Pharmacokinetic and pharmacokinetic/pharmacodynamic characterization of the dolutegravir/rilpivirine two-drug regimen in SWORD-1/-2 phase 3 studies.

AIM: SWORD-1 and SWORD-2 phase 3 studies concluded that switching virologically suppressed participants with HIV-1 from their current three- or four-drug antiretroviral regimen (CAR) to the two-drug regimen of once-daily dolutegravir (DTG, 50 mg) and rilpivirine (RPV, 25 mg) was safe, well tolerated and noninferior for maintaining HIV-1 suppression at week 48 and highly efficacious to week 148. A secondary objective was to characterize drug exposure and exposure-efficacy/safety relationships. METHODS: Adults with plasma HIV-1 RNA <50 copies/mL were randomized to switch to once-daily DTG + RPV on day 1 or to continue CAR for 52 weeks before switching. Trough plasma concentrations (C0) of DTG and RPV, the proportion of participants with HIV-1 RNA <50 copies/mL and adverse events to week 100 were summarized and subjected to exposure-response analyses in the overall population, in the subset of participants who switched from CAR containing enzyme-inducing drugs and by age category (≥50 and <50 years). The relationship between C0avg (individual average C0 across visits) and efficacy/safety was investigated. RESULTS: Although week 2 DTG and RPV C0 were lower in participants switching from enzyme-inducing antiretroviral drugs, C0 and C0avg stayed above in vitro antiviral protein binding-adjusted IC90 and to week 100 with viral suppression >89%. DTG or RPV C0avg showed no relationship with virologic failures or safety. Participants ≥50 years had similar C0avg and safety response to younger participants. CONCLUSION: No clinically relevant relationship between DTG or RPV exposures and virologic or safety response was observed, confirming the DTG + RPV switch for participants as a safe and effective treatment.

Dolutegravir-based Antiretroviral Therapy for Patients Coinfected With Tuberculosis and Human Immunodeficiency Virus: A Multicenter, Noncomparative, Open-label, Randomized Trial.

BACKGROUND: The concurrent treatment of tuberculosis and human immunodeficiency virus (HIV) is challenging, owing to drug interactions, overlapping toxicities, and immune reconstitution inflammatory syndrome (IRIS). The efficacy and safety of dolutegravir (DTG) were assessed in adults with HIV and drug-susceptible tuberculosis. METHODS: International Study of Patients with HIV on Rifampicin ING is a noncomparative, active-control, randomized, open-label study in HIV-1-infected antiretroviral therapy-naive adults (CD4+ ≥50 cells/mm3). Participants on rifampicin-based tuberculosis treatment ≤8 weeks were randomized (3:2) to receive DTG (50 mg twice daily both during and 2 weeks after tuberculosis therapy, then 50 mg once daily) or efavirenz (EFV; 600 mg daily) with 2 nucleoside reverse transcriptase inhibitors for 52 weeks. The primary endpoint was the proportion of DTG-arm participants with plasma HIV-1-RNA <50 copies/mL (responders) by the Food and Drug Administration Snapshot algorithm (intent-to-treat exposed population) at Week 48. The study was not powered to compare arms. RESULTS: For DTG (n = 69), the baseline HIV-1 RNA was >100 000 copies/mL in 64% of participants, with a median CD4+ count of 208 cells/mm3; for EFV (n = 44), 55% of participants had HIV-1 RNA >100 000 copies/mL, with a median CD4+ count of 202 cells/mm3. The Week 48 response rates were 75% (52/69, 95% confidence interval [CI] 65-86%) for DTG and 82% (36/44, 95% CI 70-93%) for EFV. The DTG nonresponses were driven by non-treatment related discontinuations (n = 10 lost to follow-up). There were no deaths or study drug switches. There were 2 discontinuations for toxicity (EFV). There were 3 protocol-defined virological failures (2 DTG, no acquired resistance; 1 EFV, emergent resistance to nucleoside reverse transcriptase inhibitors and nonnucleoside reverse transcriptase inhibitors). The tuberculosis treatment success rate was high. Tuberculosis-associated IRIS was uncommon (4/arm), with no discontinuations for IRIS. CONCLUSIONS: Among adults with HIV receiving rifampicin-based tuberculosis treatment, twice-daily DTG was effective and well tolerated. CLINICAL TRIALS REGISTRATION: NCT02178592.

An Evaluation of Different Partitioning Strategies for Bayesian Estimation of Species Divergence Times.

