Molecular Biology of Adrenomyeloneuropathy

描述(申请人提供)：ABCD1基因突变可导致肾上腺脑白质营养不良(ALD)或肾上腺脊髓神经病(AMN)，这是一种X连锁模式遗传的神经退行性疾病，突变等位基因频率大于1：17,000。这些疾病代表了不同的病理过程。ALD是由免疫介导的大脑皮层脱髓鞘引起的，通常在儿童时期表现出来。AMN是一种迟发性轴索病变，以痉挛的皮质脊髓束和脊髓-小脑束的轴突变性为特征。虽然病理不同，但它们有一个共同的生化缺陷：超长链脂肪酸的积累。有趣的是，没有基因型与表型的相关性，即使在相同的遗传背景下，相同的突变也会导致两种表型中的任何一种。一个例外是最近发现的一个突变，其中包含ABCD1起始密码子的23个碱基对被删除。在这个家族中，AMN以显性模式遗传，没有脑脱髓鞘的迹象。这种突变基因虽然缺少传统的起始密码子，但会产生一种截短的蛋白质产物。该蛋白质太大，无法在下一个下游蛋氨酸启动，这表明它是从非AUG密码子翻译而来的少数蛋白质之一。在我们的实验中，我们将检验这样一种假设，即ABCDI的这种截断形式起着显性否定的作用。我们将在患者中鉴定ABCDI蛋白的序列，并制造过度表达野生型或突变型的转基因小鼠。这些小鼠将与现有的ABCD1基因敲除小鼠杂交。ABCD1基因敲除小鼠虽然积累了很长的链脂肪酸，但不会经历神经元退化，限制了它们作为AMN动物模型的价值。基因敲除和转基因小鼠杂交的后代将在行为、形态和电生理方面进行特征分析。此外，我们还将量化它们髓鞘中脂质成分的变化。我们还将与人类ALD和AMN脊髓髓鞘的脂谱进行比较。该项目的结果将证明替代启动与疾病的相关性，并可能为进一步探讨疾病病理生物学提供有价值的试剂。

DESCRIPTION (provided by applicant): Mutations in the gene ABCD1 can cause either adrenoleukodystrophy (ALD) or adrenomyeloneuropathy (AMN), neurodegenerative disorders inherited in an X-linked pattern, with a mutant allele frequency greater than 1:17,000. These diseases represent distinct pathological processes. ALD is caused by an immune mediated demyelination of the cerebral cortex and typically manifests in childhood. AMN is a late-onset axonopathy, characterized by spastic paraperesis, and degeneration of the axons in the corticospinal and spino-cerebellar tracts. While the pathologies diverge, they share a common biochemical defect: accumulation of by very-long chain fatty acids. Intriguingly, there is no genotype to phenotype correlation, with the same mutation resulting in either phenotype, even within identical genetic contexts. One exception is a recently identified mutation, in which 23 basepairs, encompassing the start codon of ABCD1, are deleted. In this family, AMN is inherited in a dominant pattern, and there is no indication of cerebral demyelination. The mutant gene, although lacking a traditional start codon, produces a truncated protein product. The protein is too large to be initiated at the next down-stream methionine, suggesting it is one of a minority of proteins translated from a non-AUG codon. In our experiments, we will test the hypothesis that this truncated form of ABCDI acts a dominant negative. We will identify the sequence of the ABCDI protein in the patients, and make transgenic mice that over-express the wildtype or mutant form. These mice will be crossed to existing ABCD1 knock-out mice. The ABCD1 knock-out mice, while they accumulate very long chain fatty acids, do not undergo neuronal degeneration, limiting their value as an animal model for AMN. The progeny of the knock-out and transgenic mouse crosses will be characterized for behavioral, morphological, and electrophysiological changes. In addition, we will quantify changes in their myelin's lipid composition. We will also compare the lipid profiles to those of human ALD and AMN spinal cord myelin. The results of this project will demonstrate the relevance of alternative initiation to disease and could provide valuable reagents for further inquiry into the disease pathobiology.