Genetic architecture of childhood speech disorder: a review

Severe speech disorders lead to poor literacy, reduced academic attainment and negative psychosocial outcomes. As early as the 1950s, the familial nature of speech disorders was recognized, implying a genetic basis; but the molecular genetic basis remained unknown. In 2001, investigation of a large three generational family with severe speech disorder, known as childhood apraxia of speech (CAS), revealed the first causative gene; FOXP2. A long hiatus then followed for CAS candidate genes, but in the past three years, genetic analysis of cohorts ascertained for CAS have revealed over 30 causative genes. A total of 36 pathogenic variants have been identified from 122 cases across 3 cohorts in this nascent field. All genes identified have been in coding regions to date, with no apparent benefit at this stage for WGS over WES in identifying monogenic conditions associated with CAS. Hence current findings suggest a remarkable one in three children have a genetic variant that explains their CAS, with significant genetic heterogeneity emerging. Around half of the candidate genes identified are currently supported by medium (6 genes) to strong (9 genes) evidence supporting the association between the gene and CAS. Despite genetic heterogeneity; many implicated proteins functionally converge on pathways involved in chromatin modification or transcriptional regulation, opening the door to precision diagnosis and therapies. Most of the new candidate genes for CAS are associated with previously described neurodevelopmental conditions that include intellectual disability, autism and epilepsy; broadening the phenotypic spectrum to a distinctly milder presentation defined by primary speech disorder in the setting of normal intellect. Insights into the genetic bases of CAS, a severe, rare speech disorder, are yet to translate to understanding the heritability of more common, typically milder forms of speech or language impairment such as stuttering or phonological disorder. These disorders likely follow complex inheritance with polygenic contributions in many cases, rather than the monogenic patterns that underly one-third of patients with CAS. Clinical genetic testing for should now be implemented for individuals with CAS, given its high diagnostic rate, which parallels many other neurodevelopmental disorders where this testing is already standard of care. The shared mechanisms implicated by gene discovery for CAS highlight potential new targets for future precision therapies.

The importance of deep speech phenotyping for neurodevelopmental and genetic disorders: a conceptual review

Background

Speech is the most common modality through which language is communicated, and delayed, disordered, or absent speech production is a hallmark of many neurodevelopmental and genetic disorders. Yet, speech is not often carefully phenotyped in neurodevelopmental disorders. In this paper, we argue that such deep phenotyping, defined as phenotyping that is specific to speech production and not conflated with language or cognitive ability, is vital if we are to understand how genetic variations affect the brain regions that are associated with spoken language.

Speech is distinct from language, though the two are related behaviorally and share neural substrates. We present a brief taxonomy of developmental speech production disorders, with particular emphasis on the motor speech disorders childhood apraxia of speech (a disorder of motor planning) and childhood dysarthria (a set of disorders of motor execution). We review the history of discoveries concerning the KE family, in whom a hereditary form of communication impairment was identified as childhood apraxia of speech and linked to dysfunction in the FOXP2 gene. The story demonstrates how instrumental deep phenotyping of speech production was in this seminal discovery in the genetics of speech and language. There is considerable overlap between the neural substrates associated with speech production and with FOXP2 expression, suggesting that further genes associated with speech dysfunction will also be expressed in similar brain regions. We then show how a biologically accurate computational model of speech production, in combination with detailed information about speech production in children with developmental disorders, can generate testable hypotheses about the nature, genetics, and neurology of speech disorders.

Conclusions

Though speech and language are distinct, specific types of developmental speech disorder are associated with far-reaching effects on verbal communication in children with neurodevelopmental disorders. Therefore, detailed speech phenotyping, in collaboration with experts on pediatric speech development and disorders, can lead us to a new generation of discoveries about how speech development is affected in genetic disorders.

Speech feature profiles in Swedish 5-year-olds with speech sound disorder related to suspected childhood apraxia of speech or cleft palate

Purpose: To study the occurrence of speech features commonly associated with Childhood Apraxia of Speech (CAS) in Swedish children with suspected CAS (sCAS) or Speech Sound Disorder (SSD) related to Cleft Palate and/or Lip (CP ± L).Method: Thirty-four children (4.10-5.11) with SSD related to sCAS (n = 15) or repaired CP ± L (n = 19) participated. Consensus judgement of presence/absence of CAS features in single words were based on a checklist with operationalised definitions. Speech sound production measures were based on semi-narrow phonetic transcription. Intra- and inter-transcriber agreement was determined.Result: Twelve participants (ten with sCAS (67%) and two with CP ± L (11%)) shared a CAS profile of phonemic speech inconsistency for consonants and vowels and a set of four features: vowel error, voicing error, difficulty achieving initial articulatory configurations or transitionary movement gestures and stress errors. The most frequent speech difficulties in children with non-CAS CP ± L (n = 17) were consonant distortion (88%) and hypernasal resonance (76%). Prosodic impairment was rare.Conclusion: A distinct CAS speech feature profile was found for children with CAS, differing in number and distribution compared to children with CP ± L and SSD. CAS was found more frequently in CP ± L and SSD compared to reported estimates of clinical prevalence.

