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.

Childhood apraxia of speech (CAS) is a pediatric motor speech disorder, in which the “precision and consistency of movements underlying speech are impaired” due to deficits in speech motor planning and programming [1]. The clinical course of the disorder is still poorly understood, with only a handful of studies examining long-term outcomes [2-9]. Most studies have understandably focused on speech outcomes and largely in primary school age children. Understanding how the broader phenotype associated with CAS may evolve into adolescence is crucial to differential diagnosis of older individuals and will provide important prognostic information to families.

Speech Changes over Time in CAS

Several studies demonstrate that speech improves with age in CAS. Taking these findings together, 10 preschoolers with CAS (7 male, 3 female) who were unintelligible at 4–6 years, had improved articulation of single words, and were mostly intelligible in conversational speech by school age (8–10 years) [4, 6]. This trend was also noted in older children with CAS. Two school age children (Michael, 10;7 years; Caroline, 11;9 years) became more intelligible and had better performance on a single word articulation test (Edinburgh Articulation Test) at 14;6 and 15;8 years, respectively [4, 6]. Improvements in speech intelligibility were attributed to the development of word specific articulatory programs in these older children. While consonant and vowel accuracy generally improved in 3 children with CAS (4;6, 5;6, and 5;10 years) over a 3-year period, their production of later developing sounds (Late 8 – /ʃ, ʒ, l, r, s, z, θ, ð/) was poor up to school age (6;5, 7;5, and 7;7 years) [5]. This was in the context of ongoing therapy from an early age focused on phoneme accuracy and other speech production targets. Over time, they demonstrated higher word token accuracy in conversational speech and decreased total word token variability (ratio of number of different variant productions to total number of tokens produced), yet marked session-to-session variability remained a core feature [3, 5].

Children with CAS appear to have persistent deficits in syllable construction. Consonant omissions have been frequently reported in preschool, and sound and syllable deletions increasingly apparent in school age and adolescence [4-7, 10]. Syllable sequencing deficits also persisted in school age children with CAS [4]. Delayed and atypical errors most commonly heard in older children included liquid simplification, vowel and voicing errors, sound intrusion, and metathesis [2, 4-7]. Little improvement was seen in nonword repetition, with impaired performance into adolescence [4, 6].

Language and Literacy Changes over Time in CAS

Persistent expressive language impairment has been reported to occur up to school age in children with CAS [4, 7, 8]. One child (MV) showed little improvement in expressive language over a 2 years period (5;6–7;6 years) with lexical diversity and expressive grammar significantly below age expectations [8]. Another child (LH) had persistent and severe expressive language impairment from 6 to 11;4 years [7]. Deficits in expressive syntax and receptive morphology were noted, with severe short-term memory impairment impacting on sentence and number repetition tasks [7]. In a larger cohort of 10 pre-schoolers with CAS, all children tested had expressive language impairment, with only 2 scoring in the average range at school age (8–10 years) [4]. Of those with average receptive language skills in preschool, 3 subsequently demonstrated impaired receptive language on the school age assessment. These impairments were seen despite improvements in speech-sound production, associated with poor nonverbal problem-solving skills and speed of information processing. This downward trend was also noted in LH, who had severely impaired receptive language at 11;4 years, having previously been in the average range [7]. MV had average receptive language up to 7 years [8].

One study has examined literacy skills over time in CAS [4, 7, 11]. Two children showed little improvement in reading and spelling despite 4 years of intensive phonics therapy, with severely impaired skills in adolescence (Michael, 14;5 years; Caroline, 15 years). These children had difficulty discriminating between words and nonwords, had poor letter-sound correspondence, and were unable to use phonological reading and spelling strategies. The majority of their spelling errors appeared to be related to their residual speech errors, including sound and syllable deletions and insertions. In contrast, LH made progress in literacy after 5.5 years of weekly therapy [7]. Her reading skills were within the average range at 11;4 years, with reading fluency, accuracy, rate and comprehension standard scores falling within one SD of the mean. She was able to spell sight words better than regular words and sentences (97 vs. 40% correct). Her spelling errors also mirrored her speech production deficits, including epenthesis, substitutions, and sequencing errors. Deficits in reading comprehension and decoding of real and nonsense words were evident in other school aged children with CAS [4, 11].

