@article {709, title = {Clinical Spectrum and Functional Consequences Associated with Bi-Allelic Pathogenic Variants.}, journal = {J Clin Med}, volume = {8}, year = {2019}, month = {2019 Nov 19}, abstract = {

(PNPase-polynucleotide phosphorylase) is involved in multiple RNA processing functions in the mitochondria. Bi-allelic pathogenic variants cause heterogeneous clinical phenotypes affecting multiple organs without any established genotype-phenotype correlations. Defects in PNPase can cause variable combined respiratory chain complex defects. Recently, it has been suggested that PNPase can lead to activation of an innate immune response. To better understand the clinical and molecular spectrum of patients with bi-allelic variants, we captured detailed clinical and molecular phenotypes of all 17 patients reported in the literature, plus seven new patients, including a 78-year-old male with the longest reported survival. A functional follow-up of genomic sequencing by cDNA studies confirmed a splicing defect in a novel, apparently synonymous, variant. Patient fibroblasts showed an accumulation of mitochondrial unprocessed transcripts, while blood showed an increased interferon response. Our findings suggest that functional analyses of the RNA processing function of PNPase are more sensitive than testing downstream defects in oxidative phosphorylation (OXPHPOS) enzyme activities. This research extends our knowledge of the clinical and functional consequences of bi-allelic pathogenic variants that may guide management and further efforts into understanding the pathophysiological mechanisms for therapeutic development.

}, issn = {2077-0383}, doi = {10.3390/jcm8112020}, author = {Rius, Rocio and Van Bergen, Nicole J and Compton, Alison G and Riley, Lisa G and Kava, Maina P and Balasubramaniam, Shanti and Amor, David J and Fanjul-Fernandez, Miriam and Cowley, Mark J and Fahey, Michael C and Koenig, Mary K and Enns, Gregory M and Sadedin, Simon and Wilson, Meredith J and Tan, Tiong Y and Thorburn, David R and Christodoulou, John} } @article {649, title = {Recessive DES cardio/myopathy without myofibrillar aggregates: intronic splice variant silences one allele leaving only missense L190P-desmin.}, journal = {Eur J Hum Genet}, volume = {27}, year = {2019}, month = {2019 Aug}, pages = {1267-1273}, abstract = {

We establish autosomal recessive DES variants p.(Leu190Pro) and a deep intronic splice variant causing inclusion of a frameshift-inducing artificial exon/intronic fragment, as the likely cause of myopathy with cardiac involvement in female siblings. Both sisters presented in their twenties with slowly progressive limb girdle weakness, severe systolic dysfunction, and progressive, severe respiratory weakness. Desmin is an intermediate filament protein typically associated with autosomal dominant myofibrillar myopathy with cardiac involvement. However a few rare cases of autosomal recessive desminopathy are reported. In this family, a paternal missense p.(Leu190Pro) variant was viewed unlikely to be causative of autosomal dominant desminopathy, as the father and brothers carrying this variant were clinically unaffected. Clinical fit with a DES-related myopathy encouraged closer scrutiny of all DES variants, identifying a maternal deep intronic variant within intron-7, predicted to create a cryptic splice site, which segregated with disease. RNA sequencing and studies of muscle cDNA confirmed the deep intronic variant caused aberrant splicing of an artificial exon/intronic fragment into maternal DES mRNA transcripts, encoding a premature termination codon, and potently activating nonsense-mediate decay (92\% paternal DES transcripts, 8\% maternal). Western blot showed 60-75\% reduction in desmin levels, likely comprised only of missense p.(Leu190Pro) desmin. Biopsy showed fibre size variation with increased central nuclei. Electron microscopy showed extensive myofibrillar disarray, duplication of the basal lamina, but no inclusions or aggregates. This study expands the phenotypic spectrum of recessive DES cardio/myopathy, and emphasizes the continuing importance of muscle biopsy for functional genomics pursuit of {\textquoteright}tricky{\textquoteright} variants in neuromuscular conditions.