Differences and Commonalities in Children with Childhood Apraxia of Speech and Comorbid Neurodevelopmental Disorders: A Multidimensional Perspective

Childhood apraxia of speech (CAS) is a motor speech disorder often co-occurring with language impairment and complex neurodevelopmental disorders. A cohort of 106 children with CAS associated to other neurodevelopmental disorders underwent a multidimensional investigation of speech and language profiles, chromosome microarray analysis and structural brain magnetic resonance (MR). Our aim was to compare the clinical profiles of children with CAS co-occurring with only language impairment with those who, in addition to language impairment, had other neurodevelopmental disorders. Expressive grammar was impaired in the majority of the sample in the context of similar alterations of speech, typical of the core symptoms of CAS. Moreover, children with complex comorbidities also showed more severe and persistent receptive language deficits. About 25% of the participants harbored copy number variations (CNVs) already described in association to neurodevelopmental disorders. CNVs occurred more frequently in children with complex comorbidities. MR structural/signal alterations were found in a small number of children and were of uncertain pathogenic significance. These results confirm that CAS needs multidimensional diagnostic and clinical management. The high frequency of language impairment has important implications for early care and demands a personalized treatment approach in which speech and language goals are consistently integrated.

Impairment and Plasticity of Language-Related White Matter in Patients With Brain Arteriovenous Malformations

BACKGROUND AND PURPOSE

Language dysfunction is rarely seen in patients with unruptured brain arteriovenous malformation (AVM) albeit the AVM nidus involving language areas, which provides a unique disease model to study language reorganization. The objective of this study was to investigate the impairment and reorganization patterns and characteristics of language-related white matter in AVMs located at different brain areas.

METHODS

Thirty-three patients with AVMs involving language areas were prospectively enrolled. Patients were categorized into 3 groups according to the lesion locations: the frontal (14 patients), temporal (15 patients), and parietal groups (4 patients). Thirty age- and sex-matched healthy controls were enrolled as comparison. All participants underwent diffusion tensor imaging scans, and automated fiber quantification method was applied to quantitatively study the difference of segmented language-related white matter connectivity between 3 AVM groups and control group.

RESULTS

Language functions were normal in all subjects according to Western Aphasia Battery test. In the frontal group, fractional anisotropy (FA) value decreased in the left arcuate fascicle and increased in left superior longitudinal fasciculus and uncinate fascicle; in the temporal group, FA values decreased in left inferior fronto-occipital fascicle and inferior longitudinal fascicle and increased in right anterior thalamic radiation and uncinate fascicle; in the parietal group, FA values decreased in left arcuate fascicle and inferior longitudinal fascicle and increased in bilateral anterior thalamic radiations and uncinate fascicles and right inferior fronto-occipital fascicle. In fascicles with decreased FA values, the increase of radial diffusivity was common, and fascicles with increased FA values usually presented along with increased axial diffusivity values.

CONCLUSIONS

Remodeling of language-related white matter occurs when traditional language areas are involved by AVM nidus, and its reorganization patterns vary with locations of AVM nidus. Fascicle impairment is mainly caused by the myelin deficits, and its plasticity may be dominated by the axon remodeling procedure.