Taken together, these studies demonstrate that children with CAS can become more intelligible as they mature, yet have persistent sound and syllable-level errors and poor repetition of nonwords. Expressive language impairment may be evident up to school age and associated with deficits in reading and spelling. How language and literacy evolve in adolescence, and how children with CAS perform in other academic areas such as numeracy and writing require further examination. This is critical information to guide speech pathology input as children with CAS progress through high school, helping to maximize their performance in the final school years.

Here we address these gaps in the literature and describe long-term speech, language and academic outcomes in an adolescent boy with CAS. “Liam” was chosen for investigation as he had relatively pure CAS without comorbid dysarthria, and no other cognitive or neurological comorbidities. Rich phenotypic data were available on Liam from over a decade, including the results of research-based and clinical speech pathology assessments, national academic assessment, and speech pathology intervention. This was a rare opportunity to examine longitudinal change in one child with CAS from preschool to adolescence.

Case History

Liam was induced at 41 weeks of gestation after an uneventful pregnancy. He weighed 4,175 g at birth and was well in the neonatal period. There was no history of feeding difficulties, and he breastfed until 12 months of age. He met appropriate motor milestones, although he was described by his mother as “clumsy” with some motor tasks (writing, riding a bike). His fine and gross motor skills have not been formally assessed. Liam’s speech development was delayed. He did not babble as an infant, said his first words around 3 years of age and put 2 words together at 3;9 years. There was no history of regression. His hearing was normal at 3;6 years. Motor speech planning difficulties were first noted at 3;10 years, including groping during sound production and inconsistent use of phonemes in words. At this age, the assessing speech pathologist reported that Liam had “difficulty getting his lips, tongue, and teeth in the right position at the right time.” Frequent omission errors were also noted. Expressive language impairment was first diagnosed at 3;10 years, with his score in the 3rd percentile on the Clinical Evaluation of Language Fundamentals (CELF) – Preschool. He was diagnosed with CAS at 4;4 years by the third author (B.P.-F.); a speech pathologist with over 20 years of experience in CAS at the time of diagnosis. At that time, Liam’s spontaneous speech was frequently unintelligible, he had a reduced consonant inventory (no fricatives apart from glottal fricative /h/; no affricates), reduced syllable shapes, sound substitutions and omissions (17% consonants correct), distorted vowels, atypical phonological patterns (e.g., initial consonant deletion), and inconsistent word attempts. He had increased errors in multisyllabic words and phrases. He was able to produce isolated vowels and some consonants on the sequencing subtest of the Verbal Motor Production Assessment for Children, however, had difficulty sequencing 2 or more sounds. Groping was evident in nonspeech oral motor tasks. Cognitive assessment at 5 years (Wechsler Preschool and Primary Scale of Intelligence, 3rd Edition) revealed borderline verbal intelligence (IQ 74), with average nonverbal intelligence (IQ 100) and processing speed (IQ 86). Liam was severely delayed in the Communication domain on the Vineland Adaptive Behaviour Scales (standard score 46). He had average verbal (IQ 94) and nonverbal (IQ 84) intelligence on subsequent testing at 7;1 years (Kaufman Brief Intelligence Test, 2nd Edition). Difficulties in basic attention and working memory were evident at this time (Wechsler Intelligence Scale for Children, 4th Edition Digit Span Forward score 6; Backward score 5).

Oral motor assessment at 7;5 years revealed mandibular retrognathia, reduced tongue strength against mild resistance, and involuntary tongue movement at rest.

Groping was evident in nonspeech tasks. His scores on 3 subtests of the Verbal Motor Production Assessment for Children were in the severe range (Global Oromotor Control, 80%; Focal Oromotor Control, 67%; Sequencing, 52%).

Liam has had regular speech pathology intervention from 3 years of age. He had fortnightly therapy in a community health setting for around 1 year and attended a speech and language program in Prep. He commenced private speech therapy at 6;7 years – details regarding the frequency of session and goals of therapy are included in Table 1. He received 4 years of language disorder funding from Prep to Grade 3 through State Support Services, which funded 1:1 speech therapy sessions. He also had regular integration aide support in the classroom.

Table 1.

