Molecular genetic analysis of familial amyloidotic polyneuropathy

家族性淀粉样变性多神经病变（FAP）是一种常染色体显性遗传病，以淀粉样原纤维细胞外沉积和明显的外周神经和自主神经受累为特征。虽然该疾病的致病基因已被确定为转甲状腺素（TTR）基因，并在分子水平上得到了很好的表征，但淀粉样蛋白沉积的机制等许多问题仍有待阐明。我们以前通过引入含有自身启动子（0.6-hTTR30）或金属硫蛋白启动子（MT-hTTR30）的人类突变TTR基因，生产了两种转基因小鼠。在这两系中，TTR突变体的总血清浓度相同。然而，MT-hTTR30系淀粉样蛋白沉积的发病时间为6个月，比0.6-hTTR30系早9个月。这些结果表明，由TTR突变体组成的同源四聚体的浓度对淀粉样蛋白的沉积起重要作用，而不是TTR突变体分子的总量。为了分析人血清淀粉样蛋白P成分（SAP）的作用，我们也制作了SAP转基因小鼠。有趣的是，人类SAP的血清水平与整合的拷贝数大致成正比，并且在三个品系中高于人类血清水平。将这些小鼠与MT-hTTR30转基因小鼠交配，获得携带这两种基因的小鼠。在这些小鼠中，淀粉样蛋白沉积的开始没有加速，这表明人类SAP不参与淀粉样蛋白沉积的开始。奇怪的是，在FAP患者通常观察到淀粉样蛋白沉积的周围神经组织中没有淀粉样蛋白沉积。这些结果表明，在这些组织中淀粉样蛋白沉积需要TTR分子突变体的产生或高水平表达。

Familial amyloidotic polyneuropathy (FAP) is an autosomal dominant disorder characterized by extracellular deposition of amyloid fibrils and by prominent peripheral and autonomic nerve involvement. Although the gene responsible for this disease has been identified as the transthyretin (TTR) gene and well characterized at molecular level, many questions, such as the mechanism of amyloid deposition, remain to be elucidated. We formerly produced two lines of transgenic mice by introducing the human mutant TTR gene containing its own promoter (0.6-hTTR30) or metallothionein promoter (MT-hTTR30). In these two lines the total serum concentrations of human mutant TTR were the same. However, the onset of amyloid deposition in MT-hTTR30 lines was 6 months of age and was 9 months earlier than that in the 0.6-hTTR30 lines. These results suggest that the concentration of homo-tetramers composed of human mutant TTR but not the total amount of human mutant TTR molecule is important for amyloid deposition.To analyze the role of the human serum amyloid P component (SAP) which is a minor component of amyloid fibrils, we also produced SAP transgenic mice. Interestingly, the serum levels of human SAP were roughly proportional to the number of copies integrated and were higher than that of the human serum in three lines. These mice were mated with MT-hTTR30 transgenic to obtain mice carrying both genes. In these mice the onset of amyloid deposition was not accelerated suggesting that human SAP is not involved in the initiation of amyloid deposition.Strangely enough, there were no amyloid deposits in peripheral nervous tissues where amyloid deposition is commonly observed in FAP patients. These results suggest that the production of mutant TTR molecule in the chorid plexus or high level expression is required for the amyloid deposition in these tissues.