇进行胎儿超声检查、核型分析、单核苷酸多态性微阵列芯片(single nucleotide polymorphism-based microarray,SNP-Array)检测,并通过荧光原位杂交(fluorescence in situ hybridization,FISH)对结果进行验证。结果三例胎儿均发现22号染色体存在异常。例1在22q13.2q13.33区存在7.1 Mb的杂合缺失,涉及SHANK3、FBLN1等54个OMIM基因;例2为嵌合体核型,约12%的细胞22q13.31q13.33区存在6.6 Mb的杂合缺失,覆盖SHANK3、PPARA等48个OMIM基因,另有5%的细胞22q11.1q13.2区存在26.1 Mb的拷贝重复,覆盖285个OMIM基因;例3在22q11.1q11.21区存在1.7 Mb的二次重复,涉及CECR1、CECR2、ATP6V1E1等10个OMIM基因。三例胎儿父母的核型及SNP-Array检测结果均未见异常,提示胎儿为新发变异。结论22号染色体微缺失/微重复所致疾病的严重性不仅与其范围有关,还与染色体结构、基因剂量及环境等密切相关。在产前诊断中综合运用超声和多种遗传学检测技术可以显著提高表型变异较大的遗传学异常的检出率。     

Hyperinsulinemic hypoglycemia in seven patients with de novo NSD1 mutations

Sotos syndrome is an overgrowth syndrome characterized by distinctive facial features and intellectual disability caused by haploinsufficiency of the NSD1 gene. Genotype–phenotype correlations have been observed, with major anomalies seen more frequently in patients with 5q35 deletions than those with point mutations in NSD1. Though endocrine features have rarely been described, transient hyperinsulinemic hypoglycemia (HI) of the neonatal period has been reported as an uncommon presentation of Sotos syndrome. Eight cases of 5q35 deletions and one patient with an intragenic NSD1 mutation with transient HI have been reported. Here, we describe seven individuals with HI caused by NSD1 gene mutations with three having persistent hyperinsulinemic hypoglycemia. These patients with persistent HI and Sotos syndrome caused by NSD1 mutations, further dispel the hypothesis that HI is due to the deletion of other genes in the deleted 5q35 region. These patients emphasize that NSD1 haploinsufficiency is sufficient to cause HI, and suggest that Sotos syndrome should be considered in patients presenting with neonatal HI. Lastly, these patients help extend the phenotypic spectrum of Sotos syndrome to include HI as a significant feature.     

Partial NSD1 deletions cause 5% of Sotos syndrome and are readily identifiable by multiplex ligation dependent probe amplification

Background: Most cases of Sotos syndrome are caused by intragenic NSD1 mutations or 5q35 microdeletions. It is uncertain whether allelic or genetic heterogeneity underlies the residual cases and it has been proposed that other mechanisms, such as 11p15 defects, might be responsible for Sotos cases without NSD1 mutations or 5q35 microdeletions. Objective: To develop a multiplex ligation dependent probe amplification (MLPA) assay to screen NSD1 for exonic deletions/duplications. Methods: Analysis was undertaken of 18 classic Sotos syndrome cases in which NSD1 mutations and 5q35 microdeletions were excluded. Long range polymerase chain reaction (PCR) was used to characterise the mechanism of generation of the partial NSD1 deletions. Results: Eight unique partial NSD1 deletions were identified: exons 1–2 (n = 4), exons 3–5, exons 9–13, exons 19–21, and exon 22. Using long range PCR six of the deletions were confirmed and the precise breakpoints in five cases characterised. This showed that three had arisen through Alu-Alu recombination and two from non-homologous end joining. Conclusions: MLPA is a robust, inexpensive, simple technique that reliably detects both 5q35 microdeletions and partial NSD1 deletions that together account for ∼15% of Sotos syndrome.     

Reversed clinical phenotype due to a microduplication of Sotos syndrome region detected by array CGH: microcephaly, developmental delay and delayed bone age

Haploinsufficiency of the NSD1 gene due to 5q35 microdeletions or intragenic mutations is the major cause of Sotos syndrome characterized by generalized overgrowth, large hands and feet with advanced bone age, craniofacial dysmorphic features, learning disability, and possible susceptibility to tumors. Here, we report on a 14-month-old boy with a reverse phenotype of Sotos syndrome due to the reciprocal duplication of the 5q35.3 region, including the NSD1 gene, detected by array CGH. The phenotype includes delayed bone age, microcephaly, seizures, and failure to thrive. Our case suggests that the gene dosage effect of the NSD1 gene is the likely cause for the reversed phenotype of Sotos syndrome in this patient.     

NSD1 mutations in Sotos syndrome

Sotos syndrome is a genetic disorder characterized by a typical facial appearance, macrocephaly, accelerated growth, developmental delay, and a variable range of associated abnormalities. The NSD1 gene was recently found to be responsible for Sotos syndrome, and more than 150 patients with NSD1 alterations have been identified. A significant ethnic difference is found in the prevalence of different types of mutation, with a high percentage of microdeletions identified in Japanese Sotos syndrome patients and with intragenic mutations in most non-Japanese patients. NSD1 aberrations are rather specific for Sotos syndrome, but have also been detected in patients lacking one or more major criteria of the disorder, namely overgrowth, macrocephaly, and advanced bone age. Thus, new diagnostic criteria should be considered. Studies have reported different frequencies of mutations versus non-mutations in Sotos syndrome, thus indicating allelic or locus hetereogeneity. Although some authors have suggested genotype/phenotype correlations, further studies are needed.     

