Loss of the SEDL gene product (Sedlin) causes X-linked spondyloepiphyseal dysplasia tarda: Identification of a molecular defect in a Japanese family

A 23-year-old man was diagnosed as having X-linked spondyloepiphyseal dysplasia tarda (SEDT; MIM 313400) based on his disproportionately short trunk, short stature, characteristic radiological features of the spine (posterior hump, end plate sclerosis, and disc space narrowing) and the hips (short and thick femoral necks), and positive family history. This Japanese family was found to have an intragenic deletion flanking intron 2 and exon 3 of the SEDL gene that not only included the 5' untranslated region but also the coding sequence for the first methionine through the 25th alanine. This mutation was present in the proband and his unaffected mother (a heterozygote), but not in an unaffected sister and an unaffected uncle. The nature of the mutation predicted that the SEDL protein (Sedlin) was not produced in the proband, indicating that loss of Sedlin caused SEDT.     

X连锁迟发性脊柱骨骺发育不良快速基因诊断方法的研究

目的探讨建立X连锁迟发性脊柱骨骺发育不良（SEDT）快速基因诊断的方法。方法发现一个4代68人累及8例患者的SEDT大家系,呈X连锁隐性遗传。在应用PCR和DNA测序方法对SEDL进行基因突变分析后,提取外周血淋巴细胞RNA,应用RT-PCR扩增cDNA直接测序,建立快速基因诊断方法。结果RT-PCR结果显示,家系8例患者均为SEDL基因外显子6插入突变（c.370-371ins A,）,并发现1例无症状患儿携带相同突变（症状发生前）,6例女性携带者为杂合突变,家系其他成员和正常对照中均未见该插入突变。结沦RT-PCR检测扩增SEDL基因cDNA直接测序是一种快速基因诊断的方法。     

SEDL基因突变与X连锁迟发性脊柱骨骺发育不良研究进展

SEDL基因于定位于X短臂（Xp22.2）,含有6个外显子,第3～6外显子为编码外显子,翻译起始密码位于外显子3,翻译产物为含有140个氨基酸的Sedlin。SEDL基因是一个高度保守的基因,参与在内质网至高尔基体间囊泡运输的定位和融合,与蛋白质转运有关。X-连锁迟发性脊柱骨骺发育不良（SEDT）是累及脊椎椎体和身体承重大关节的骨软骨发育障碍性疾病,呈X-连锁隐性遗传。临床特点为短躯干性侏儒和进行性的大关节退行性变,X线检查腰部椎体前部上下缘凹陷、中后部呈驼峰状突起。1999年首次发现SEDT的致病基因为SEDL,迄今为止已在SEDL基因上发现47种突变,其中缺失突变最为常见。本文简要综述了SEDL基因的结构与功能以及SEDT的分子遗传学研究进展,有助于SEDT的基因诊断与产前诊断。     

X连锁迟发性脊椎骨骺发育不良家系SEDL基因突变分析

目的 鉴定中国西南地区一个4代迟发性脊椎骨骺发育不良大家系的分子遗传缺陷.方法 采用X染色体荧光标记微卫星标记物进行连锁分析,并通过直接序列分析筛查SEDL基因突变.结果 DXS987与DXS8051之间呈现连锁(最大LOD值:3.82;θ=0),致病基因定位于Xp22.2-Xp23.1;序列分析发现SEDL基因第4外显子发生点突变(c.239A＞G),导致在第80位编码氨基酸由组氨酸置换为精氨酸(H80R).结论 SEDL基因与此中国迟发性脊椎骨骺发育不良大家系表型完全连锁,并发现该基因新的致病突变(H80R).     

X-连锁迟发性脊椎骨骺发育不良家系基因突变研究

目的 研究X-连锁迟发性脊椎骨骺发育不良(X-linked spondyloepiphyseal dysplasia tarda,SEDL)患者的发病机理,并探讨该病的快速基因诊断方法.方法 应用逆转录聚合酶链反应,结合序列分析方法,对一个X-SEDL家系2例患者及育龄女性进行SEDL基因突变分析.结果 cDNA序列分析显示患者为G209A突变,并对突变所在第4外显子进行PCR扩增并测序进一步证实.患者女儿为该突变的携带者.结论 由于SEDL基因较小,直接对患者提取总RNA,逆转录后直接进行PCR扩增、测序,可直接发现基因阅读框内的多种类型的突变,相对于针对每一个外显子单独扩增检测更加直接、快速.     

