Evaluation of an adapted virtual training for master trainers of the WHO Caregiver Skills Training Program during the COVID-19 pandemic

LAY ABSTRACT

The COVID-19 pandemic interrupted in-person professional activities. We developed and evaluated a remote training approach for master trainers of the Caregiver Skills Training Program. Master trainers support community practitioners, who in turn deliver the Caregiver Skills Training Program to caregivers of children with developmental delays or disabilities. The Caregiver Skills Training Program teaches caregivers how to use strategies to enhance learning and interactions during everyday play and home activities and routines with their child. The aim of this study was to evaluate the remote training of master trainers on Caregiver Skills Training Program. Twelve out of the 19 practitioners who enrolled in the training completed the study. The training consisted of a 5-day in-person session completed prior to the pandemic, followed by supporting participants' ability to identify Caregiver Skills Training Program strategies through coding of video recordings over 7 weekly meetings and group discussions and ended with participants independently coding a set of 10 videos for Caregiver Skills Training Program strategies. We found all but one participant was able to reliably identify Caregiver Skills Training Program strategies from video recordings despite a lack of ability to practice the Caregiver Skills Training Program strategies with children due to the pandemic. Taken together, our findings illustrate the feasibility and value of remote training approaches in implementing interventions.

Mediation of meaningful outcomes in early intervention: a commentary on Carruthers et al. (2023)

Across the spectrum of behavioral, naturalistic developmental behavioral, and developmental/relational interventions for young children with autism, there has been limited empirical testing of the mechanism of these early intervention approaches. Testing mediation provides insights to the how or why the intervention condition may be preferred in comparison to a control in the population sample (Kraemer, American Journal of Psychiatry, 2016, 173, 672). Combined with an understanding of moderation (for whom or under what conditions), we move toward a better understanding of how to personalize interventions to build on strengths and maximize skill gains for autistic children. Yet, to date there are very few published texts of mechanism in early intervention for young children with autism. This commentary explores a recently published article by Carruthers et al (2023) and examines themes and considerations for measurement of intervention outcomes and mediators.

The devil is in the details: Advancing our collective understanding of naturalistic developmental behavioral interventions

Given the growing body of randomized trials examining various Naturalistic Developmental Behavioral Intervention (NDBI) approaches, a dialog has emerged exploring the overlap in strategies across NDBIs to create single measures that propose to capture core strategies across the interventions. This commentary will ask readers to consider the current state of the science, the potential value of looking not only for similarities but also for differences across approaches, and present five scientific next steps to advance our collective understanding of the NDBIs including: (a) operationalizing intervention strategies and outcomes, (b) expansion of the effectiveness evidence base and begin testing implementation strategies for individual NDBIs, (c) rigorous testing of core intervention components and the mechanism of each intervention, (d) personalization, and (e) supporting transparency with a priori trial registration.

Developmental Play Skills as Outcomes of Early Intervention

Play is critical in the development of cognitive and language skills in young children with autism; however, few studies have examined the impact of the intervention on the development of play skills. The current study aims to address the change in developmental skills, including play after participation in the JASPER intervention, and to examine the initiation of joint attention as a moderator of the effect of treatment on changes in play skills. The study included 109 preschool-age children who participated in the JASPER intervention and examined changes in developmental skills, including play skills. Children who received JASPER improved significantly in both play diversity (F(1,99) = 4.89, p = 0.029, ES = 0.22) and complexity (F(1,98) = 5.21, p = 0.025; ES = 0.23) compared to children in control conditions. These gains in play skills were associated with concurrent improvements in cognition and communication skills. Additionally, children with more initiations of joint attention skills at entry made greater progress in play diversity (F(1,97) = 15.85, p < 0.001 ES = 0.40) and complexity (p = 0.096). Play and joint attention skills are critical intervention targets and outcomes for children with autism.

