Understanding Hereditary Nerve Deafness

Audiological characteristics of the Monge family of Costa Rica

“…Congenital deafness attributed to sex-linked origin is estimated between 1 percent (Proctor and Proctor, 1967;Ruben and Rozycki, 1971) and 3 percent (Hereditary Deafness Public Service Programs, 1975;Konigsmark, 1972).…”

“…Most hereditary hearing losses are due to mutations on non-sex chromosomes, with approximately 70 percent (Anderson and Wedenberg, 1968;Fraser, 1964) to 90 percent (Paparella et al, 1975;Proctor and Proctor, 1967) caused by autosomal recessive transmission. Holmes (1977) reports a total of 947 identified genetic mutations of autosomal recessive origin with at least 30 (Brown, 1967) to 45 (Sank, 1969) of these abnormal genes known to cause hearing loss.…”

“…Referred to as the penetrance of a trait, ranging from complete to nearly zero with any given type of abnormal gene, this statistical concept measures the proportion of individuals carrying a specific genetic mutation who actually manifest the expected trait (Brown, 1967;Schuknecht, 1967 (Bergstrom, 1976;Proctor and Proctor, 1967). Therefore, 80 percent of those who display other characteristics of the syndrome, such as white forelock, will have normal hearing.…”

“…Teig (1968) demonstrated a higher incidence of pathological tone decay or auditory adaptation among subjects with inherited deafness whose hearing levels exceeded 50 dB. Furthermore, histological studies performed on temporal bone tissues derived from cases with hereditary deafness revealed degenerative changes secondary to cochlear involvement, including atrophy of the spiral ganglion and central nuclei (Konigsmark, Mengel, and Berlin, 1971;Makishima and Snow, 1975;Proctor and Proctor, 1967). While most research delineates the cochlea as the primary site of lesion in cases of inherited, low frequency deafness, it becomes apparent that more central structures may become involved, particularly as the deafness advances.…”

“…A physiological change in the cochlear apex may occur as the result of alterations in the biochemical/bioelectrical consistency of the endolymph (Paparella et al, 1975;Proctor and Proctor, 1967).…”