Two different mutations in the thyroid peroxidase gene of a large inbred Amish kindred: power and limits of homozygosity mapping.
Two different mutations in the thyroid peroxidase gene of a large inbred Amish kindred: power and limits of homozygosity mapping.
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DOI：
10.1210/jcem.84.3.5541
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发表时间：
1999-03
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影响因子：
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通讯作者：
Silvana Pannain;R. E. Weiss;Charles E. Jackson;Donald Dian;John S. Beck;V. C. Sheffield;Nancy J. Cox;Samuel Refetoff
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文献类型：
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作者：
Silvana Pannain;R. E. Weiss;Charles E. Jackson;Donald Dian;John S. Beck;V. C. Sheffield;Nancy J. Cox;Samuel Refetoff
大约10%的先天性甲状腺功能减退症新生儿不能将碘化物转化为有机碘。这种碘化物有机化缺陷的患病率为1/40，000新生儿，可能是由甲状腺过氧化物酶（TPO）、过氧化氢生成系统、TPO底物甲状腺球蛋白或TPO抑制剂的缺陷引起的。我们确定了一个严重的甲状腺功能减退症的发病率很高，由于一个完整的碘化物有机化缺陷，在最年轻的一代五个核心家庭属于近亲阿米什亲属。系谱记录使我们能够追溯到7-8代前的祖先夫妇，并确定了常染色体隐性遗传模式。最初的纯合性的研究，通过使用TPO基因内的两个多态性标记的下降没有连锁的表型。事实上，来自2个核心家庭的15个受影响的兄弟姐妹中有4个是杂合子，导致受影响和未受影响的家庭成员的纯合子值分别为73%和53%。一个全基因组的纯合性屏幕使用DNA池从受影响的和未受影响的家庭成员定位缺陷的一个位点接近TPO基因。使用TPO基因内的4个额外的多态性标记的连锁分析减少了纯合子未受影响的兄弟姐妹的数量为零，而不改变最初在受影响的纯合性百分比。TPO基因测序发现2个错义突变E799 K和R648 Q。TPO 779 K在11例患者的两个等位基因中均被发现，在3例患者的复合杂合子中均存在两种突变，1例不同病因的甲状腺功能减退症患者中未发现TPO突变。这些结果证明了DNA池策略在定位缺陷基因中的作用，以及当2个相对罕见的突变共存于近交群体中时连锁分析的陷阱。
Approximately 10% of newborns with congenital hypothyroidism are unable to convert iodide into organic iodine. This iodide organification defect has a prevalence of 1 in 40,000 newborns and may be caused by defects in the thyroid peroxidase enzyme (TPO), the hydrogen peroxide-generating system, the TPO substrate thyroglobulin, or inhibitors of TPO. We identified a high incidence of severe hypothyroidism due to a complete iodide organification defect in the youngest generation of five nuclear families belonging to an inbred Amish kindred. Genealogical records permitted us to trace their origin to an ancestral couple 7-8 generations back and to identify an autosomal recessive pattern of inheritance. Initial studies of homozygosity by descent using two polymorphic markers within the TPO gene showed no linkage to the phenotype. In fact, 4 of 15 affected siblings from 2 of the nuclear families were heterozygous, resulting in homozygosity values of 73% and 53% in affected and unaffected family members, respectively. A genome-wide homozygosity screen using DNA pools from affected and unaffected family members localized the defect to a locus close to the TPO gene. Linkage analysis using 4 additional polymorphic markers within the TPO gene reduced the number of homozygous unaffected siblings to zero without altering the percent homozygosity initially found in the affected. Sequencing of the TPO gene revealed 2 missense mutations, E799K and R648Q. TPO 779K was found in both alleles of the 11 affected homozygotes, both mutations were present in each of the 3 affected compound heterozygotes, and there were no TPO mutations in 1 subject with hypothyroidism of different etiology. These results demonstrate the power of the DNA pooling strategy in the localization of a defective gene and the pitfalls of linkage analysis when 2 relatively rare mutations coexist in an inbred population.