良性家族性婴儿惊厥和阵发性运动障碍综合征基因位点异质性：5个家系的研究

背景：良性家族性婴儿惊厥(benign familial infantile convulsion，BFIC)疾病基因定位研究主要在西方国家进行，尽管现在已经报道了3个染色体位点与疾病基因连锁，但直到目前疾病基因仍未被找到和证实。要最终克隆BFIC疾病基因首先要对BFIC疾病基因进行定位和位点异质性研究。目的：研究BFIC家系的疾病基因与BFIC位点的连锁关系并检测是否存在疾病基因位点异质性。设计：以5个BFIC家系成员的基因型为研究对象，回顾性观察对比研究。单位：一所大学的细胞生物学与医学遗传学研究室。对象：本研究于2001—07月／2003—07在郑州大学医学院细胞生物学与医学遗传学教研室完成。共采集5个BFIC家系(图1—5)，分别来自河南省新乡、南阳、周口、鹤璧四地区，受试者共70例，其中BBIC患者28例，非BFIC患者42例。纳入标准：①符合国际抗癫痫联盟颁布的癫痫发作分类的标准确诊者；排除标准：脑电图、脑CT、磁共振检测结果有异常以及有中毒、脑外伤病史者。方法：应用聚合酶链反应(PCR)、变性聚丙烯酰胺凝胶电泳和银染技术得到家系成员的基因型。从BFIC家系成员外周血中抽提DNA，选择D19S245，D19S250，D16S3131，D16S3133，D2S399和D2S2330等6个基因短片段重复序列(STR)作为DNA标记，检测家系成员的基因型。将基因型信息输入计算机由LINKAGE软件包中的MLINK程序完成连锁分析边。最后，由LINKAGE软件包中的MLINK程序检测疾病基因位点异质性。主要观察指标：家系成员基因型的连锁分析结果和异质性检测结果。结果：连锁分析结果显示，在常染色体显性遗传(AD)模式下，标记位点D19S250处，家系2，3，5在重组率为0．000，外显率为90％时，获得最大两点检测限(LOD)值总和为2．151；标记位点D16S3131处，家系2，5在重组率为0．085，外显率为70％，60％时，获得最大两点LOD值分别为1．056，1．155；提示这两个位点与疾病基因可能存在连锁关系。在其它位点处未获得提示连锁关系的信息。异质性检测显示，可能与D16S3131存在连锁关系的家系占39．8％，可能与D19S250存在连锁关系的家系占41．3％，而与这两个标记位点均不存在连锁关系的家系占18．8％。BFIC家系之间存在位点异质性。结论：本研究发现了BFIC致病基因可能与D19S250或D16S3131存在连锁关系，BFIC存在位点异质性，从而为精确定位BFIC疾病基因提供了重要信息。     

瘢痕疙瘩候选基因与染色体2q23微卫星扫描及连锁分析的多家系研究

目的：从与瘢痕疙瘩发病可能存在密切关系的基因出发，分析中国汉族瘢痕疙瘩家系致病基因与染色体2q23区域是否存在连锁关系，以定位易感基因位点。方法：采用微卫星扫描及连锁分析方法，选取3个中国汉族瘢痕疙瘩家系中69名成员的外周静脉血标本，根据文献选择位于2q23区域11个微卫星标记，应用多重聚合酶链式反应（mPCR）扩增产物片断，测定PCR产物片段，获得每个样本的基因分型。运用连锁分析软件LINKAGE的MLINK程序计算每个标记位点的LOD值，根据两点间LOD值判断是否存在连锁关系。结果：在重组率θ=0～0．5时，这些微卫星标记的两点LOD值绝大部分都小于1，排除连锁关系存在。结论：中国汉族瘢痕疙瘩家系易感基因位点不在染色体2q23区域。说明瘢痕疙瘩易感基因位点存在异质性。     

