Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Case Reports
. 2016 Aug;31(9):1127-37.
doi: 10.1177/0883073816643402. Epub 2016 Apr 19.

Novel Compound Heterozygous Mutations Expand the Recognized Phenotypes of FARS2-Linked Disease

Melissa A Walker  1 , Kyle P Mohler  2 , Kyle W Hopkins  2 , Derek H Oakley  3 , David A Sweetser  4 , Michael Ibba  2 , Matthew P Frosch  3 , Ronald L Thibert  5
Affiliations
Case Reports

Novel Compound Heterozygous Mutations Expand the Recognized Phenotypes of FARS2-Linked Disease

Melissa A Walker et al. J Child Neurol. 2016 Aug.

Abstract

Mutations in mitochondrial aminoacyl-tRNA synthetases are an increasingly recognized cause of human diseases, often arising in individuals with compound heterozygous mutations and presenting with system-specific phenotypes, frequently neurologic. FARS2 encodes mitochondrial phenylalanyl transfer ribonucleic acid (RNA) synthetase (mtPheRS), perturbations of which have been reported in 6 cases of an infantile, lethal disease with refractory epilepsy and progressive myoclonus. Here the authors report the case of juvenile onset refractory epilepsy and progressive myoclonus with compound heterozygous FARS2 mutations. The authors describe the clinical course over 6 years of care at their institution and diagnostic studies including electroencephalogram (EEG), brain magnetic resonance imaging (MRI), serum and cerebrospinal fluid analyses, skeletal muscle biopsy histology, and autopsy gross and histologic findings, which include features shared with Alpers-Huttenlocher syndrome, Leigh syndrome, and a previously published case of FARS2 mutation associated infantile onset disease. The authors also present structure-guided analysis of the relevant mutations based on published mitochondrial phenylalanyl transfer RNA synthetase and related protein crystal structures as well as biochemical analysis of the corresponding recombinant mutant proteins.

Keywords: FARS2; mitochondrial tRNA synthetase; progressive myoclonus epilepsy.

PubMed Disclaimer

Figures

Figure 1
Figure 1. Multiple sequence alignment of orthologous proteins
Multiple sequence alignment of N-terminal mitochondrial phenylalanyl transfer RNA synthetase peptide sequences from multiple species. Conserved residues are presented in green. The location of the mutations carried by the patient are boxed in red (proline-85) and blue (histidine-135). Both residues are highly conserved through bacterial species.
Figure 2
Figure 2. Structure-guided analysis of FARS2 mutations
Structure-guided analysis of FARS2 mutations. Phe-AMP bound FARS2 quarternary structure with domains labeled (PBD id 3CMQ), the locations of proline-85 and histidine-135 are highlighted in red and blue, respectively (A). proline-85 is buried within several aromatic residues (B). histidine-135 is located within conserved inter-motif region forming one of two catalytic domain loops which associate with the acceptor stem of the tRNA molecule in the crystal structure of the orthologous protein T. Thermophilus-PheRS-bound to tRNA-Phe (PBD id 1EIY), pictured here in cyan with orthologous domain aligned with FARS2 in green, tRNA-Phe is drawn in yellow.
Figure 3
Figure 3. Analysis of recombinant mutant enzymes
Recombinant mutant mtPheRS proteins were expressed and purified in E. coli per established protocols. End point aminoacylation reactions indicated that mutant P85A mtPheRS charges tRNA very similarly to WT, but H135D demonstrated severe aminoacylation deficiency. Determination of the steady-state kinetics for tRNA revealed that mutant P85A has a two-fold increase in catalytic efficiency when compared to WT, while kinetic parameters for H135D were unable to be determined using standard techniques, reinforcing the previously observed aminoacylation deficiency. End-point pyrophosphate exchange experiments were also performed. At a phenylalanine concentration of 15 μM, twice the reported Km for human mtPheRS, mutant P85A is unable to produce a measurable amount of activity, suggesting that the Km of P85A for phenylalanine is higher than the reported WT value. Mutant H135D mtPheRS showed a moderate amount of activity, suggesting that the observed aminoacylation deficiency is likely due to a defect in tRNA binding and not amino acid activation. The stability of WT and mutant proteins was assessed by active site titration after incubation at either room temperature or 37 °C. At room temperature, neither mutation has a measurable impact on protein stability. However, when tested at 37 °C, mutant P85A appears to have decreased stability when compared to WT.
Figure 4
Figure 4. MRI brain
MRI brain performed at age 15 years, 2 months prior to death revealing T2 hyperintensity within the left caudate and left medial temporal lobe, and the right medial occipital lobe along the superior bank of the right calcarine sulcus with encephalomalacia of the calcaravis. Notably, earlier corpus callostomy for refractory seizures was complicated by the right subdural fluid collection also seen in this image, requiring external ventricular drain placement.
Figure 5
Figure 5. Microscopic analysis of brain and spinal cord on autopsy
Microscopic analysis of the brain and spinal cord revealed a diffuse, predominantly cortical, as well as subcortical process characterized by laminar cortical neuron loss and gliosis, with the the primary visualcortex, seen in low (A) and high (B) power, and the lateral occipital cortex, seen in low (C) and high (D) power markedly affected. A single focal region of spongiform change was observed in the thalamus, shown at low (E) and high (F) power.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Konovalova S, Tyynismaa H. Mitochondrial aminoacyl-tRNA synthetases in human disease. Mol Genet Metabol. 2013;108:206–211. - PubMed
    1. Hallmann K, Zsurka G, Moskau-Hartmann S, Kirschner J, Korinthenberg R, Ruppert AK, Ozdemir O, Weber Y, Becker F, Lerche H, Elger CE, Thiele H, Nürnberg P, Sander T, Kunz WS. A homozygous splice-site mutation in CARS2 is associated with progressive myoclonic epilepsy. Neurology. 2014;83:2183–7. - PubMed
    1. Scheper GC, van der Klok T, van Andel RJ, van Berkel CG, Sissler M, Smet J, Muravina TI, Serkov SV, Uziel G, Bugiani M, Schiffmann R, Krägeloh-Mann I, Smeitink JA, Florentz C, Van Coster R, Pronk JC, van der Knaap MS. Mitochondrial aspartyl-tRNA synthetase deficiency causes leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation. Nat Genet. 2007;39:534–9. - PubMed
    1. Steenweg ME, Ghezzi D, Haack T, Abbink TE, Martinelli D, van Berkel CG, Bley A, Diogo L, Grillo E, Te Water Naudé J, Strom TM, Bertini E, Prokisch H, van der Knaap MS, Zeviani M. Leukoencephalopathy with thalamus and brainstem involvement and high lactate ‘LTBL’ caused by EARS2 mutations. Brain. 2012;135:1387–94. - PubMed
    1. Bayat V, Thiffault I, Jaiswal M, Tétreault M, Donti T, Sasarman F, Bernard G, Demers-Lamarche J, Dicaire MJ, Mathieu J, Vanasse M, Bouchard JP, Rioux MF, Lourenco CM, Li Z, Haueter C, Shoubridge EA, Graham BH, Brais B, Bellen HJ. Mutations in the mitochondrial methionyl-tRNA synthetase cause a neurodegenerative phenotype in flies and a recessive ataxia (ARSAL) in humans. PLoS Biol. 2012;10(3):e1001288. - PMC - PubMed

Publication types