Influence of a Brief Autism Education Intervention on Peer Engagement and Inclusion At Mainstream Day Camps: A Mixed-Methods Pilot Study

To explore the benefits of a brief autism education intervention on peer engagement and inclusion of autistic children at day camps. A convergent, parallel, two-arm (intervention/no intervention), non-randomized, mixed-methods design was used. The individualized, peer-directed, 5-10 min intervention included four components: (1) diagnostic label, (2) description and purpose of unique behaviors, (3) favorite activities and interests, and (4) strategies to engage. A timed-interval behavior-coding system was used to evaluate engagement between each autistic camper and their peers based on videos taken at camp (days 1, 2, 5). Interviews with campers and camp staff explored why changes in targeted outcomes may have occurred. Percent intervals in which the autistic campers were jointly engaged with peers improved in the intervention group (n = 10) and did not change in the control group (n = 5). A large between group intervention effect occurred by day 5 (Z = - 1.942, η² = 0.29). Interviews (5 autistic campers, 34 peers, 18 staff) done on the last day of camp in the intervention group garnered three themes: (1) Changed behavioral attribution, (2) Knowledge facilitates understanding and engagement, and (3) (Mis)perceptions of increased inclusion. A brief educational intervention that includes individualized explanatory information and strengths-based strategies might improve peers' understanding of and social engagement with autistic children in community programs such as camps.

Spoken language outcomes in limited language preschoolers with autism and global developmental delay: RCT of early intervention approaches

Preschool autistic children with significant global developmental delays and very limited language skills are at high risk for remaining minimally verbal at entry into primary school. This study compared two early intervention models for improving social communication and spoken language outcomes in 164 children who received intervention in their community preschool program for 6 months, with a six-month follow-up. The primary outcome measure was a standardized language assessment, and secondary measures focused on social communication. Results indicated children on average made 6 months gain in language development in the active 6 months of intervention with no difference between intervention models. Children who initiated joint attention more frequently, or who had higher receptive language at baseline made more progress if assigned to receive JASPER, a naturalistic developmental behavioral intervention. Children who received Discrete Trial Training made greater spoken language progress from exit to follow-up. These findings suggest that progress can be made in autistic children who have very little spoken language and who receive targeted early interventions. Individual trajectories vary and depend in part on initial abilities in social communication and receptive language. Future research might consider methods to systematically personalize approaches to fit child characteristics and family preference. LAY SUMMARY: This study compared two different early intervention approaches for teaching spoken language to minimally verbal, globally delayed autistic preschoolers. Children were given an hour of therapy daily for 6 months and then reassessed 6 months later. The majority of the 164 participants were from historically excluded populations (low income and minority), and therapy was delivered in school community settings by expert clinicians. Results indicated that the participants made significant progress regardless of intervention approach: 6 months gain in standardized language scores over 6 months, but slower progress during the period after therapy ended. Children who initiated joint attention more frequently, or who had higher language understanding at baseline made more progress if assigned to receive JASPER, a naturalistic developmental behavioral intervention. Children who received Discrete Trial Training made greater language progress during 6-month period after therapy ended. These findings suggest that progress can be made in children with ASD who have very little spoken language and who receive targeted early interventions.

Brief Report: An Exploratory Study of Young Dual Language Learners with Autism in a School-Based Intervention

Due to core challenges in social communication experienced by many young children with autism, children on the spectrum who are also dual language learners (DLLs) may benefit from developmentally-appropriate language supports in school settings. The current study examined whether home language status moderated the effect of a play-based intervention, JASPER, delivered in the classroom, in children with autism. Fifty-nine preschool children with autism received JASPER over eight weeks. Children who received JASPER improved significantly more in their language skills from entry to exit than children in preschool as usual. Home language status moderated the effect of treatment on receptive language where children of diverse linguistic backgrounds made greater gains in receptive language.

Using the Clinical Global Impression scale to assess social communication change in minimally verbal children with autism spectrum disorder

Assessing improvements in social communication behaviors in minimally verbal children with autism spectrum disorder (ASD) is often challenging. The Clinical Global Impression Scale (CGI) is a 7-point scale that has been adapted so that clinicians can easily and quickly rate social communication behaviors. The current study evaluated the CGI-Improvement (CGI-I) subscale as a measure of social communication change in minimally verbal children with ASD. The sample included 54 minimally verbal school-age children with ASD enrolled in a social communication intervention trial. CGIs were rated by interventionists and the study coordinator at baseline and at Week 6 of intervention, and were compared to scores on the Communication Complexity Scale (CCS). Results indicated that CGI ratings corresponded with CCS scores at baseline and Week 6. Children who were rated as more severe on social communication at baseline demonstrated lower complexity of communication compared to those who were rated as less severe. Those who demonstrated fast response to intervention at Week 6 showed greater improvement in their joint attention than those who were slower responders. These results provide support for the utility and validity of the CGI-I as a measure of social communication change in minimally verbal children. This study tested the CGI, a clinician rating scale, with a group of children with ASD with limited language who received intervention to improve social interactions and communication. Children's CGI ratings were comparable to other assessments in measuring social communication. The CGI may be a useful tool for those interested in quickly and easily tracking changes in children's social communication over the course of treatment. LAY SUMMARY: This study tested the Clinical Global Impression (CGI), a clinician rating scale, with a group of children with ASD with limited language who received intervention to improve social interactions and communication. Children's CGI ratings were comparable to other assessments in measuring social communication. The CGI may be a useful tool for those interested in quickly and easily tracking changes in children's social communication over the course of treatment.

