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Causation of Permanent Unilateral and Mild Bilateral Hearing Loss in Children Trends in Amplification \i>lum< U Number I MaitdjJSOi I7-2Ï «. 20(m S|ii| Publ«|»iti<ms lO.1177/lO84ifaBO731 WSS hosted nl Anne Marie Tharpe, PhD, and Douglas P. Sladen, PhD Children with permanent unilateral or mild hilateral hearing loss have heen a focus of concern hy audiologists, educators, and physicians for at least 2 decades. These c hildren are know n to he at risk for psychoeducational difficulties. However, despite this concern, little has heen learned ahout the causative factors of these hearing losses and how those factors might he contrihuting to child development. Ihis review of known causes of permanent unilateral and mild hilateral hearing loss in children is meant to draw attention to the importance ofthe search for etiologic factors. iTiat is, the identification of the hearing loss should not signal the end of the diagnostic process hut, rather, the heginning of a search for causation. With the comhined efforts of audiologists, otolar\ngologists, pediatricians, geneticists, and other medical professionals, we may enhance our understanding of the primary causes of unilateral and mild hilateral hearing loss and, jx-rhaps, create links hetween causative factors and ¡wychosocial and psychoeducational outcomes. nilateral (UHL) and mild bilateral (MBHL) permanent hearing loss have long heen implicated for putting children at risk for academic difficulty,'"^ For purposes of this article, the term "mild" hilateral hearing loss may include v\hat are often termed "minimal" degrees of loss. Bess et al** defined minimal degrees of hearing loss as (1) unilateral sensorineural hearing loss, defined as av crage airconduction thresholds (O.S, 1.0, 2.0 kHz) 20 dB HL or more in the impaired ear and an average air-hone gap no greater than 10 dB at LO, 2.0, and 4.0 kHz and average air-conduction thresholds in the normal hearing ear of IS dB I IL or less; (2) hilateral sensorineural hearing loss, defined as average pure-tone thresholds hetween 20 and 40 dB HL hilaterally with average air-hone gaps no greater than 10 dB at frequencies 1.0, 2.0, and 4.0 kHz; and (3) highfrequency sensorineural hearing loss defined as airconduction thresholds greater than 25 dB HL at 2 or more frequencies ahcne 2 kHz (ie, 3.0, 4.0, 6.0, or 8.0 kll/) in I or hoth ears with air-hone gaps at .T.O and 4.0 kHz no greater than 10 dB. On average, children with these losses have high academic failure rates as compared v\ith those of their normal hearing peers.'^'' The psychoeducational and psychosocial implications of UHI and MBHL are rcviev\ed earlier in this issue hy Tharpe.^ Despite considerahle interc st in the effects of these losses on child development, little attention has heen paid to the underlying etiologies. In fact, contemporary reports of causes of LHL are no more illuminating than reports from the 1960s through the 1980s—hefore newhorn hearing screening. That is, earlv reports indicated that hetween 359r and 65% of children with UHL had unknown etiologies.'•''•"' More tecentiv, in reports from the 1990s, unknown etiology was again reported to ¡lecount for approximately 3S% to 60% of cases of Ulli ."•'- Ihis is indeed surprising given the recent completion of the sequencing ofthe human genome and other medical advances that have improved our ahility to identify genetic, metaholic, and viral causes of hearing loss in infancy, lhe most commonly reported known etiologies of UHL include viral complications (approximately 25%),'•'"'•'" meningitis (approximatelv 15%),''"'head trauma (approximately S^ to 12%),"' prenatal or perinatal disorders (12%),^ and genetic disorders. U From tho \andcrbill Hill Wilkerson Center, University Medical Center. Nashxillc. Tennessee. Vanderbilt Address correspondence to: Anne Marie Tharpe, PhD, Vanderbilt I5ill Wilkerson Center, 121 S 21st A\e Soulb. #8.^10, Meiiical Center Last, Soutb Tower, Nashville, I N .