瘢痕疙瘩候选基因与染色体7p11微卫星扫描及连锁分析的多家系研究

目的：从与瘢痕疙瘩发病可能存在密切关系的基因出发，分析中国汉族瘢痕疙瘩家系致病基因与染色体7p11区域是否存在连锁关系，以定位易感基因位点。 方法：采用微卫星扫描及连锁分析方法，选取3个中国汉族瘢痕疙瘩家系中69名成员的外周静脉血标本，根据文献选择位于7p11区域4个微卫星标记，应用多重聚合酶链式反应（mPCR）扩增产物片断，测定PCR产物片段，获得每个样本的基因分型。运用连锁分析软件LINKAGE的MLINK程序计算每个标记位点的LOD值，根据两点间LOD值判断是否存在连锁关系。 结果：在重组率θ=0-0．5时，这些微卫星标记的两点LOD值绝大部分都小于1，排除连锁关系存在。 结论：中国汉族瘢痕疙瘩家系易感基因位点不在染色体7p11区域。说明瘢痕疙瘩易感基因位点存在异质性。     

1个牙本质生长不全Ⅱ型家系疾病基因的连锁分析

目的对一个牙本质生长不全Ⅱ型家系疾病基因进行定位.方法提取该家系18个成员的外周血DNA;在染色体4q21上选择6个短串联重复序列(short tandem repeat,STR)位点,即D4S1534、GATA62A11、DSP(P)、DMP1、SPP1和D4S1563;用连锁分析法分析该家系疾病基因与上述6个STR位点的连锁关系并进行染色体单倍型分析.结果有2个位点最大LOD值＞3,分别是位点GATA62A11,得到最大连锁值3.86,(θ=0);位点DSP(P)最大连锁值4.72(θ=0).单倍型分析显示疾病基因位于4q21上的D4S1534-DMP1区域内.结论牙本质生长不全Ⅱ型家系的疾病基因定位在4q21上.     

中国汉族瘢痕疙瘩家系易感基因位点的定位分析

背景：转化生长因子13是目前与瘢痕关系最为密切的细胞因子，而SMAD蛋白介导的信号通路是转化生长因子B下游信号传递的主要途径。人SMAD蛋白基因在15q22.31-q23及18q21．1染色体区域。实验假定Smad基因为选择的瘢痕疙瘩家系易感基因位点。目的：定位中国汉族瘢痕疙瘩家系的易感基因位点。设计、时间及地点：两个家系、大样本的微卫星扫描连锁分析实验，于2007-02／06在上海基康公司实验室完成。材料：选择6个国内不同地区的瘢痕疙瘩家系2个4代发病的NM、LN家系中32位和19位成员，严格遵照赫尔辛基宣言规定的准则采集血样和病理组织标本。方法：采集2个家系51名成员的外周静脉血样，提取基因组DNA；选取位于15q22．31-q23及18q21．1染色体区域的7个微卫星标记位点D15S108、D15S216、D15S534、D18S363、D18S460、D18S467、D18S846，对这些微卫星位点进行聚合酶链反应扩增，产物片断基因分型，再进行连锁分析。主要观察指标：NM和LN瘢痕疙瘩家系外显率为90％时各位点LOD值。结果：NM、LN两个瘢痕疙瘩家系在外显率分别为90％条件下，重组率0=0-～0．5时，这些微卫星标记的两点LOD值绝大部分都小于1，排除连锁关系存在。结论：分析结果发现中国汉族瘢痕疙瘩家系易感基因位点不在染色体15q22．31-q23及18q21．1区域。     