Acceptability and feasibility of the World Health Organization's Caregiver Skills Training Programme (WHO CST) delivered via eLearning, videoconferencing, and in-person hybrid modalities in Hong Kong

BACKGROUND

Local children with developmental disabilities were deprived of learning opportunities due to recent social and health incidents, resulting in elevating challenging behaviors and familial conflicts. This study explored the acceptability and feasibility of the World Health Organization's Caregiver Skills Training Programme (WHO CST) in alternative delivery modes under new normal and post COVID-19 period.

METHOD

CST was delivered via eLearning (EL), videoconferencing (VC), and in-person hybrid (IP) modes to 34 parent-child dyads, being randomly assigned to modes of asynchronous non-interfering EL (n = 9), synchronous with online coaching VC (n = 7), synchronous with in-person coaching IP (n = 9) and Wait-list Control WLC (n = 9). Data from two standardized scales of General Health Questionnaire (GHQ-12) and Strengths and Difficulties Questionnaire (SDQ), and Post-session and Home Visit Feedback Form by Caregivers that included both structured and open-ended questions were collected before and after intervention. Both quantitative and qualitative approaches were used in studying the collected data.

RESULTS

High levels of acceptability and feasibility of the training programme were supported by ratings on comprehensiveness and relevance, agreement with their personal values, duration, and usefulness. IP and VC groups yielded more positive changes than EL and WLC groups with 3, 16, 13, and -3% in General Health Questionnaire (GHQ-12), -13, -15, -6 and 0% in Difficulties-total, and 36.5, 35.5, 5.8 and 2.4% in Prosocial Scale at Strengths and Difficulties Questionnaire (SDQ) for EL, VC, IP, and WLC groups respectively from baseline to 12 weeks after intervention. Results from two standardized scales echoed with qualitative observations that the programme helped improve caregivers' well-being, child's communication, and behaviors across intervention groups.

CONCLUSIONS

Current findings revealed that CST delivered in three alternative modes were acceptable and feasible, and yielded positive impacts toward both caregivers and children. In-person coaching, and skill-practicing sessions were effective in mitigating child's challenging behaviors while personal interaction, either face-to-face or virtual, is a significant factor in uplifting caregivers' well-being, whereas the self-learning model was appreciated by the busy caregivers. In clinical practice, needs and goals of families and the constraints of remote interventions at the settings should be balanced.

Joint engagement is a potential mechanism leading to increased initiations of joint attention and downstream effects on language: JASPER early intervention for children with ASD

BACKGROUND

Social communication interventions benefit children with ASD in early childhood. However, the mechanisms behind such interventions have not been rigorously explored. This study examines the mechanism underlying a naturalistic developmental behavioral intervention, JASPER (Joint Attention, Symbolic Play, Engagement, and Regulation), delivered by educators in the community. Specifically, the analyses focus on the mediating effect of joint engagement on children's initiations of joint attention (IJA) skills and whether IJA postintervention are associated with later gains in children's receptive and expressive language.

METHODS

One hundred seventy-nine children, age 2-5 years, were randomized to immediate JASPER treatment or waitlist (treatment as usual) control. Independent assessors blinded to time and treatment coded children's time jointly engaged and IJA during a 10-min teacher-child interaction at baseline, exit, and follow-up. Age-equivalent receptive and expressive language scores from the Mullen Scales of Early Learning were collected at baseline and follow-up. Mediation analyses with linear mixed models were used to explore the potential mediating effect of joint engagement on IJA.

RESULTS

Joint engagement significantly mediated 69% of the intervention effect on young children's IJA and IJA predicted improvements in standardized language scores.

CONCLUSIONS

Small but sustained changes in child-initiated joint engagement improved IJA, a core challenge in children with ASD, which in turn led to improvements in language.