^72^2-8242; e-mail: [email protected]. Keywords: unilateral; mild hilateral; children; hearing loss; etiology 17 18 Trends in Amplifitution I Vol, 12. No. 1, Marc h 2008 Even less is known about the etiology of permanent MBHL primarily because moderate to profound degrees of hearing loss are targeted in our newborn screening programs'^ thus, lesser degrees of loss are often not identified until school age. The late age of identification of iMBHL'^ may contribute to our lack of knowledge about causative factors. That is. in some cases, a delay in identification of hearing loss may limit our ability to interpret etiologic evaluations reliabl\ (eg, cytomegalovirus) or may affect parental memory of possible illnesses or injuries that could account for tbe loss. For these reasons, much of \\ hat we know about etiologs of hearing loss in children is related to moderate or greater degrees of loss. Ho\\e\er, for everx child with bilateral profound bearing loss, 1 or 2 are born witb lesser degrees of bilateral or UllL. Ibe US National Health and Nutrition Examination Suney III revealed that l.S'i of schoolaged children bad bilateral low-frequency bearing loss, and greater than ?>'r bad bilateral high-frequency loss of slight to mild degree''*; therefore, tbe large numbers of children witb MBHL warrant closer examination of etiologic factors, fable I provides a listing of known causes of Ul IL and MBHL and their prevalence. Common Etiologies Although information regarding tbe etiologies of permanent UHL and MBHL is limited, it is reasonable to sus]iect tbat in addition to tbe few know n etiologies of MBHL and UHL some of tbe same factors that result in more severe degrees of bearing loss can also cause lesser degrees of loss. Tbe following re\ iev\ includes tbe currently documented causes of permanent UHL and MBHL in children. Prematurity Prematurity (ie, preterm births less tban 37 weeks) represents a constellation of possible etiologies, and frequently, we are unable to distinguisb tbe various contributing factors to bearing loss in these infants. Morbidity associated with prematurity includes birtb asphyxia, intracranial bemorrbage, ot()l()\ic medications, and bronchopulmonary dysplasia, among others. Several limitations prevent tbe determination of tbe prevalence of MBHL or UHL in premature babies. As discussed hy Ross et al'^ earlier in tbis issue, newborn screening programs are designed to identify bearing losses tbat are of moderate degree or greater. As such, tbe equipment and protocols used for newborn screening (ie, tor measuring otoacoustic emissions and auditor) brainstem responses) are designed to identify losses greater tban ajiproximately 40 dB HL; tberefore, if data are obtained from traditional newborn screening protocols, reports on tbe prevalence of bearing loss in premature babies will typically not reflect accurate estimations of MBHL and UHL. One of tbe few studies reporting on bearing loss hy degree in bigb-risk populations avoided these limitations by conducting bebavioral testing w ben tbe infants were 8 to 12 montbs of age.'*"* Tbe iNational Institutes of Health Identification of Neonatal Hearing Impairment project examined \\oil-baby nursery graduates witb risk factors and neonatal intensive care unit infants (including premature infants) and identified UHL in 3.4'^f and bilateral bearing loss in l.l'r of babies vAth bigb risk factors. Of tbose with bilateral loss, approximately ()^'( were of mild degree; bowex er. tbose numbers may have included infants witb conductive as well as permanent loss. Of tbose infants predicted to ba\e permanent bilateral bearing loss, tbere were appro.ximatek equal numbers of ears having mild, moderate, severe, and profound degrees of loss."* Herrgârd et al' prospectively followed S8 premature (<32 weeks) infants until S years of age. Tbey found approximately Vr of these infants bad permanent MBHL or UHL. Genetic Connexin. More tban ISO genes for syndromic and nonsyndromic deafness have been "mapped" to cbromosomal regions, and of tbese, at least 80 b;ne been identified. However, by far, connexin mutations are tbe most common cau.se of genetic bearing loss in the United States. Mutations involving tbe GJB2 gene tbat encodes tbe gap junction protein connexin 26 are tbe commonest form of deafness in many populations, accounting for ^O'^i- to -^0% of genetic cases.''