Research Tuesday January Edition – Speech Impairment in Down Syndrome: A Review

Once again I am joining the ranks of SLPs who are blogging about research related to the field of speech pathology.   Today I am reviewing a 2013 article in the Journal of Speech, Language, and Hearing Research, by Kent and Vorperian, which summarizes research on disorders of speech production in Down syndrome (DS)

Title: Speech Impairment in Down Syndrome: A Review

Purpose: To inform clinical services and guide future research on assessment and treatment of DS.

Method: The authors performed searches using Medline, Google Scholar, Psychinfo, and HighWire Press, etc., for articles published since 1950 related to 4 areas of speech production: (a) voice, (b) speech sounds (including articulation, phonology and resonance), (c) fluency and prosody, and (d) intelligibility in individuals with DS.

Summary:

Craniofacial Anatomy (Highlights):

• Compared to controls individuals with DS have reduced volumes of the airway, andible, adenoid and tonsil and a smaller mid- and lower-face skeleton and hard palate
• Small maxilla but a normal mandible
• Poorly differentiated midface muscles and muscle variation which is not seen in controls
• Interestingly, “assessments of stiffness do not necessarily support the contention that hypotonia is a pervasive characteristic (Connaghan, 2004)”
• Furthermore, children with DS do not have true macroglossia but rather have relatively large tongues compared to the  bony confines of the oral cavity.
• Conclusion:  The craniofacial anatomy in DS is characterized by a compact mid-and lower-face skeleton, a tongue of average size, and a palate that is high and often shelf-like. The developmental trajectory of orofacial characteristics is not well established.

Voice: Data on voice in DS have been collected from about 600 participants, including children and adults and indicate soem degree of dysphonia in individuals with DS.

• Newborn infants have a disturbed cry which is most likely due to abnormalities in respiratory and laryngeal function
• Vocal pitch and fundamental frequency
  • Review of studies yielded mixed results on vocal f0, with the majority of studies reporting no difference between individuals with DS and TD controls.
• Voice quality: 
  • variability in results among studies so results are inconclusive 
    • perceptual studies note breathiness and roughness
    • some acoustic studies report increased frequency perturbations (e.g., higher values of jitter), amplitude perturbations (e.g., higher values of shimmer) and increased noise in phonation (e.g., reduced signal-to-noise ratio, S/N)

Speech Sound Disorders:—

• —Delay in canonical babbling

• Articulatory and phonological studies show inconsistent articulatory errors as well as both delayed (i.e., developmental) and disordered (i.e., non-developmental) patterns in children with DS by ~ 3 years of age

• —Speech difficulties are not highly correlated with language and cognition but rather related to anatomy and motor control issues 
• Nasality may be caused by abnormalities in the nasal cavities, sinuses and the tissue boundaries between the oral and nasal passages

Fluency and prosody:

•  Stuttering and/or cluttering occur in DS at rates of 10 to 45%, compared to about 1% in the general population.
• Research also points to significant disturbances in prosody due to have limitations in the perception, imitation and spontaneous production of prosodic features secondary to

  motor difficulties, speech/motor coordination issues, and/or segmental (articulatory) errors that impede the effective production of speech across multisyllabic sequences.

Intelligibility:

• Serious problem in DS, that persists throughout life for many individuals and interferes with social and vocational pursuits
• Disturbances in voice, articulation and resonance, fluency and prosody all contribute to decreased intelligibility

Co-occurrence Factors:

• “Speech problems in DS may be related to peripheral factors such as anatomic differences in the vocal tract, impaired hearing acuity during recurrent otitis media, and impaired motor function (dysarthria and/or apraxia) or to central factors such as language and cognitive dysfunctions. It is likely that several factors interact in the development and persistence of speech disorders in DS”. 
  

Implications:  Given the latest findings, it is very important for SLPs to perform detailed and comprehensive speech assessments and engage in targeted treatment planning in order to improve DS individuals functioning in social, academic and vocational areas.