Peculiarities in the gestural repertoire: an early marker for Rett syndrome?

Early neural dysfunction reflected in degraded auditory cortex responses in pre-regression heterozygous Mecp2 rats

Rett syndrome, a genetic disorder caused by mutations in the X-linked Mecp2 gene, is characterized by typical early development followed by rapid developmental regression between 6 and 18 months of age. Affected individuals exhibit seizures, cognitive impairments, motor deficits, and difficulties in speech-language processing. Post-regression rodent models of Rett syndrome have been observed to follow similar regression, presenting sensory processing difficulties during auditory discrimination tasks, as well as degraded auditory cortical responses. However, little is known about the auditory processing prior to the onset of regression symptoms. This study documents primary auditory cortex responses to sounds in pre-regression heterozygous Mecp2 rats compared to age-matched wild-type controls. Pre-regression Mecp2 rats exhibited weaker and delayed cortical responses to speech sounds, alterations in the temporal processing of rapidly presented sounds, and an overrepresentation of high-frequency tones in conjunction with a reduction in the cortical representation of low-frequency tones. Despite these impairments, pre-regression Mecp2 rats demonstrated intact neural classifier performance for consonant discrimination, which is consistent with the high accuracy these pre-regression Mecp2 rats exhibit for a behavioral consonant discrimination task. These findings reveal that cortical deficits in Mecp2 rats emerge before behavioral regression. Insights derived from this study expand upon the current understanding of the progression of sensory processing deficits in Rett syndrome and other neurodevelopmental disorders and lay the groundwork for the development of therapeutics for this population.

Phonic and Motor Stereotypies in Autism Spectrum Disorder: Video Analysis and Neurological Characterization

Stereotypies are among the core symptoms of Autism spectrum disorder (ASD) and can cause significant clinical impairment. At present, phonic stereotypies in ASD have been scarcely explored. This study investigates the frequency, variability, and typologies of phonic and motor stereotypies in children with ASD and their association with clinical neurological variables. We examined 35 patients by recording standardized video sessions and administering the Autism Diagnostic Observation Schedule-Second Edition (ADOS-2). Phonic stereotypies were present in 83.0% of the patients. The most prevalent subtypes were noncommunicative vocalizations (60.0%), single syllables (37.1%), and echolalic stereotypies (22.9%). Noncommunicative vocalizations were more frequent in nonverbal patients (OR = 4.629, p = 0.008), while echolalic stereotypies were more represented in verbal patients (OR = 0.279, p = 0.028). Patients with intellectual disability (ID) showed a higher number (F(1,26) = 9.406, p = 0.005) and variability (F(1,25) = 7.174, p = 0.013) of motor stereotypies, with a higher number (F(1,26) = 13.268, p = 0.005) and variability (F(1,26) = 9.490, p = 0.005) of stereotypies involving the head/trunk/shoulders category. Patients with guttural stereotypies showed a higher variability of total motor stereotypies (OR = 1.487, p = 0.032) and self-directed motor stereotypies (OR = 4.389, p = 0.042). These results, combined with a standardized video-analysis, document the frequency and variability of phonic stereotypies among children with ASD. Correlations between specific phonic stereotypies and verbal abilities should be investigated further.

Overshooting Subcellular Redox-Responses in Rett-Mouse Hippocampus during Neurotransmitter Stimulation

Rett syndrome (RTT) is a neurodevelopmental disorder associated with disturbed neuronal responsiveness and impaired neuronal network function. Furthermore, mitochondrial alterations and a weakened cellular redox-homeostasis are considered part of the complex pathogenesis. So far, overshooting redox-responses of MeCP2-deficient neurons were observed during oxidant-mediated stress, hypoxia and mitochondrial inhibition. To further clarify the relevance of the fragile redox-balance for the neuronal (dys)function in RTT, we addressed more physiological stimuli and quantified the subcellular redox responses to neurotransmitter-stimulation. The roGFP redox sensor was expressed in either the cytosol or the mitochondrial matrix of cultured mouse hippocampal neurons, and the responses to transient stimulation by glutamate, serotonin, dopamine and norepinephrine were characterized. Each neurotransmitter evoked more intense oxidizing responses in the cytosol of MeCP2-deficient than in wildtype neurons. In the mitochondrial matrix the neurotransmitter-evoked oxidizing changes were more moderate and more uniform among genotypes. This identifies the cytosol as an important reactive oxygen species (ROS) source and as less stably redox buffered. Fura-2 imaging and extracellular Ca²⁺ withdrawal confirmed cytosolic Ca²⁺ transients as a contributing factor of neurotransmitter-induced redox responses and their potentiation in the cytosol of MeCP2-deficient neurons. Chemical uncoupling demonstrated the involvement of mitochondria. Nevertheless, cytosolic NADPH- and xanthine oxidases interact to play the leading role in the neurotransmitter-mediated oxidizing responses. As exaggerated redox-responses were already evident in neonatal MeCP2-deficient neurons, they may contribute remarkably to the altered neuronal network performance and the disturbed neuronal signaling, which are among the hallmarks of RTT.