^•^'' Members of tbe connexin gene familv are tbougbt to participate in tbe recycling of potassium back into tbe cocblear endolympb, a critical step in tbe physiology of sound perception." Most connexin deafness reported thus far hiis been profound in degree, but tbe murine model (mice used as a disease model) provides a clear precedent for reported nonpenetrance at birtb,^' stiggesting tbe opportunity for less severe degrees of bearing loss. Furtbermore, Wake et al"" found a Causation of Hearing Loss in Children / Tfiarpc, Shuicii Table 1. Caus( Cienclic Connexin Mitochondrial Enlarged vestibular aqueduct Sudden Auditory neuropathy- Noise induced \ iral/bacterial Mumps Otitis media Congenital C.M\ Meningitis Prematurity 19 Known Causes of UHL or MBHL and Prevalence Estimates Krequeiuy of Occurrence Accounts for 3()'>i to 4()'> of all genetic hearing loss; 1% to 16^r of these cases are estimated to result in MRHL. Accounts for less than \9c of prelingual deafness and 5'f of postlingual, nonsyndromic hearing loss; 21% of these cases are MHIIL. Accounts for S% to y^r of all cases of unknown etiology; M<'¡ ol children with tVA have MBHL, an additional unknown number will have LI IL. Three percent to Ví of all cases occur in children; as many as 98% have UHL. Accounts for less than }% of all pédiatrie hearing loss; appro.vimatelx ii'r of cases have borderline normal, MBHL. and there ha\e been (c\\ reports of UHL, Approximately lO'i of all children in the United States have noise-induced hearing loss; approximately 2i)'i of these arc \IBHL. Accounts for approximately 2% of childhood hearing loss; HO'r to 4S'; of these cases are UHL. Five percent to 2()'r of all cases of otitis media will result in SNHL; the majority of these cases are bilateral, high-frequency SNHL, with some reports of LHL. Thirteen percent to 24'r of all children with asymptomatic CM\ and up MYi of children with symptomatic CM\' will haxe SNHL; 17'; of the asymptomatic and 12% ofthe symptomatic cases are MBHL; S2'r ofthe asymptomatic cases and ^^'r ofthe symptomatic cases are LHL Ten percent of all children with bacterial meningitis are left with SNHL; 4'r to Mn of these are LHL; 14'ï arc- MBHL. Five percent of premature infants have MBHL or UHL. Reference Liu et al"-" Wake et a l " Marazita et a l " Jacobs et aP" C allison and Horn"" .^rjmand and Webber" Wynn et aP" I'oiTsl et al*' Madden et aP" Mskar et aP' Unala et aP' Mutlu vl aT' Arnold et al'"' Vartiainen and Karjalainen"' Ogawa et al"^ Fowler et al"' Dahle et al'" Fortnum and l)a\is Herrgard et al'' Note: MlîHL = mild bilateral hearing loss; SNHL = sensorineurai hearing loss; UHl = unilateral hearing loss. large proportion (16'f) of their cohort of Asian children w ith slight to mild bilateral sensorineurai hearing loss were homozygous for the V37I change in the GJB2 gene. They concluded that this change is a mutation associated with hearing loss and is a common cause of slight to mild sensorineurai hearing loss in Asian children. Similarly, Kenna et al~' reported on a cohort of children «ith biallelic (ie, both alternative forms of the gene) Cx26 mutations (M.Í4T or V37I) and found that they had a slightly higher incidence of mild degrees of hearing loss (including UHL) than previous studies indicated. Others haw reported hearing loss resulting from GJB2 mutations in the mild hearing loss range, including high-frequency hearing loss (4 to 8 kH/).-^ Mitochondrial 12S ribosomal (rRNA). In the United States. 10*^* ofthose with hearing loss resulting from pharmacologie ototoxicity have mutations involving the mitochondrial 12S ribosomal (rRNA) gene, including the A15S5G substitution, which is associated with extreme sensitivity to aminoglycoside ototoxicity.^' This mutation is very common in China, accounting for up to a third of all patients with aminoglycoside ototoxicity.-'' Individuals with these mutations have a higher susceptibility to aminoglycosides at low t r dosages than the av erage population. Ototoxicity is the ability of a chemical or drug to cause damage to the inner ear or, on rare occasions, the central auditory pathway. The mechanism for how aminoglycosides get into hair cells remains unknown, but it is possible to have hair cell loss without associated hearing loss. The hearing loss assoc iated with ototoxicity is typically high frequency and bilateral. Enlarged Vestibular Aqueduct Syndrome A well-known cause of UHL and MBHL in children is enlarged vestibular aqueduct (EVA) syndrome. The vestibular aqueduct is the bony canal extending from 20 I ri'nds in Amplification/\o\. 