先天性髋脱位与同源盒基因传递不平衡研究

背景目前研究表明遗传因素在先天性髋脱位(congenital dislocation of the hip,CDH)的发病中起重要作用.但迄今为止,从基因水平研究其发生机制报道较少.同源盒(homeobox,HOX)基因是胚胎发育和脊椎动物肢体发育的重要调控基因,因此推测HOX基因可能与CDH的发病有关.目的探讨CDH与HOX基因是否存在相关性.设计核心家系内对照关联研究.单位一所大学医院的发育儿科、遗传研究室及小儿外科.对象101个CDH核心家系303名成员均为中国医科大学第二临床学院小儿骨科病房1999-12/2001-01间全部住院CDH患者及其父母,所有患者均有典型的临床表现,经X射线检查及手术确诊.方法在胚胎肢体发育调控相关基因-HOX基因A簇、B簇、C簇和D簇所在的染色体区域7P14-15,17q21,12q13和2q31内选择4个微卫星DNA标记D7S1808,D17S1820,D12S1686和Hox4EP,应用聚合酶链反应及变性聚丙烯酰胺凝胶电泳技术,对101个先天性髋脱位核心家系的303名成员进行基因型分析,并进行传递不平衡检验(TDT).主要观察指标确定101个CDH核心家系303名成员4个微卫星DNA标记D7S1808,D17S1820,D12S1686和Hox4EP的基因型,对父母传递和不传递给患者的等位基因进行传递不平衡检验.结果在D12S1686多态性标记位点上共检测到16个等位基因,TDT分析显示,CDH与D12S1686遗传标记位点不存在传递不平衡(X2=6.171,P=0.965).在D7S1808多态性标记位点上共检测到10个等位基因,CDH与D7S1808遗传标记位点的第7个等位基因存在传递不平衡(X2=6.045,P=0 014).在D17S1820多态性标记位点上共检测到12个等位基因,CDH与D17S1820遗传标记位点的第4个等位基因存在传递不平衡(X2=6.025,P=0.014).在Hox4EP多态性标记位点上共检测到16个等位基因,CDH与Hox4EP遗传标记位点的第4个等位基因存在传递不平衡(X2=6.461,P=0.011).结论CDH与HOX基因A簇、B簇和D簇可能有关联,HOX A簇、B簇和D簇基因可能是先天性髋脱位的易感基因.     

原发性红斑肢痛症一家系排除与2q24．1-32区间连锁分析

【目的】研究原发性红斑肢痛症与2亏染色体长臂2q24．1-32区间的连锁情况。【方法】收集一个原发性红斑肢痛症家系成员的血样抽提DNA,选用2号染色体长臂2q24．1-32区间内7个微卫星标记对该家系成员进行基因扫描,并对基因分型结果进行连锁分析及单倍型分析。【结果】连锁分析所得两点LOD值结果（重组率0—0时）〈-2,单倍型分析发现该疾病表型与基因型不共分离。【结论】排除该家系与2号染色体体长臂2q24．1-32区间连锁,提示原发性红斑肢痛症具有遗传异质性。该家系可能有新的致病基因位点。     

先天性髋脱位与同源盒基因传递不平衡研究

背景：目前研究表明遗传因素在先天性髋脱位(congenital dislocation of the hip.CDH)的发病中起重要作用但迄今为止，从基因水平研究其发生机制报道较少。同源盒(homeobox，HOX)基因是胚胎发育和脊椎动物肢体发育的重要凋控基因，因此推测HOX基因可能与CDH的发病有关。目的：探讨CDH与HOX基因是否存在相关性。设计：核心家系内对照关联研究。单位：一所大学医院的发育儿科、遗传研究室及小儿外科。对象：101个CDH核心家系303名成员均为中国医科大学第二临床学院小儿骨科病房1999—12／2001—01间全部住院CDH患者及其父母，所有患者均有典型的临床表现，经X射线检查及手术确诊。方法：在胚胎肢体发育调控相关基因-HOX基因A簇、B簇、C簇和D簇所存的染仁体区域7P14—15．17q21，12q13和2q31内选择4个微卫星DNA标记D7S1808，D17S1820，D12S1686和Hox4EP，应用聚合酶链反应及变性聚丙烯酰胺凝胶电泳技术，对101个先天性髋脱位核心家系的303名成员进行基因型分析，并进行传递小平衡检验(TDT)。主要观察指标：确定101个CDH核心家系303名成员4个微卫星DNA标记D7S1808，D17S1820，D12S1686和Hox4EP的基因型．对父母传递和不传递给患者的等位基因进行传递不平衡检验。结果：在D12S1686多态性标记位点上共检测到16个等位基因．TDT分析显示，CDH与D12S1686遗传标记他点不存在传递不平衡(x^2=6．171，P=0965)。在D7S1808多态性标记位点上共检测到10个等位基因．CDH与D7S1808遗传标记位点的第7个等位基因存在传递不平衡(x^2=6．045，P=0.014)。在D17S1820多态性标记位点上共检测到12个等位基因，CDH与D17S1820遗传标记位点的第4个等位基因存在传递不平衡(x^2=6.025，P=0.014)在Hox4EP多态性标记位点上共检测到16个等位基因，CDH与Hox4EP遗传标记位点的第4个等位基因存在传递不平衡(x^2=6．461，P=0．011)。结论：CDH与HOX基因A簇、B簇和D簇可能有关联．HOX A簇、B簇和D簇基因可能是先天性髋脱位的易感基因。     