Disturbed redox homeostasis and oxidative stress: Potential players in the developmental regression in Rett syndrome

Rett syndrome (RTT) is a neurodevelopmental disorder affecting mostly girls. A seemingly normal initial development is followed by developmental stagnation and regression, leading to severe mental impairment with autistic features, motor dysfunction, irregular breathing and epilepsy. Currently, a cure does not exist. Due to the close association of RTT with mitochondrial alterations, cellular redox-impairment and oxidative stress, compounds stabilizing mitochondrial function, cellular redox-homeostasis, and oxidant detoxification are increasingly considered as treatment concepts. Indeed, antioxidants and free-radical scavengers ameliorate certain aspects of the complex and severe clinical presentation of RTT. To further evaluate these strategies, reliable biosensors are needed to quantify redox-conditions in brain and peripheral organs of mouse models or in patient-derived cells. Genetically-encoded redox-sensors meet these requirements. Expressed in transgenic mouse-models such as our unique Rett-redox indicator mice, they will report for any cell type desired the severity of oxidant stress throughout the various disease stages of RTT. Furthermore, these sensors will be crucial to evaluate in vitro and in vivo the outcome of mitochondria- and redox-balance targeted treatments.

Typical vs. atypical: Combining auditory Gestalt perception and acoustic analysis of early vocalisations in Rett syndrome

BACKGROUND

Early speech-language development of individuals with Rett syndrome (RTT) has been repeatedly characterised by a co-occurrence of apparently typical and atypical vocalisations.

AIMS

To describe specific features of this intermittent character of typical versus atypical early RTT-associated vocalisations by combining auditory Gestalt perception and acoustic vocalisation analysis.

METHODS AND PROCEDURES

We extracted N = 363 (pre-)linguistic vocalisations from home video recordings of an infant later diagnosed with RTT. In a listening experiment, all vocalisations were assessed for (a)typicality by five experts on early human development. Listeners' auditory concepts of (a)typicality were investigated in context of a comprehensive set of acoustic time-, spectral- and/or energy-related higher-order features extracted from the vocalisations.

OUTCOMES AND RESULTS

More than half of the vocalisations were rated as 'atypical' by at least one listener. Atypicality was mainly related to the auditory attribute 'timbre', and to prosodic, spectral, and voice quality features in the acoustic domain.

CONCLUSIONS AND IMPLICATIONS

Knowledge gained in our study shall contribute to the generation of an objective model of early vocalisation atypicality. Such a model might be used for increasing caregivers' and healthcare professionals' sensitivity to identify atypical vocalisation patterns, or even for a probabilistic approach to automatically detect RTT based on early vocalisations.

Same or different: Common pathways of behavioral biomarkers in infants and children with neurodevelopmental disorders?

The extent to which early motor patterns represent antecedents to later communicative functions, and the emergence of gesture and/or sign as potential communicative acts in neurodevelopmental disorders (NDDs), are research questions that have received recent attention. It is important to keep in mind that different NDDs have different neurological underpinnings, with correspondingly different implications for their conceptualization, detection, and treatment.

Early development in Rett syndrome - the benefits and difficulties of a birth cohort approach

PURPOSES

Typically, early (pre-diagnostic) development in individuals later diagnosed with Rett syndrome (RTT) has been investigated retrospectively using parent reports, medical records and analysis of home videos. In recent years, prospective research designs have been increasingly applied to the investigation of early development in individuals with late phenotypical onset disorders, for example, autism spectrum disorder.

METHODS

In this study, data collected by the Danish National Birth Cohort lent itself to prospective exploration of the early development of RTT, in particular early motor-, speech-language, and socio-communicative behaviors, mood, and sleep.

RESULTS AND CONCLUSIONS

Despite limitations, this quasi prospective methodology proved promising. In order to add substantially to the body of knowledge, however, specific questions relating to peculiarites in early development could usefully be added to future cohort studies. As this involves considerable work, it may be more realistic to consider a set of indicators which point to a number of developmental disorders rather than to one.