Effectiveness of a technology-assisted, family volunteers delivered, brief, multicomponent parents' skills training intervention for children with developmental disorders in rural Pakistan: a cluster randomized controlled trial

Background

Globally, there is a large documented gap between needs of families and children with developmental disorders and available services. We adapted the World Health Organization’s mental health Gap-Intervention Guidelines (mhGAP-IG) developmental disorders module into a tablet-based android application to train caregivers of children with developmental disorders. We aimed to evaluate the effectiveness of this technology-assisted, family volunteers delivered, parents’ skills training intervention to improve functioning in children with developmental disorders in a rural community of Rawalpindi, Pakistan.

Methods

In a single-blinded, cluster randomized controlled trial, 30 clusters were randomised (1:1 ratio) to intervention (n = 15) or enhanced treatment as usual (ETAU) arm (n = 15). After screening, 540 children (18 participants per cluster) aged 2–12 years, with developmental disorders and their primary caregivers were recruited into the trial. Primary outcome was child’s functioning, measured by Childhood Disability Assessment Schedule for Developmental Disorders (DD-CDAS) at 6-months post-intervention. Secondary outcomes were parents’ health related quality of life, caregiver-child joint engagement, socio-emotional well-being of children, family empowerment and stigmatizing experiences. Intention-to-treat analyses were done using mixed-models adjusted for covariates and clusters.

Results

At 6-months post-intervention, no statistically significant mean difference was observed on DD-CDAS between intervention and ETAU (mean [SD], 47.65 [26.94] vs. 48.72 [28.37], Adjusted Mean Difference (AMD), − 2.63; 95% CI − 6.50 to 1.24). However, parents in the intervention arm, compared to ETAU reported improved health related quality of life (mean [SD] 65.56 [23.25] vs. 62.17 [22.63], AMD 5.28; 95% CI 0.44 to 10.11). The results were non-significant for other secondary outcomes.

Conclusions

In the relatively short intervention period of 6 months, no improvement in child functioning was observed; but, there were significant improvements in caregivers’ health related quality of life. Further trials with a longer follow-up are recommended to evaluate the impact of intervention.

Trial registration Clinicaltrials.gov, NCT02792894. Registered April 4, 2016, https://clinicaltrials.gov/ct2/show/NCT02792894

The influence of disclosure of an autism diagnosis on peer engagement and interactions for a child with autism in summer camps: a case study

PURPOSE

Little research has evaluated how disclosure of an autism diagnosis influences peer engagement and understanding of children with autism in community recreation programs. This study describes outcomes of disclosing an autism diagnosis for a child with autism participating in mainstream, community summer camps.

METHODS

This case study includes a 9-year-old boy diagnosed with autism who participated in two camps, one in which he disclosed and one in which he did not disclose. Quantitative data on peer engagement states and reciprocal interactions were coded through structured behavioral observation of video recorded on the first, second, and last day of each program. Qualitative interviews about perceived outcomes of disclosure were completed with the child with autism, camp leaders, and peers in the disclosure camp.

RESULTS

Peer engagement and reciprocal interactions improved following the disclosure protocol and continued to improve on the final day of the camp, which was not observed in the non-disclosure camp. A key qualitative theme revealed that changed behavioral attribution was the main contributor to improved inclusion following disclosure.

CONCLUSIONS

This study provides preliminary data to support that disclosure may be a simple intervention to improve peer engagement and understanding of children with autism in community programs.IMPLICATIONS FOR REHABILITATIONChildren with Autism Spectrum Disorder are at high risk of experiencing social exclusion, especially in community programs.A disclosure protocol (disclosure + explanation for behaviors) could be a simple intervention to facilitate peer acceptance and inclusion of children with autism, however this intervention has not been evaluated in a real life context.This study provides preliminary evidence to support the use of a simple disclosure protocol for families who want to disclose, within short-term community programs.

Development of the WHO Caregiver Skills Training Program for Developmental Disorders or Delays

Globally, 52.9 million children under the age of 5 experience a developmental disability, such as sensory impairment, intellectual disability, and autism spectrum disorders. Of these 95% live in low-and-middle-income countries. Most of these children lack access to care. In light of the growing evidence that caregivers can learn skills to support their children's social communication and adaptive behavior and to reduce their challenging behavior, the World Health Organization developed a novel Caregiver Skills Training Program (CST) for families of children with developmental disorders or delay to address such treatment gap. This report outlines the development process, content, and global field-testing strategy of the WHO CST program. The CST program is designed to be feasible, scalable, and adaptable and appropriate for implementation in low-resource settings by nonspecialists. The program was informed by an evidence review utilizing a common elements approach and was developed through extensive stakeholder consultation and an iterative revision process. The program is intended for a global audience and was designed to be adapted to the cultural, socioeconomic, geographic, and resource context in which it is used to ensure that it is comprehensible, acceptable, feasible, and relevant to target users. It is currently undergoing field-testing in more than 30 countries across all world regions.