X-连锁迟发性脊椎骨骺发育不良家系SEDL基因突变研究

目的：确定中国汉族中一个X－连锁迟发性脊椎骨骺发育不良（spondyloepiphyseal dyskplasia tarda,SEDL)大家系SEDL基因突变类型，探讨SEDL发病的分子基础。方法：用聚合酶链反应扩增产物双向直接测序方法检测了患者构成SEDL基因可读框的第3－6外显子及相邻侧翼区的DNA序列，将测序结果与GenBank公布的SEDL基因正常序列对比找出突变。然后在家系其他成员中证实该突变。结果：在2例患者（Ⅳ15、Ⅴ3）SEDL基因第2内含子剪接受体处发现了IVS2－2A→C突变，4个外显子的核苷酸序列未见改变。该突变在4例女性携带者得到证实，她们的基因型表现为野生型与突变型杂合现象。家系中2名未受累男性和15名无关健康个体未检测到这一突变。在该家系还检测出4个无症状的携带者。结论：首次发现SEDL基因IVS2－2A→C突变。该突变引起SEDL基因第2内含子3'端剪接受体改变，使之不能与外显子3正常剪接，可能是SEDL发病的分子基础。检测该突变可进行基因诊断，有重要的临床价值。     

NID1 variant associated with occipital cephaloceles in a family expressing a spectrum of phenotypes

Autosomal dominant Dandy‐Walker malformation and occipital cephalocele (ADDWOC) is a rare, congenital, and incompletely penetrant malformation that is considered to be part of the Dandy‐Walker spectrum of disorders. Affected individuals often present with an occipital cephalocele with a bony skull defect, but typically have normal neurological development. Here, we report on a three‐generation family in which individuals have variable phenotypes that are consistent with the ADDWOC spectrum: arachnoid cysts in the proband and his maternal grandfather, an occipital cephalocele in the proband and his brother, and a small bony defect in the proband's mother. Whole exome sequencing identified a rare heterozygous variant in NID1 (NM_002508.2:c.1162C>T, (p.Gln388Ter)) in the proband, his brother, and his mother. Sanger sequencing confirmed the presence of this variant in the maternal grandfather. The identical c.1162C>T variant was previously identified in variably affected members of a three‐generation family with ADDWOC. This case report provides further evidence that variants in NID1 may be clinically relevant for the development of a phenotype that is consistent with ADDWOC, and extends the phenotype of NID1‐associated ADDWOC to include arachnoid cysts. Given that the Dandy‐Walker malformation itself is not a pre‐requisite to this spectrum of phenotypes, we also suggest a novel term for the NID1‐associated disorder in order to give emphasis to this phenotypic variability: “Autosomal Dominant Posterior Fossa Anomalies with Occipital Cephaloceles.”     

Detection of a novel missense mutation in the mevalonate kinase gene in one Chinese family with DSAP

Disseminated superficial actinic porokeratosis (DSAP) is the most common form of porokeratosis and a severe chronic autosomal dominant cutaneous disorder with high genetic heterogeneity. Recently, the mevalonate kinase (MVK) gene has been identified as a candidate gene responsible for DSAP and multiple mutations have been reported. Here, we report identification of a novel missense mutation in the MVK gene in a Chinese family with DSAP. A 50-year-old male was diagnosed as proband of DSAP based on the clinical and histological findings, which show numerous hyperpigmented macules by physical examination and cornoid lamella by skin biopsy. Similar skin symptoms were also observed in his father, who died many years ago. We prepared genomic DNA from the proband, unaffected individuals from his family members, as well as 100 unrelated healthy controls. PCR was then conducted using the above genomic DNA as template and the MVK gene-specific primers. The PCR product was subjected to direct sequencing and the sequence was compared to that of MVK gene within the NCBI database. We detected a heterozygous C to G transition at nucleotide 643 in exon 7 of MVK gene of the proband. This will result in an amino acid change at codon 215 (P.Arg215Gly.), which is from an arginine codon (CGA) to a Glycine codon (GGA). We did not detect any mutation in the unaffected family members or the 100 unrelated healthy controls, demonstrating that this is a novel missense mutation in MVK gene and therefore, contributes to the molecular diagnosis of DSAP.     

Microduplication of 15q13.3 and Xq21.31 in a family with tourette syndrome and comorbidities

Tourette syndrome (TS) is a childhood onset neurodevelopmental disorder. Although it is widely accepted that genetic factors play a significant role in TS pathogenesis the etiology of this disorder is largely unknown. Identification of rare copy number variations (CNVs) as susceptibility factors in several neuropsychiatric disorders such as attention deficit‐hyperactivity disorder (ADHD), autism and schizophrenia, suggests involvement of these rare structural changes also in TS etiology. In a male patient with TS, ADHD, and OCD (obsessive compulsive disorder) we identified two microduplications (at 15q13.3 and Xq21.31) inherited from a mother with subclinical ADHD. The 15q duplication included the CHRNA7 gene; while two genes, PABPC5 and PCDH11X, were within the Xq duplication. The Xq21.31 duplication was present in three brothers with TS including the proband, but not in an unaffected brother, whereas the 15q duplication was present only in the proband and his mother. The structural variations observed in this family may contribute to the observed symptoms, but further studies are necessary to investigate the possible involvement of the described variations in the TS etiology. © 2013 Wiley Periodicals, Inc.     

