Definition and Components of Language and Speech

• Language: A communication system acquired through use, involving symbols sequenced to share attention and ideas.
• Speech: One mechanism for expressing language, but other methods like gestures, sign language, and iconic symbols can also be used.

Pre-linguistic Skills and Joint Attention

• Joint attention, the ability to share focus with another, is crucial for language acquisition.

Disorders Affecting Speech and Language Acquisition

• Defined by inclusionary (specific deficits) and exclusionary (absence of other explanations) criteria.
• Common conditions disrupt the typical progression of speech and language in children, measured relative to peers.

Diagnostic Criteria

• ICD-10 (WHO) and DSM-5 (APA) provide classifications:
  • ICD-10 distinguishes receptive, expressive, and mixed disorders.
  • DSM-5 groups these under "communication disorders" with subcategories:
    • Language disorder
    • Speech sound disorder
    • Childhood-onset fluency disorder (stuttering)
    • Social (pragmatic) communication disorder
    • Unspecified communication disorder

Speech Disorders

• Speech sound disorder: Persistent difficulty with speech sound production affecting intelligibility.
• Dysfluency (e.g., stuttering):
  • Repetition of sounds, syllables, or words; silent blocks; and associated physical movements.
  • Often resolves between ages 3-5 but can become chronic with risk factors like family history.

Pragmatic Language Impairment

• Affects everyday language use without the social and behavioral features of ASD.

Severe and Rare Conditions

• Childhood Apraxia of Speech (CAS)/Verbal Dyspraxia: Impaired motor planning for speech, debated underlying mechanisms.
• Dysarthria: Weakness or involuntary movements affecting articulation, often in acquired disorders.
• Phonation Issues: Problems with voice projection and breath control, worsening intelligibility.

Neurological Paroxysmal Disorders

• DSM-5 includes speech and language disorders linked to epilepsy, affecting development and acquired abilities.
• Certain anticonvulsants may exacerbate speech issues.

Prevalence and Demographics

1. Late Talkers (2-Year-Olds):

   • Approximately 15% of 2-year-olds exhibit delayed speech, termed "late talking toddlers."
   • Causes are multifactorial and include:
     • Family history of delayed language acquisition.
     • Socioeconomic factors, such as poverty and low maternal education.
   • Male sex, family history, and preterm birth are identified as risk factors.

2. Speech Delay in Early School Age (6-Year-Olds):

   • Overall prevalence: 3.8%.
   • Gender difference: More prevalent in boys (4.5%) than girls (3.1%).
   • Speech delay and language impairment comorbidity:
     • 1.3% overall.
     • 0.51% when the language impairment is specific (normal nonverbal intellect).
   • Persistent Specific Language Impairment (SLI):
     • 5-8% of children with SLI also experience speech delay.

3. Primary Specific Speech and Language Disorders (5–6-Year-Olds):

   • Prevalence is 7.4% overall (8% boys, 6% girls) based on a composite language score of below 1.25 SD.
   • Parental education is associated, with lower levels linked to higher prevalence.

Risk and Long-Term Implications

• Persistent phonological difficulties (e.g., deletion/substitution errors) can lead to:

  • Reading and spelling challenges.
  • Academic struggles.
  • Social acceptance issues in school.

• Intellectual impairment is associated with persistent speech and language delays in kindergarten:

  • Affects 50% of girls.
  • Affects 20% of boys.

Screening and Identification

• No evidence supports targeted screening for speech and language delay to improve outcomes.
• Most cases are identified through clinical surveillance or presentation.

Speech Production and Phonological System

• Speech relies on a phonemic system:

  • Phonological Component: Rules for sound contrast and structure.
  • Articulatory Component: Sensory-motor movements of speech organs.
  • Praxic Component: Planning and programming spatiotemporal movements for speech.
  • Prosodic Component: Stress, intonation, and voice quality conveying meaning and affect.

• Development of Speech Sounds:

  • By 6 months, infants can produce most of the 46 phonemes in English.
  • Early consonants: ‘p, b, t, d’ (anterior articulation).
  • Later consonants: ‘k, g’ (posterior articulation) and ‘r, l, s, th, ch, y, z’ (more complex sounds).