12. No. 1, March 2008 the vestibule to the endolymphatic sac in the temporal bone and contains the membranous endolymphatic duct. Along with the endolymphatic sac, the \cstihular aqueduct is thought to help regulate the concentration of ions in the cochlear fluids. It is speculated that an E\A will result in the expansion of the endolymphatic sac and duct. Such an enlargement may result in a chemical imbalance, causing hearing loss. Ixpically. the diameter of the \cstibular aqueduct at its midpoint ranges between 0.5 and 1.4 mm. .\ commonly accepted definition of KV A syndrome is a diameter greater than 1.5 mm at the midpoint. The diagnosis of l:\ A is achieved with the use of computed tomography imaging of the temporal bones and magnetic resonance imaging. This particular cause of hearing loss has been reported to account for 5% to 7^r of hearing loss that has previously been classified as having unknown c tiology" •"** and is the most common form of inner oar malformation associated with scnsorineuial hearino loss.^*^ .\ recent study found EVA in M'/f of children with sensorineural hearing loss in their cohort^". llowi'Ncr. these authors defined a large vestibular aqueduct as one in which both of its widths were iib()\c' the •^»Sth percentile (>1.9 mm at the operciilum and/or >0.9 mm at the midpoint) of the control group, a definition that is not yet widely accepted and may overestimate the incidence of FA A. IA A malformations have been linked to Pendred Syndrome, branchiootorenal syndrome, CHARGI Association, and Waardenburg Syndrome.^' Hearing loss that occurs with l:\A has a sudden onset or gradual progression. The disorder is twice as likely to be bilateral than unilateral and will often result in some degree of hearing loss ranging Irom minimal to profound." Children who have been diagnosed with E\A are strongly encouraged to protect their remaining hearing by taking precautions against damaging the delicate structures of the \estibular aqueduct. Such precautions include a\<)iding contact sports and extreme changes in barometric pressure. Sudden Idiopathic Sudden hearing loss has been characterized as hearing thresholds of 30 dB or greater at 2 or 3 consecutive frequencies.""^"* Anecdotally. patients with sudden hearing loss report a decrease in hearing oN'ernight or a rapid progression in hearing loss over sexeral days. Furthermore, the hearing loss typically occurs in only I ear. Only 2% of patients with sudden hearing loss are affected bilaterally. The exact cause of sudden hearing loss is only found in approximately lO'^ir of patients,^"" with the rest being categorized as sudden idiopathic. For those w ho receive a definiti\e diagnosis, viral and vascular factors, membrane puncture, and autoimmune disease are most often implicated. *•* The prevalence of sudden hearing loss in children is lower than in adults. Specifically, only S'^ of all cases of sudden hearing loss occurs in patients under 21 years of age.^*" and only 3.5% occurs in patients under 14 years of age.^ Ireatment options for sudden hearing loss are limited because the exact etiology is often unknowtT; hov\t\cr. common treatments include the use of vasodilators, steroids, diuretics, and anticoagulants. Spontaneous recoser) is common among patients with sudden hearing loss. In fact, the rate of spontaneous recovery has been reported to occur in as many as 65'r of patients with sudden loss.^** Roman et al" reported that partial hearing reco\ery occurred in approximately 29'r of their small sample of children v\ith sudden hearing loss. Of those, half had their hearing loss imprcne to a lc\el of a mild degree of loss. In addition, an absence of recoNcry was significantly correlated with 3 factors: severe initial hearing loss, association of vertigo, and "downward" sloping audiometric curve. Auditory Neuropathy/Dyssynchrony Auditory neuropathy/dyssNnchrony (A.