Isolating active ingredients in a parent-mediated social communication intervention for toddlers with autism spectrum disorder

BACKGROUND

Behavioral interventions are commonplace in the treatment of autism spectrum disorders, yet relatively little is known about how and why these interventions work. This study tests the relationship between isolated core components of a packaged social communication intervention and the primary outcome, joint engagement, to better understand how the intervention is affecting change in individuals.

METHODS

A total of 86 toddlers and their parents were enrolled in the study and randomized to one of two treatments, the joint attention, symbolic play, engagement, and regulation (JASPER) parent-mediated intervention or a psychoeducational intervention. Measures regarding the parent's use of intervention strategies were collected before and after the 10-week intervention. Additional measures of child and parent joint engagement were also collected.

RESULTS

A significant effect of treatment was found for all four of the core strategies of the intervention, favoring a larger increase in the JASPER condition. A hierarchical linear regression revealed several individual predictors of joint engagement, including parent-rated buy-in, interventionist-rated parent involvement, and parental use of strategies. To complement the hierarchical analysis, we also tested the potential mediating effect the strategies may have on the relationship between treatment and joint engagement. Results showed that the strategy of mirrored pacing mediated the relationship between treatment and joint engagement in the positive direction.

CONCLUSIONS

These results strongly suggest that the mirrored pacing strategy is an active ingredient of the JASPER treatment.

Longitudinal Effects of Adaptive Interventions With a Speech-Generating Device in Minimally Verbal Children With ASD

There are limited data on the effects of adaptive social communication interventions with a speech-generating device in autism. This study is the first to compare growth in communications outcomes among three adaptive interventions in school-age children with autism spectrum disorder (ASD) who are minimally verbal. Sixty-one children, ages 5-8 years, participated in a sequential, multiple-assignment randomized trial (SMART). All children received a developmental behavioral communication intervention: joint attention, symbolic play, engagement and regulation (JASP) with enhanced milieu teaching (EMT). The SMART included three 2-stage, 24-week adaptive interventions with different provisions of a speech-generating device (SGD) in the context of JASP+EMT. The first adaptive intervention, with no SGD, initially assigned JASP+EMT alone, then intensified JASP+EMT for slow responders. In the second adaptive intervention, slow responders to JASP+EMT were assigned JASP+EMT+SGD. The third adaptive intervention initially assigned JASP+EMT+SGD; then intensified JASP+EMT+SGD for slow responders. Analyses examined between-group differences in change in outcomes from baseline to Week 36. Verbal outcomes included spontaneous communicative utterances and novel words. Nonlinguistic communication outcomes included initiating joint attention and behavior regulation, and play. The adaptive intervention beginning with JASP+EMT+SGD was estimated as superior. There were significant (p < .05) between-group differences in change in spontaneous communicative utterances and initiating joint attention. School-age children with ASD who are minimally verbal make significant gains in communication outcomes with an adaptive intervention beginning with JASP+EMT+SGD. Future research should explore mediators and moderators of the adaptive intervention effects and second-stage intervention options that further capitalize on early gains in treatment.

Does gender influence core deficits in ASD? An investigation into social-communication and play of girls and boys with ASD

Due to the predominance of boys diagnosed with autism spectrum disorders (ASD), girls are rarely studied independently. Research specifically focusing on play and social-communication in girls with ASD is extremely varied. We were interested in whether girls with ASD demonstrated equivalent social-communication and play skills in early childhood relative to boys, using two measures focused on the specific quantification of these variables. We also examined whether the associations between developmental variables and social-communication and play differed by gender. Forty girls with ASD were individually matched to 40 boys based on ASD severity. Our results suggest that girls and boys were more similar than different, however they also raise questions about the potential differential associations between development and requesting ability in girls and boys with ASD.

Psychosocial treatments for individuals with autism spectrum disorder across the lifespan: new developments and underlying mechanisms

Researchers have studied many interventions to address the core impairment in social interactions in autism spectrum disorder. We reviewed the social skills intervention literature over the past two years (2012-2014). Social skills intervention studies have increased by 35% over our previous review of 2010-2012. Nearly equal numbers of studies reported results using single subject research designs (n = 29) and group designs (n = 25). Consistent with our previous review, many studies focused on joint attention/joint engagement for young children and interventions addressing peer interactions for older children. Advancements in this review period included more replications of intervention models, longitudinal outcomes, and a focus on minimally verbal children. Notably absent are social interventions for adults, and interventions addressing school-based inclusion. In addition to these target areas, future studies should isolate active ingredients of social interventions, include broader participant representation, and further examine the relation between neural development and behavioral outcomes.