Atypical development of Broca's area in a large family with inherited stuttering

Developmental stuttering is a condition of speech dysfluency, characterized by pauses, blocks, prolongations and sound or syllable repetitions. It affects around 1% of the population, with potential detrimental effects on mental health and long-term employment. Accumulating evidence points to a genetic aetiology, yet gene-brain associations remain poorly understood due to a lack of MRI studies in affected families. Here we report the first neuroimaging study of developmental stuttering in a family with autosomal dominant inheritance of persistent stuttering. We studied a four-generation family, 16 family members were included in genotyping analysis. T1-weighted and diffusion-weighted MRI scans were conducted on seven family members (six male; aged 9-63 years) with two age and sex matched controls without stuttering (n = 14). Using Freesurfer, we analysed cortical morphology (cortical thickness, surface area and local gyrification index) and basal ganglia volumes. White matter integrity in key speech and language tracts (i.e. frontal aslant tract and arcuate fasciculus) was also analysed using MRtrix and probabilistic tractography. We identified a significant age by group interaction effect for cortical thickness in the left hemisphere pars opercularis (Broca's area). In affected family members this region failed to follow the typical trajectory of age-related thinning observed in controls. Surface area analysis revealed the middle frontal gyrus region was reduced bilaterally in the family (all cortical morphometry significance levels set at a vertex-wise threshold of P < 0.01, corrected for multiple comparisons). Both the left and right globus pallidus were larger in the family than in the control group (left P = 0.017; right P = 0.037), and a larger right globus pallidus was associated with more severe stuttering (rho = 0.86, P = 0.01). No white matter differences were identified. Genotyping identified novel loci on chromosomes 1 and 4 that map with the stuttering phenotype. Our findings denote disruption within the cortico-basal ganglia-thalamo-cortical network. The lack of typical development of these structures reflects the anatomical basis of the abnormal inhibitory control network between Broca's area and the striatum underpinning stuttering in these individuals. This is the first evidence of a neural phenotype in a family with an autosomal dominantly inherited stuttering.

Neural Changes Induced by a Speech Motor Treatment in Childhood Apraxia of Speech: A Case Series

We report a case series of children with childhood apraxia of speech, by describing behavioral and white matter microstructural changes following 2 different treatment approaches.Five children with childhood apraxia of speech were assigned to a motor speech treatment (PROMPT) and 5 to a language, nonspeech oral motor treatment. Speech assessment and brain MRI were performed pre- and post-treatment. The ventral (tongue/larynx) and dorsal (lips) corticobulbar tracts were reconstructed in each subject. Mean fractional anisotropy and mean diffusivity were extracted. The hand corticospinal tract was assessed as a control pathway. In both groups speech improvements paralleled changes in the left ventral corticobulbar tract fractional anisotropy. The PROMPT treated group also showed fractional anisotropy increase and mean diffusivity decrease in the left dorsal corticobulbar tract. No changes were detected in the hand tract. Our results may provide preliminary support to the possible neurobiologic effect of a multimodal speech motor treatment in childhood apraxia of speech.

Speech and language phenotype in Phelan-McDermid (22q13.3) syndrome

Communication difficulties are a core feature of Phelan-McDermid syndrome (PMS). However, a specific speech and language phenotype has not been delineated, preventing prognostic counselling and development of targeted therapies. We examined speech, language, social and functional communication abilities in 21 individuals with PMS (with SHANK3 involvement), using standardised assessments. Mean age was 9.7 years (SD 4.1) and 57% were female. Deletion size ranged from 41 kb to 8.3 Mb. Nine participants (45%) were non-verbal. Four (19%) had greater verbal ability, speaking in at least 4-5 word sentences, but with speech sound errors. Standard scores for receptive and expressive language were low (typically >3 SD below the mean). Language age equivalency was 13-16 months on average (range 2-53 months). There was a significant association between deletion size and the ability to use phrases. Participants with smaller deletion sizes were more likely to be able to use phrases (odds ratio: 0.36, 95% CI: 0.14-0.95, p = 0.040). Adaptive behaviour (life skills) was low in all areas (>2 SD below mean). Scores in communication were markedly lower than for daily living (p = 0.008) and socialisation (p < 0.001). A common linguistic profile was characterised by severe impairment across receptive, expressive and social language domains. Yet data indicated greater communicative intent than appeared to be capitalised by current therapies. Early implementation of augmentative (e.g. computer-assisted) modes of communication, alongside promotion of oral language, is essential to harness this intent, accelerate language development and reduce frustration. Future trials should examine the added benefit of targeted speech motor interventions in those with greater verbal capacity.

Altered brain structures in the dorsal and ventral language pathways in individuals with and without developmental language disorder (DLD)

Developmental Language Disorder (DLD) is a neurodevelopmental disorder characterized by difficulty learning and using language, and this difficulty cannot be attributed to other developmental conditions. The aim of the current study was to examine structural differences in dorsal and ventral language pathways between adolescents and young adults with and without DLD (age range: 14-27 years) using anatomical magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI). Results showed age-related structural brain differences in both dorsal and ventral pathways in individuals with DLD. These findings provide evidence for neuroanatomical correlates of persistent language deficits in adolescents/young adults with DLD, and further suggest that this brain-language relationship in DLD is better characterized by taking account the dynamic course of the disorder along development.