\/AD) is an auditor) disorder in which patients typical!) demonstrate hearing loss for pure tones, impaired speech perception that is out of proportion to pure tone loss, ahsent or abnormal auditory brainstem responses, and normal outer hair cell Function as measured by otoacoustic emissions and cochlear microphonics. The audiometric configurations associated with AN/AD \ar) considerahly, from normal pure tone sensitixit) to profound loss, and UllL and MIÎIIL have been reported.^'*•"' In such cases, pure tone thresholds are wry poor predictors of the degree of difficult) or handicap that a child may be experiencing. However, on rare occasions, speech perception ability may be only minimal!) affected, at least in optimum acoustic conditions.^' It appears that there ma) be many causative factors associated with AiN/AI), including mutations of the otoferlin gene (OTOF),"*"^* hxporbilirubinemia,'**''^ aspli)\ia.^^"'^ and prematurit)."*^ Several possible sites of lesion have been posited for AN/AD, including abnormalit) of the peripheral auditory system localized Causation of Hearing loss in Children / Tharpe, Shulcii to the inner hair cells, the eighth nerve, or the synapse of the inner hair cells and eighth nerve."*^ Noise Induced Hearing loss caused b\ noise exposure is not limited to the adult population. In fact, 5.2 million, 6 to 19 year olds (or approximately lO'^^r of children sur\eycd in this age range) have hearing loss related to noise exposure'*'; however, the authors do not indicate if these losses are temporary or permanent in nature. In addition, evidence of high-frequency hearing loss in nearly one third of a cohort of college students has been reported.** Noise-induced hearing loss occurs as a result of chronic or acute noise exposure. Cienetic factors have also been implicated in tbe susceptibility one bas to noise.^^"^ Cbronic exposure bas been cbaracterized by prolonged exposure to sounds that exceed 85 dP SPL for an 8-bour period, and acute noise exposure occurs as tbe result of events such as an explosion or gunshot close to tbe ear. Acoustic trauma results in immediate bearing loss, wbereas bearing loss from cbronic noise exposure occurs gradually over time. Hearing loss of tbis nature is initially restricted to tbe bigb-frequency regions (3 to 6 kHz) and e\entually, witb additional exposure, extends into tbe lower frequencies. Hearing loss secondary to noise exposure occurs as a result of damage to tbe bair cells of tbe cocblea. Specifically, cbanges in sound pressure create a sbearing force on tbe stereocilia of tbe bair cells lining tbe basilar membrane of tbe cocblea, wbicb leads to our perception of sound. Hvcc'ssivc force caused by bigb levels of noise can lead to cellular metabolic (nerload, cell damage, and cell deatb resulting in bearing loss."*' Possible environmental sources that may contribute to noise-induced bearing loss in children include fireworks, lawn mowers, and IONS.'"'" In fact, several popular toys sucb as bike borns, toy cell pbones, and arcade games bavc been sbown to produce bigb enougb intensity levels to barm bearing." '" In addition to toys, cbildren may be at risk for noise-induced bearing loss from prolonged use of personal audio players and attending musical concerts.''" Portnuff and Fligor^' recently examined tbe safety of listening to tbe popular iPod de\ice. By using current Occupational Safety and Healtb standards,^^ they concluded tbat users can listen for 4.S consecutive bours with tbe volume set at 70'^f witbout risk of bearing loss if using tbe stock ear pbones tbat are supplied witb tbe device. Tbe allowable 11 number of safe listening hours was shown to decrease with increased volume and witb dillerent forms of beadpbones (ie, ear buds vs supra aural beadpbones). Tbe authors encourage tbe data to be interpreted witb caution because not everyone bas tbe same risk of bearing loss from prolonged noise exposure and tbere is no wav to predict tbose v\bo bave more or less sensitive ears. Viral/Bacterial Mumps. Tbe mumps virus was a common cause of acquired UHL before tbe introduction of tbe mumps vaccine in 1967. Most developed countries bave experienced a yO'f to 95% decrease in tbe incidence of mumps as a result of tbe availability of immunizations'^. However, reports of recent outbreaks of mumps bave appeared in tbe United Slates, tbe United Kingdom, and oiber developed countries.""