Table 1 Speech disorder phenotypes.
From: Genetic architecture of childhood speech disorder: a review
Speech disorder | Operational definition | Prevalence | Natural history & tractability | Aetiology |
|---|---|---|---|---|
Articulation [39] | Disorder of speech sound production. Consistently distorts one or more speech sounds (phones) in absence of known cause (e.g., hearing loss, cleft palate, missing teeth). Prosody unaffected. | 5% preschoolers | Highly tractable, majority resolve by 7 years^ | Complex multifactorial |
Phonological [39] | Disorder in understanding/use of speech sounds (phonemes) of language to convey meaning. Child makes atypical errors seen in <10% of peers, e.g. phonological process of “backing”, where a posteriorly produced sound is used in place of an anteriorly produced sound, e.g., says key for tea, or gog for dog. Vowels, prosody unaffected. | 5% preschoolers^ | Highly tractable, majority resolve by 7 years | Complex multifactorial |
Stuttering [40] | Disorder of speech fluency characterized by repetitions (of sounds, syllables, words and/or phrases), prolongation of sounds, and hesitations and/or blocks. | 10% preschoolers | Tractable in some, 65% developmental forms resolve by 7 years | Monogenic, complex multifactorial |
Dysarthria [13] | Disorder of central or peripheral nervous system affecting neuromuscular control and tone, e.g., spasticity, ataxia, fluctuating tone, involuntary movements. This results in imprecision of speech due to impairments in one or more areas of phonation, articulation, prosody, resonance. | 0.1% preschoolers | Less tractable, never resolves but responsive to therapy | Monogenic, complex multifactorial |
Childhood apraxia of speech (CAS) [7] | Disorder of motor programming/planning. Core features: 1. inconsistent production of consonants and vowels across repeated productions, 2. lengthened and impaired coarticulatory transitions between sounds and syllables (e.g., omissions of sounds, vowel errors, repetitions), 3. inappropriate prosody/disrupted intonation, e.g., placing stress on a typically unstressed syllable or using equal stress across all syllables. | 0.1% preschoolers | Less tractable, rarely resolves but responsive to therapy | Monogenic, complex multifactorial |
