Decompensation of cardiorespiratory function and emergence of anemia during pregnancy in a case of mitochondrial myopathy, lactic acidosis, and sideroblastic anemia 2 with compound heterozygous YARS2 pathogenic variants.

Myopathy, lactic acidosis, and sideroblastic anemia 2 (MLASA2) is an autosomal recessive mitochondrial disorder caused by pathogenic variants in YARS2. YARS2 variants confer heterogeneous phenotypes ranging from the full MLASA syndrome to a clinically unaffected state. Symptom onset is most common in the first decade of life but can occur in adulthood and has been reported following intercurrent illness. Early death can result from respiratory muscle weakness and cardiomyopathy. We report a case of MLASA2 with compound heterozygous YARS2 pathogenic variants; a known pathogenic nonsense variant [NM_001040436.3:c.98C>A (p.Ser33Ter)] and a likely pathogenic missense variant not previously associated with disease [NM_001040436.3:c.948G>T (p.Arg316Ser)]. The proband initially presented with a relatively mild phenotype of myopathy and lactic acidosis. During pregnancy, anemia emerged as an additional feature and in the postpartum period she experienced severe decompensation of cardiorespiratory function. This is the first reported case of pregnancy-related complications in a patient with YARS2-related mitochondrial disease. This case highlights the need for caution and careful counseling when considering pregnancy in mitochondrial disease, due to the risk of disease exacerbation and pregnancy complications.

Sideroblastic anemia associated with multisystem mitochondrial disorders.

BACKGROUND: Sideroblastic anemia represents a heterogeneous group of inherited or acquired diseases with disrupted erythroblast iron utilization, ineffective erythropoiesis, and variable systemic iron overload. In a cohort of 421 patients with multisystem mitochondrial diseases, refractory anemia was found in 8 children. RESULTS: Five children had sideroblastic anemia with increased numbers of ring sideroblasts >15%. Two of the children had a fatal course of MLASA1 syndrome (mitochondrial myopathy, lactic acidosis, and sideroblastic anemia [SA]) due to a homozygous, 6-kb deletion in the PUS1 gene, part of the six-member family of pseudouridine synthases (pseudouridylases). Large homozygous deletions represent a novel cause of presumed PUS1-loss-of-function phenotype. The other three children with SA had Pearson syndrome (PS) due to mtDNA deletions of 4 to 8 kb; two of these children showed early onset of PS and died due to repeated sepsis; the other child had later onset of PS and survived as the hematological parameters normalized and the disease transitioned to Kearns-Sayre syndrome. In addition, anemia without ring sideroblasts was found in three other patients with mitochondrial disorders, including two children with later onset of PS and one child with failure to thrive, microcephaly, developmental delay, hypertrophic cardiomyopathy, and renal tubular acidosis due to the heterozygous mutations c.610A>G (p.Asn204Asp) and c.674C>T (p.Pro225Leu) in the COX10 gene encoding the cytochrome c oxidase assembly factor. CONCLUSIONS: Sideroblastic anemia was found in fewer than 1.2% of patients with multisystem mitochondrial disease, and it was usually associated with an unfavorable prognosis.

Clinical and molecular study in a long-surviving patient with MLASA syndrome due to novel PUS1 mutations.

Myopathy-lactic acidosis-sideroblastic anemia (MLASA) syndrome is a rare autosomal recessive disease. We studied a 43-year-old female presenting since childhood with mild cognitive impairment and sideroblastic anemia. She later developed hepatopathy, cardiomyopathy, and insulin-dependent diabetes. Muscle weakness appeared in adolescence and, at age 43, she was unable to walk. Two novel different mutations in the PUS1 gene were identified: c.487delA (p.I163Lfs*4) and c.884 G>A (p.R295Q). Quantitative analysis of DNA from skeletal muscle biopsies showed a significant increase in mitochondrial DNA (mtDNA) content in the patient compared to controls. Clinical and molecular findings of this patient widen the genotype-phenotype spectrum in MLASA syndrome.

Mutation of the human mitochondrial phenylalanine-tRNA synthetase causes infantile-onset epilepsy and cytochrome c oxidase deficiency.

Mitochondrial aminoacyl-tRNA synthetases (aaRSs) are essential enzymes in protein synthesis since they charge tRNAs with their cognate amino acids. Mutations in the genes encoding mitochondrial aaRSs have been associated with a wide spectrum of human mitochondrial diseases. Here we report the identification of pathogenic mutations (a partial genomic deletion and a highly conserved p. Asp325Tyr missense variant) in FARS2, the gene encoding mitochondrial phenylalanyl-tRNA synthetase, in a patient with early-onset epilepsy and isolated complex IV deficiency in muscle. The biochemical defect was expressed in myoblasts but not in fibroblasts and associated with decreased steady state levels of COXI and COXII protein and reduced steady state levels of the mt-tRNA(Phe) transcript. Functional analysis of the recombinant mutant p. Asp325Tyr FARS2 protein showed an inability to bind ATP and consequently undetectable aminoacylation activity using either bacterial tRNA or human mt-tRNA(Phe) as substrates. Lentiviral transduction of cells with wildtype FARS2 restored complex IV protein levels, confirming that the p.Asp325Tyr mutation is pathogenic, causing respiratory chain deficiency and neurological deficits on account of defective aminoacylation of mt-tRNA(Phe).

Mitochondrial myopathy, lactic acidosis, and sideroblastic anemia (MLASA) plus associated with a novel de novo mutation (m.8969G>A) in the mitochondrial encoded ATP6 gene.