Speech therapy targets and frequency of intervention from 6 to 15 years

Speech therapy targets and frequency of intervention from 6 to 15 years
Speech therapy targets and frequency of intervention from 6 to 15 years

Liam was initially referred to a research study of the genetics of speech disorders, as he had CAS and a history of speech and language disorder in his extended family. The study had approval from The Royal Children’s Hospital Human Research Ethics Committee (27053), and written informed consent was obtained from Liam’s parents. He was assessed on 3 separate occasions (7;4, 9;4, and 10;5 years) by the first author (S.J.T.) as part of his participation in the research study. A battery of standardized age-appropriate assessments was used to phenotype Liam’s speech, language, phonological processing, and literacy skills as described below. Audiovisual recordings of the assessments were made using a Marantz PMD671 digital recorder, Countryman Isomax headset microphone, and a Sony DCR-SR85 digital camera. Two speech pathologists (S.J.T., A.T.M.) independently rated research-based speech and oral motor assessments, then reached consensus on discrepant ratings.

Research Assessment Battery

Speech production in single words was examined using the Goldman-Fristoe Test of Articulation, Second Edition (GFTA-2) [12]. The GFTA-2 uses a series of colored pictures of objects and actions to elicit all of the sounds of English.

Connected speech tasks included reading a short passage (The Rainbow Passage), a picture description task (The Cookie Theft), and a 10-minute conversation with the researcher. These tasks were regarded as more indicative of Liam’s functional communication [13, 14].

Single word and connected speech tasks were analyzed for articulation and phonological speech error patterns and features of CAS. Phonological errors were classified with reference to the normative study by Dodd et al. [15, 16].

Consistency of speech production was examined using the inconsistency assessment of the Diagnostic Evaluation of Articulation and Phonology (DEAP) [16]. Liam was asked to name 25 pictures 3 times in one session, with other tasks administered in between.

Challenging speech tasks included repetition of multisyllabic real words and nonwords. Australian recordings of the stimuli were presented, and Liam was instructed to repeat exactly what he had heard. The Nonword Memory Test [17] consists of 28 nonwords. The total number of words correctly repeated was compared to mean scores (± SD) for the normative sample. The Multisyllabic Word Repetition task [18] consists of 52 words that are generally familiar to school age children. Raw scores were calculated as the number of items correctly repeated, and compared to the mean scores (± SD) of individuals with a history of moderate-severe speech disorder and aged-matched individuals with typical speech [19].

Receptive and expressive language was examined using the CELF-4 [20]. The Receptive Language Index score measures performance on tasks assessing comprehension of grammatical rules, relationships between words, and the ability to follow oral commands containing functional language. The Expressive Language index score measures performance on tasks evaluating the ability to recall and reproduce sentences of varying length and complexity, to formulate complex sentences and to complete sentences using grammatical rules. A standard score of 80 or below on the CELF-4 Receptive or Expressive Language Index indicated impairment, as per recently proposed criteria, that is, language ability >1.25 SD below the population mean on standardized language tests [21].

Phonological processing skills including phonological awareness (the ability to attend to, identify and manipulate sounds in spoken words), phonological memory (use of the speech sound system to store information in short-term memory), and rapid naming (retrieval of sound-based information from long-term memory) were examined using the Comprehensive Test of Phonological Processing (CTOPP) [22]. Composite standard scores were calculated with reference to normative data.

Literacy was assessed using the Wide Range Achievement Test, 4th Edition (WRAT-4) [23]. The Word Reading subtest examined letter identification and recognition of single words, while the Spelling subtest examined the ability to encode sounds into written form through a dictated spelling format. Standard scores for each subtest were calculated with reference to normative data.

Liam’s CAS diagnosis was confirmed by 2 speech pathologists (S.J.T., A.T.M.). Diagnostic criteria were adapted from Murray et al. [24] based on the 3 consensus features of CAS proposed by the American Speech-Language-Hearing Association; (1) inconsistent errors; (2) lengthened and disrupted coarticulatory transitions between sounds/syllables; and (3) inappropriate prosody [1] (Table 2).

Table 2.

CAS speech features (categorised under the 3 ASHA consensus diagnostic criteria) present in Liam

CAS speech features (categorised under the 3 ASHA consensus diagnostic criteria) present in Liam
CAS speech features (categorised under the 3 ASHA consensus diagnostic criteria) present in Liam

At this time, all available clinical speech, language, and literacy assessments were obtained from Liam’s past and current treating speech pathologists. Original test forms from clinical assessments were collected where possible. His performance results on the National Assessment Program – Literacy and Numeracy (NAPLAN) were obtained from his school. NAPLAN is an assessment of academic performance conducted annually for all Australian students in years 3, 5, 7, and 9, across the domains of reading, writing, spelling, grammar/punctuation, and numeracy [25].