The explosive growth of molecular sequence data has made it possible to estimate species divergence times under relaxed-clock models using genome-scale data sets with many gene loci. In order to improve both model realism and to best extract information about relative divergence times in the sequence data, it is important to account for the heterogeneity in the evolutionary process across genes or genomic regions. Partitioning is a commonly used approach to achieve those goals. We group sites that have similar evolutionary characteristics into the same partition and those with different characteristics into different partitions, and then use different models or different values of model parameters for different partitions to account for the among-partition heterogeneity. However, how to partition data in practical phylogenetic analysis, and in particular in relaxed-clock dating analysis, is more art than science. Here, we use computer simulation and real data analysis to study the impact of the partition scheme on divergence time estimation. The partition schemes had relatively minor effects on the accuracy of posterior time estimates when the prior assumptions were correct and the clock was not seriously violated, but showed large differences when the clock was seriously violated, when the fossil calibrations were in conflict or incorrect, or when the rate prior was mis-specified. Concatenation produced the widest posterior intervals with the least precision. Use of many partitions increased the precision, as predicted by the infinite-sites theory, but the posterior intervals might fail to include the true ages because of the conflicting fossil calibrations or mis-specified rate priors. We analyzed a data set of 78 plastid genes from 15 plant species with serious clock violation and showed that time estimates differed significantly among partition schemes, irrespective of the rate drift model used. Multiple and precise fossil calibrations reduced the differences among partition schemes and were important to improving the precision of divergence time estimates. While the use of many partitions is an important approach to reducing the uncertainty in posterior time estimates, we do not recommend its general use for the present, given the limitations of current models of rate drift for partitioned data and the challenges of interpreting the fossil evidence to construct accurate and informative calibrations.

Shoulder Arthroscopy With Versus Without Suprascapular Nerve Release: Clinical Outcomes and Return to Sport Rate in Elite Overhead Athletes.

PURPOSE: To compare the clinical outcomes and return to sport rate between elite overhead athletes who underwent shoulder arthroscopy and decompression of the suprascapular nerve (SSN) versus overhead athletes who underwent shoulder arthroscopy without SSN release. METHODS: From 2007 to 2014, high-level overhead athletes diagnosed with a rotator cuff tear and/or a glenoid labral lesion and SSN entrapment were included in the study if their symptoms did not improve with nonoperative treatment and if they agreed to undergo surgery and participate. Their preoperative University of California at Los Angeles (UCLA) shoulder score, bilateral postoperative Constant scores, postoperative UCLA score, and return to sport rate were evaluated and compared with those of a group of elite athletes who had a similar diagnosis but refused to undergo SSN decompression during shoulder arthroscopy. RESULTS: Thirty-five athletes (25 male, 10 female) were included in the SSN decompression group (group 1), and 21 athletes were included in the non-SSN decompression group (group 2). The mean age was 27 years (range: 19-34) and 24 years (range: 21-32) in group 1 and group 2, respectively (P = .56). The mean follow-up time was 38.4 months (24-50 months) in group 1 and 42.2 months (26-53 months) in group 2 (P = .09). Both groups had significantly improved UCLA scores after surgery (P < .05). The postoperative UCLA (P = .01) and Constant scores (P < .001) were significantly higher in the SSN decompression group. The mean difference in Constant score between the affected and the unaffected side was 4 points (range: 2-12) in the SSN decompression group and 8 points (range: 4-14) in the non-SSN decompression group postoperatively (P = .0002). In both groups, 100% of patients reached the patient acceptable symptom state value for Constant score at follow-up. For the UCLA score, patients who underwent SSN decompression had significantly higher pre- to postoperative improvement than the nondecompression group (P = .016). The return to sport rate was 97% in group 1 and 84% in group 2. The mean length of career was 2.1 years (range: 1.5-2.4 years) and 2.3 years (range: 1.2-3.2 years) in group 1 and group 2, respectively. CONCLUSIONS: In elite overhead athletes with shoulder pathology and SSN entrapment, combined shoulder arthroscopy and SSN release yield superior clinical outcomes, greater improvement in UCLA score, and a higher return to sport rate than shoulder arthroscopy without SSN decompression. Regardless of SSN treatment, both groups achieved the patient acceptable symptom state after shoulder arthroscopy. LEVEL OF EVIDENCE: Level III, comparative case series.

