A specific pathway can be identified between genetic characteristics and behaviour profiles in Prader-Willi syndrome via cognitive, environmental and physiological mechanisms

Establishing the transdiagnostic contextual pathways of emotional outbursts

Emotional outbursts or temper outbursts are challenging behaviours commonly experienced by people with neurodevelopmental disorders and people who have experienced childhood adversity, which can negatively impact individuals and their families. Emotional outbursts may manifest in different situations via unique pathways distinguished by context-specific differences in the regulation and expression of emotions. Caregivers (N = 268) of young people (6-25 years) with emotional outbursts completed a bespoke caregiver-report questionnaire. Potential pathways were identified by examining the patterns of antecedents and setting events related to outbursts through factor and cluster analyses. Six contextual factors were derived from the Emotional Outburst Questionnaire. Based on these factors, the responses were classified into three clusters, which may represent potential pathways of emotional outbursts. The three clusters were characterized by the increased likelihood of outbursts: (1) across all setting events and triggers; (2) in safe setting events; (3) in unsafe setting events. These potential pathways may be related to: (1) differences in sensory processing; (2) masking of emotions in unsafe environments; (3) differences in safety perception. This framework supports a transdiagnostic account of emotional outbursts and may facilitate the development of pathway-specific intervention strategies.

The influence of emotional contexts on mental flexibility in Prader-Willi syndrome

BACKGROUND

The present study investigated the influence of emotional contexts on mental flexibility in adults with Prader-Willi syndrome (PWS) using a voluntary task-switching paradigm that was implemented with emotionally valenced pictures. The study aims were to assess whether adults with PWS have impaired switching abilities, whether the deficit is specific to PWS or linked to intellectual disabilities, and the influence of emotional contexts on performance.

METHOD

The task-switching performance of 30 adults with PWS was compared with that of 30 healthy adults matched on chronological age, and to that of 30 adults with intellectual disabilities but without PWS, matched on intellectual quotient level and chronological age. Indicators of switching performance were switching cost and repetition bias. Emotional contexts were operationalised with positive, neutral and negative task-irrelevant pictures.

RESULTS

Adults with PWS showed a large increase in switching costs compared with the two control groups, and this effect did not vary across emotional contexts. More fine-tuned examination revealed subtle performance modulations: negative contexts tended to increase the repetition bias in all three groups while positive contexts slowed down global performance in PWS.

CONCLUSIONS

The results confirmed previous studies, showing impaired switching abilities in PWS over and beyond the influence of intellectual level, but revealed no robust variations in switching deficits across emotional contexts.

Understanding the psycho-social context for a new early intervention for resistance to change that aims to strike a beneficial balance between structure and flexibility

BACKGROUND

Emotional and behavioural problems linked to changes to expectations - resistance to change - are linked to disability in neurodevelopmental disorders, including autism spectrum disorder (ASD), Prader-Willi (PWS) and fragile X syndromes (FXS). Structuring routines is best practice for minimising current resistance to change. But complete structure is impractical and flexibility in early life may actually reduce later resistance by supporting cognitive development. We aimed to examine the psycho-social context of families with children at risk of developing resistance to change so as to identify design requirements for an intervention that strikes a beneficial balance between structure and flexibility.

METHODS

Thirty-six caregivers of children aged 4-12 years (17 ASD, 15 PWS, and 4 FXS) took part in an interview designed collaboratively with 12 professional stakeholders.

RESULTS

Children need to feel like they are in control of flexibility but they also need support in choice making, understanding plans (using individually tailored visuals) and anxiety reduction. Caregivers need an accessible approach that they have full control over, and which they can tailor for their child. Caregivers also need clear guidance, education and support around structure and flexibility.

CONCLUSIONS

We propose a digital approach which addresses the needs identified. It tackles the most perplexing challenge by presenting flexibility to children in the context of a game that children can feel they have full control over, whilst caregivers can maintain control in reality. Furthermore, individualised support for children and caregivers would be enabled.

