Case Report: Tuberous sclerosis complex-associated hemihypertrophy successfully treated with mTOR inhibitor sirolimus

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by a mutation in either of the two tumor suppressor genes, TSC1 and TSC2. Due to dysregulated activity of the mammalian target of rapamycin (mTOR) pathway, hamartomas or benign tumors frequently occur in many organs and are often treated with mTOR inhibitors. Hemihypertrophy is a rare complication of TSC. Although not being a tumor, progressive overgrowth of the affected limb may cause cosmetic and functional problems, for which the efficacy of mTOR inhibitors has not been reported previously. We herein report a case of TSC-associated hemihypertrophy. In this case, genetic studies revealed TSC1 loss of heterozygosity as the cause of hemihypertrophy. Clinically, pharmacological treatment with an mTOR inhibitor sirolimus successfully ameliorated cosmetic and functional problems with no intolerable adverse effects

Biallelic variants in LIG3 cause a novel mitochondrial neurogastrointestinal encephalomyopathy

none67si: Abnormal gut motility is a feature of several mitochondrial encephalomyopathies, and mutations in genes such as TYMP and POLG, have been linked to these rare diseases. The human genome encodes three DNA ligases, of which only one, ligase III (LIG3), has a mitochondrial splice variant and is crucial for mitochondrial health. We investigated the effect of reduced LIG3 activity and resulting mitochondrial dysfunction in seven patients from three independent families, who showed the common occurrence of gut dysmotility and neurological manifestations reminiscent of mitochondrial neurogastrointestinal encephalomyopathy. DNA from these patients was subjected to whole exome sequencing. In all patients, compound heterozygous variants in a new disease gene, LIG3, were identified. All variants were predicted to have a damaging effect on the protein. The LIG3 gene encodes the only mitochondrial DNA (mtDNA) ligase and therefore plays a pivotal role in mtDNA repair and replication. In vitro assays in patient-derived cells showed a decrease in LIG3 protein levels and ligase activity. We demonstrated that the LIG3 gene defects affect mtDNA maintenance, leading to mtDNA depletion without the accumulation of multiple deletions as observed in other mitochondrial disorders. This mitochondrial dysfunction is likely to cause the phenotypes observed in these patients. The most prominent and consistent clinical signs were severe gut dysmotility and neurological abnormalities, including leukoencephalopathy, epilepsy, migraine, stroke-like episodes, and neurogenic bladder. A decrease in the number of myenteric neurons, and increased fibrosis and elastin levels were the most prominent changes in the gut. Cytochrome c oxidase (COX) deficient fibres in skeletal muscle were also observed. Disruption of lig3 in zebrafish reproduced the brain alterations and impaired gut transit in vivo. In conclusion, we identified variants in the LIG3 gene that result in a mitochondrial disease characterized by predominant gut dysmotility, encephalopathy, and neuromuscular abnormalities.This work was supported by Telethon Grant GGP15171 to E.B. and R.D.G. and by a donation from Kobe city to the Department of General Pediatrics, Kobe University Graduate School of Medicine (K550003302). S.C. was supported by a Dutch Cancer Foundation grant (KWF11011). V.C. and A.M. were supported by the Italian Ministry of Health (“Ricerca Corrente” funding). R.D.G. is the recipient of grants from University of Ferrara (FAR and FIR funds).openBonora, Elena; Chakrabarty, Sanjiban; Kellaris, Georgios; Tsutsumi, Makiko; Bianco, Francesca; Bergamini, Christian; Ullah, Farid; Isidori, Federica; Liparulo, Irene; Diquigiovanni, Chiara; Masin, Luca; Rizzardi, Nicola; Cratere, Mariapia Giuditta; Boschetti, Elisa; Papa, Valentina; Maresca, Alessandra; Cenacchi, Giovanna; Casadio, Rita; Martelli, Pierluigi; Matera, Ivana; Ceccherini, Isabella; Fato, Romana; Raiola, Giuseppe; Arrigo, Serena; Signa, Sara; Sementa, Angela Rita; Severino, Mariasavina; Striano, Pasquale; Fiorillo, Chiara; Goto, Tsuyoshi; Uchino, Shumpei; Oyazato, Yoshinobu; Nakamura, Hisayoshi; Mishra, Sushil K; Yeh, Yu-Sheng; Kato, Takema; Nozu, Kandai; Tanboon, Jantima; Morioka, Ichiro; Nishino, Ichizo; Toda, Tatsushi; Goto, Yu-Ichi; Ohtake, Akira; Kosaki, Kenjiro; Yamaguchi, Yoshiki; Nonaka, Ikuya; Iijima, Kazumoto; Mimaki, Masakazu; Kurahashi, Hiroki; Raams, Anja; MacInnes, Alyson; Alders, Mariel; Engelen, Marc; Linthorst, Gabor; de Koning, Tom; den Dunnen, Wilfred; Dijkstra, Gerard; van Spaendonck, Karin; van Gent, Dik C; Aronica, Eleonora M; Picco, Paolo; Carelli, Valerio; Seri, Marco; Katsanis, Nicholas; Duijkers, Floor A M; Taniguchi-Ikeda, Mariko; De Giorgio, RobertoBonora, Elena; Chakrabarty, Sanjiban; Kellaris, Georgios; Tsutsumi, Makiko; Bianco, Francesca; Bergamini, Christian; Ullah, Farid; Isidori, Federica; Liparulo, Irene; Diquigiovanni, Chiara; Masin, Luca; Rizzardi, Nicola; Cratere, Mariapia Giuditta; Boschetti, Elisa; Papa, Valentina; Maresca, Alessandra; Cenacchi, Giovanna; Casadio, Rita; Martelli, Pierluigi; Matera, Ivana; Ceccherini, Isabella; Fato, Romana; Raiola, Giuseppe; Arrigo, Serena; Signa, Sara; Sementa, Angela Rita; Severino, Mariasavina; Striano, Pasquale; Fiorillo, Chiara; Goto, Tsuyoshi; Uchino, Shumpei; Oyazato, Yoshinobu; Nakamura, Hisayoshi; Mishra, Sushil K; Yeh, Yu-Sheng; Kato, Takema; Nozu, Kandai; Tanboon, Jantima; Morioka, Ichiro; Nishino, Ichizo; Toda, Tatsushi; Goto, Yu-Ichi; Ohtake, Akira; Kosaki, Kenjiro; Yamaguchi, Yoshiki; Nonaka, Ikuya; Iijima, Kazumoto; Mimaki, Masakazu; Kurahashi, Hiroki; Raams, Anja; MacInnes, Alyson; Alders, Mariel; Engelen, Marc; Linthorst, Gabor; de Koning, Tom; den Dunnen, Wilfred; Dijkstra, Gerard; van Spaendonck, Karin; van Gent, Dik C; Aronica, Eleonora M; Picco, Paolo; Carelli, Valerio; Seri, Marco; Katsanis, Nicholas; Duijkers, Floor A M; Taniguchi-Ikeda, Mariko; De Giorgio, Robert