An Exploration of the Use of Eye Gaze and Gestures in Females With Rett Syndrome

PURPOSE

This study investigated the communicative use of eye gaze and gestures in females with Rett syndrome.

METHOD

Data on 151 females with Rett syndrome participating in the Australian Rett Syndrome Database was used in this study. Items from the Communication and Symbolic Behavior Scales Developmental Profile Infant-Toddler Checklist (Wetherby & Prizant, 2002) were used to measure communication. Relationships between the use of eye gaze and gestures for communication were investigated using logistic regression. The influences of MECP2 mutation type, age, and level of motor abilities on the use of eye gaze and gestures were investigated using multivariate linear regression.

RESULTS

Both eye gaze and the use of gestures predicted the ability to make requests. Women aged 19 years or older had the lowest scores for eye gaze. Females with better gross motor abilities had higher scores for the use of eye gaze and gestures. The use of eye gaze did not vary across mutation groups, but those with a C-terminal deletion had the highest scores for use of gestures.

CONCLUSIONS

Eye gaze is used more frequently than gestures for communication, and this is related to age, MECP2 mutation type, and gross motor abilities.

Behavioural biomarkers of typical Rett syndrome: moving towards early identification

The dynamic course of Rett syndrome (RTT) is still said to begin with a period of apparently normal development although there is mounting evidence that individuals with RTT show behavioural peculiarities and abnormalities during their infancy. Their spontaneous general movements are abnormal from birth onwards. Normal cooing vocalisation and canonical babbling (if at all required) are interspersed with abnormalities such as proto-vowel and proto-consonant alternations produced on ingressive airstream, breathy voice characteristics, and pressed or high-pitched vocalisations. The gestural repertoire is limited. Certain developmental motor and speech-language milestones are not at all acquired or show a significant delay. Besides abnormal blinking, repetitive and/or long lasting tongue protrusion, and bizarre smiling, there are already the first body and/or hand stereotypies during the first year of life. We are currently on a promising way to define a specific set of behavioural biomarkers pinpointing RTT.

Developmental profile of speech-language and communicative functions in an individual with the preserved speech variant of Rett syndrome

OBJECTIVE

We assessed various aspects of speech-language and communicative functions of an individual with the preserved speech variant of Rett syndrome (RTT) to describe her developmental profile over a period of 11 years.

METHODS

For this study, we incorporated the following data resources and methods to assess speech-language and communicative functions during pre-, peri- and post-regressional development: retrospective video analyses, medical history data, parental checklists and diaries, standardized tests on vocabulary and grammar, spontaneous speech samples and picture stories to elicit narrative competences.

RESULTS

Despite achieving speech-language milestones, atypical behaviours were present at all times. We observed a unique developmental speech-language trajectory (including the RTT typical regression) affecting all linguistic and socio-communicative sub-domains in the receptive as well as the expressive modality.

CONCLUSION

Future research should take into consideration a potentially considerable discordance between formal and functional language use by interpreting communicative acts on a more cautionary note.

Monozygotic twins with Rett syndrome: Phenotyping the first two years of life

The first two years of life for children with Rett syndrome (RTT) have previously been viewed as relatively asymptomatic. However, it is possible that subtle symptoms may be present in early development. To identify possible early indicators of RTT, we analysed videotapes of two twin girls with RTT. The videotapes were analysed to (a) describe the motor and communicative development of this twin pair with RTT; and to (b) explore whether early abnormalities and their age of onset differed between the twins and were related to their later clinical phenotypes. The results indicated several neurodevelopmental abnormalities present before the children exhibited any obvious signs of regression. Abnormalities were evident in the motor, speech-language and communicative domains. These data support an emerging evidence base showing the presence of developmental abnormalities in children with RTT during the first year of life. The results have implications for early screening and clinical assessment.

Monozygotic twins with Rett syndrome: Phenotyping the first two years of life

The first two years of life for children with Rett syndrome (RTT) have previously been viewed as relatively asymptomatic. However, it is possible that subtle symptoms may be present in early development. To identify possible early indicators of RTT, we analysed videotapes of two twin girls with RTT. The videotapes were analysed to (a) describe the motor and communicative development of this twin pair with RTT; and to (b) explore whether early abnormalities and their age of onset differed between the twins and were related to their later clinical phenotypes. The results indicated several neurodevelopmental abnormalities present before the children exhibited any obvious signs of regression. Abnormalities were evident in the motor, speech-language and communicative domains. These data support an emerging evidence base showing the presence of developmental abnormalities in children with RTT during the first year of life. The results have implications for early screening and clinical assessment.