^""' Histopatbologic examination of tbe temporal bones from individuals vsbo suffered bearing loss after infection witb mumps indicates a severe atropby of tbe organ of corti and stria vascularis. Endolympbatic bydrops bave also been noted, along witb damage to tbe endolympbatic duct and fibrous tissue in tbe endolympbatic sac."' Otitis media. ,\ rarely reported but viable cause of acquired sensory UHL or MBHL is middle ear disease witb effusion. Tbe mecbanism causing tbis drop in bone-conduction tbresbold is unknown. However, some bave speculated tbat bacteria travels Irom tbe middle-ear space tbrougb tbe round windovx. causing damage to tbe basal end of tbe cocblea.'**'*" It bas also been proposed tbat tbe accumulation of fluid in tbe middle space reduces oxvgen to tbe cocblea via tbe round window affecting cocblear function.*''"' An early bistory of ear disease in young cbildren. especially w ben combined witb a bistory of multiple sets of myringotoniy tube insertions, appears to be a prerequisite to bearing loss in tbe bigb frequencies.''^"^ Mutlu et al*' found evidence of temporary and permanent sensory bearing loss at I or 2 bigb frequencies in ^)'f of a cobort of cbildren v\ itb otitis media witb effusion. Tbe bearing loss was most frequently observed at 2 kHz, which is consistent witb damage to tbe region of tbe cocblear basal turn. Congenital cytomegalovirus. Congenital cytomegalovirus (Ci\I\ ) is tbe leading cause of nongenetic sensory bearing loss and tbe leading cause ol unilateral prelinguistic bearing loss in cbildren.** C .M\ infc ctions var\ in frequency according to maternal age, race, and socioeconomic status. Congenital infection 22 I r e m h in . \ m p l i ß c a ü o i i / \ o [ . 1 2 . N o . I. M a r c h 20()K occurs in 0.2'^^ to 2.^"^/ of all live birtbs," witb an average incidence of 1%. Tbis translates to approximately 10000 to 80000 infants born in tbe United States eacb year witb congenital CM\ infection,****' making CMV tbe most common congenital viral infection.^" Initial C"M\' infection, wbicb may have few symptoms, is always followed by a prolonged, inapparent infection during wbicb tbe virus resides in cells witbout causing detectable damage or illness.''' Sev ere impairment of tbe body s immune system by medication or disease increases tbe likelibood tbat tbe virus v\ill be reactivated from tbe latent or dormant state. Infectious CM\ can be sbed in tbe bodily fluids of any previously infected person and tbus may be found in urine, saliva, blood, tears, semen, and breast milk. Tbe sbedding of tbe virus may take place intermittently, without any detectable signs and witbout causing svinptoms. Becurrent disease rarely occurs unless tbe immune system is suppressed as a result of tberapeutic drugs or disease. Tberefore, for tbe vast majority of people, C \ l \ ' infection is not a serious problem. However, CMV infection can be barmful to certain bigb-risk groups, including tbe unborn babv during pregnancy. Tbe bearing loss associated with CM\' can range in degree, can be unilateral or bilateral, and can have onset montbs or years after birth. ' " ' Only approximately 14% of tbe infections are identified at birtb, witb tbe remaining H(->'( being asymptomatic.-' In cases not recognized at birtb, it can be dillicult to impossible to diagnose because of tbe bigb incidence of postnatal infection. Nance** bas speculated tbat tbe neurologic deficits associated witb C M \ ' may be to blame for tbe poor academic performance of cbildren v\itb UHL secondary to infection, ratber tban tbe bearing loss per se. Meningitis. Hearing loss is tbe most common complication of bacterial meningitis among cbildren. Tbe incidence of bearing loss witb streptococcus pneumoniae is greater tban neisseria meningitidis (35.9% and 23.9%. respectively).'' UHL occurs in 4% to 30%"'''' and MBHL in approximatelv 14% of tbose witb bacterial meningitis.'* Altbougb most cases of postmeningitic bearing loss are permanent, tbere are reported cases of spontaneous recoven.