}, issn = {1476-5438}, doi = {10.1038/s41431-019-0393-6}, author = {Riley, Lisa G and Waddell, Leigh B and Ghaoui, Roula and Evesson, Frances J and Cummings, Beryl B and Bryen, Samantha J and Joshi, Himanshu and Wang, Min-Xia and Brammah, Susan and Kritharides, Leonard and Corbett, Alastair and MacArthur, Daniel G and Cooper, Sandra T} } @article {396, title = {A novel mutation in GMPPA in siblings with apparent intellectual disability, epilepsy, dysmorphism, and autonomic dysfunction.}, journal = {Am J Med Genet A}, volume = {173}, year = {2017}, month = {2017 Aug}, pages = {2246-2250}, abstract = {

GMPPA encodes the GDP-mannose pyrophosphorylase A protein (GMPPA). The function of GMPPA is not well defined, however it is a homolog of GMPPB which catalyzes the reaction that converts mannose-1-phosphate and guanosine-5{\textquoteright}-triphosphate to GDP-mannose. Previously, biallelic mutations in GMPPA were reported to cause a disorder characterized by achalasia, alacrima, neurological deficits, and intellectual disability. In this study, we report a female proband with achalasia, alacrima, hypohydrosis, apparent intellectual disability, seizures, microcephaly, esotropia, and craniofacial dysmorphism. Exome sequencing identified a previously unreported homozygous c.853+1G>A variant in GMPPA in the proband and her affected sister. Their unaffected parents were heterozygous, and unaffected brother homozygous wild type for this variant. Lymphoblast cells from the affected sisters showed complete loss of the GMPPA protein by Western blotting, and increased levels of GDP-mannose in lymphoblasts on high performance liquid chromatography. Based on our findings and the previous report describing patients with an overlapping phenotype, we conclude that this novel variant in GMPPA, identified by exome sequencing in the proband and her affected sister, is the genetic cause of their phenotype and may expand the known phenotype of this recently described glycosylation disorder.

}, keywords = {Abnormalities, Multiple, Child, Child, Preschool, Craniofacial Abnormalities, Epilepsy, Exome, Facies, Female, Heterozygote, Humans, Intellectual Disability, Microcephaly, Muscular Atrophy, Mutation, Missense, Nucleotidyltransferases, Pedigree, Phenotype, Seizures}, issn = {1552-4833}, doi = {10.1002/ajmg.a.38292}, author = {Gold, Wendy A and Sobreira, Nara and Wiame, Elsa and Marbaix, Alexandre and Van Schaftingen, Emile and Franzka, Patricia and Riley, Lisa G and Worgan, Lisa and H{\"u}bner, Christian A and Christodoulou, John and Ad{\`e}s, Lesley C} } @article {342, title = {MECR Mutations Cause Childhood-Onset Dystonia and Optic Atrophy, a Mitochondrial Fatty Acid Synthesis Disorder.}, journal = {Am J Hum Genet}, volume = {99}, year = {2016}, month = {2016 Dec 01}, pages = {1229-1244}, abstract = {

Mitochondrial fatty acid synthesis (mtFAS) is an evolutionarily conserved pathway essential for the function of the respiratory chain and several mitochondrial enzyme complexes. We report here a unique neurometabolic human disorder caused by defective mtFAS. Seven individuals from five unrelated families presented with childhood-onset dystonia, optic atrophy, and basal ganglia signal abnormalities on MRI. All affected individuals were found to harbor recessive mutations in MECR encoding the mitochondrial trans-2-enoyl-coenzyme A-reductase involved in human mtFAS. All six mutations are extremely rare in the general population, segregate with the disease in the families, and are predicted to be deleterious. The nonsense c.855T>G (p.Tyr285), c.247_250del (p.Asn83Hisfs4), and splice site c.830+2_830+3insT mutations lead to C-terminal truncation variants of MECR. The missense c.695G>A (p.Gly232Glu), c.854A>G (p.Tyr285Cys), and c.772C>T (p.Arg258Trp) mutations involve conserved amino acid residues, are located within the cofactor binding domain, and are predicted by structural analysis to have a destabilizing effect. Yeast modeling and complementation studies validated the pathogenicity of the MECR mutations. Fibroblast cell lines from affected individuals displayed reduced levels of both MECR and lipoylated proteins as well as defective respiration. These results suggest that mutations in MECR cause a distinct human disorder of the mtFAS pathway. The observation of decreased lipoylation raises the possibility of a potential therapeutic strategy.

