Fujita R, Hanauer A, Sirugo G, Heilig R, Mandel J L
Unité 184 de Biologie Moléculaire et de Génie, Génétique de Institut National de la Santé et de la Recherche Médicale, Faculté de Médecine, Strasbourg, France.
Proc Natl Acad Sci U S A. 1990 Mar;87(5):1796-800. doi: 10.1073/pnas.87.5.1796.
The gene for Friedreich ataxia (FA), a severe recessive neurodegenerative disease, has previously been shown to be tightly linked to the polymorphic markers D9S15 and D9S5 on human chromosome 9. In addition, the observation of linkage disequilibrium suggested that D9S15 is within 1 centimorgan (cM) of the disease locus, FRDA. Although D9S5 did not show recombination with FRDA, its localization was less precise (0-5 cM) due to its lower informativeness. We have now identified additional polymorphisms at both marker loci. Two cosmids spanning 50 kilobases around D9S5 were isolated, and a probe derived from one of them detects an informative three-allele polymorphism. We have found a highly polymorphic microsatellite sequence at D9S15 which is rapidly typed by the DNA polymerase chain reaction. The polymorphism information contents at the D9S5 and D9S15 loci have been increased from 0.14 to 0.60 and from 0.33 to 0.74, respectively. With the additional polymorphisms the lod (log10 odds ratio) score for the D9S15-FRDA linkage is now 48.10 at recombination fraction theta = 0.005 and for D9S5-FRDA, the lod score is 27.87 at theta = 0.00. We have identified a recombinant between D9S15 and FRDA. However, due to the family structure, it will be of limited usefulness for more precise localization of FRDA. The linkage disequilibrium previously observed between D9S15 and FRDA is strengthened by analysis of the haplotypes using the microsatellite polymorphism, while weaker but significant disequilibrium is found between D9S5 and FRDA. Extended haplotypes that encompass D9S5 and D9S15 show a strikingly different distribution between chromosomes that carry the FA mutation and normal chromosomes. This suggests that both marker loci are less than 1 cM from the FRDA gene and that a small number of mutations account for the majority of FA cases in the French population studied. D9S5 and D9S15 are thus excellent start points to isolate the disease gene.
弗里德赖希共济失调（FA）是一种严重的隐性神经退行性疾病，其相关基因先前已被证明与人类9号染色体上的多态性标记D9S15和D9S5紧密连锁。此外，连锁不平衡的观察结果表明，D9S15位于疾病基因座FRDA的1厘摩（cM）范围内。尽管D9S5未显示与FRDA发生重组，但其定位因信息性较低而不够精确（0 - 5 cM）。我们现在在这两个标记位点都鉴定出了额外的多态性。分离出了两个跨越D9S5周围50千碱基的黏粒，其中一个衍生出的探针检测到一种信息丰富的三等位基因多态性。我们在D9S15处发现了一个高度多态的微卫星序列，可通过DNA聚合酶链反应快速分型。D9S5和D9S15位点的多态性信息含量分别从0.14增加到了0.60和从0.33增加到了0.74。有了这些额外的多态性，在重组率θ = 0.005时，D9S15与FRDA连锁的lod（对数优势比）分数现在为48.10，对于D9S5与FRDA，在θ = 0.00时，lod分数为27.87。我们在D9S15和FRDA之间鉴定出了一个重组体。然而，由于家系结构，它对于FRDA更精确的定位用途有限。通过使用微卫星多态性对单倍型进行分析，先前观察到的D9S15和FRDA之间的连锁不平衡得到了加强，而在D9S5和FRDA之间发现较弱但显著的不平衡。包含D9S5和D9S15的扩展单倍型在携带FA突变的染色体和正常染色体之间显示出明显不同的分布。这表明这两个标记位点都距离FRDA基因不到1 cM，并且少数突变占了所研究法国人群中大多数FA病例的原因。因此，D9S5和D9S15是分离疾病基因的绝佳起点。