Fifty microdeletions among 112 cases of Sotos syndrome: low copy repeats possibly mediate the common deletion

Sotos syndrome (SoS) is an autosomal dominant overgrowth syndrome with characteristic craniofacial dysmorphic features and various degrees of mental retardation. We previously showed that haploinsufficiency of the NSD1 gene is the major cause of SoS, and submicroscopic deletions at 5q35, including NSD1, were found in about a half (20/42) of our patients examined. Since the first report, an additional 70 SoS cases consisting of 53 Japanese and 17 non-Japanese have been analyzed. We found 50 microdeletions (45%) and 16 point mutations (14%) among all the 112 cases. A large difference in the frequency of microdeletions between Japanese and non-Japanese patients was noted: 49 (52%) of the 95 Japanese patients and only one (6%) of the 17 non-Japanese had microdeletions. A sequence-based physical map was constructed to characterize the microdeletions. Most of the microdeletions were confirmed to be identical by FISH analysis. We identified highly homologous sequences, i.e., possible low copy repeats (LCRs), in regions flanking proximal and distal breakpoints of the common deletion, This suggests that LCRs may mediate the deletion. Such LCRs seem to be present in different populations. Thus the different frequency of microdeletions between Japanese and non-Japanese cases in our study may have been caused by patient-selection bias.     

Evaluation of NSD2 and NSD3 in overgrowth syndromes

Sotos syndrome is an overgrowth condition predominantly caused by truncating mutations, missense mutations restricted to functional domains, or deletions of NSD1. NSD1 is a member of a protein family that includes NSD2 and NSD3, both of which show 70-75% sequence identity with NSD1. This strong sequence similarity suggests that abrogation of NSD2 or NSD3 function may cause non-NSD1 Sotos cases or other overgrowth phenotypes. To evaluate this hypothesis, we mutationally screened NSD2 and NSD3 in 78 overgrowth syndrome cases in which NSD1 mutations and deletions had been excluded. Additionally, we used microsatellite markers within the vicinity of the genes to look for whole gene deletions. No truncating mutations or gene deletions were identified in either gene. We identified two conservative missense NSD2 alterations in two non-Sotos overgrowth cases but neither was within a functional domain. We identified three synonymous and two intronic variants in NSD2 and two synonymous base substitutions in NSD3. Our results suggest that despite strong sequence similarity between NSD1, NSD2 and NSD3, the latter genes are unlikely to be making a substantial contribution to overgrowth phenotypes and thus may operate in distinct functional pathways from NSD1.     

Mutations in NSD1 are responsible for Sotos syndrome, but are not a frequent finding in other overgrowth phenotypes

Recently, deletions encompassing the nuclear receptor binding SET-Domain 1 (NSD1) gene have been described as the major cause of Japanese patients with the Sotos syndrome, whereas point mutations have been identified in the majority of European Sotos syndrome patients. In order to investigate a possible phenotype-genotype correlation and to further define the predictive value of NSD1 mutations, we performed mutational analysis of the NSD1 gene in 20 patients and one familial case with Sotos syndrome, five patients with Weaver syndrome, six patients with unclassified overgrowth/mental retardation, and six patients with macrocephaly/mental retardation. We were able to identify mutations within the NSD1 gene in 18 patients and the familial case with Sotos syndrome (90%). The mutations (six nonsense, eight frame shifts, three splice site, one missense, one in-frame deletion) are expected to result in an impairment of NSD1 function. The best correlation between clinical assessment and molecular results was obtained for the Sotos facial gestalt in conjunction with overgrowth, macrocephaly, and developmental delay. In contrast to the high mutation detection rate in Sotos syndrome, none of the patients with Weaver syndrome, unclassified overgrowth/mental retardation and macrocephaly/mental retardation, harbored NSD1 mutations. We tested for large deletions by FISH analysis but were not able to identify any deletion cases. The results indicate that the great majority of patients with Sotos syndrome are caused by mutations in NSD1. Deletions covering the NSD1 locus were not found in the patients analyzed here.     

Heterogeneity of NSD1 alterations in 116 patients with Sotos syndrome

Sotos syndrome is an overgrowth syndrome characterized by distinctive facial features, learning difficulties, and macrocephaly with frequent pre- and postnatal overgrowth with advanced bone age. Here, we report on our experience in the molecular diagnostic of Sotos syndrome on 116 patients. Using direct sequencing and a quantitative multiplex PCR of short fluorescent fragments (QMPSF)-based assay allowing accurate detection of both total and partial NSD1 deletions, we identified NSD1 abnormalities in 104 patients corresponding to 102 Sotos families (90%). NSD1 point mutations were detected in 80% of the index cases, large deletions removing the NSD1 gene entirely in 14%, and intragenic NSD1 rearrangements in 6%. Among the 69 detected distinct point mutations, 48 were novel. The QMPSF assay detected an exonic duplication and a mosaic partial deletion. QMPSF mapping of the 15 large deletions revealed the heterogeneity of the deletions, which vary in size from 1 to 4.5 Mb. Clinical features of NSD1-positive Sotos patients revealed that the phenotype in patients with nontruncating mutations was less severe that in patients with truncating mutations. This study confirms the heterogeneity of NSD1 alterations in Sotos syndrome and therefore the need to complete sequencing analysis by screening for partial deletions and duplications to ensure an accurate molecular diagnosis of this syndrome.