A novel mutation in exon b (R259C) of the MTM1 gene is associated with a mild myotubular myopathy. Mutation in brief no. 125. Online

The genetic basis of the relatively mild myopathic symptoms exhibited in a male was investigated. Mutation screening of a candidate gene, MTM1, represented a chance of establishing the molecular defect and the mode of inheritance. SSCA detected variation of the exon b PCR products from the proband and his mother, compared to that observed upon analysis of the PCR products from other members of the family and 159 unrelated X chromosomes. Sequencing revealed a C775 to T transition, in the proband and his mother, but not in his unaffected brother. To confirm the presence of a base change in this region, a Cfol site was introduced into the PCR product of the wildtype allele by using the forward primer 5'-AGAAAATAAGACGGTCATTGcG-3' (mismatch base in small font) with the exon b reverse primer as used by Laporte et al (1996). Analysis of DNA from other members of the family using this method revealed that this is a new mutation in the proband's mother. This mutation would result in a Arg259->Cys substitution.     

X-连锁迟发性脊椎骨骺发育不良家系SEDL基因突变及基因诊断

目的 确定一个X-连锁迟发性脊椎骨骺发育不良(X-linked spondyloepiphyseal dysplasia tarda,SEDL)家系的基因突变类型;建立一种快速基因诊断方法.方法 采用体格检查、影像学检查及家系分析进行临床诊断.针对SEDL基因的第3～6外显子及其侧翼序列设计4对引物,建立基于PCR的变性高效液相色谱技术(denaturing high performance liquid chromatography,DHPLC)快速基因分型方法.常规酚-氯仿法从该家系3代18名成员的外周血中提取基因组DNA,经PCR/DHPLC分析,筛查出SEDL基因突变所在的片段,对该片段进行序列分析以确定突变位点及类型.结果 DHPLC分析发现该家系的SEDL基因突变位点在第4外显子片段,序列分析证实为c.218C》T突变,导致氨基酸序列S73L改变.在该家系的18名成员中,3例男性患者,5例女性肯定携带者和2例未婚女性携带者均带有该突变,其余表型正常的8名成员中未检测到这一突变.各成员的DHPLC峰型所代表的基因型与表型结果相吻合.结论 首次报告中国人SEDL基因c.218C》T突变,丰富了中国人SEDL基因的突变谱.采用的技术快速、可靠,能对SEDL进行快速基因分型和产前诊断.     

A possible bichromatid mutation in a male gamete giving rise to a female mosaic for two different mutations in the X-linked gene WAS

In genetic disorders caused by point mutations or small frameshift mutations, affected members of the same family are expected to have the same mutation in the causative gene. We have recently evaluated a family in which this was not the case. Maternal cousins with Wiskott-Aldrich syndrome (WAS; MIM 301000) had two different but contiguous single base pair deletions in WAS. The proband had an A deletion in codon 242 in exon 7 of WAS; his two cousins had a C deletion in codon 241. The mother of the proband was heterozygous for the A deletion allele, but her three sisters, including the mother of the affected cousins, were heterozygous for the C deletion. Both deletions occurred on the haplotype from the unaffected maternal great-grandfather. The maternal grandmother, who was a carrier of WAS, based on a non-random pattern of X chromosome inactivation in T cells, was mosaic for both deletions. These findings are most consistent with the mutations originating in a male gamete with different mutations on the two strands of DNA, a bichromatid mutation.     

SPG3A-遗传性痉挛性截瘫中的不完全外显性和遗传早现

目的通过分析遗传性痉挛性截瘫一家系(hereditary spastin paraplegia,HSP)SPG3A/atlastin基因突变与临床特征的关系,阐明显性遗传中的不完全外显性和遗传早现。方法收集1个HSP家系的临床资料,对家系成员以及100名正常对照进行神经系统检查,并对atlastin全编码序列和基因SPG4/spastin(S44和P45Q)和SPG6/nipa1含([GCG]5-11)的第1外显子进行DNA测序并分析。结果在先证者及其受累儿子和无症状父亲的外周血DNA中发现SPG3AV253I突变而在家系其他成员和正常对照个体中均未发现该突变。结论这是第2例由于SPG3AV253I突变引起的不完全外显性的家系报道,家系中有着相同突变位点个体的标记表型变异(遗传不外显)显示了遗传修饰和环境因素的影响。家系中越来越早的发病和症状加重与遗传早现相一致,这在SPG3A-HSP中尚属首例。     