Speech Milestones

• Single Words: Expected by 20 months for girls and 23 months for boys (97th centile).
• Simple Sentences: Three- to four-word sentences by 3 years for both genders.
• Progression:
  • 6–7 months: Syllabic babble (e.g., ba, da).
  • 12 months: Two to three words with meaning.
  • 21–24 months: Two- to three-word combinations.
• 2–3 years: Vocabulary explosion (up to 500 words in 6 months).
• Mean Length of Utterance (MLU): Formula: Child's age in years + 1.
  • Example: A 3-year-old typically forms sentences with an average of four morphemes.
• Intelligibility (Rule of Fours):
  • 1-year-old: 25% understandable.
  • 2-year-old: 50% understandable.
  • 3-year-old: 75% understandable.
  • 4-year-old: ~100% understandable.

Assessment Tools

• Communication Development Inventories (e.g., MacArthur CDI):

  • Measure emerging communication skills between 16–30 months.
  • Examples: UK SureStart Language Measures, MacArthur Communicative Development Inventory.

• Standardized Measures:

  • Used by speech and language therapists to evaluate:
    • Speech and language development.
    • Daily life impact of communication difficulties.

Key Insights

• Girls and first-born children often develop speech earlier and exhibit more advanced sentence use.
• Speech development involves a complex interplay of motor skills, cognitive processes, and environmental interactions.
• Early monitoring and standardized assessments are essential to identify and address delays effectively.

Key Observations

• Speech Sounds:

  • Progress from simpler sounds (e.g., p, b, t) to more complex ones (e.g., r, th).
  • Typical processes (e.g., fronting, consonant harmony) resolve as speech matures.

• Language Comprehension:

  • Evolves from recognizing simple tones and words to understanding complex sentences and implied meanings.
  • By age 7, children can grasp nuanced language such as humor.

Language Comprehension and Recognition

• Processes Involved:
  • Auditory Processing: Handling and interpreting sound information.
  • Phonological Processing: Knowledge and manipulation of speech sounds.
  • Lexical Processing: Understanding word-level meanings.
  • Semantic Processing: Comprehension of broader meanings in context.
• Breakdowns in Language Comprehension:
• Specific Language Impairment (SLI) often involves:
  • Poor spoken word recognition.
  • Potential deficits in auditory processing, phonology, lexical access, or semantics.

Specific Language Impairment (SLI)

• Debated Causes:

  • Domain-Specific Deficit: Affects grammar or linguistic structures.
  • Processing Deficit: Issues with auditory temporal processing
  • Cognitive Deficits: Reduced procedural memory or general processing capacity 
  • Likely a combination of these factors.

• Memory Implications:

  • Expressive Language Disorders: Primarily affect verbal memory.
  • Mixed Receptive-Expressive Disorders: Affect both verbal and visual memory, including working memory.

• Differentiation from ASD:

  • Receptive language impairments and ASD can overlap (e.g., echolalia).
  • Language regression in the second year is a key indicator of ASD.

Neural Basis of Language

1. Developmental Progression:

   • Phonological Processing: Present in the first months of life.
   • Semantic Processing: Begins around 12 months.
   • Syntactic Processing: Matures by 30 months.

2. Functional Abnormalities in SLI:

   • Structural and functional abnormalities in:
     • Inferior Frontal Cortex
     • Temporal Cortex
   • Reduced left asymmetry in the planum temporale.

3. Hemisphere Specialization:

   • Left Hemisphere:
     • Syntactic and lexical-semantic processing (segmental features).
   • Right Hemisphere:
     • Prosodic accentuation and boundary marking (suprasegmental features).
   • Interhemispheric Integration:
     • Via the posterior corpus callosum for coordination between hemispheres.

Neurophysiological Evidence

• Mismatch Negativity (MMN):

  • Reflects preconscious processing of sound discrimination.
  • Linked to impaired language development in preterm children and those with SLI.

• Event-Related Potentials (ERPs):

  • Delayed or atypical patterns in infants with high familial risk for SLI.

• Functional MRI (fMRI):

  • Abnormal activity in:
    • Temporal cortex.
    • Orbitofrontal dorsolateral and medial frontal cortex.

Connectivity and Brain Maturation

• Early Connectivity:

  • Ventral pathway (temporal → inferior frontal gyrus): Present at birth.
  • Dorsal pathway (temporal → premotor cortex): Matures later, supporting complex language functions.

• Developmental Disorders:

  • May result from disconnection between language-relevant regions, affecting functional connectivity (Perani, 2011).

Genetics of Primary Speech and Language Impairments

Primary speech and language impairments have a strong genetic basis, supported by family history and twin studies. 

Genetic Background

1. Family and Twin Studies:

   • Family history of late talking predicts "late talking toddlers" (Zubrick et al., 2007).
   • Twin studies highlight heritability in speech and language development (Dale et al., 1998).

