High-risk factors for congenital hearing loss include a family history of congenital hearing loss or delayed-onset sensory hearing loss of childhood, physical findings (birthweight less than 1,500 grams, craniofacial anomalies, the variable physical signs of Waardenburg’s syndrome), and maternal prenatal infections (cytomegalovirus, syphilis, rubella, herpes).
Prelingual deafness can also arise from severe vital function depression at birth when Apgar scores are in the 0 to 3 range at five minutes. Hyperbilirubinemia severe enough to require exchange transfusion; treatment of postnatal infection with ototoxic drugs, such as gentamicin, tobramycin, kanamycin, and streptomycin; systemic infections including meningitis, congenital syphilis, mumps, and measles all can result in bilateral profound deafness. Closed head trauma and neurodegenerative diseases including Tay-Sachs disease, neurofibromatosis, Gaucher’s disease, Niemann-Pick disease, and myoclonic epilepsy are rare additional etiologies of deafness that manifest themselves in childhood.
Genetic causes for prelingual and postlingual deafness are thought to account for 50 percent of the sensorineural hearing loss in childhood. The remainder are either environmental (about 25 percent) or sporadic idiopathic (about 25 percent). Genetic hearing loss can be congenital or delayed, progressive or stable, unilateral or bilateral, syndromic or nonsyndromic. The majority of genetic hearing losses are thought to be recessive (about 75 percent); 20 percent are attributable to dominant genes and a small percentage are X-linked disorders. Autosomal dominant disorders include Waardenburg’s syndrome (20 percent associated with hearing loss); Stickler’s syndrome (sensorineural or mixed hearing loss, 15 percent); branchiootorenal syndrome; Treacher Collins syndrome (sensorineural or mixed hearing loss); neurofibromatosis II; and dominant progressive hearing loss. Autosomal recessive disorders associated with sensorineural hearing loss are Pendred’s syndrome, Usher syndrome, and Jervell and Lange-Nielsen syndrome. Sex-linked syndromes associated with sensorineural hearing loss are Norie’s syndrome, otopalatodigital syndrome, Wildervaank’s syndrome, and Alport’s syndrome. Most hereditary hearing loss in early childhood is “nonsyndromic,” that is, there are no other apparent abnormalities. While mutations in any of dozens of genes can cause hearing loss, a gene that controls the production of a protein called connexin 26 is responsible for a large proportion of such cases, with studies on various populations reporting differing prevalences (Dahl et al., 2001; Erbe, Harris, Runge-Samuelson, Flanary, and Wackym, 2004; Gurtler et al., 2003; Nance, 2003).
Recently a condition termed “auditory neuropathy” (Starr, Picton, Sininger, Hood, and Berlin, 1996) has been identified in individuals with severe to profound hearing loss. Patients with this condition typically