The RDoC approach for translational psychiatry: Could a genetic disorder with psychiatric symptoms help fill the matrix? the example of Prader-Willi syndrome

The Research Domain Criteria project (RDoc) proposes a new classification system based on information from several fields in order to encourage translational perspectives. Nevertheless, integrating genetic markers into this classification has remained difficult because of the lack of powerful associations between targeted genes and RDoC domains. We hypothesized that genetic diseases with psychiatric manifestations would be good models for RDoC gene investigations and would thereby extend the translational approach to involve targeted gene pathways. To explore this possibility, we reviewed the current knowledge on Prader-Willi syndrome, a genetic disorder caused by the absence of expression of some of the genes of the chromosome 15q11-13 region inherited from the father. Indeed, we found that the associations between genes of the PW locus and the modification identified in the relevant behavioral, physiological, and brain imaging studies followed the structure of the RDoC matrix and its six domains (positive valence, negative valence, social processing, cognitive systems, arousal/regulatory systems, and sensorimotor systems).

Psychological treatment strategies for challenging behaviours in neurodevelopmental disorders: what lies beyond a purely behavioural approach?

PURPOSE OF REVIEW

Challenging behaviour shown by individuals with neurodevelopmental disorders (NDDs) has a major negative impact. There is robust evidence for the efficacy of treatments based on applied behaviour analysis. However, such approaches are limited in important ways - providing only part of the whole solution. We reviewed the literature to provide an overview of recent progress in psychological treatments for challenging behaviour and how these advance the field beyond a purely behavioural approach.

RECENT FINDING

We identified 1029 articles via a systematic search and screened for those implementing a psychological intervention with individuals with NDD (or caregivers) and measuring the potential impact on challenging behaviour. Of the 69 included studies published since 2018, more than 50% implemented a purely behavioural intervention. Other studies could generally be categorized as implementing parent training, meditation, skill training or technology-assisted interventions.

SUMMARY

Greater consideration of the interplay between behavioural and nonbehavioural intervention components; systematic approaches to personalization when going beyond the behavioural model; mental health and broad social communication needs; and models that include cognitive and emotional pathways to challenging behaviour; is needed to advance the field. Furthermore, technology should not be overlooked as an important potential facilitator of intervention efforts.

Investigation of the relationship between electrodermal and behavioural responses to executive tasks in Prader-Willi syndrome: An event-related experiment

BACKGROUND

Recent work suggests that maladaptive behaviors in genetic developmental disorders may emerge from autonomic dysfunctions impacting higher order executive functions. In Prader-Willi syndrome (PWS), executive functions are not well understood and investigations of possible underlying causes at the autonomic level are lacking.

AIMS

This study aimed at clarifying the status of inhibition and working memory updating functions in PWS and searched for sympathetic signatures as well as to examine their links with executive performance.

METHODS AND PROCEDURES

The performance of thirty adults with PWS was compared to that of thirty healthy adults on two tasks assessing inhibition and working memory updating while electrodermal activity (EDA) was recorded.

OUTCOMES AND RESULTS

PWS adults underperformed healthy adults in the inhibition and the working memory updating tasks and showed abnormal skin conductance responses. Distinct EDA have been found in PWS and healthy adults. Furthermore, while EDA reflected distinct cognitive processes, correlations between electrodermal and behavioural data were absent when examining the two groups separately.

CONCLUSIONS AND IMPLICATIONS

PWS is associated with a slight impairment of inhibition and a severe impairment of working memory updating. Furthermore, there are specific sympathetic autonomic signatures in PWS that do not present straightforward links with executive dysfunctions.

Improving the Health and Well-Being of Adults With Conditions of a Genetic Origin: Views from Professionals, Syndrome Support Groups and Parents

BACKGROUND

Advances in medical genetics herald the possibility that health and social care services could be more responsive to the needs arising from a person's genotype. This development may be particularly important for those men and women whose learning disability (known internationally as intellectual disability) is linked to a neurodevelopmental condition of genetic origin.

METHOD

This possibility is tested through interviews with samples of (i) professional 'opinion former' with nationally recognised clinical and/or academic interests in learning disabilities and genetics; (ii) representatives of syndrome organisations prompting the interests of families where someone has a neurodevelopmental condition, and parent-members of these same organisations.

RESULTS

The reporting and discussion of the interview data considers the possibility that notwithstanding the successes of the social model of disability, the health and wellbeing of people whose learning disability is associated with a neurodevelopmental condition could be better served by a more medicalised approach to their interests.

CONCLUSION

While a more medicalised approach to this populations' disabilities would appear to be beneficial, so long as it is focused on interventions to improve their lives rather than catalogues their deficiencies.