Global Dispersal Pattern of HIV Type 1 Subtype CRF01_AE: A Genetic Trace of Human Mobility Related to Heterosexual Sexual Activities Centralized in Southeast Asia.

BACKGROUND: Human immunodeficiency virus type 1 (HIV-1) subtype CRF01_AE originated in Africa and then passed to Thailand, where it established a major epidemic. Despite the global presence of CRF01_AE, little is known about its subsequent dispersal pattern. METHODS: We assembled a global data set of 2736 CRF01_AE sequences by pooling sequences from public databases and patient-cohort studies. We estimated viral dispersal patterns, using statistical phylogeographic analysis run over bootstrap trees estimated by the maximum likelihood method. RESULTS: We show that Thailand has been the source of viral dispersal to most areas worldwide, including 17 of 20 sampled countries in Europe. Japan, Singapore, Vietnam, and other Asian countries have played a secondary role in the viral dissemination. In contrast, China and Taiwan have mainly imported strains from neighboring Asian countries, North America, and Africa without any significant viral exportation. DISCUSSION: The central role of Thailand in the global spread of CRF01_AE can be probably explained by the popularity of Thailand as a vacation destination characterized by sex tourism and by Thai emigration to the Western world. Our study highlights the unique case of CRF01_AE, the only globally distributed non-B clade whose global dispersal did not originate in Africa.

Bayesian estimation of nonsynonymous/synonymous rate ratios for pairwise sequence comparisons.

The nonsynonymous/synonymous rate ratio (ω = d(N)/d(S)) is an important measure of the mode and strength of natural selection acting on nonsynonymous mutations in protein-coding genes. The simplest such analysis is the estimation of the d(N)/d(S) ratio using two sequences. Both heuristic counting methods and the maximum-likelihood (ML) method based on a codon substitution model are widely used for such analysis. However, these methods do not have nice statistical properties, as the estimates can be zero or infinity in some data sets, so that their means and variances are infinite. In large genome-scale comparisons, such extreme estimates (either 0 or ∞) of ω and sequence distance (t) are common. Here, we implement a Bayesian method to estimate ω and t in pairwise sequence comparisons. Using a combination of computer simulation and real data analysis, we show that the Bayesian estimates have better statistical properties than the ML estimates, because the prior on ω and t shrinks the posterior of those parameters away from extreme values. We also calculate the posterior probability for ω > 1 as a Bayesian alternative to the likelihood ratio test. The new method is computationally efficient and may be useful for genome-scale comparisons of protein-coding gene sequences.

Dating the origin of hepatitis B virus reveals higher substitution rate and adaptation on the branch leading to F/H genotypes.

The evolution of hepatitis B virus (HBV), particularly its origins and evolutionary timescale, has been the subject of debate. Three major scenarios have been proposed, variously placing the origin of HBV in humans and great apes from some million years to only a few thousand years ago (ka). To compare these scenarios, we analyzed 105 full-length HBV genome sequences from all major genotypes sampled globally. We found a high correlation between the demographic histories of HBV and humans, as well as coincidence in the times of origin of specific subgenotypes with human migrations giving rise to their host indigenous populations. Together with phylogenetic evidence, this suggests that HBV has co-expanded with modern humans. Based on the co-expansion, we conducted a Bayesian dating analysis to estimate a precise evolutionary timescale for HBV. Five calibrations were used at the origins of F/H genotypes, D4, C3 and B6 from respective indigenous populations in the Pacific and Arctic and A5 from Haiti. The estimated time for the origin of HBV was 34.1ka (95% highest posterior density interval 27.6-41.3ka), coinciding with the dispersal of modern non-African humans. Our study, the first to use full-length HBV sequences, places a precise timescale on the HBV epidemic and also shows that the "branching paradox" of the more divergent genotypes F/H from Amerindians is due to an accelerated substitution rate, probably driven by positive selection. This may explain previously observed differences in the natural history of HBV between genotypes F1 and A2, B1, and D.

Sustained Virologic Suppression With Dolutegravir/Lamivudine in a Test-and-Treat Setting Through 48 Weeks.