Overall, speech pathology and NAPLAN data were available at 17 timepoints from 3;10 to 15 years (Fig. 1).

Fig. 1.

Timeline of research and clinical speech pathology assessments from age 3–15 years. NAPLAN testing was conducted in Year 3 (8 years), Year 5 (10 years), Year 7 (12 years) and Year 9 (14 years) (indicated by stars). DEAP, Diagnostic Evaluation of Articulation and Phonology Inconsistency Assessment; NWR, Non-word Memory Test; GFTA, Goldman-Fristoe Test of Articulation; CTOPP, Comprehensive Test of Phonological Processing; WRAT, Wide Range Achievement Test; WRMT, Woodcock Reading Mastery Test; MSW, Multisyllabic Word Repetition task; Quick Screener, A Quick Test of Articulation and Phonology; Schonell, Schonell Graded Word Reading and Spelling test. ^ External clinical assessment.

Fig. 1.

Timeline of research and clinical speech pathology assessments from age 3–15 years. NAPLAN testing was conducted in Year 3 (8 years), Year 5 (10 years), Year 7 (12 years) and Year 9 (14 years) (indicated by stars). DEAP, Diagnostic Evaluation of Articulation and Phonology Inconsistency Assessment; NWR, Non-word Memory Test; GFTA, Goldman-Fristoe Test of Articulation; CTOPP, Comprehensive Test of Phonological Processing; WRAT, Wide Range Achievement Test; WRMT, Woodcock Reading Mastery Test; MSW, Multisyllabic Word Repetition task; Quick Screener, A Quick Test of Articulation and Phonology; Schonell, Schonell Graded Word Reading and Spelling test. ^ External clinical assessment.

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Lexical Stress

Liam’s lexical stress production in multisyllabic words was examined using an acoustic measure of stress contrastivity, namely, the pairwise variability index (PVI) [26, 27]. PVI quantifies relative stress across adjacent syllables within a word. It provides a separate measure for each of the suprasegmentals that denote lexical stress – vowel duration (ms), peak intensity of the vowel (dB), and fundamental frequency. Typically developing children use these suprasegmentals to contrast weak and strong syllables within words at around 2–3 years of age [28]. Normalized PVI is derived by calculating the difference in vowel duration (or vowel intensity) between adjacent vowels, divided by the average duration multiplied by 100.

Liam’s single word productions on the GFTA-2 conducted at 7;4 years, and the DEAP Inconsistency Assessment and multisyllabic word repetition task conducted at 10;5 years were used for lexical stress analysis. Three and 4 syllable real words were analyzed, with a trochaic (strong-weak; SW) or iambic (weak-strong; WS) stress pattern across the first 2 syllables. A total of 47 word tokens were included in the analysis (34 SW words; 13 WS words); acoustic measures were derived using Praat [29] according to previously published methods. PVIs for vowel duration (PVI_duration) and peak vowel intensity (PVI_intensity) were calculated.

Speech

Liam’s consonant inventory, syllable shapes, phonological patterns, and consonant and vowel accuracy from 3;10 to 10;5 years are shown in Table 3.

Table 3.

Liam’s speech features from 3;10 to 10;5 years

Liam’s speech features from 3;10 to 10;5 years
Liam’s speech features from 3;10 to 10;5 years

He had acquired all consonant sounds by 7;5 years and was able to produce a variety of syllable shapes. Consonant accuracy measured in percent consonants correct (PCC) improved with age (17% PCC at 3;10 years; 95% at 7;10 years). He had a number of delayed and atypical phonological patterns in his speech, with voicing, fronting, and gliding still evident at 10;5 years. Atypical patterns included initial consonant deletion. He had impaired performance of a number of speech tasks at 10;5 years, including poor repetition of nonwords and multisyllabic words and high token-to-token variability (DEAP inconsistency score 32%). The presence of inconsistent errors past 7 years of age is regarded as atypical (B. Dodd, personal communication). Errors evident on word repetition tasks included sound substitutions and omissions (e.g., /vʌlnrəbəl/ → /vʌnəbl/), syllable deletions (e.g., /pærəlɛl/ → /pærɛl/), metathesis (e.g., /ɛnəmi/ → /ɛməni/), and vowel errors, with more errors noted as syllable length increased (nonword repetition: 2 syllables 43% correct; 3 syllables 29% correct; 4 syllables 14% correct; 5 syllables 0% correct). Maximum repetition rate of monosyllables was slow (/ta/ 4.3 syllables/s; /ka/ 4.0 syllables/s), and he was unable to correctly repeat a trisyllabic sequence (pataka).