Understanding mitochondrial complex I assembly in health and disease

AbstractComplex I (NADH:ubiquinone oxidoreductase) is the largest multimeric enzyme complex of the mitochondrial respiratory chain, which is responsible for electron transport and the generation of a proton gradient across the mitochondrial inner membrane to drive ATP production. Eukaryotic complex I consists of 14 conserved subunits, which are homologous to the bacterial subunits, and more than 26 accessory subunits. In mammals, complex I consists of 45 subunits, which must be assembled correctly to form the properly functioning mature complex. Complex I dysfunction is the most common oxidative phosphorylation (OXPHOS) disorder in humans and defects in the complex I assembly process are often observed. This assembly process has been difficult to characterize because of its large size, the lack of a high resolution structure for complex I, and its dual control by nuclear and mitochondrial DNA. However, in recent years, some of the atomic structure of the complex has been resolved and new insights into complex I assembly have been generated. Furthermore, a number of proteins have been identified as assembly factors for complex I biogenesis and many patients carrying mutations in genes associated with complex I deficiency and mitochondrial diseases have been discovered. Here, we review the current knowledge of the eukaryotic complex I assembly process and new insights from the identification of novel assembly factors. This article is part of a Special Issue entitled: Biogenesis/Assembly of Respiratory Enzyme Complexes

Characterization of mitochondrial FOXRED1 in the assembly of respiratory chain complex I

Human mitochondrial complex I is the largest enzyme of the respiratory chain and is composed of 44 different subunits. Complex I subunits are encoded by both nuclear and mitochondrial (mt) DNA and their assembly requires a number of additional proteins. FAD-dependent oxidoreductase domain-containing protein 1 (FOXRED1) was recently identified as a putative assembly factor and FOXRED1 mutations in patients cause complex I deficiency; however, its role in assembly is unknown. Here, we demonstrate that FOXRED1 is involved in mid-late stages of complex I assembly. In a patient with FOXRED1 mutations, the levels of mature complex I were markedly decreased, and a smaller ∼475 kDa subcomplex was detected. In the absence of FOXRED1, mtDNA-encoded complex I subunits are still translated and transiently assembled into a late stage ∼815 kDa intermediate; but instead of transitioning further to the mature complex I, the intermediate breaks down to an ∼475 kDa complex. As the patient cells contained residual assembled complex I, we disrupted the FOXRED1 gene in HEK293T cells through TALEN-mediated gene editing. Cells lacking FOXRED1 had ∼10% complex I levels, reduced complex I activity, and were unable to grow on galactose media. Interestingly, overexpression of FOXRED1 containing the patient mutations was able to rescue complex I assembly. In addition, FOXRED1 was found to co-immunoprecipitate with a number of complex I subunits. Our studies reveal that FOXRED1 is a crucial component in the productive assembly of complex I and that mutations in FOXRED1 leading to partial loss of function cause defects in complex I biogenesis