Executive functioning in Cornelia de Lange syndrome: domain asynchrony and age-related performance

BACKGROUND

The aim of this study was to examine executive functioning in adolescents and adults with Cornelia de Lange syndrome (CdLS) to identify a syndrome and age-related profile of cognitive impairment.

METHODS

Participants were 24 individuals with CdLS aged 13-42 years (M = 22; SD = 8.98), and a comparable contrast group of 21 individuals with Down syndrome (DS) aged 15-33 years (M = 24; SD = 5.82). Measures were selected to test verbal and visual fluency, inhibition, perseverance/flexibility, and working memory and comprised both questionnaire and performance tests.

RESULTS

Individuals with CdLS showed significantly greater impairment on tasks requiring flexibility and inhibition (rule switch) and on forwards span capacity. These impairments were also reported in the parent/carer-rated questionnaire measures. Backwards Digit Span was significantly negatively correlated with chronological age in CdLS, indicating increased deficits with age. This was not identified in individuals with DS.

CONCLUSIONS

The relative deficits in executive functioning task performance are important in understanding the behavioural phenotype of CdLS. Prospective longitudinal follow-up is required to examine further the changes in executive functioning with age and if these map onto observed changes in behaviour in CdLS. Links with recent research indicating heightened responses to oxidative stress in CdLS may also be important.

Rigidity in routines and the development of resistance to change in individuals with Prader-Willi syndrome

BACKGROUND

Individuals with Prader-Willi syndrome (PWS) commonly show debilitating resistance to change, which has been linked to cognitive deficits in task switching. Anecdotal reports suggest that exposure to flexibility in routines during development may be beneficial for limiting subsequent resistance to change in people with PWS, which is consistent with a beneficial role of such exposure on the development of task switching, highlighted in typical children. Here, we aim to investigate the development of resistance to change in individuals with PWS and hypothesise that exposure to increased rigidity in routines will be associated with increased subsequent resistance to change.

METHODS

An author-compiled informant report interview and two previously validated questionnaires were administered to the caregivers of 10 individuals with PWS (5-23 years). The interview examined rigidity in routines and resistance to change across life stages defined by easily distinguishable events (before school, during primary school, during secondary school, after school, currently), using open-ended and structured yes/no and 5-point Likert questions. Open-ended data were coded using an author-compiled system. Responses from two additional informants and data from the questionnaires were used to assess inter-informant reliability and concurrent validity of the structured questions.

RESULTS

The validity of the interview was supported by acceptable inter-rater reliability of the open-ended coding system and inter-informant reliability, internal consistency and concurrent validity of structured questions. Descriptive analyses of ratings of behaviour change showed a pattern of increasing resistance to change over the life course for the four oldest individuals, who had all been exposed to substantial rigidity in routines before and during primary school. Furthermore, only one individual - currently in primary school - was exposed to very little rigidity in routines before and during primary school, and he had showed a decrease in resistance to change after entering primary school. Open-ended data showed that more individuals currently evidencing little resistance to change had been exposed to parent or self-imposed flexibility in routines, than those currently evidencing substantial resistance to change. However, correlational analyses on rigidity and resistance to change ratings highlighted the possibility that rigidity during primary school is most relevant for developing resistance to change. Finally, open-ended data emphasised an important beneficial role of rigidity in routines for limiting the current challenging behaviour of individuals with high resistance to change.

CONCLUSION

Because task switching appears to evidence a period of high developmental sensitivity during early primary school years, we propose that this period may represent a critical time when increasing flexibility in the routines of children with PWS could limit the development of resistance to change. However, a careful balance would need to be struck, given the apparent benefit of rigid routines on current behaviour. Further work in this area is much needed.

Dissociation of Cross-Sectional Trajectories for Verbal and Visuo-Spatial Working Memory Development in Rubinstein-Taybi Syndrome

Working memory (WM) impairments might amplify behavioural difference in genetic syndromes. Murine models of Rubinstein–Taybi syndrome (RTS) evidence memory impairments but there is limited research on memory in RTS. Individuals with RTS and typically developing children completed WM tasks, with participants with RTS completing an IQ assessment and parents/carers completing the Vineland Adaptive Behavior Scales. A cross-sectional trajectory analysis was conducted. There were significant WM span deficits in RTS relative to mental age. Verbal WM span was positively associated with mental age; however, this was not observed for visuo-spatial span. There is a dissociation between WM domains in RTS. Individuals may have difficulties with tasks relying on WM span, above difficulties predicted by overall ability.