Lexical Stress Analysis (Table 4)

Words with a target SW stress pattern across the first 2 syllables should be produced with a positive normalized PVI, while words with a target WS stress pattern should be produced with a negative normalized PVI. At 7;4 years, Liam produced SW words with positive mean PVI_intensity but negative mean PVI_duration on average. The data in Table 4 suggest that he had difficulty coordinating duration and intensity parameters to produce the target prosodic patterns across multisyllable words. Children typically achieve adult-like stress contrastivity in words with a SW stress pattern by 3 years of age [28]. He had negative mean normalized PVI_duration and PVI_intensity at 7;4 and 10;5 years, indicating appropriate placement of stress on the second syllable in words with WS stress.

Table 4.

Mean normalised PVI for vowel duration and intensity at 2 different ages

Mean normalised PVI for vowel duration and intensity at 2 different ages
Mean normalised PVI for vowel duration and intensity at 2 different ages

The value of normalized PVI may also give an indication of lexical stress, with a larger value (either positive or negative) indicating a greater level of stress contrastivity. A PVI approaching zero represents more equal stress. At 7;4 years, the value of Liam’s PVI_duration means were small in magnitude for both SW (–5.74) and WS (–23.6) words. As a point of reference, PVI duration means between 22.4 (SD 25.8) and 49.6 (SD 26.8) for SW words, and –94.3 (SD 25.5) and –116.23 (SD 17.9) for WS words were reported in typically developing children aged 3–7 years [28], although these values are not directly comparable to Liam’s means as different tokens were used. Liam’s PVI intensity means were close to zero (SW 0.42; WS –0.01) indicating more equal stress. Similar means were evident at 10;5 years. Taken together, these findings suggest that Liam was producing speech with reduced stress contrastivity between adjacent syllables and that this persisted up to 10 years of age.

Language (Fig. 2; Table 5)

Liam had moderate-severe expressive language impairment from 3 to 8 years of age, with scores at or below the 5th percentile on the CELF. A shift was noted at 11 years, with average expressive language (standard score 85 at 11 years; 80 at 13 years; 83 at 15 years). This was in contrast to average receptive language skills (standard scores 80 or above) from 3 to 15 years. Of note, his receptive language scores fell significantly at 13 years with performance in the 4th percentile.

Table 5.

CELF subtest scaled scores

CELF subtest scaled scores
CELF subtest scaled scores
Fig. 2.

Liam’s Receptive Language Index (blue) and Expressive Language Index (orange) standard scores on the Clinical Evaluation of Language Fundamentals from 3 to 15 years of age. Index scores are on a normalised standard score scale that has a mean of 100 and a standard deviation of 15. Error bars reflect confidence intervals at 95% level.

Fig. 2.

Liam’s Receptive Language Index (blue) and Expressive Language Index (orange) standard scores on the Clinical Evaluation of Language Fundamentals from 3 to 15 years of age. Index scores are on a normalised standard score scale that has a mean of 100 and a standard deviation of 15. Error bars reflect confidence intervals at 95% level.

Close modal

Analysis of his performance on the different receptive and expressive language subtests revealed impairments across the domains of syntax, semantics, and morphology. His ability to apply word structure rules (Word Structure) and form semantically and grammatically correct spoken sentences (Formulated Sentences) were areas of relative weakness. Repetition of spoken sentences improved from 8;11 years (Recalling Sentences). He was able to interpret spoken sentences and directions of increasing length and complexity (Concepts and Following Directions; Sentence Structure), yet had difficulty listening to spoken paragraphs and understanding and answering questions about the text.

Academic Outcomes

NAPLAN results are reported on a 10-band scale spanning Grade 3 to Year 9, comparing an individual student’s performance to grade-level peers across Australia. Liam’s NAPLAN scores across all domains at age 8 years (Grade 3), 10 years (Grade 5), 12 years (Year 7), and 14 years (Year 9) relative to Australian students nationwide are shown in Figure 3.

Fig. 3.

Liam’s NAPLAN scores (denoted by x) in Grades 3, 5, 7, and 9 compared to the middle 60% of students in Australia in reading, writing, spelling, grammar/punctuation, and numeracy.

Fig. 3.

