Auditory and Visual Processing in Williams Syndrome

Article excerpt

ABSTRACT

WiUiams syndrome is a neurodevelopmental disorder caused by a deletion on chromosome 7. It is characterized by a range of medical problems in addition to severe impairments in visuospatial processing and oversensitivity to sounds, including hypersensitivity to sounds (hyperacusis) and extreme fear from sounds (phonophobia). In spite of impairments in visuospatial processing, object and face processing abilities are relatively preserved in WS. The present review discusses the growing research in the field linking the unique sensory phenotype in WS with underlying structural and functional brain abnormalities. In addition, possible associations between the genetic defect and the abnormal sensory processing are presented. Because Williams syndrome is etiologically homogeneous, it may serve as a model to promote understanding of visuospatial and auditory processing in humans. The findings may also have important implications for other developmental psychopathologies, such as autism, schizophrenia and attention deficit hyperactivity disorder.

'When I hear the sound of an electric drill,

I feel as if it is drilling into my body."

Tamar is a 16-year-old girl with Williams syndrome who has had phonophobia and hyperacusis since an early age.

INTRODUCTION

Williams syndrome (WS) is a neurodevelopmental disorder caused by a hemizygous microdeletion of approximately 1.6 Mb containing -28 genes on the long arm of chromosome 7 (7qll.23). Its estimated prevalence ranges from 1:7500 to 1:20000 live births (1). Affected subjects have a wide range of medical diseases and a unique behavioral and cognitive profile. The main physical characteristics are typical faces, supravalvular aortic stenosis, failure to thrive, short stature, transient neonatal hypercalcemia, and delayed language and motor development (2, 3). Behaviorally, WS subjects have a strong social appetite and a low level of social fear (4). The mean cognitive level is within the range of mild to moderate retardation, with some peaks and valleys in mental domains, particularly severe visuospatial construction deficits accompanied by a relative strength in expressive language (5) and relatively spared face and object recognition. In addition, subjects have a strong attraction to music and a strong auditory fascination alongside extreme hyperacusis and phonophobia.

Because WS is etiologically homogeneous, it serves as an excellent model for the study of the biological developmental processes underlying sensory processing in humans. The findings may also have important implications for other developmental psychiatric disorders associated with pathological sensory processing and sensitivity, such as autism, schizophrenia, post-traumatic stress disorder, and attention deficit hyperactivity disorder. The aim of this work was to review the current research linking the auditory and visual abnormalities in WS with underlying impairments, as seen in neuroimaging and electrophysiological findings. Possible associations between the WS chromosomal deletion and the abnormal sensory processing are presented as well.

AUDITORY PROCESSING

PERIPHERAL FINDINGS

Middle-ear morbidity in WS is common; the reported incidence of otitis media ranges from 19% to 61% (6, 7). In the inner ear, auditory and electroacoustic findings in subjects with WS have indicated a mild cochlear hearing loss in the high frequencies, which tends to worsen with age (8-10), while prolonged cochlear nerve conduction time is indicated in brainstem auditory evoked response (BAER) (11). Findings reveal an association of cochlear hearing loss with acoustic reflex dysfunction in WS (1 1). Moreover, preliminary studies have suggested a deficit in the efferent auditory system which modifies cochlear function (7, 12). Acoustic reflex as well as the efferent auditory system protect against loud sound, and their dysfunction in WS may contribute to cochlear vulnerability especially to repeated exposures to high level sounds. …