Background: We assessed the efficacy and safety of dolutegravir/lamivudine (DTG/3TC) in a US test-and-treat setting at a secondary 48-week time point of the multicenter, single-arm, phase IIIb STAT study. Methods: Participants were eligible adults newly diagnosed with human immunodeficiency virus (HIV)-1 and had started once-daily DTG/3TC within 14 days of diagnosis, before laboratory results were available. Antiretroviral therapy (ART) was modified if baseline testing indicated DTG or 3TC resistance, hepatitis B virus (HBV) coinfection, or creatinine clearance <30 mL/min per 1.73 m2, and these participants remained in the study. A proportion with HIV-1 ribonucleic acid (RNA) <50 copies/mL at Week 48 was calculated among all participants (intention-to-treat-exposed [ITT-E] missing = failure analysis) and those with available data (observed analysis). Results: At Week 48, 82% of all participants regardless of ART (107 of 131; ITT-E missing = failure) and 97% with available data (107 of 110; observed analysis) achieved HIV-1 RNA <50 copies/mL. High proportions of virologic response were seen overall, including in participants with high viral load (≥500 000 copies/mL; 89%) or low CD4+ cell count (<200 cells/mm3; 78%) at baseline. Ten participants had treatment modification (baseline HBV coinfection, n = 5; participant/proxy decision, n = 2; baseline M184V resistance mutation, adverse event [AE; rash], and pregnancy, n = 1 each) before Week 48. Two participants met confirmed virologic failure criteria. No treatment-emergent resistance was observed. Ten participants reported drug-related AEs (all grade 1-2); no serious drug-related AEs occurred. Conclusions: Results demonstrated high proportions of participants with sustained virologic suppression, no treatment-emergent resistance, and good safety over 48 weeks, supporting first-line use of DTG/3TC in a test-and-treat setting.

Dolutegravir/lamivudine as a first-line regimen in a test-and-treat setting for newly diagnosed people living with HIV.

OBJECTIVES: Dolutegravir/lamivudine (DTG/3TC) is indicated for treatment-naive and experienced people with HIV; however, questions remain about its utility in a test-and-treat setting because of potential transmitted resistance and baseline hepatitis B virus (HBV) co-infection. We present feasibility and efficacy of DTG/3TC in newly diagnosed individuals in a test-and-treat setting. DESIGN: The single-arm STAT study evaluated DTG/3TC in a US test-and-treat setting. METHODS: Eligible adults initiated DTG/3TC 14 days or less after HIV-1 diagnosis without availability of baseline laboratory results. If baseline testing indicated DTG or 3TC resistance, HBV co-infection, or creatinine clearance less than 30 ml/min per 1.73 m2, participants remained on study with treatment modification. Efficacy endpoints included proportions of participants with HIV-1 RNA less than 50 copies/ml at Week 24, regardless of antiretroviral regimen, among all participants (intention-to-treat exposed) and those with available HIV-1 RNA data (observed). RESULTS: Of 131 participants enrolled, 8% were female and 50% were non-white. Through Week 24, treatment was modified in eight participants [five with HBV co-infection, one with baseline M184V, one for adverse event (rash), one participant decision]. At Week 24, 78% (102/131) of all participants and 92% (102/111) of those with available data achieved HIV-1 RNA less than 50 copies/ml. Incidence of drug-related adverse events was low (7%); no drug-related serious adverse events occurred. CONCLUSION: These data demonstrate the feasibility, efficacy, and safety of using DTG/3TC as a first-line regimen in a test-and-treat setting, with therapy adjustments for baseline resistance or HBV co-infection occurring safely via routine clinical care as needed [ClinicalTrials.gov, NCT03945981; see Supplemental Digital Content 1, video abstract (Video abstract summarizing the STAT study design and results), http://links.lww.com/QAD/C189].

Brief Report: Durable Suppression and Low Rate of Virologic Failure 3 Years After Switch to Dolutegravir + Rilpivirine 2-Drug Regimen: 148-Week Results From the SWORD-1 and SWORD-2 Randomized Clinical Trials.