Liam’s NAPLAN scores (denoted by x) in Grades 3, 5, 7, and 9 compared to the middle 60% of students in Australia in reading, writing, spelling, grammar/punctuation, and numeracy.

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Liam’s reading, writing, spelling, and grammar/punctuation were below the national average in Grades 3 and 5. Reading and writing were particularly poor, with his performance at the minimum Australian standard for reading in Grade 3 (band 2) and for writing in Grade 5 (band 4). His phonological awareness skills were in the average range at 7;5 years (CTOPP Phonological Awareness standard score 97; Phonological Memory 70). A literacy assessment at 9;4 years revealed average reading and spelling (WRAT-4 Word Reading Standard score 89, Sentence Comprehension 92, Spelling 96). This disparity with the NAPLAN results likely reflects differences in test administration (WRAT spelling to dictation vs. NAPLAN error correction and proofreading) with more words spelt correctly when dictated [30]. An independent clinical evaluation of literacy skills in Years 5 and 6 revealed reading and spelling skills were 1–2 years below age expectations (Schonell Word Reading age equivalent 9 years and Spelling 8;9 years in Year 5/10;9 years and Word Reading age equivalent 9.11 years and Spelling 10.2 years in Year 6/11;10 years).

Improvements in all areas were evident in secondary school, and by his final year of NAPLAN assessment (Year 9), Liam was performing above the national average in reading, writing, and grammar/punctuation. He had average word reading (Word Identification standard score 87), reading fluency (Oral Reading fluency score 91), and listening comprehension (Listening Comprehension score 84) on an independent clinical evaluation of reading at 12;10 years (Woodcock Reading Mastery Test, 3rd Edition; WRMT-III). Yet difficulties with nonsense word reading (Word Attack standard score 77) and reading comprehension (Word comprehension standard score 78; Passage comprehension 61) were evident. His spelling scores on the NAPLAN continued to fall below the national average up to 14 years of age. His numeracy skills were strong relative to language-based domains, with scores at or above the national average in both primary and secondary school (8–14 years).

Our study is the first to report long-term speech, language, and academic outcomes in CAS from preschool to adolescence (3–15 years). Previously studies report 3 or 4 years follow-up, predominately from preschool (4–6 years) to school age (6–11 years). Liam made significant improvement over time, and at 15 years of age had intelligible speech, average receptive and expressive language skills, and scored above the national average in reading, writing, grammar/punctuation, and mathematics. Deficits in reading comprehension, decoding of nonsense words, and spelling persisted into adolescence. Liam had speech pathology intervention for a number of years, including several bursts of intensive therapy, thus it is important that these longitudinal changes are considered in light of this.

Speech Outcomes

Liam’s speech development mirrored other reported cases of CAS [3-7]. Over time, his speech became more intelligible and his consonant accuracy improved, with 95% PCC by 7 years. He had delayed and atypical phonological error patterns, including fronting, gliding, and voicing, which are commonly reported in school age children and adolescents with CAS [4, 7, 10, 31]. He also had persistent syllable structure deficits identified in other CAS cases, with frequent omissions (initial, medial, and final consonant deletion) evident up to 5;3 years and reduction of initial and final consonant clusters up to 6;7 years. Sound and syllable omissions were still apparent at 10 years in his responses to word and nonword repetition tasks, along with metathesis and vowel errors. Several studies report these types of errors (sound and syllable omissions, sound reversal and insertions, vowel errors) in the speech of older individuals with CAS [6, 31, 32]. These error types are diagnostic of CAS and may serve as a useful sign of the disorder in adolescents and adults whose conversational speech errors have largely resolved. This observation is supported by a recent study which found adults with a probable history of CAS had significantly more sequencing errors (e.g., assimilations, migration, metathesis, omissions, and insertions) than controls [33]. Prosodic errors also persisted, with reduced stress contrastivity evident at 10 years. This was not unexpected given that more than half of children with suspected CAS have excessive, equal, or misplaced stress, and these errors may be apparent as late as 14 years of age [34, 35]. Liam performed poorly on multisyllabic word and nonword repetition tasks, which is typically reported in CAS and a core deficit in cases with CAS and FOXP2 mutations [36, 37]. Deficits in nonword repetition and sequencing are postulated to be part of a sequential processing deficit underlying CAS [33].