Detection of mosaic RB1 mutations in families with retinoblastoma

The RB1 gene mutation detection rate in 1,020 retinoblastoma families was increased by the use of highly sensitive allele specific‐PCR (AS‐PCR) to detect low‐level mosaicism for 11 recurrent RB1 CGA>TGA nonsense mutations. For bilaterally affected probands, AS‐PCR increased the RB1 mutation detection sensitivity from 92.6% to 94.8%. Both RB1 oncogenic changes were detected in 92.7% of sporadic unilateral tumors (357/385); 14.6% (52/357) of unilateral probands with both tumor mutations identified carried one of the tumor mutations in blood. Mosaicism was evident in 5.5% of bilateral probands (23 of 421), in 3.8% of unilateral probands (22 of 572), and in one unaffected mother of a unilateral proband. Half of the mosaic mutations were only detectable by AS‐PCR for the 11 recurrent CGA>TGA mutations, and not by standard sequencing. This suggests that significant numbers of low‐level mosaics with other classes of RB1 mutations remain unidentified by current technology. We show that the use of linkage analysis in a two‐generation retinoblastoma family resulted in the erroneous conclusion that a child carried the parental mutation, because the founder parent was mosaic for the RB1 mutation. Of 142 unaffected parental pairs tested, only one unaffected parent of a proband (0.7%) showed somatic mosaicism for the proband's mutation, in contrast to an overall 4.5% somatic mosaicism rate for retinoblastoma probands, suggesting that mosaicism for an RB1 mutation is highly likely to manifest as retinoblastoma. Hum Mutat 0, 1–10, 2009. © 2009 Wiley‐Liss, Inc.     

Whole exome sequencing and functional studies identify an intronic mutation in TRAPPC2 that causes SEDT

Skeletal dysplasias are challenging to diagnose because of their phenotypic variability, genetic heterogeneity, and diverse inheritance patterns. We conducted whole exome sequencing of a Turkish male with a suspected X‐linked skeletal dysplasia of unknown etiology as well as his unaffected mother and maternal uncle. Bioinformatic filtering of variants implicated in skeletal system development revealed a novel hemizygous mutation, c.341‐(11_9)delAAT, in an intron of TRAPPC2, the causative locus of spondyloepiphyseal dysplasia tarda (SEDT). We show that this deletion leads to the loss of wild‐type TRAPPC2 and the generation of two functionally impaired mRNAs in patient cells. These consequences are predicted to disrupt function of SEDLIN/TRAPPC2. The clinical and research data were returned, with appropriate caveats, to the patient and informed his disease status and reproductive choices. Our findings expand the allelic repertoire of SEDT and show how prior filtering of the morbid human genome informed by inheritance pattern and phenotype, when combined with appropriate functional tests in patient‐derived cells, can expedite discovery, overcome issues of missing data and help interpret variants of unknown significance. Finally, this example shows how the return of a clinically confirmed mutational finding, supported by research allele pathogenicity data, can assist individuals with inherited disorders with life choices.     

Familial X;Y translocation in a malformed male infant and his mother

A male infant, the proband, with 46,Y,der(X),t(X;Y)(p22.3; q11.1), and his mother with 46,X,der(X),t(X;Y)(q22.3;q11.1) are presented. The proband was involved with a peculiar face, congenital heart disease, dry and scaly skin, and growth and psychomotor retardation. He died on the 111th day after birth. At necropsy a congenital heart disease was found, but there was no other major visceral malformation. The mother of the proband was healthy except for her short stature associated with disproportionately short limbs. Steroid sulfatase activity in her skin fibroblasts and lymphocytes was only half that of normal females.     

单纯17q25.3拷贝数重复导致全面性发育迟缓和多发性先天异常一例

目的探讨单纯17q25.3拷贝数重复的临床特征、遗传方式及基因型与表型的关系。方法应用全外显子测序、染色体微阵列、染色体核型分析、荧光原位杂交技术联合对先证者及其家系成员进行分析。结果先证者为一例4岁的多发性先天异常男性患儿,表现为全面性发育迟缓、矮小、智力障碍、脑发育不良、小头、特殊面容、肌张力低下、注意力缺陷多动障碍、共济失调、骨骼和心血管异常等。全外显子测序和染色体微阵列分析鉴定其在染色体17q25.3→qter发生5.7 Mb拷贝数重复,可能为患儿致病的原因。荧光原位杂交证实先证者该拷贝数重复是遗传自携带该片段平衡易位的母亲,其外祖母和舅舅也为该片段平衡易位携带者,而小姨未见异常。结论本研究结果丰富了单纯17q25.3拷贝数重复的临床表型谱,为遗传咨询提供了依据,并初步提示了P4HB、ACTG1、BAIAP2及TBCD基因为17q25.3拷贝数重复候选基因。