This study will try to identify and understand the genetic factors that lead to an inner ear malformation called "enlarged vestibular aqueducts", that can be associated with hearing loss.
Patients with sensorineural hearing loss with or without inner ear malformations and their parents and siblings may be eligible for this study. Participants and their immediate family members, may undergo some or all of the following tests and procedures:
- Medical and family history, including questions about hearing, balance and other ear-related issues, and review of medical records.
- Routine physical examination.
- Blood draw or buccal swab (brushing inside the cheek to collect cells) - Tissue is collected for DNA analysis to look for changes in genes that may be related to hearing loss.
- Hearing tests - The subject listens for tones emitted through a small earphone.
- Balance test (VEMP) to see if balance functions of the inner ear are associated with the hearing loss Electrodes will be placed behind your ear and at the base of your neck. From a reclining position, you will be asked to raise your head while clicking sounds are played into your ears. - Ultrasound tests - An inner ear malformation called EVA (enlargement of the vestibular aqueduct) indicates that a genetic disorder called Pendred syndrome may be the cause. Because thyroid abnormalities are also associated with Pendred syndrome, an ultrasound examination of the thyroid gland may be done.
- Computed tomography (CT) and magnetic resonance imaging (MRI) scans - These tests show the structure of the inner ear. For CT, the subject lies still for a short time while X-ray images are obtained. For MRI, the patient lies on a stretcher that is moved into a cylindrical machine with a strong magnetic field. The magnetic field and radio waves produce images of the inner ear. The radio waves cause loud thumping noises that can be muffled by the use of earplugs.
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Nonsyndromic hereditary hearing impairment is a genetically heterogeneous disorder that can be caused by mutations in any one of at least 60 different genes. Enlargement of the vestibular aqueduct (EVA) is a radiologic finding known to be associated with mutations in one of these genes, the Pendred syndrome gene (SLC26A4, formerly known as PDS). EVA may thus serve as a clinically useful marker to facilitate the diagnosis of hearing impairment. Recent data from our laboratory and others indicates that only a subset of individuals with EVA have SLC26A4 mutations, and therefore some EVA cases are likely to be caused by other genes, nongenetic factors, or a combination of these etiologies. Families with two or more individuals with hearing impairment and EVA will be enrolled in this study in order to identify other genetic factors that cause EVA. Siblings and parents may also be enrolled in order to define inheritance and to perform molecular genetic analyses.