Language Outcomes

Liam’s receptive and expressive language skills followed distinct trajectories over a 10-year period, with a shift noted around preadolescence (11–13 years). His expressive language improved, with standard scores progressing from below the 5th percentile at the start of primary school into the average range by his final year. His expressive language scores remained stable into adolescence. Other longitudinal studies suggest that the majority of children with CAS show little improvement at school age [4, 7, 8]. In a longitudinal cohort of 10 children with CAS, only one made gains in expressive language from 5 to 7 years, moving from the 5th to the 42nd percentile [4]. A second child had average expressive language at 9 years (standard score 86). These studies do not report language outcomes past 11 years of age, so it may be that changes in adolescence would have been seen given longer follow-up.

In contrast to expressive language, Liam’s receptive language skills declined sharply in adolescence, with scores below the 5th percentile at 13 years. Receptive language had previously been in the average range throughout preschool and primary school. He had a 6-month break in therapy at this time. A very low score on the Understanding Spoken Paragraphs subtest primarily drove Liam’s poor receptive language score at 13 years. Different modes of assessment vary in the cognitive load they place on the test-taker’s working memory, with attentional resource capacity/allocation and processing speed crucial to the understanding of spoken narrative [38]. Liam evidenced working memory impairments at 7 years that may have degraded his performance on the subtest. The low Understanding Spoken Paragraphs score may also be due to measurement error. The reliability of this subtest is not high (test–retest stability coefficient 0.76; internal consistency coefficient 0.70). There is also a degree of error reflected in the CELF scores, with Liam’s true receptive language score falling within a range from 65 and 83 (95% CI). Of note, Liam performed poorly on other receptive language tasks around 12–13 years (WRMT-III Passage Comprehension standard score 61, Word comprehension 78 at 12;10 years; CELF-4 Word Classes-Receptive 6 at 13;4 years) and deterioration in receptive language was evident in younger cohorts with CAS [4, 7]. Liam’s receptive language skills returned to the average range at 15 years.

Academic Outcomes

Liam’s poor NAPLAN performance from Grade 3 to Year 7 is likely a direct result of his speech and language impairment. Significant differences in NAPLAN outcomes were found for children in the Longitudinal Study of Australian Children who had speech and language problems, compared with typically developing peers [39]. Despite improvements in their NAPLAN performance over time, they had consistently lower scores across all tests (reading, writing, spelling, grammar, and numeracy) up to Year 7 and did not “close the gap.” Around preadolescence, Liam’s expressive language skills improved and by his final year of NAPLAN assessment (Year 9), he was performing above the national average in reading, writing, and grammar/punctuation. His spelling scores continued to fall below the national average up to 14 years of age.

Liam’s numeracy skills were strong relative to language-based domains, with scores at or above the national average in both primary and secondary school (8–14 years). Numeracy in CAS has received little attention to date. Around one-third of parents report their child with CAS has difficulties with mathematics [40]. One individual with persistent speech impairment in a large CAS kindred (PM family) scored 1.8 SD below the mean on the Numerical Operations subtest of the Wechsler Individual Achievement Test [41]. Ten other affected family members had standard scores of 80 or above. Of note, 6 PM family members with persistent speech deficits (aged 9–55 years) had specific learning disorder with impairments in reading and written expression.

There are limited data available on how language and literacy abilities evolve in CAS past primary school age. A handful of multiplex family studies have examined language skills in adults with CAS or suspected CAS in childhood. In the KE family with a FOXP2 mutation, affected family members (aged 9–75 years, mean 25.3 years) had comparable performance to adults with aphasia on tests of receptive grammar, nonword repetition, object naming, production of inflectional and derivational morphology, regular and irregular past tense production, non-word reading and spelling [42]. In the PM family, family members with persistent speech disorder had impaired expressive language (CELF-4 Expressive Language Index 40–70), while receptive language skills ranged from severely impaired to average (CELF-4 Receptive Language Index 63–92) [41]. Interestingly, family members with resolved speech sound disorder (13–51 years) had average receptive and expressive language skills. Liam’s reading and spelling outcomes appeared better than those of 2 adolescents with CAS aged 14;5 and 15 years, who had severely impaired skills despite years of phonics therapy [11]. Their spelling errors (deletions, intrusive sounds, perseverations) were reportedly analogous to their speech errors. At 15 years, Liam evidenced sound omissions, substitutions, and additions when reading aloud (e.g., soloist read as “solist” and satirical as “sartiriatical”) and spelling (e.g., permanent spelt “pernament” and enthusiastic spelt “infusiatic”). Deficits in nonword reading and spelling have also been reported in adult family members from other CAS kindreds [31, 32].