Development of socio-communicative skills in 9- to 12-month-old individuals with fragile X syndrome

We investigated the early socio-communicative development of individuals with fragile X syndrome (FXS) by undertaking a retrospective analysis of family videos. Videos were analyzed to identify existing communicative forms and functions. Analyses were undertaken on seven children who were later diagnosed with FXS. The children were filmed when they were 9-12 months old and before being diagnosed. Fourteen different communicative forms and six different communicative functions were observed. All participants were observed to express the functions of 'Attention to self' and 'Answering', but none indicated 'Requesting action', 'Requesting information', 'Choice making', or 'Imitating'. Results suggest that children with FXS may have a limited range of communicative forms and functions when they are from 9 to 12 months of age. However, further research is necessary to gain a specific developmental profile of socio-communicative forms and functions in FXS.

Three different profiles: early socio-communicative capacities in typical Rett syndrome, the preserved speech variant and normal development

BACKGROUND AND AIMS

This is the first study aiming to compare pre-diagnostic socio-communicative development of a female with typical Rett syndrome (RTT), a female with the preserved speech variant of RTT (PSV) and a control toddler.

METHODS

We analysed 1275 min of family videos at the participants' age between 9 and 24 months and used the Inventory of Potential Communicative Acts (IPCA) to delineate their repertoires of communicative forms and functions.

RESULTS

The results revealed different profiles for the three different conditions. The repertoire of communicative gestures and (pre)linguistic vocalizations was most comprehensive in the control toddler, followed by the female with PSV and the female with RTT.

CONCLUSION

These findings contribute to the growing knowledge about early developmental abnormalities in RTT. In order to define distinctive profiles for typical and atypical RTT and evaluate their specificity, a larger body of evidence is needed.

Early socio-communicative forms and functions in typical Rett syndrome

Rett syndrome (RTT) is a severe neurological disorder characterized by a developmental regression in motor and speech-language domains. There is, however, limited research on socio-communicative development of affected children before the onset of regression. We analyzed audio-video recordings made by parents of six 9- to 12-month old girls later diagnosed with typical RTT, applying the Inventory of Potential Communicative Acts (IPCA) to identify early communicative forms and functions. Each girl used at least one communicative form (e.g., body movement, eye gaze, or vocalizations) to gain attention and answer, but none were observed to make choices or request information. Varying numbers of children were observed to perform other communicative functions according to the IPCA including social convention, rejecting or requesting an object. Non-verbal forms (e.g., reaching, moving closer, eye contact, smiling) were more common than non-linguistic verbal forms (e.g., unspecified vocalizations, pleasure vocalizations, crying). (Pre-)linguistic verbal forms (e.g., canonical or variegated babbling, proto-words) were not used for communicative purposes. These data suggest that atypical developmental patterns in the socio-communicative domain are evident prior to regression in young individuals later diagnosed with RTT.

Parental reports on early language and motor milestones in fragile X syndrome with and without autism spectrum disorders

OBJECTIVE

This study examined features of early language and motor milestones in children with fragile X syndrome (FXS) and contrasted these features with a diagnosis of Autism Spectrum Disorder (ASD) later in life in these children.

METHODS

We retrospectively examined parental report of age of onset for walking and first words for primarily boys with FXS, both with ASD (FXS + ASD) and FXS-only. The diagnosis of ASD was established by DSM-IV criteria, which were complemented by the ADOS. The age of onset was analyzed as a continuous and categorical variable, which were compared to the upper limit of typically developing children.

RESULTS

Individuals with FXS-only are more delayed in the onset of first words than first walks. The finding represents a pattern suggesting a continuum as robustly demonstrated in individuals with FXS + ASD vs. FXS-only.

CONCLUSION

Our results support validity of FXS + ASD co-morbidity as a distinct phenotype in individuals with FXS.

Changing the perspective on early development of Rett syndrome

We delineated the achievement of early speech-language milestones in 15 young children with Rett syndrome (MECP2 positive) in the first two years of life using retrospective video analysis. By contrast to the commonly accepted concept that these children are normal in the pre-regression period, we found markedly atypical development of speech-language capacities, suggesting a paradigm shift in the pathogenesis of Rett syndrome and a possible approach to its early detection.

Changing the perspective on early development of Rett syndrome

We delineated the achievement of early speech-language milestones in 15 young children with Rett syndrome (MECP2 positive) in the first two years of life using retrospective video analysis. By contrast to the commonly accepted concept that these children are normal in the pre-regression period, we found markedly atypical development of speech-language capacities, suggesting a paradigm shift in the pathogenesis of Rett syndrome and a possible approach to its early detection.