^' In fact, one study reported approximately 10% of subjects bad a rapid recoven of bearing. ' lhe bearing loss is caused bv cocblear damai;e earlv in tbe illness, witb at least one report indicating tbat tbe bearing loss occurred vsithin 6 bours of tbe diagnosis.'^ lbe cocblear aqueduct, wbicb links tbe seala tympani to tbe subaraebnoid space, is tbe likely conduit lor transmission of bacteria to tbe eocblea. Mtbougb viral meningitis is more common tban bacterial, bacterial is more often associated witb bearing loss. •* Bacterial meningitis is also a more serious infection and can be life tbreatening. Unilateral Atresia or Microtia Congenital aural atresia (C V\) or microtia is a birtb defect occurring in approximately 1 per 10000 live birtbs as a syndromic or nonsyndromic disorder."** C'A \ pbenotypes range from mild symptoms (narrowing of tbe external auditory canal and bypoplasia of tbe tympanic membrane and middle ear cavity) to severe symptoms (including tbe entire absence of tbe middle ear in combination witb anotia, bony atresia of tbe external auditory canal, and hypoplasia of inner ear structures)^** and is frequently associated witb cbromosomal abnormalities, especially deletions on tbe long arm of cbromosome IS (I8q).*"' Unilateral CAA occurs in approximately 70% of cases and occurs sligbtly more often in boys tban in girls,"" Surgical remediation of unilateral C AA for purposes of improving tbe conductive bearing loss is often not recommended at all or, in some cases, is not recommended until adolescence or adulthood. Such surgery is noted to be one of tbe most difficult otologic surgeries and, on average, results in small improvements in bearing sensitivitv.'*'^^ Future Needs Despite tbe widespread implementation of newborn bearing screening programs in tbe United States, systematic etiologic evaluations, especially genetic evaluation and counseling, bave not become routine"'. However, it is clear from a survey of parents of cbildren witb bearing loss tbat tbey want information about tbe cause of tbeir cbilds bearing loss.^"' In faet, etiology of tbeir cbild's bearing loss is rated as tbe top question parents bave after notification of a bearing loss diagnosis. Nance''' bas proposed tbat by screening all newborn infants for just 4 important causes of deafness (DFNiBl, CM\, Pendred syndrome, and tbe mt I2S rRiNA \155SG mutation) more tban balf of all infants w itb normal bearing at birtb w bo are at bigb risk for delayed onset bearing loss in infancy would be detected in addition to detecting infants at birtb wbo bave tbe commonest genetic, tbe commonest C^ausation of Hearing Loss in Children / Tharpe, Sladett environmental, and the commonest preventable causes of deafness. As demonstrated by this rc\ie\\. that recommended screening protocol is likely to identify numerous cases of permanent L'HL and MBHL that would typically not be identified through newborn hearing screening programs that target more severe degrees of hearing loss. As witb any screening protocols, the benefits and limitations of sucb recommendations will require careful consideration before implementation. References 1. Bess FH, Tharpe AM. Case histor\ data on unilati-rally hearing-impaired children. Ear Hear. I986;7:14-19. 2. Culbertson JL, Gilhert Lh. Children with unilateral sensorineural hearing loss. Ear Hear. l986;7:.-?8-42. 3. Oyier RF, Oyler AL. Matkin ND. Unilateral hearing loss: demographics and educational impact. Lati^ ,S;> Hear Sen-Schools. 1988;19:201 210. 4. Bo\o R, Martini A. Agnoletto M, et al. Auditory and academic performance of children with unilateral hearing loss. ScandAudiol Sujrpl. 1988:30:71-74. 5. Keller WD, Bundy RS. Affects of unilateral hearing loss upon educational achievement. Child Care Health Dev. 198O;6:93-IOO. 6. Bess FH, Dodd-Murphy J, Parker R.A. Children with minimal sensorineural hearing loss: prexalence, educational performance, and functional status. Ear Hear. 1998;19:339-354. 7. Davis J. Shepard N, Stelmachowitz P, Gorga M. Characteristics of hearing-impaired children in the puhlic schools: II: psychoeducational data. J Speech Hear Disord. 198I;46:13O-I37. 8. Tharpe AM. 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