Taken together with previous longitudinal studies, our findings suggest that while diverse speech symptomatology may be seen in individuals with CAS, they may share a developmental pattern of speech improvement with age. As CAS is a symptom complex with a range of cognitive and other motor sequencing comorbidities [43, 44], the long-term trajectory for the broader CAS phenotype is more variable. This is likely due to distinct deficits underlying CAS [43]. For example, our case AN with CAS and a FOXP2 mutation had more severely impaired speech and language than Liam at a similar age (39% PCC at 8 years; receptive language 0.1 percentile, expressive language <0.1 percentile) [37]. We have established that both individuals have distinct underlying etiologies and associated neural phenotypes [45, 46]. Variants in a number of different genes have been identified in CAS, including FOXP2, GRIN2A, KANSL1, and BCL11A as well as 16p11.2 deletions and other copy number variations [37, 47-50]. This suggests multiple different subtypes of CAS with distinct speech and language trajectories.

Limitations of the Study and Future Directions

This is a single descriptive case study and as such had a number of limitations. Liam’s literacy skills were evaluated in research and clinical settings using different assessment tools, with variable findings. He performed in the average range on the WRAT-4 at 9;4 years; yet, his reading and spelling skills were 1–2 years below age expectations in years 5 and 6 on the Schonell Graded Word Reading and Spelling Test. The different psychometric properties of the tests likely account for these discrepant results. Scores on the Schonell are expressed as reading ages, based on a sample of British children from one location in the late 1960s/early 1970s. Conversely, the WRAT-4 reports standard scores and percentile ranks, based on a national sample of over 3,000 individuals. The limitations of age equivalent scores vs standard scores are well documented [51]. At this time, Liam scored below the national average on NAPLAN reading and spelling. This may due to the different mode of assessment used as highlighted previously. Assessment at 12;10 years on the WRMT III revealed difficulties with reading comprehension and reading nonsense words. Future studies examining reading and spelling using the same assessment tool will further clarify the evolution of literacy skills in CAS.

While language was examined using the same assessment tool from 3 to 15 years, the CELF provides only limited information regarding language skills. We have not explored Liam’s pragmatic or higher-level language skills, nor considered the impact of his metalinguistic skills on his language and literacy development. Future longitudinal studies investigating these aspects would provide a more comprehensive view of language in CAS over time.

The research speech tasks were independently rated by 2 experienced speech pathologists and consensus reached on discrepant ratings; however, inter-rater agreement was not determined.

We have detailed Liam’s speech therapy from 3 years of age, including frequency and targets of therapy, yet have not examined the correlation between therapy and the evolution of Liam’s speech, language, and literacy skills over time.

While the magnitude of Liam’s PVI means suggested deficits in stress contrastivity, his PVI data could not be directly compared to a sample of typically developing children aged 3–7 years [28] and 8–11 years [52], as different word tokens were used. Change in stress contrastivity with age in CAS would be an interesting area of future study.

Further long-term studies in a larger subset of individuals are needed to confirm the trends seen here. Yet, the results presented here a positive prognosis for speech, receptive and expressive language and academic areas such as writing and mathematics for a subset of individuals with CAS.

The authors thank Liam and his family for taking part in the study.

A.P.V. serves as chief science officer of Redenlab who provide assistance with acoustic analysis. The other authors report no disclosures.

S.J.T. supported by National Health and Medical Research Council (NHMRC) Postgraduate Scholarship (101777), Australian National University Gowrie Scholarship, and Speech Pathology Australia Nadia Verrall Memorial Research Grant. A.P.V. supported by NHMRC Fellowship (1135683). A.T.M. supported by NHMRC Practitioner Fellowship (1105008). I.E.S. supported by NHMRC Program Grant (628952) and Practitioner Fellowship (1006110). Project also supported by NHMRC Centre for Research Excellence Grant (1116976), NHMRC Project Grant (1127144), and Australian Research Council Discovery Project (DP120100285) to A.T.M. and I.E.S.

S.J.T. designed the study and wrote the manuscript. A.P.V. performed acoustic analysis. S.J.T and R.C. performed research and clinical assessments. S.J.T., B.P.-F., and A.T.M. performed phenotypic analysis. A.T.M., and I.E.S. supervised the study.

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