Puzzle Pieces: Neural Structure and Function in Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder of genomic imprinting, presenting with a behavioural phenotype encompassing hyperphagia, intellectual disability, social and behavioural difficulties, and propensity to psychiatric illness. Research has tended to focus on the cognitive and behavioural investigation of these features, and, with the exception of eating behaviour, the neural physiology is currently less well understood. A systematic review was undertaken to explore findings relating to neural structure and function in PWS, using search terms designed to encompass all published articles concerning both in vivo and post-mortem studies of neural structure and function in PWS. This supported the general paucity of research in this area, with many articles reporting case studies and qualitative descriptions or focusing solely on the overeating behaviour, although a number of systematic investigations were also identified. Research to date implicates a combination of subcortical and higher order structures in PWS, including those involved in processing reward, motivation, affect and higher order cognitive functions, with both anatomical and functional investigations indicating abnormalities. It appears likely that PWS involves aberrant activity across distributed neural networks. The characterisation of neural structure and function warrants both replication and further systematic study.

Executive functions and Prader-Willi syndrome: global deficit linked with intellectual level and syndrome-specific associations

The aim of this study was to support the growing evidence suggesting that Prader-Willi Syndrome (PWS) might present with an impairment of executive functions (EFs) and to investigate whether this impairment is specific to patients with PWS or due to their intellectual disability (ID). Six tasks were administered to assess EFs (inhibition, switching, updating, cognitive estimation, and planning) to 17 patients with PWS and 17 age-matched healthy individuals. Performance was significantly impaired in the PWS group on all EFs and after controlling for IQ level, intergroup differences remained only for switching and cognitive estimation. In conclusion, PWS seems to be associated with a global impairment of EFs that appears to be closely linked with intellectual impairment but also with the PWS itself.

Temper outbursts in Prader-Willi syndrome: causes, behavioural and emotional sequence and responses by carers

BACKGROUND

Temper outbursts are common in Prader-Willi syndrome but rarely described in detail. This study investigated the phenomenology of temper outbursts in terms of antecedents, sequence of behaviours and emotions and intervention strategies used.

METHOD

A semi-structured interview about temper outbursts was conducted with the main carers of seven children (9.5 to 16.7 years) and seven adults (24.7 to 47.10 years) with Prader-Willi syndrome (10 male, 4 female). Reliability and validity of the interview results was established.

RESULTS

Various setting events increased and reduced the likelihood of temper outbursts. The most common antecedent was a change to routine or expectation. There were marked similarities in the sequence of behaviours and emotions during temper outbursts, with anger rising quickly followed by expressions of remorse and distress at the end of an outburst.

DISCUSSION

The sequence of behaviours and emotions within outbursts was similar to that described in temper tantrums in typical development. Cognitive and emotional processes are likely to be important in the understanding of temper outbursts with implications for early intervention.

Social and emotional processing in Prader-Willi syndrome: genetic subtype differences

Background

People with Prader-Willi syndrome (PWS) demonstrate social dysfunction and increased risk of autism spectrum disorder, especially those with the maternal uniparental disomy (mUPD) versus paternal deletion genetic subtype. This study compared the neural processing of social (faces) and nonsocial stimuli, varying in emotional valence, across genetic subtypes in 24 adolescents and adults with PWS.

Methods

Upright and inverted faces, and nonsocial objects with positive and negative emotional valence were presented to participants with PWS in an oddball paradigm with smiling faces serving as targets. Behavioral and event-related potential (ERP) data were recorded.

Results

There were no genetic subtype group differences in accuracy, and all participants performed above chance level. ERP responses revealed genetic subtype differences in face versus object processing. In those with deletions, the face-specific posterior N170 response varied in size for face stimuli versus inverted faces versus nonsocial objects. Persons with mUPD generated N170 of smaller amplitude and showed no stimulus differentiation. Brain responses to emotional content did not vary by subtype. All participants elicited larger posterior and anterior late positive potential responses to positive objects than to negative objects. Emotion-related differences in response to faces were limited to inverted faces only in the form of larger anterior late positive potential amplitudes to negative emotions over the right hemisphere. Detection of the target smiling faces was evident in the increased amplitude of the frontal and central P3 responses but only for inverted smiling faces.