腓骨肌萎缩症2型大家系的基因定位及分子诊断

目的:研究一个腓骨肌萎缩症2型(Chareot-Marie-Tooth Disease type2,CMT2)大家系的临床及遗传学特征,定位和克隆该家系的致病基因用于分子诊断。方法:采集山东省一个CMT2大家系,采用家系分析法观察该家系的遗传规律,并采用连锁分析试剂盒(Version 2.5)进行全基因组扫描,用LINKAGE软件(Version 5.1)中的MLINK程序作连锁分析,运用直接测序法对20个候选基因的外显子及外显子-内含子边界区序列进行测序,结果用CHROMOSOME软件进行序列分析。结果:该CMT2家系符合常染色体显性遗传的特征,连锁分析表明位于10p14存在一个致病基因位点,测序分析显示脱氢酶E1和转酮酶结构域1(DHTKD1)的一个无义突变[c.1455T>G(p.Tyr485*)]存在于该家系的所有8个患者中,而不存在于该家系任何未受累者及250名正常对照者中。结论:本研究结果提示DHTKD1的无义突变可能是CMT2发病的分子基础。     

常染色体显性遗传视网膜色素变性家系的分子遗传学研究

目的对1例4代常染色体显性遗传视网膜色素变性家系进行致病基因定位,并对候选基因进行突变筛查。方法收集1例视网膜色素变性家系,抽取家系成员外周血并提取DNA,用连锁分析法对与疾病相关联的22个已知基因进行定位,并对定位区域内的候选基因进行突变筛查。结果两点连锁分析结果显示,在微卫星标记D7S484处取得最大LOD值为1.51（θ=0.00时）;聚合酶链反应直接测序法筛查候选基因RP9,未发现突变。结论该家系可能存在RP9基因大的碱基缺失突变或基因重排,也可能存在1个新的致病基因。     

Usefulness of combined genetic data in Hungarian families affected by autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common hereditary diseases. Mutations of two known genetic loci (PKD1: 16p13.3 and PKD2: 4q21.2) can lead to bilateral renal cysts. The PKD1 locus is the more common (～85%), with a more severe phenotype. Because of the genetic complexity of ADPKD and the size and complexity of the PKD1 gene, pedigree-based linkage analysis is a useful tool for the genetic diagnosis in families with more than one subject affected. We tested linkage or non-linkage to the closely linked DNA markers flanking the PKD1 (D16S663 and D16S291) and one intragenic D16S3252 and PKD2 (D4S1563 and D4S2462) in 30 ADPKD-affected families, to determine the distributions of alleles and the degree of microsatellite polymorphisms (in 91 patients and 125 healthy subjects). To characterize the markers, used heterozygosity levels, polymorphism information content and LOD scores were calculated. The D16S663 marker included 12 kinds of alleles, while D16S291 had 10 alleles and D16S3252 had 8. D4S1563 had 12 alleles and D4S2462 had 11. In a search for a common ancestral relationship, we considered the patients’ alleles with the same repeat number. Only one haplotype was detected in more than one (2) unrelated families. The calculated two-point LOD scores indicated a linkage to PKD1 in 22 families (74%). In four families (13%) with a linkage to PKD2, the patients reached the end-stage renal disease after the age of 65 years. One family was linked to neither gene (3%), and in three families (10%) a linkage to both genes was possible. In the latter three families, the numbers of analyzed subjects were small (4–5), and/or some markers were only partially or non-informative. However, the elderly affected family members exhibited the clinical signs of the PKD1 form in these cases. The new Hungarian population genetic information was compared with available data on other populations.     