BACKGROUND: The SWORD trials showed that in participants who achieved virologic suppression taking 3-drug or 4-drug regimens, switching to the 2-drug regimen dolutegravir plus rilpivirine was noninferior in maintaining HIV-1 RNA <50 copies/mL at the week 48 primary endpoint. We present pooled week 148 analysis results from both studies. SETTING: SWORD-1: 65 centers, 13 countries; SWORD-2: 60 centers, 11 countries. METHODS: SWORD-1 and SWORD-2 are identical, open-label, phase III studies. Participants with screening HIV-1 RNA <50 copies/mL for ≥6 months; no prior virologic failure; and no documented resistance-associated major protease inhibitor, integrase inhibitor, nucleoside reverse transcriptase inhibitor (NRTI), or non-NRTI mutations or integrase resistance-associated substitution R263K were randomly assigned 1:1 to switch to once-daily dolutegravir 50 mg plus rilpivirine 25 mg on day 1 (early-switch group) or to continue their current antiretroviral regimen and, if virologically suppressed at week 48, switch to dolutegravir plus rilpivirine at week 52 (late-switch group) until week 148. RESULTS: Using snapshot algorithm at week 148, 432 of 513 (84%) early-switch participants (148 weeks of exposure) and 428 of 477 (90%) late-switch participants (96 weeks of exposure) maintained HIV-1 RNA <50 copies/mL. Eleven participants (1%) on dolutegravir plus rilpivirine met the confirmed virologic withdrawal criterion through week 148 (early-switch group, n = 8; late-switch group, n = 3) with no integrase resistance identified. Non-NRTI resistance-associated mutations were identified in 6 participants (<1%). Drug-related adverse events (grades 2-4) were observed in 31 (6%) early-switch and 16 (3%) late-switch participants. Significant improvements in bone biomarkers were observed. Significant improvements were observed in renal biomarkers in participants taking tenofovir disoproxil fumarate pre-switch. CONCLUSION: Switching to the 2-drug regimen dolutegravir plus rilpivirine maintained virologic suppression for a high proportion of participants through 3 years, with low rates of virologic failure and a well-tolerated safety profile.

The impact of Measles-Rubella vaccination on the morbidity and mortality from Congenital Rubella Syndrome in 92 countries.

Since 2011, GAVI, The Vaccine Alliance, has funded eligible countries to introduce rubella-containing vaccination (RCV) into their national schedule. Two key indicators used to monitor the impact - the future deaths and DALYs (Disability Adjusted Life Years) averted through vaccination conducted in specific periods - are poorly understood for rubella and Congenital Rubella Syndrome (CRS). We calculate these indicators using an age-structured dynamic transmission model for rubella, with historical vaccination coverage projections during 2001-30 in 92 low and middle-income countries considered most likely to require global support to achieve the Global Vaccine Action Plan's objectives. 131,000 CRS deaths and 12.5 million DALYs may be prevented with immunization campaigns at best-estimate coverage during 2001-30, relative to those without additional support. The impact depended on the time period considered and the method for attributing deaths averted to vaccination in specific periods. The analyses support ongoing activities to reduce CRS-related morbidity and mortality.

Efficacy and safety of dolutegravir-rilpivirine for maintenance of virological suppression in adults with HIV-1: 100-week data from the randomised, open-label, phase 3 SWORD-1 and SWORD-2 studies.

BACKGROUND: Primary analyses of the SWORD-1 and SWORD-2 trials at 48 weeks showed that switching to a two-drug regimen of dolutegravir plus rilpivirine was non-inferior to continuing a standard three-drug or four-drug antiretroviral regimen for maintenance of virological suppression in people with HIV-1. Here, we present efficacy and safety data from the 100-week analysis of the trials. METHODS: SWORD-1 and SWORD-2 are identically designed, randomised, open-label phase 3 studies at 65 centres in 13 countries and 60 centres in 11 countries, respectively. Adults aged 18 years or older who were on a standard three-drug or four-drug antiretroviral therapy (ART) and had had fewer than 50 HIV-1 RNA copies per mL of plasma for at least 6 months were randomly assigned (1:1) to 50 mg dolutegravir plus 25 mg rilpivirine orally once daily (early-switch group) or to continue their standard regimen for 52 weeks before switching to the dolutegravir plus rilpivirine combination (ie, the late-switch group). In this analysis of week 100 data, the efficacy endpoint of interest was the proportion of participants with fewer than 50 copies of HIV-1 RNA per mL of plasma (per the US Food and Drug Administration snapshot algorithm). This outcome was assessed in all randomly assigned participants who received at least one dose of the study drug. Data were analysed after the last participant completed week 100 (Sept 15, 2017) and verified through the data cutoff (Nov 21, 2017). SWORD-1 and SWORD-2 are registered with ClinicalTrials.gov, numbers NCT02429791 and NCT02422797, respectively. FINDINGS: 513 participants were randomly assigned to dolutegravir plus rilpivirine (ie, the early-switch group) and 511 to continue their standard ART regimen, 477 of whom then switched to dolutegravir plus rilpivirine at week 52 (ie, the late-switch group). At week 100, 456 (89% [95% CI 86-92]) of 513 participants in the early-switch group and 444 (93% [91-95]) of 477 in the late-switch group had fewer than 50 HIV-1 RNA copies per mL. Drug-related adverse events occurred in 103 (20%) participants in the early-switch group and 58 (12%) in the late-switch group. The most common drug-related adverse events were headache (11 participants in the early-switch group [2%] vs eight [2%] in the late-switch group) and nausea (eight [2%] vs five [1%]). INTERPRETATION: The combination of dolutegravir plus rilpivirine sustained virological suppression of HIV-1, was associated with a low frequency of virological failure, and had a favourable safety profile, which support its use as a nucleoside reverse transcriptase inhibitor-sparing and protease inhibitor-sparing alternative to three-drug regimens that reduces overall exposure to ART. FUNDING: ViiV Healthcare and Janssen Pharmaceutica.