Conclusion

Persons with the mUPD subtype of PWS may show atypical face versus object processes, yet both subtypes demonstrated potentially altered processing, attention to and/or recognition of faces and their expressions.

[Behavioral characteristics of children with Prader-Willi syndrome in preschool and school age: an exploratory study on ritualistic behavior]

Parents of 64 children and youths with Prader-Willi syndrome (PWS) describe their children's behaviour on the "Temperament and Atypical Behavior Scale" (TABS) and the German version of the "Developmental Behavior Checklist" (VFE). In the younger age group, there are no specific behavioural abnormalities which characterize a behavioral phenotype. In the older age group the data reveal elevated levels of abnormal behaviors (communication disturbance, social relations and disruptive behaviors). Parents stress ritualistic behaviors as especially challenging. The results concerning form and age-dependency of abnormal behaviors are discussed in the context of prevention and treatment options.

The neuroanatomy of genetic subtype differences in Prader-Willi syndrome

Despite behavioral differences between genetic subtypes of Prader-Willi syndrome (PWS), no studies have been published characterizing brain structure in these subgroups. Our goal was to examine differences in the brain structure phenotype of common subtypes of PWS [chromosome 15q deletions and maternal uniparental disomy 15 (UPD)]. Fifteen individuals with PWS due to a typical deletion [(DEL) type I; n = 5, type II; n = 10], eight with PWS due to UPD, and 25 age-matched healthy-weight individuals (HWC) participated in structural magnetic resonance imaging (MRI) scans. A custom voxel-based morphometry processing stream was used to examine regional differences in gray and white matter volume (WMV) between groups, covarying for age, sex, and body mass index (BMI). Overall, compared to HWC, PWS individuals had lower gray matter volumes (GMV) that encompassed the prefrontal, orbitofrontal and temporal cortices, hippocampus and parahippocampal gyrus, and lower WMVs in the brain stem, cerebellum, medial temporal, and frontal cortex. Compared to UPD, the DEL subtypes had lower GMV primarily in the prefrontal and temporal cortices, and lower white matter in the parietal cortex. The UPD subtype had more extensive lower gray and WMVs in the orbitofrontal and limbic cortices compared to HWC. These preliminary findings are the first structural neuroimaging findings to support potentially separate neural mechanisms mediating the behavioral differences seen in these genetic subtypes.

Salivary flow rate and oral findings in Prader-Willi syndrome: a case-control study

BACKGROUND. Prader-Willi syndrome (PWS) is a rare complex multisystemic genetic disorder. AIM. The objective of this study was to provide a systematic assessment of whole saliva secretion and oral manifestations associated with PWS. DESIGN. Fifty individuals (5-40 years) with PWS and an age- and sex-matched control group were included. Whole saliva was collected. All participants underwent an anamnestic interview. Radiological and dental clinical examinations were carried out to identify hypodontia, dental caries, enamel defects and gingival inflammation. RESULTS. Mean whole salivary flow rate was 0.12 ± 0.11 mL/min in the study group compared with 0.32 ± 0.20 mL/min in the control group (P < 0.001). Hypodontia was significantly more common in PWS (P < 0.001), and dental caries in the age group >19 years was significantly lower in PWS (P = 0.04) compared with the controls. There was no significant difference in the prevalence of dental caries in the primary dentition or in the frequency of enamel defects in the permanent dentition between the two groups. Median Gingival Index was significantly higher in the Prader-Willi group compared with the controls (P = 0.02). CONCLUSIONS. Low salivary flow is a consistent finding in PWS. Nevertheless, despite dry mouth and dietary challenges, dental caries is not increased in Norwegian individuals with PWS.