Quantitative trait locus mapping of human blood pressure to a genetic region at or near the lipoprotein lipase gene locus on chromosome 8p22.

Resistance to insulin-mediated glucose disposal is a common finding in patients with non-insulin-dependent diabetes mellitus (NIDDM), as well as in nondiabetic individuals with hypertension. In an effort to identify the generic loci responsible for variations in blood pressure in individuals at increased risk of insulin resistance, we studied the distribution of blood pressure in 48 Taiwanese families with NIDDM and conducted quantitative sib-pair linkage analysis with candidate loci for insulin resistance, lipid metabolism, and blood pressure control. We found no evidence for linkage of the angiotensin converting enzyme locus on chromosome 17, nor the angiotensinogen and renin loci on chromosome 1, with either systolic or diastolic blood pressures. In contrast, we obtained significant evidence for linkage or systolic blood pressure, but not diastolic blood pressure, to a genetic region at or near the lipoprotein lipase (LPL) locus on the short arm of chromosome 8 (P = 0.002, n = 125 sib-pairs, for the haplotype generated from two simple sequence repeat markers within the LPL gene). Further strengthening this linkage observation, two flanking marker loci for LPL locus, D8S261 (9 cM telomeric to LPL locus) and D8S282 (3 cM centromeric to LPL locus), also showed evidence for linkage with systolic blood pressure (P = 0.02 and 0.0002 for D8S261 and D8S282, respectively). Two additional centromeric markers (D8S133, 5 cM from LPL locus, and NEFL, 11 cM from LPL locus) yielded significant P values of 0.01 and 0.001, respectively. Allelic variation around the LPL gene locus accounted for as much as 52-73% of the total interindividual variation in systolic blood pressure levels in this data set. Thus, we have identified a genetic locus at or near the LPL gene locus which contributes to the variation of systolic blood pressure levels in nondiabetic family members at high risk for insulin resistance and NIDDM.     

Gene mapping of familial autosomal dominant dilated cardiomyopathy to chromosome 10q21-23.

Dilated cardiomyopathy (DCM) is the most common form of primary myocardial disorder, accounting for 60% of all cardiomyopathies. In 20-30% of cases, familial inheritance can be demonstrated; an autosomal dominant transmission is the usual type of inheritance pattern identified. Previously, genetic heterogeneity was demonstrated in familial autosomal dominant dilated cardiomyopathy (FDCM). Gene localization to chromosome 1 (1p1-1q1 and 1q32), chromosome 3 (3p25-3p22), and chromosome 9 (9q13-9q22) has recently been identified. We report one family with 26 members (12 affected) with familial autosomal dominant dilated cardiomyopathy in which linkage to chromosome 10 at the 10q21-q23 locus is identified. Using short tandem repeat polymorphism (STR) markers with heterozygosity > 70%, 169 markers (50% of the genome) were used before linkage was found to markers D10S605 and D10S201 with a pairwise LOD score = 3.91, theta = 0, penetrance = 100% for both markers. Linkage to 1p1-1q1, 1q32, 3p25-3p22, and 9q13-9q22 was excluded. We conclude that a new locus for pure autosomal dominant FDCM exists, and that this gene is localized to a 9 cM region of 10q21-10q23. The search for the disease causing gene and the responsible mutation(s) is ongoing.     

