Identification of novel compound heterozygous mutations in ACO2 in a patient with progressive cerebral and cerebellar atrophy
Identification of novel compound heterozygous mutations in ACO2 in a patient with progressive cerebral and cerebellar atrophy
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DOI：
10.1002/mgg3.698
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发表时间：
2019-07-01
影响因子：
2
通讯作者：
Nakayama, Atsuo
中科院分区：
文献类型：
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作者：
Fukada, Masahide;Yamada, Keitaro;Nakayama, Atsuo
背景三羧酸循环（TCA）是线粒体基质内的一系列分解代谢反应，是细胞能量代谢的中心途径。已知影响TCA循环的遗传缺陷会导致严重的多系统疾病。方法对1例进行性小脑和脑萎缩、张力减退、共济失调、癫痫发作、发育迟缓、眼科异常和听力损失患者的基因组DNA进行全外显子组测序。我们还使用患者成纤维细胞进行了生化研究。结果在编码TCA循环的顺乌头酸酶2的ACO2中发现了新的复合杂合突变（c.1534G > A，p.Asp512Asn和c.1997G > C，p.Gly666Ala）。在患者成纤维细胞中，顺乌头酸酶活性降低至对照的15%，顺乌头酸酶2水平降低至对照的36%。由于患者成纤维细胞中乌头酸酶2的这种减少通过蛋白酶体抑制而部分恢复，因此突变型乌头酸酶2被认为是相对不稳定的，并且在合成后迅速降解。此外，乌头酸酶2的父源变体（p.Gly666Ala）的活性是野生型的55%，该变体在活性中心附近具有突变。结论患者成纤维细胞中乌头酸酶活性的显著降低是由于突变导致的乌头酸酶2量和活性降低的组合。乌头酸酶活性降低直接抑制TCA循环，导致线粒体功能障碍，这可能导致与线粒体疾病中观察到的症状相似的症状。
Background The tricarboxylic acid (TCA) cycle is a sequence of catabolic reactions within the mitochondrial matrix, and is a central pathway for cellular energy metabolism. Genetic defects affecting the TCA cycle are known to cause severe multisystem disorders. Methods We performed whole exome sequencing of genomic DNA of a patient with progressive cerebellar and cerebral atrophy, hypotonia, ataxia, seizure disorder, developmental delay, ophthalmological abnormalities and hearing loss. We also performed biochemical studies using patient fibroblasts. Results We identified new compound heterozygous mutations (c.1534G > A, p.Asp512Asn and c.1997G > C, p.Gly666Ala) in ACO2, which encodes aconitase 2, a component of the TCA cycle. In patient fibroblasts, the aconitase activity was reduced to 15% of that of the control, and the aconitase 2 level decreased to 36% of that of the control. As such a decrease in aconitase 2 in patient fibroblasts was partially restored by proteasome inhibition, mutant aconitase 2 was suggested to be relatively unstable and rapidly degraded after being synthesized. In addition, the activity of the father-derived variant of aconitase 2 (p.Gly666Ala), which had a mutation near the active center, was 55% of that of wild-type. Conclusion The marked reduction of aconitase activity in patient fibroblasts was due to the combination of decreased aconitase 2 amount and activity due to mutations. Reduced aconitase activity directly suppresses the TCA cycle, resulting in mitochondrial dysfunction, which may lead to symptoms similar to those observed in mitochondrial diseases.