Unravelling the history of hepatitis B virus genotypes A and D infection using a full-genome phylogenetic and phylogeographic approach.

Hepatitis B virus (HBV) infection constitutes a global public health problem. In order to establish how HBV was disseminated across different geographic regions, we estimated the levels of regional clustering for genotypes D and A. We used 916 HBV-D and 493 HBV-A full-length sequences to reconstruct their global phylogeny. Phylogeographic analysis was conducted by the reconstruction of ancestral states using the criterion of parsimony. The putative origin of genotype D was in North Africa/Middle East. HBV-D sequences form low levels of regional clustering for the Middle East and Southern Europe. In contrast, HBV-A sequences form two major clusters, the first including sequences mostly from sub-Saharan Africa, and the second including sequences mostly from Western and Central Europe. Conclusion: We observed considerable differences in the global dissemination patterns of HBV-D and HBV-A and different levels of monophyletic clustering in relation to the regions of prevalence of each genotype.

The global spread of HIV-1 subtype B epidemic.

Human immunodeficiency virus type 1 (HIV-1) was discovered in the early 1980s when the virus had already established a pandemic. For at least three decades the epidemic in the Western World has been dominated by subtype B infections, as part of a sub-epidemic that traveled from Africa through Haiti to United States. However, the pattern of the subsequent spread still remains poorly understood. Here we analyze a large dataset of globally representative HIV-1 subtype B strains to map their spread around the world over the last 50years and describe significant spread patterns. We show that subtype B travelled from North America to Western Europe in different occasions, while Central/Eastern Europe remained isolated for the most part of the early epidemic. Looking with more detail in European countries we see that the United Kingdom, France and Switzerland exchanged viral isolates with non-European countries than with European ones. The observed pattern is likely to mirror geopolitical landmarks in the post-World War II era, namely the rise and the fall of the Iron Curtain and the European colonialism. In conclusion, HIV-1 spread through specific migration routes which are consistent with geopolitical factors that affected human activities during the last 50years, such as migration, tourism and trade. Our findings support the argument that epidemic control policies should be global and incorporate political and socioeconomic factors.

Uncertainty in the Timing of Origin of Animals and the Limits of Precision in Molecular Timescales.

The timing of divergences among metazoan lineages is integral to understanding the processes of animal evolution, placing the biological events of species divergences into the correct geological timeframe. Recent fossil discoveries and molecular clock dating studies have suggested a divergence of bilaterian phyla >100 million years before the Cambrian, when the first definite crown-bilaterian fossils occur. Most previous molecular clock dating studies, however, have suffered from limited data and biases in methodologies, and virtually all have failed to acknowledge the large uncertainties associated with the fossil record of early animals, leading to inconsistent estimates among studies. Here we use an unprecedented amount of molecular data, combined with four fossil calibration strategies (reflecting disparate and controversial interpretations of the metazoan fossil record) to obtain Bayesian estimates of metazoan divergence times. Our results indicate that the uncertain nature of ancient fossils and violations of the molecular clock impose a limit on the precision that can be achieved in estimates of ancient molecular timescales. For example, although we can assert that crown Metazoa originated during the Cryogenian (with most crown-bilaterian phyla diversifying during the Ediacaran), it is not possible with current data to pinpoint the divergence events with sufficient accuracy to test for correlations between geological and biological events in the history of animals. Although a Cryogenian origin of crown Metazoa agrees with current geological interpretations, the divergence dates of the bilaterians remain controversial. Thus, attempts to build evolutionary narratives of early animal evolution based on molecular clock timescales appear to be premature.