儿童视网膜母细胞瘤发生发展密切相关的可疑新基因位点研究

背景近年来研究表明视网膜母细胞瘤(retinoblastoma,RB)的发生和病变的进展除了与已知的Rb1基因有相关性外,可能还有其他抑癌基因的参与.目的探讨其他可能参与RB发生发展的基因存在的位点,并试图寻找和确定具有监测及预后价值的杂合性缺失(LOH)检测指标.设计以RB患者为研究对象的病例分析.单位一所军医大学医院的基因诊断治疗中心.对象本研究在第三军医大学西南医院基因诊断治疗中心完成,研究对象为1998-05/2001-10在本校三所附属医院门诊就诊的RB患者16例.纳入标准符合RB诊断标准的年龄小于3岁的患儿;排除标准有家族遗传史者.其中男10例,女6例;累及双眼者12例,累及单眼者4例.方法在患者的RB肿瘤及外周血标本中运用荧光聚合酶链反应(PCR)分别扩增13号染色体上14个微卫星DNA标记,分析测定各位点LOH发生率;同时通过家系分析确定位点缺失的遗传学来源.主要观察指标患者13号染色体上LOH发生频率.结果16例RB患者中,12例在13号染色体上1个或1个以上位点发生LOH.其中3个位点D13S265、D13S263和D13S153(位于Rb1基因内)LOH发生机率最高.12个LOH阳性标本中有10个位点的缺失被确定发生在父系来源的染色体中.LOH阳性及阴性组RB的确诊时间分别为504和1 086 d,两组相比差异具有显著性意义(t=2.357,P＜0.05).结论LOH阳性组的患者RB确诊时间早于LOH阴性组.除已确定的Rb1基因外,D13S263(13q14.1-14.2)和D13S265(13q31-32)两个位点的LOH现象也可能对RB患者的早期干预和功能监测具有一定提示作用.     

Mapping of the X-linked agammaglobulinemia locus by use of restriction fragment-length polymorphism.

A molecular linkage analysis in 11 families with X-linked agammaglobulinemia (XLA) localized the XLA gene to the proximal part of the long arm of the human X chromosome. Significant linkage was detected between XLA and loci defined by two polymorphic DNA probes called 19-2 for the DXS3 locus and S21 for the DXS17 locus. Both localize to the region Xq21.3-Xq22. Most likely recombination distances (theta) and associated logarithm of the odds (lod) scores for the XLA-DXS3 and XLA-DXS17 pairs were theta = 0.04 morgans (lod, 3.65) and theta = 0 (lod, 2.17), respectively. Tight linkage between XLA and the locus DXS43 defined by the X short arm probe D2 (localized to Xp22-Xp21) was strongly excluded and we obtained no evidence for significant linkage between XLA and any other X short arm probe. The probe pair 19-2 and S21 should be informative for molecular linkage-based analysis of XLA segregation in the majority of families afflicted with this disorder.     

强直性脊柱炎易感基因定位的比较研究

目的：比较分析中国人群与欧美人群在强直性脊柱炎(AS)易感基因定位方面的异同点。方法：采用全基因组扫描法对中国9个AS家系101份DNA样本进行基因分型和连锁分析：采用比较分析法对国外3个课题组的基因定位数据作统计学处理。结果：两群均在HLA区域尤其是D6S276附近存在连锁遗传标记：除HLA区域外．中国人群在D3S1292(3q)、D4S1535(4q)和D18S64(18q)处可能存在与AS相连锁的标记，而欧美人群在D1S255(1p)、D3S1300(3p)、D6S441(6q)、D9S1862(9q)、D11S4094(11q)、D16S515(16q)和D19S420(19q)等处存存与AS相连锁的标记。结论：中国人群与欧美人群在HLA区域肯定存在1个或1个以上易感基因或标记；此外，不同人群在非HLA区域的不同部位还存在多个AS易感基因或标记。总之，多个易感基因的协同作用是AS发生的遗传基础。     

Mother-child double incompatibility at vWA and D5S818 loci in paternity testing.