Mitochondrial myopathy, lactic acidosis and sideroblastic anemia (MLASA) is a rare mitochondrial disorder that has previously been associated with mutations in PUS1 and YARS2. In the present report, we describe a 6-year old male with an MLASA plus phenotype. This patient had features of MLASA in the setting of developmental delay, sensorineural hearing loss, epilepsy, agenesis of the corpus callosum, failure to thrive, and stroke-like episodes. Sequencing of the mitochondrial genome identified a novel de novo, heteroplasmic mutation in the mitochondrial DNA (mtDNA) encoded ATP6 gene (m.8969G>A, p.S148N). Whole exome sequencing did not identify mutations or variants in PUS1 or YARS2 or any known nuclear genes that could affect mitochondrial function and explain this phenotype. Studies of fibroblasts derived from the patient revealed a decrease in oligomycin-sensitive respiration, a finding which is consistent with a complex V defect. Thus, this mutation in MT-ATP6 may represent the first mtDNA point mutation associated with the MLASA phenotype.

Severe pulmonary arterial hypertension in congenital sideroblastic anemia from PUS1 mutation - a case report.

BACKGROUND: Myopathy, lactic acidosis and inherited sideroblastic anemia (MLASA) are a group of rare intriguing disorders with wider pathophysiological implications. One of the causes of MLASA is the mutation in PUS1 gene that encodes for pseudouridine synthase. This PUS1 mutation results in MLASA in which anemia and myopathy predominate. Severe pulmonary arterial hypertension has not been previously reported in patients with PUS1 gene mutation. CASE REPORT: A 17 year old girl with congenital sideroblastic anemia presented with worsening of breathlessness. Severe pulmonary artery hypertension was documented on investigations. A homozygous variant in exon 3 of gene PUS1,( chromosome 12:g.131932301 C > T c.430 C > T) was found on sanger sequencing. CONCLUSION: We document severe pulmonary arterial hypertension in a patient of congenital sideroblastic anemia from PUS1 gene. We hypothesis that cross talk with TGFb pathways might occur in PUS1 mutation, and that might cause severe PAH. This observation might have therapeutic implications.

A distinct mitochondrial myopathy, lactic acidosis and sideroblastic anemia (MLASA) phenotype associates with YARS2 mutations.

Nuclear-encoded disorders of mitochondrial translation are clinically and genetically heterogeneous. Genetic causes include defects of mitochondrial aminoacyl-tRNA synthetases, and factors required for initiation, elongation and termination of protein synthesis as well as ribosome recycling. We report on a new case of myopathy, lactic acidosis and sideroblastic anemia (MLASA) syndrome caused by defective mitochondrial tyrosyl aminoacylation. The patient presented at 1 year with anemia initially attributed to iron deficiency. Bone marrow aspirate at 5 years revealed ringed sideroblasts but transfusion dependency did not occur until 11 years. Other clinical features included lactic acidosis, poor weight gain, hypertrophic cardiomyopathy and severe myopathy leading to respiratory failure necessitating ventilatory support. Long-range PCR excluded mitochondrial DNA rearrangements. Clinical diagnosis of MLASA prompted direct sequence analysis of the YARS2 gene encoding the mitochondrial tyrosyl-tRNA synthetase, which revealed homozygosity for a known pathogenic mutation, c.156C>G;p.F52L. Comparison with four previously reported cases demonstrated remarkable clinical homogeneity. First line investigation of MLASA should include direct sequence analysis of YARS2 and PUS1 (encoding a tRNA modification factor) rather than muscle biopsy. Early genetic diagnosis is essential for counseling and to facilitate appropriate supportive therapy. Reasons for segregation of specific clinical phenotypes with particular mitochondrial aminoacyl tRNA-synthetase defects remain unknown.

Myopathy, lactic acidosis and sideroblastic anemia 1 (MLASA1): A 25-year follow-up.

Mitochondrial myopathy, lactic acidosis and sideroblastic anemia 1 (MLASA1) is a rare disease caused by biallelic pathogenic variants in the PUS1 gene. There are eleven MLASA1 patients reported worldwide with the majority of the patients originating from the Shiraz region of Iran. The rarity of this disease poses challenges to counseling patients due to a lack of natural history data. This report reviews what is known regarding MLASA1 and describes two brothers with MLASA1 who were cared for over the course of 10 years at the University of California Los Angeles. The brothers suffered from chronic anemia, transfusion dependency and muscle wasting that lead to respiratory insufficiency and death in one of the brothers.

In human pseudouridine synthase 1 (hPus1), a C-terminal helical insert blocks tRNA from binding in the same orientation as in the Pus1 bacterial homologue TruA, consistent with their different target selectivities.

Human pseudouridine (Ψ) synthase Pus1 (hPus1) modifies specific uridine residues in several non-coding RNAs: tRNA, U2 spliceosomal RNA, and steroid receptor activator RNA. We report three structures of the catalytic core domain of hPus1 from two crystal forms, at 1.8Å resolution. The structures are the first of a mammalian Ψ synthase from the set of five Ψ synthase families common to all kingdoms of life. hPus1 adopts a fold similar to bacterial Ψ synthases, with a central antiparallel ß-sheet flanked by helices and loops. A flexible hinge at the base of the sheet allows the enzyme to open and close around an electropositive active-site cleft. In one crystal form, a molecule of Mes [2-(N-morpholino)ethane sulfonic acid] mimics the target uridine of an RNA substrate. A positively charged electrostatic surface extends from the active site towards the N-terminus of the catalytic domain, suggesting an extensive binding site specific for target RNAs. Two α-helices C-terminal to the core domain, but unique to hPus1, extend along the back and top of the central ß-sheet and form the walls of the RNA binding surface. Docking of tRNA to hPus1 in a productive orientation requires only minor conformational changes to enzyme and tRNA. The docked tRNA is bound by the electropositive surface of the protein employing a completely different binding mode than that seen for the tRNA complex of the Escherichia coli homologue TruA.