Dynamics of the most common pathogenic mtDNA variant m.3243A > G demonstrate frequency-dependency in blood and positive selection in the germline.

The A-to-G point mutation at position 3243 in the human mitochondrial genome (m.3243A > G) is the most common pathogenic mtDNA variant responsible for disease in humans. It is widely accepted that m.3243A > G levels decrease in blood with age, and an age correction representing ~ 2% annual decline is often applied to account for this change in mutation level. Here we report that recent data indicate that the dynamics of m.3243A > G are more complex and depend on the mutation level in blood in a bi-phasic way. Consequently, the traditional 2% correction, which is adequate 'on average', creates opposite predictive biases at high and low mutation levels. Unbiased age correction is needed to circumvent these drawbacks of the standard model. We propose to eliminate both biases by using an approach where age correction depends on mutation level in a biphasic way to account for the dynamics of m.3243A > G in blood. The utility of this approach was further tested in estimating germline selection of m.3243A > G. The biphasic approach permitted us to uncover patterns consistent with the possibility of positive selection for m.3243A > G. Germline selection of m.3243A > G shows an 'arching' profile by which selection is positive at intermediate mutant fractions and declines at high and low mutant fractions. We conclude that use of this biphasic approach will greatly improve the accuracy of modelling changes in mtDNA mutation frequencies in the germline and in somatic cells during aging.

Reanalysis of mtDNA mutations of human primordial germ cells (PGCs) reveals NUMT contamination and suggests that selection in PGCs may be positive.

The resilience of the mitochondrial genome (mtDNA) to a high mutational pressure depends, in part, on negative purifying selection in the germline. A paradigm in the field has been that such selection, at least in part, takes place in primordial germ cells (PGCs). Specifically, Floros et al. (Nature Cell Biology 20: 144-51) reported an increase in the synonymity of mtDNA mutations (a sign of purifying selection) between early-stage and late-stage PGCs. We re-analyzed Floros' et al. data and determined that their mutational dataset was significantly contaminated with single nucleotide variants (SNVs) derived from a nuclear sequence of mtDNA origin (NUMT) located on chromosome 5. Contamination was caused by co-amplification of the NUMT sequence by cross-specific PCR primers. Importantly, when we removed NUMT-derived SNVs, the evidence of purifying selection was abolished. In addition to bulk PGCs, Floros et al. reported the analysis of single-cell late-stage PGCs, which were amplified with different sets of PCR primers that cannot amplify the NUMT sequence. Accordingly, there were no NUMT-derived SNVs among single PGC mutations. Interestingly, single PGC mutations show adecreaseof synonymity with increased intracellular mutant fraction. More specifically, nonsynonymous mutations show faster intracellular genetic drift towards higher mutant fraction than synonymous ones. This pattern is incompatible with predominantly negative selection. This suggests that germline selection of mtDNA mutations is a complex phenomenon and that the part of this process that takes place in PGCs may be predominantly positive. However counterintuitive, positive germline selection of detrimental mtDNA mutations has been reported previously andpotentially may be evolutionarily advantageous.

A Clinical Diagnostic System for Late-Stage Neuropsychiatric Lyme Borreliosis Based upon an Analysis of 100 Patients.

Many late-stage chronic Lyme disease clinical findings are neuropsychiatric. A total clinical assessment is critical in diagnosis, especially since controversy surrounds the reliability of laboratory testing. The clinical findings of one hundred Lyme disease patients with chronic neuropsychiatric symptoms were entered into a database. The prevalence of each clinical finding pre-infection and post-infection was compared and calculated within the 95% confidence interval. Patients had minimal symptoms pre-infection, but a high post-infection prevalence of a broad spectrum of acquired multisystem symptoms. These findings included impairments of attention span, memory, processing, executive functioning, emotional functioning, behavior, psychiatric syndromes, vegetative functioning, neurological, musculoskeletal, cardiovascular, upper respiratory, dental, pulmonary, gastrointestinal, genitourinary, and other symptoms. The most prevalent symptoms included sustained attention impairments, brain fog, unfocused concentration, joint symptoms, distraction by frustration, depression, working memory impairments, decreased school/job performance, recent memory impairments, difficulty prioritizing multiple tasks, fatigue, non-restorative sleep, multitasking difficulties, sudden mood swings, hypersomnia, mental apathy, decreased social functioning, insomnia, tingling, word finding difficulties, name retrieval, headaches, sound hypersensitivity, paresis, anhedonia, depersonalization, cold intolerance, body temperature fluctuations, light sensitivity and dysfluent speech. The average patient had five symptoms pre-infection and 82 post-infection. Pattern recognition is critical in making a diagnosis. This study was used to develop three clinical assessment forms.