BACKGROUND: In a paternity dispute case, 17 autosomal short tandem repeats (STR) were examined and signified a possible paternal mismatch at vWA locus and a maternal mismatch at D5S818 locus in the child under investigation. METHODS: Seventeen autosomal, 17 Y-chromosome and six X-chromosome repeat loci were used in parentage analysis. The mutated vWA and D5S818 alleles were amplified, cloned and sequenced to analyze the repeat structure. RESULTS: The vWA locus genotype in the mother, questioned child and suspected father were 18/19, 16/18 and 14/18, and were 13/15, 11/12 and 11/14, respectively, for the D5S818 locus. A complete match with the mother at six X-chromosome STR loci and with the father at 17 Y-chromosome STR loci was observed. Nucleotide sequence analysis of the family at vWA alleles indicated the maternal loss of the repeat motif TCTA by two repeat units and a loss of AGAT repeat by one unit in the D5S818 locus leading to an allele mismatch in the child. The probability of maternity and paternity were 0.999999 and 0.999999, respectively. CONCLUSIONS: This is the first study of a maternally transmitted microsatellite mutation in the loci D5S818 and vWA in paternity DNA testing. The results convincingly established that the mother and suspected father are the biological parents of the questioned child.     

Locus heterogeneity of autosomal dominant long QT syndrome.

Autosomal dominant long QT syndrome (LQT) is an inherited disorder that causes syncope and sudden death from cardiac arrhythmias. In genetic linkage studies of seven unrelated families we mapped a gene for LQT to the short arm of chromosome 11 (11p15.5), near the Harvey ras-1 gene (H ras-1). To determine if the same locus was responsible for LQT in additional families, we performed linkage studies with DNA markers from this region (H ras-1 and MUC2). Pairwise linkage analyses resulted in logarithm of odds scores of -2.64 and -5.54 for kindreds 1977 and 1756, respectively. To exclude the possibility that rare recombination events might account for these results, we performed multipoint linkage analyses using additional markers from chromosome 11p15.5 (tyrosine hydroxylase and D11S860). Multipoint analyses excluded approximately 25.5 centiMorgans of chromosome 11p15.5 in K1756 and approximately 13 centiMorgans in K1977. These data demonstrate that the LQT gene in these kindreds is not linked to H ras-1 and suggest that mutations in at least two genes can cause LQT. While the identification of locus heterogeneity of LQT will complicate genetic diagnosis, characterization of additional LQT loci will enhance our understanding of this disorder.     

Evidence for oligogenic inheritance of type 1 diabetes in a large Bedouin Arab family.

Based on a genomic search for linkage, a locus contributing to type 1 diabetes in a large Bedouin Arab family (19 affected relatives) maps to the long arm of chromosome 10 (10q25; nonparametric linkage = 4.99; P = 0.00004). All affected relatives carry one or two high-risk HLA-DR3 haplotypes that are rarely found in other family members. One chromosome 10 haplotype, the B haplotype, was transmitted from a heterozygous parent to 13 of 13 affected offspring compared to 10 of 23 unaffected siblings. Recombination events occurring on this haplotype place the susceptibility locus in an 8-cM interval between markers D10S1750 and D10S1773. Two adjacent markers, D10S592 and D10S554, showed evidence of linkage disequilibrium with the disease locus. A 273-bp allele at D10S592 was transmitted to 8 of 10 affected offspring compared to 3 of 14 unaffected siblings, and a 151-bp allele at D10S554 was transmitted to 15 of 15 affected offspring compared with 10 of 24 unaffected siblings. D10S554 and D10S592 and the closest flanking markers are contained in a 1,240-kb yeast artificial chromosome, a region small enough to proceed with positional cloning.     

The Colton blood group locus. A linkage analysis

Accumulated family information was compiled in an attempt to verify the chromosomal location of the Colton blood group locus (CO). Two-point linkage analysis of CO and 46 other polymorphic loci excludes CO from 1p36 to 1q23, 3q21 to 3q26, 4q13 to 4q28, 6p24 to 6 cen, and 19p13.2 to 19 cen and from linkage groups bounded by ABO and ORM, PI and IGHG, and HP and GOT2. The dwindling odds of linkage between CO:JK are reinforced (z =−5.28 at theta = 0.20). Close linkage of CO with ACP1 and D2S5 could not be demonstrated. The proposed chromosome 2 location of CO is therefore questioned.