School of Biology, College of Science, University of Tehran, Tehran, Iran.
Department of Neurology, Tehran University of Medical Sciences, Tehran, Iran.
J Neurol. 2021 Feb;268(2):640-650. doi: 10.1007/s00415-020-10171-4. Epub 2020 Sep 8.
Charcot-Marie-Tooth (CMT) disease is a prevalent and heterogeneous peripheral neuropathy. Most patients affected with the axonal form of CMT (CMT2) do not harbor mutations in the approximately 90 known CMT-associated genes. We aimed to identify causative genes in two CMT2 pedigrees.
Neurologic examination, laboratory tests and brain MRIs were performed. Genetic analysis included exome sequencing of four patients from the two pedigrees. The predicted effect of a deep intronic mutation on splicing was tested by regular and real-time PCR and sequencing.
Clinical data were consistent with CMT2 diagnosis. Inheritance patterns were autosomal recessive. Exome data of CMT2-101 did not include mutations in known CMT-associated genes. Sequence data, segregation analysis, bioinformatics analysis, evolutionary conservation, and information in the literature strongly implicated HADHA as the causative gene. An intronic variation positioned 23 nucleotides away from following intron/exon border in GDAP1 was ultimately identified as cause of CMT in CMT2-102. It was shown to affect splicing.
The finding of a HADHA mutation as a cause of CMT is of interest because its encoded protein is a subunit of the mitochondrial trifunctional protein (MTP) complex, a mitochondrial enzyme involved in long chain fatty acid oxidation. Long chain fatty acid oxidation is an important source of energy for skeletal muscles. The mutation found in CMT2-102 is only the second intronic mutation reported in GDAP1. The mutation in the CMT2-102 pedigree was outside the canonical splice site sequences, emphasizing the importance of careful examination of available intronic sequences in exome sequence data.
Charcot-Marie-Tooth（CMT）病是一种常见且具有异质性的周围神经病。大多数患有轴索性 CMT（CMT2）的患者并不携带大约 90 个已知的 CMT 相关基因中的突变。我们旨在鉴定两个 CMT2 家系中的致病基因。
进行了神经学检查、实验室检查和脑部 MRI。遗传分析包括对来自两个家系的四名患者进行外显子组测序。通过常规和实时 PCR 及测序测试了深内含子突变对剪接的预测影响。
临床数据符合 CMT2 诊断。遗传模式为常染色体隐性遗传。CMT2-101 的外显子组数据不包括已知的 CMT 相关基因中的突变。序列数据、分离分析、生物信息学分析、进化保守性以及文献信息强烈表明 HADHA 是致病基因。在 GDAP1 中，距下游内含子/外显子边界 23 个核苷酸处的一个内含子变异最终被确定为 CMT2-102 中的 CMT 原因。它被证明会影响剪接。
发现 HADHA 突变是 CMT 的原因是很有趣的，因为其编码的蛋白是线粒体三功能蛋白（MTP）复合物的一个亚基，MTP 复合物是一种参与长链脂肪酸氧化的线粒体酶。长链脂肪酸氧化是骨骼肌的重要能量来源。在 CMT2-102 中发现的突变仅为 GDAP1 中报告的第二个内含子突变。CMT2-102 家系中的突变位于典型剪接位点序列之外，这强调了在外显子组序列数据中仔细检查可用内含子序列的重要性。