IL-8 single-chain homodimers and heterodimers: interactions with chemokine receptors CXCR1, CXCR2, and DARC

Covalent single-chain dimers of the chemokine interleukin-8 (IL-8) have been designed to mimic the dimeric form of IL-8 in solution and facilitate the production of heterodimer variants of IL-8. Physical studies indicated that use of a simple peptide linker to join two subunits, while allowing receptor binding and activation, led to self-association of the tethered dimers. However, addition of a single disulfide crosslink between the tethered subunits prevented this multimer from forming, yielding a species of dimer molecular weight. Crosslinked single-chain dimers bind to both IL-8 neutrophil receptors CXCR1 and CXCR2 as well as to DARC, as does a double disulfide-linked dimer with no peptide linker. In addition, neutrophil response to these dimers as measured by chemotaxis or beta-glucuronidase release is similar to that elicited by wild-type IL-8, providing evidence that the dissociation of the dimeric species is not required for these biologically relevant activities. Finally, through construction of single-chain heterodimer mutants, we show that only the first subunit's ELR motif is the single-chain variants.

Monomeric variants of IL-8: effects of side chain substitutions and solution conditions upon dimer formation

IL-8 dimers have been observed in NMR and X-ray structures of the protein. We have engineered IL-8 monomers by mutations of residues throughout the dimer interface, which introduce hindrance determinants to dimerization. These IL-8 variants are shown by NMR to have wild-type monomer folding, but by ultracentrifugation to have a range of dimerization constants from microM to mM, as compared with a dimerization constant of about 10 microM for wild-type IL-8, under physiological salt and temperature conditions. The monomeric variants of IL-8 bind the erythrocyte chemokine receptor DARC, as well as the neutrophil IL-8 receptors CXCR1 and CXCR2 with affinities similar to that of wild-type IL-8. In addition, the monomeric variants were shown to have agonist activity, with similar potency to wild-type, in both Ca(2+)-flux assays on CXCR1 and CXCR2 transfected cells, and in chemotaxis assays on neutrophils. Thus, these variants confirm that monomeric IL-8 is functionally equivalent to wild-type in vitro assays. We have also investigated the effects of various solution conditions upon IL-8 dimer formation using analytical ultracentrifugation. At salt concentrations, temperatures, and pH conditions lower than physiological, the dimerization affinity of IL-8 is greatly enhanced. This suggests that, under some conditions, IL-8 dimer formation may occur at concentrations of IL-8 considerably lower than 10 microM, with consequences in vivo that are yet to be determined.

Sedimentation equilibrium measurements of the intermediate-size tobacco mosaic virus protein polymers

Short-column sedimentation equilibrium methods have been applied for the first time to tobacco mosaic virus (TMV) protein (0.1 M ionic strength orthophosphate) at pH 6.5 and at pH 7.0 to estimate molecular weights. Previous sedimentation velocity experiments at pH 6.5, 20 degrees C have led to the conclusion that the major boundary with an S0(20),w value of 24.4 +/- 0.1 S consists of a distribution of polymers which are mainly three-turn, 48-51-subunit helical rod aggregates. The directly measured z-average molecular weights together with sedimentation velocity data are entirely consistent with this assignment of a three-turn aggregate. Molecular weights have also been determined under two conditions where a large mass fraction of the protein sediments with an S0(20),w value of 20.3 +/- 0.2 S. At pH 6.5, 6-8 degrees C, the aggregates in this boundary are metastable and correspond to 50-60% of the preparation. At pH 7.0, 20 degrees C at equilibrium, 65-75% of the protein sediments at 20.3 S. The 20.3S boundary is very similar under both conditions and is interpreted as being composed of a distribution of protein aggregates centered about 39 +/- 2 subunits. This result is important in the interpretation of previous kinetic measurements of TMV self-assembly. The current view is that the 34-subunit structure of TMV protein, in the form of a cylindrical disk which is made up of two 17-subunit layers and has been characterized in single-crystal X-ray diffraction studies, plays a central role in the initial binding steps with RNA. The present results are not consistent with the view that there is a significant concentration of the TMV protein disk structure in solution under the usual conditions of TMV self-assembly.