An N-of-1 Randomized Controlled Trial of Interventions for Children With Inconsistent Speech Sound Errors

Purpose The aim of this study was to test the hypothesis that children with inconsistent speech errors would respond differentially to 1 of 3 specific interventions depending on their primary underlying impairment: Children with deficient motor planning were expected to respond best to an auditory-motor integration (AMI) intervention, and children with deficient phonological planning were expected to respond best to a phonological memory and planning (PMP) intervention. Method Twelve participants were diagnosed with a motor planning (n = 7) or phonological planning (n = 5) deficit based on a comprehensive assessment, which included the Syllable Repetition Task as an important source of diagnostic evidence. An N-of-1 randomized controlled trial was used. Each child experienced all 3 interventions: AMI, PMP, and control (CTL); however, these interventions were randomly allocated to sessions within weeks (3 sessions per week × 6 weeks for 18 sessions). The AMI intervention procedures targeted knowledge of the acoustic-phonetic target and integration of auditory and somatosensory feedback during speech practice. The PMP intervention procedures targeted segmenting and recompiling the phonological plan for each word. The CTL intervention was standard drill practice. The child was taught 5 pseudowords in a meaningful context in each intervention condition. Results Same-day (SD) probes assessed transfer from taught pseudowords to untaught real words, and next-day (ND) probes assessed retention of that learning. Nonparametric resampling tests with pooling of p values across children with the same diagnosis were used to assess the results. Pooled p values indicated a significant benefit of AMI over PMP for the group with a motor planning deficit (p = 2.01E-04 for SD probes and 2.97E-03 for ND probes) and a significant benefit of PMP over AMI for the group with a phonological planning deficit (p = 1.22E-02 for SD probes and 1.32E-02 for ND probes). Response to the CTL intervention was variable within groups. Conclusion In this study, the child's underlying psycholinguistic deficit helped to predict response to intervention.

Looking to the Future: Speech, Language, and Academic Outcomes in an Adolescent with Childhood Apraxia of Speech

OBJECTIVE

The clinical course of childhood apraxia of speech (CAS) is poorly understood. Of the few longitudinal studies in the field, only one has examined adolescent outcomes in speech, language, and literacy. This study is the first to report long-term speech, language, and academic outcomes in an adolescent, Liam, with CAS.

METHODS

Speech, language, literacy, and academic outcome data were collected, including 3 research-based assessments. Overall, data were available at 17 time points from 3;10 to 15 years.

RESULTS

Liam had moderate-to-severe expressive language impairment and poor reading, writing, and spelling up to 10 years. His numeracy was at or above the national average from 8 to 14 years. He made gains in preadolescence, with average expressive language at 11 years and above average reading and writing at 14 years. Nonword reading, reading comprehension, and spelling remained areas of weakness. Receptive language impairment was evident at 13 years, which was an unexpected finding.

CONCLUSION

Findings from single cases can be hypothesis generating but require verification in larger cohorts. This case shows that at least some children with CAS may gain ground in adolescence, relative to same age peers, in expressive language and academic areas such as reading and writing.

Initial studies of the phenotype and persistence of speech motor delay (SMD)

Speech Motor Delay (SMD) is a recently proposed childhood motor speech disorder characterized by imprecise and unstable speech, prosody, and voice that does not meet criteria for either Childhood Dysarthria or Childhood Apraxia of Speech. The goals of the present research were to obtain information on the phenotype of SMD and initial information on the persistence of SMD in children receiving treatment for idiopathic Speech Delay (SD). Five questions about the phenotype and persistence of SMD were posed using a database of audio-recordings and participant records and longitudinal data from audio-recordings of children with early SMD treated for SD. Three phenotype questions examined associations between participant risk factors and prevalence of SMD, and described the most frequent speech, prosody, and voice signs of early SMD. To provide initial estimates of the persistence of SMD, two questions examined associations between the persistence of SMD and participant risk factors using the audio-recordings of 14 participants with SMD treated for idiopathic SD. Phenotype findings indicated that SMD is characterized by across-the-board delays in the spatiotemporal precision and stability of speech, prosody, and voice production. Persistence findings indicated that although most participants normalized early SMD by 6 years of age, SMD persisted until at least late adolescence in 21.4% of participants. Findings are interpreted to support the construct validity of SMD and the potential for research using additional assessment modalities to explicate its genomic and neuromotor causal pathways. Abbreviations: CAS: Childhood Apraxia of Speech; CD: Childhood Dysarthria; MSD: Motor Speech Disorder; No MSD: No Motor Speech Disorder; PSI: Precision-Stability Index; SD: Speech Delay; SMD: Speech Motor Delay; SSD: Speech Sound Disorders.