Academic journal article Journal of Medical Speech - Language Pathology

Acoustic Analysis of Voice and Speech Characteristics in Presymptomatic Gene Carriers of Huntington's Disease: Biomarkers for Preclinical Sign Onset?

Academic journal article Journal of Medical Speech - Language Pathology

Acoustic Analysis of Voice and Speech Characteristics in Presymptomatic Gene Carriers of Huntington's Disease: Biomarkers for Preclinical Sign Onset?

Article excerpt

Purpose: The study compared presymptomatic carriers of expanded CAG repeat in the huntingtin gene with matched control participants to determine whether measures of speech motor variability and timing, already found to be significantly different in manifest Huntington's disease (HD), are significantly different for individuals at risk for HD. Measures included spectral characteristics of sustained vowel phonation, voice onset time, diadochokinetic variability, utterance duration, and speech rate changes.

Method: Eighteen carrier participants and matched control participants performed diadochokinetic tasks, produced vowels, and repeated sentences at habitual and increased speed.

Results: The carrier group showed significantly greater variability in syllable duration for intratrain coefficient of variation of duration; lower mean number of syllables per breath; lower diadochokinetic rates; lower mean duration for vowels; and higher mean jitter, shimmer, and noise--harmonic ratio (NHR).

Backward stepwise logistic regression retained three variables in the model: intratrain coefficient of variation of duration, repetition rate for /path', and mean NHR. Discriminant analysis constructed a prediction equation. The discriminant function showed strong accuracy for classifying participants.

Conclusions: Individuals at risk for HD showed increased speech variability, reduced repetition rate, and vocal instability. Speech rate, speech and vocal stability, and vocal endurance may ultimately be used to identify presymptomatic carriers for preclinical signs.

INTRODUCTION

Huntington's disease (HD), an inherited, progressive disorder, involves gradual degeneration of neurons in the basal ganglia and cerebral cortex, characterized clinically by an extrapyramidal movement disorder, cognitive deficits, and psychiatric impairments (Squitieri et al., 2000). The definition of disease onset is based on the presence of motor impairments consistent with HD. Cell death in HD may be attributable to impaired energy metabolism, free radical generation, excitotoxicity, inhibition of transcription, and other factors (Shannon, 2004b). Although the first signs of the disease are typically seen in middle age, signs can appear as early as childhood or adolescence (Freed, 2000). The genetic marker associated with HD is an expanded number of CAG repeats on the IT15 gene on chromosome 4 (Huntington's Disease Collaborative Research Group, 1993). Research has shown that the number of CAG repeats is inversely correlated with the age of onset of HD (Duyao et al., 1993). Pre-symptomatic identification of changes, whether in cognition, motor behavior, speech production, or imaging biomarkers, would allow for possible use of disease-modifying medication early in onset or even before symptoms appear (DeKosky & Marek, 2003). Striatal atrophy begins years before the onset of clinical symptoms of manifest HD, and Aylward et al. (2004) found that 6 of 17 pre-symptomatic participants observed longitudinally showed reduction in striatal volume to between one-third and one-half of normal volume at the time of clinical onset. Although there is presently no proven neuroprotective therapy for HD, a trend toward slowing of disease progression has been observed for manifest HD with coenzyme Q (Shoulson, 2004). Ultimately, treatment directed toward inhibiting disease progression could be given preclinically to delay or prevent HD. Consistent with that goal, the present study sought to identify potential speech production differences.

Involuntary movements are generally the first reported symptom in the diagnosis of HD (Kirkwood, Su, Conneally, & Foroud, 2001). Choreic movements are most commonly seen (Freed, 2000). Bradykinesia, irregular timing of movements, and motor impersistence accompany the choreic movements, and dystonia appears over time. People with HD have shown abnormalities in motor control and processing of sensory information, and voluntary motor performance is affected both for execution of simple movements and for motor programming of complex movements (Thompson et al. …

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