INSERM UMR1163, Université Paris Descartes-Sorbonne Paris Cité, Institut Imagine, Paris, France.
Departments of Pediatrics, Neurology and Genetics, Hôpital Necker-Enfants Malades, Paris, France.
Hum Mol Genet. 2019 May 1;28(9):1445-1462. doi: 10.1093/hmg/ddy441.
Mitochondria contain a dedicated translation system, which is responsible for the intramitochondrial synthesis of 13 mitochondrial DNA (mtDNA)-encoded polypeptides essential for the biogenesis of oxidative phosphorylation (OXPHOS) complexes I and III-V. Mutations in nuclear genes encoding factors involved in mitochondrial translation result in isolated or multiple OXPHOS deficiencies and mitochondrial disease. Here, we report the identification of disease-causing variants in the MRPS28 gene, encoding the small mitoribosomal subunit (mtSSU) protein bS1m in a patient with intrauterine growth retardation, craniofacial dysmorphism and developmental delay. Whole exome sequencing helped identify a seemingly homozygous missense variant NM_014018.2:c.356A>G, p.(Lys119Arg) which affected a highly conserved lysine residue. The variant was present in the mother in a heterozygous state, but not in the father who likely carried a large deletion spanning exon 2 and parts of introns 1 and 2 that could account for the apparent homozygosity of the patient. Polymerase chain reaction (PCR) amplification and Sanger sequencing of MRPS28 cDNA from patient fibroblasts revealed the presence of a truncated MRPS28 transcript, which lacked exon 2. Molecular and biochemical characterization of patient fibroblasts revealed a decrease in the abundance of the bS1m protein, decreased abundance of assembled mtSSU and inhibited mitochondrial translation. Consequently, OXPHOS biogenesis and cellular respiration were compromised in these cells. Expression of wild-type MRPS28 restored mitoribosomal assembly, mitochondrial translation and OXPHOS biogenesis, thereby demonstrating the deleterious nature of the identified MRPS28 variants. Thus, MRPS28 joins the increasing number of nuclear genes encoding mitoribosomal structural proteins linked to mitochondrial disease.
线粒体含有一个专门的翻译系统，负责在线粒体内部合成 13 个线粒体 DNA（mtDNA）编码的多肽，这些多肽对氧化磷酸化（OXPHOS）复合物 I 和 III-V 的生物发生至关重要。核基因突变导致编码线粒体翻译相关因子的基因发生突变，会导致孤立或多种 OXPHOS 缺陷和线粒体疾病。在这里，我们报道了在一名宫内生长迟缓、颅面畸形和发育迟缓的患者中，MRPS28 基因（编码小线粒体核糖体亚单位（mtSSU）蛋白 bS1m）的致病变异的鉴定。全外显子组测序有助于鉴定出一种看似纯合的错义变异 NM_014018.2:c.356A>G，p.（Lys119Arg），该变异影响高度保守的赖氨酸残基。该变异在母亲中以杂合状态存在，但在父亲中不存在，父亲可能携带跨越外显子 2 和部分内含子 1 和 2 的大片段缺失，这可以解释患者的表观纯合性。从患者成纤维细胞中扩增和 Sanger 测序 MRPS28 cDNA 发现存在截断的 MRPS28 转录本，该转录本缺失外显子 2。对患者成纤维细胞的分子和生化特征分析发现 bS1m 蛋白丰度降低，组装的 mtSSU 丰度降低，线粒体翻译受到抑制。因此，这些细胞中的 OXPHOS 生物发生和细胞呼吸受到损害。表达野生型 MRPS28 恢复了线粒体核糖体的组装、线粒体翻译和 OXPHOS 生物发生，从而证明了鉴定的 MRPS28 变异的有害性质。因此，MRPS28 加入了越来越多与线粒体疾病相关的编码线粒体核糖体结构蛋白的核基因突变。
