Mistranslating the genetic code with leucine in yeast and mammalian cells.

Translation fidelity relies on accurate aminoacylation of transfer RNAs (tRNAs) by aminoacyl-tRNA synthetases (AARSs). AARSs specific for alanine (Ala), leucine (Leu), serine, and pyrrolysine do not recognize the anticodon bases. Single nucleotide anticodon variants in their cognate tRNAs can lead to mistranslation. Human genomes include both rare and more common mistranslating tRNA variants. We investigated three rare human tRNALeu variants that mis-incorporate Leu at phenylalanine or tryptophan codons. Expression of each tRNALeu anticodon variant in neuroblastoma cells caused defects in fluorescent protein production without significantly increased cytotoxicity under normal conditions or in the context of proteasome inhibition. Using tRNA sequencing and mass spectrometry we confirmed that each tRNALeu variant was expressed and generated mistranslation with Leu. To probe the flexibility of the entire genetic code towards Leu mis-incorporation, we created 64 yeast strains to express all possible tRNALeu anticodon variants in a doxycycline-inducible system. While some variants showed mild or no growth defects, many anticodon variants, enriched with G/C at positions 35 and 36, including those replacing Leu for proline, arginine, alanine, or glycine, caused dramatic reductions in growth. Differential phenotypic defects were observed for tRNALeu mutants with synonymous anticodons and for different tRNALeu isoacceptors with the same anticodon. A comparison to tRNAAla anticodon variants demonstrates that Ala mis-incorporation is more tolerable than Leu at nearly every codon. The data show that the nature of the amino acid substitution, the tRNA gene, and the anticodon are each important factors that influence the ability of cells to tolerate mistranslating tRNAs.

Blepharoclonus in Parkinsonism.

Background and Objectives: In clinical practice, we have observed that patients with Parkinson disease (PD) often have blepharoclonus, but its prevalence is not well described in the literature. Understanding the relative frequencies of blepharoclonus in PD and atypical parkinsonian syndromes may shed light on the diagnostic utility of this clinical sign. We aimed to assess (1) the frequency of blepharoclonus in patients with PD in a single-center cohort; (2) the association of blepharoclonus with disease stage, tremor severity, and non-motor symptoms; and (3) the frequency of blepharoclonus in synucleinopathy vs non-synucleinopathy-associated parkinsonism. Methods: We prospectively enrolled 85 patients, 75 with PD and 10 with atypical parkinsonism. Blepharoclonus was considered present if eyelid fluttering was sustained for >5 seconds after gentle eye closure. For each patient, demographics were collected, and we completed selected questions from the MDS-UPDRS (Unified Parkinson's Disease Rating Scale) part 2, REM Sleep Behavior Disorder Questionnaire, and MDS-UPDRS part 3 tremor assessments and recorded the presence/absence of dyskinesia. Results: 63 of 75 patients with PD (84%) had blepharoclonus. Among the 10 patients with atypical parkinsonism, 5 had synucleinopathy syndromes. Blepharoclonus was present in 3 of 5 patients with synucleinopathy and 0 of 5 patients with non-synucleinopathy-associated parkinsonian syndromes. Discussion: Blepharoclonus is prevalent in our PD cohort, suggesting possible utility as a clinical marker for PD. The absence of blepharoclonus in a patient with parkinsonism may suggest a non-synucleinopathy (e.g., tauopathy). Analysis of a larger cohort of both PD and atypical parkinsonism would be needed to establish whether blepharoclonus distinguishes PD from atypical parkinsonism, or synucleinopathy from non-synucleinopathy.

Validation of a New Patient-Reported Outcome Measure of the Functional Impact of Essential Tremor on Activities of Daily Living.

Background: The Essential Tremor Rating Assessment Scale (TETRAS) is a popular scale for essential tremor (ET), but its activities of daily living (ADL) and performance (P) subscales are based on a structured interview and physical exam. No patient-reported outcome (PRO) scale for ET has been developed according to US regulatory guidelines. Objective: Develop and validate a TETRAS PRO subscale. Methods: Fourteen items, rated 0-4, were derived from TETRAS ADL and structured cognitive interviews of 18 ET patients. Convergent validity analyses of TETRAS PRO versus TETRAS ADL, TETRAS-P, and the Quality of Life in Essential Tremor Questionnaire (QUEST) were computed for 67 adults with ET or ET plus. Test-retest reliability was computed at intervals of 1 and 30 days. The influence of mood (Hospital Anxiety and Depression Scale, HADS) and coping behaviors (Essen Coping Questionnaire, ECQ) was examined with multiple linear regression. Results: TETRAS PRO was strongly correlated (r > 0.7) with TETRAS ADL, TETRAS-P, and QUEST and exhibited good to excellent reliability (Cronbach alpha 95%CI = 0.853-0.926; 30-day test-retest intraclass correlation 95%CI = 0.814-0.921). The 30-day estimate of minimum detectable change (MDC) was 6.6 (95%CI 5.2-8.0). TETRAS-P (rsemipartial = 0.607), HADS depression (rsemipartial = 0.384), and the coping strategy of information seeking and exchange of experiences (rsemipartial = 0.176) contributed statistically to TETRAS PRO in a multiple linear regression (R2 = 0.67). Conclusions: TETRAS PRO is a valid and reliable scale that is influenced strongly by tremor severity, moderately by mood (depression), and minimally by coping skills. The MDC for TETRAS PRO is probably sufficient to detect clinically important change.