}, keywords = {Basal Ganglia, Cells, Cultured, Child, Child, Preschool, Dystonic Disorders, Fatty Acids, Female, Fibroblasts, Genetic Complementation Test, Humans, Infant, Male, Mitochondria, Mitochondrial Diseases, Models, Molecular, Mutation, Mutation, Missense, Optic Atrophy, Oxidoreductases Acting on CH-CH Group Donors, Pedigree, RNA Splice Sites, Saccharomyces cerevisiae}, issn = {1537-6605}, doi = {10.1016/j.ajhg.2016.09.021}, author = {Heimer, Gali and Ker{\"a}t{\"a}r, Juha M and Riley, Lisa G and Balasubramaniam, Shanti and Eyal, Eran and Pietik{\"a}inen, Laura P and Hiltunen, J Kalervo and Marek-Yagel, Dina and Hamada, Jeffrey and Gregory, Allison and Rogers, Caleb and Hogarth, Penelope and Nance, Martha A and Shalva, Nechama and Veber, Alvit and Tzadok, Michal and Nissenkorn, Andreea and Tonduti, Davide and Renaldo, Florence and Kraoua, Ichraf and Panteghini, Celeste and Valletta, Lorella and Garavaglia, Barbara and Cowley, Mark J and Gayevskiy, Velimir and Roscioli, Tony and Silberstein, Jonathon M and Hoffmann, Chen and Raas-Rothschild, Annick and Tiranti, Valeria and Anikster, Yair and Christodoulou, John and Kastaniotis, Alexander J and Ben-Zeev, Bruria and Hayflick, Susan J} } @article {413, title = {Whole-exome sequencing identifies novel variants in PNPT1 causing oxidative phosphorylation defects and severe multisystem disease.}, journal = {Eur J Hum Genet}, volume = {25}, year = {2016}, month = {2016 01}, pages = {79-84}, abstract = {

Recent advances in next-generation sequencing strategies have led to the discovery of many novel disease genes. We describe here a non-consanguineous family with two affected boys presenting with early onset of severe axonal neuropathy, optic atrophy, intellectual disability, auditory neuropathy and chronic respiratory and gut disturbances. Whole-exome sequencing (WES) was performed on all family members and we identified compound heterozygous variants (c.[760C>A];[1528G>C];p.[(Gln254Lys);(Ala510Pro)] in the polyribonucleotide nucleotidyltransferase 1 (PNPT1) gene in both affected individuals. PNPT1 encodes the polynucleotide phosphorylase (PNPase) protein, which is involved in the transport of small RNAs into the mitochondria. These RNAs are involved in the mitochondrial translation machinery, responsible for the synthesis of mitochondrially encoded subunits of the oxidative phosphorylation (OXPHOS) complexes. Both PNPT1 variants are within highly conserved regions and predicted to be damaging. These variants resulted in quaternary defects in the PNPase protein and a clear reduction in protein and mRNA expression of PNPT1 in patient fibroblasts compared with control cells. Protein analysis of the OXPHOS complexes showed a significant reduction in complex I (CI), complex III (CIII) and complex IV (CIV). Enzyme activity of CI and CIV was clearly reduced in patient fibroblasts compared with controls along with a 33\% reduction in total mitochondrial protein synthesis. In vitro rescue experiments, using exogenous expression of wild-type PNPT1 in patient fibroblasts, ameliorated the deficiencies in the OXPHOS complex protein expression, supporting the likely pathogenicity of these variants and the importance of WES in efficiently identifying rare genetic disease genes.

}, keywords = {Axons, Exome, Exoribonucleases, High-Throughput Nucleotide Sequencing, Humans, Intellectual Disability, Male, Mitochondria, Mutation, Optic Atrophy, Oxidative Phosphorylation, Pedigree, Protein Structure, Quaternary}, issn = {1476-5438}, doi = {10.1038/ejhg.2016.128}, author = {Alodaib, Ahmad and Sobreira, Nara and Gold, Wendy A and Riley, Lisa G and Van Bergen, Nicole J and Wilson, Meredith J and Bennetts, Bruce and Thorburn, David R and Boehm, Corinne and Christodoulou, John} }