2. Genetic Complexity:

   • The genetic contribution is heterogeneous and multifaceted, involving multiple linkage regions and genes.
   • Linkage studies have identified regions on chromosomes 16q and 19q (SLI Consortium, 2004; Newbury et al., 2005).

Key Genes and Variants

1. CNTNAP2:

   • Variants in the Exon 13–15 region influence early language acquisition (age 2).
   • Associated with:
     • SLI (Specific Language Impairment).
     • Increased susceptibility to autism when combined with other risk factors.
   • Encodes a neurexin protein involved in neuronal cell adhesion.
   • Enriched expression in language-related brain circuits 
   • Heritable marker: Linked to nonsense word repetition tasks, a measure of phonological working memory.

2. FOXP2:

   • A transcription factor that regulates CNTNAP2.
   • Mutations cause a rare monogenic form of speech and language disorder, as seen in the ‘K family’ 

Phenotypes and Chromosomal Anomalies

1. Sex Aneuploidies:

   • Klinefelter Syndrome (XXY), Triple X Syndrome (XXX), and XYY Syndrome:
     • May present with overlapping phenotypes to primary SLI.
     • Require investigation in speech and language impairment 

2. 22q11 Deletion Syndrome:

   • Affects up to 1/3 of children with velopharyngeal insufficiency (hyper/hypo nasal phonation).
   • Microarray analysis is recommended as a first-line test (Burnell et al., 2014; Ockeleon et al., 2014).

Clinical Implications

1. Genetic Investigations:

   • While multifactorial polygenic transmission is not yet clinically applicable, genetic testing is important in:
     • Primary language impairments with atypical presentations.
     • Secondary language impairments caused by identifiable genetic conditions.

2. Recommendations:

   • Microarray analysis: A first-line genetic test in children with suspected speech and language disorders, particularly those with associated structural or phonation anomalies.

Syndromes of Sex Aneuploidy and Associated Language Phenotypes

47 XYY Syndrome

• Genetic Characteristics:
  • Primary nondisjunction of the Y chromosome.
  • ~10% are mosaics (46 XY/47 XYY).
  • Incidence: ~1 per 1,000 male live births.
• Language Phenotype:
  • Common speech and language difficulties:
    • Speech disfluency.
    • Word-finding problems.
    • Expressive language deficits (e.g., difficulty with narratives).
    • Problems understanding complex sentence structures.
  • Auditory memory problems are frequent.
  • Reading difficulties are prevalent.
  • IQ: Slightly below the population mean but can range to superior levels.

47 XXY Syndrome (Klinefelter Syndrome Group)

• Genetic Characteristics:
  • Surplus of X chromosomes in males.
  • Caused by meiotic disjunction during gametogenesis (ovum or sperm).
  • ~50% are maternally derived.
  • Incidence: ~1 per 750 male births.
• Language Phenotype:
  • Specific expressive speech and language deficits:
    • Word retrieval issues.
    • Syntax problems.
    • Difficulty giving narratives.
  • Underlying auditory processing and short-term auditory memory deficits.
  • Cognitive Profile:
    • Verbal IQ is lower than performance IQ.
  • Behavioral Characteristics:
    • Often socially unresponsive.
    • Tendency to withdraw from group activities.

47 XXX Syndrome (Triple X Syndrome)

• Genetic Characteristics:
  • Arises from primary nondisjunction of maternally or paternally derived X chromosomes.
  • Incidence: ~1 per 1,000 female births.
• Language Phenotype:
  • Severe expressive language delay is common.
  • Poor short-term auditory memory is often observed.

Turner Syndrome (45 X and Variants)

• Genetic Characteristics:
  • Second X chromosome is absent or abnormal.
  • Incidence: ~1 per 2,000–2,500 female births.
• Language Phenotype:
  • Verbal skills are generally intact, but:
    • Verbal fluency may be reduced.
  • Behavioral Characteristics:
    • Challenges with peer relationships are common.

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• Common Themes Across Syndromes:
  • Expressive language difficulties (e.g., narratives, syntax, word retrieval).
  • Auditory memory and processing deficits.
• Cognitive Profiles:
  • Verbal IQ often lower than performance IQ, except in Turner Syndrome.
• Social Challenges:
  • Social withdrawal in 47 XXY.
  • Peer relationship difficulties in Turner Syndrome.

References

Arzimanoglou, A., O'Hare, A., Johnston, M., & Ouvrier, R. (Eds.). (2018). Aicardi's Diseases of the Nervous System in Childhood (4th ed.). Mac Keith Press.