Delineation of behavioral phenotypes in genetic syndromes: characteristics of autism spectrum disorder, affect and hyperactivity

We investigated autism spectrum disorder (ASD) symptomatology, hyperactivity and affect in seven genetic syndromes; Angelman (AS; n = 104), Cri du Chat (CdCS; 58), Cornelia de Lange (CdLS; 101), Fragile X (FXS; 191), Prader-Willi (PWS; 189), Smith-Magenis (SMS; 42) and Lowe (LS; 56) syndromes (age range 4-51). ASD symptomatology was heightened in CdLS and FXS. High levels of impulsivity were seen in SMS, AS, CdCS, FXS and adults with CdLS. Negative affect was prominent in adults with CdLS, while positive affect was prominent in adults with AS and FXS. Heightened levels of overactivity and impulsivity were identified in FXS, AS and SMS while low levels were identified in PWS. These findings confirm and extend previously reported behavioral phenotypes.

The relationship between specific cognitive impairment and behaviour in Prader-Willi syndrome

BACKGROUND

Individuals with Prader-Willi syndrome (PWS) have been shown to demonstrate a particular cognitive deficit in attention switching and high levels of preference for routine and temper outbursts. This study assesses whether a specific pathway between a cognitive deficit and behaviour via environmental interaction can exist in individuals with PWS.

METHODS

Four individuals with PWS participated in a series of three single-case experiments including laboratory-based and natural environment designs. Cognitive (computer-based) challenges placed varying demands on attention switching or controlled for the cognitive demands of the tasks while placing no demands on switching. Unexpected changes to routines or expectations were presented in controlled games, or imposed on participants' natural environments and compared with control conditions during which no unexpected changes occurred. Behaviour was observed and heart rate was measured.

RESULTS

Participants showed significantly increased temper outburst related behaviours during cognitive challenges that placed demands on attention switching, relative to the control cognitive challenges. Participants showed significantly increased temper outburst related behaviours when unexpected changes occurred in an experimental or the natural environment compared with when no changes occurred.

CONCLUSIONS

Difficult behaviours that could be triggered reliably in an individual by a specific cognitive demand could also be triggered via manipulation of the environment. Results suggest that a directional relationship between a specific cognitive deficit and behaviour, via environmental interaction, can exist in individuals with PWS.

Neural correlates of task switching in paternal 15q11-q13 deletion Prader-Willi syndrome

We report a first study of brain activity linked to task switching in individuals with Prader-Willi syndrome (PWS). PWS individuals show a specific cognitive deficit in task switching which may be associated with the display of temper outbursts and repetitive questioning. The performance of participants with PWS and typically developing controls was matched in a cued task switching procedure, and brain activity was contrasted on switching and non-switching blocks using fMRI. Individuals with PWS did not show the typical frontal-parietal pattern of neural activity associated with switching blocks, with significantly reduced activation in regions of the posterior parietal and ventromedial prefrontal cortices. We suggest that this is linked to a difficulty in PWS in setting appropriate attentional weights to enable task-set reconfiguration. In addition to this, PWS individuals did not show the typical pattern of deactivation, with significantly less deactivation in an anterior region of the ventromedial prefrontal cortex. One plausible explanation for this is that individuals with PWS show dysfunction within the default mode network, which has been linked to attentional control. The data point to functional changes in the neural circuitry supporting task switching in PWS even when behavioural performance is matched to controls and thus highlight neural mechanisms that may be involved in a specific pathway between genes, cognition and behaviour.

Epigenetics and biomarkers in the staging of neuropsychiatric disorders

Epigenetics, or alterations in the phenotype or gene expression due to mechanisms other than changes in the underlying DNA sequence, reflects the sensitivity and responsiveness of human and animal brains in constantly varying circumstances regulating gene expression profiles that define the biomarkers and present the ultimate phenotypical outcomes, such as cognition and emotion. Epigenetics is associated with functionally relevant alterations to the genome in such a fashion that under the particular conditions of early, adolescent, and adult life, environmental signals may activate intracellular pathways that remodel the "epigenome," triggering changes in gene expression and neural function. Thus, genetic influences in neuropsychiatric disorders that are subject to clinical staging, epigenetics in schizophrenia, epigenetic considerations in the expression of sensorimotor gating resulting from disease conditions, biomarkers of drug use and addiction, current notions on the role of dopamine in schizophrenia spectrum disorders, and the discrete interactions of biomarkers in persistent memory were to greater or lesser extents reflected upon. The relative contributions of endophenotypes and epistasis for mediating epigenetic phenomena and the outcomes as observed in the analysis of biomarkers appear to offer a multitude of interactive combinations to further complicate the labyrinthine machinations of diagnosis, intervention, and prognosis.