We did a computerised and manual search on PubMed to identify studies, with particular focus on original reports published within the past 10 years. Selection criteria included a judgment about the importance of studies and their relevance to the well-informed general practitioner. Keywords used were “acquired deafness”, “genetic deafness”, or “sensorineural hearing loss” plus “neonates”, “children”, or “young adults” plus “[a]etiology”, “diagnosis”, “classification”, “prevention”,
SeminarSensorineural hearing loss in children
Section snippets
Diagnosis
The diagnosis of SNHL depends on the demonstration of reduced hearing acuity by auditory testing. Hearing is measured in decibels (dB) with the threshold of 0 dB for each frequency denoting the value at which normal young adults perceive a tone burst of a given intensity and frequency 50% of the time. A child's hearing acuity is classed as normal if it is within 20 dB of these defined thresholds. Severity of hearing loss is graded as mild (20–40 dB), moderate (41–55 dB), moderately severe
Classification
In addition to the degree and frequency of SNHL for a given child, other features, such as type of loss, time of onset, and causality should be defined wherever possible. In general, type of loss is categorised as conductive, sensorineural, or mixed and either stable or progressive. Time of onset is established as either congenital or acquired (or late-onset). Causality is broadly divided into genetic (hereditary) or non-genetic (environmental) categories.
Although this approach enables the
Epidemiology
SNHL is the most common sensory deficit in more developed societies.5, 6 In the USA, congenital SNHL occurs about three times more frequently than Down's syndrome, six times more frequently than spina bifida, and over 50 times more frequently than phenylketonuria.7, 8, 9 An estimated 4000 infants are born each year with severe to profound bilateral hearing loss,10, 11 and another 8000 are born with unilateral or mild to moderate bilateral SNHL.12 Thus, at least one child in 1000 is born with
Genetic SNHL in neonates
By aetiology, more than half of neonates with SNHL have inherited hearing loss (figure 3). In most cases, both parents have normal hearing and, as a result of simple mendelian recessive inheritance, have a child with non-syndromic SNHL (75–80% of cases). Autosomal dominant (about 20%), X-linked (2–5%), and mitochondrial (about 1%) contributions to the burden of inherited congenital SNHL also occur.
Because autosomal recessive SNHL is heterogeneous, the finding that mutations in a gene called GJB2
Acquired SNHL in neonates
Although many women are exposed to infectious pathogens during pregnancy, only a few of these infections damage the placenta and fetus. Those that cause such damage remain important causes not only of acquired SNHL but also of visual loss and behavioural and neurological dysfunction. They are traditionally grouped as TORCH infections (toxoplasmosis, others, rubella, cytomegalovirus, and herpes simplex viruses); a more complete list is shown in the panel.49 The incidence of congenital rubella
Genetic SNHL in infants and young children
The relative contribution of genetics to the total number of infants and young children with SNHL is unknown. Inherited hearing loss diagnosed among children of these age-groups is congenital hearing loss that was present but missed during the neonatal period, negligible or mild congenital hearing loss that was undetectable by available screening methods but has become more serious and thus detectable, or late-onset SNHL. In children with late-onset and progressive hearing loss, dilatation of
Acquired SNHL in infants and young children
The most common cause of intermittent mild to moderate hearing loss in infants and young children is the conductive hearing loss caused by acute otitis media or otitis media with effusion.59 Acquired SNHL in infants and children is most commonly caused by bacterial meningitis. Altogether, bacterial meningitis accounts for about 6% of all cases of SNHL in children.60 The prevalence is about seven per 100 000 with a heavy age bias for younger children.61 75% of affected children are younger than
School-aged children
Hearing loss that is presumed to be late onset and at least moderate in severity is diagnosed in 1·2–3·3 per 10 000 school-aged children.14 Some of this hearing loss is probably mild congenital progressive hearing loss that does not become severe enough to be detected until early childhood. Mild hearing loss that remains stable, by contrast, can escape detection especially if only a few frequencies are affected. As a result, much less is known about this degree of hearing loss. Increasingly,
Genetic SNHL in school-aged children
Autosomal dominant non-syndromic SNHL is commonly first detected in school-aged children during routine audiological screening (table 1).66 Some types of syndromic SNHL are also first recognised at this time, reflecting the diagnosis of associated comorbidity that was not previously noted on physical examination. Common examples included Pendred's and Usher's syndromes, both inherited as autosomal recessive diseases so a family history is unhelpful as an indicator of risk (table 2).48, 67, 68
Acquired SNHL in school-aged children
There are no prevalence estimates of acquired SNHL in school-aged children. New-onset SNHL can reflect silent congenital cytomegalovirus infection;54 however, if threshold shifts are restricted to the range 3–6 kHz, noise trauma should be considered. In the USA, about 12·5% of children aged 6–19 years (7 million children) have mild hearing loss at about 6 kHz, including about 6% of 7-year-olds.69, 70 Data from Germany and Finland are similar, with a loss of 20 dB or more in at least one
Neonates
Although mutations in many different genes are predictive of SNHL, the gene that accounts for most cases by far is GJB2. Allele variants of this gene cause roughly half of cases of congenital autosomal recessive non-syndromic SNHL in the white population. In children of northern European ancestry, the most common SNHL-causing allele variant of GJB2 is the c35delG mutation (hereafter called 35delG), which has a carrier frequency of about 2·5% in the general population.73 The prevalence of this
Prevention
No satisfactory therapy is yet available to correct SNHL by the replacement of inner and outer hair cells, although the ability to generate new hair cells in the mature organ of Corti in mammals does pave the way for research focused on optimising repair of inner-ear damage at a structural and functional level.129, 130, 131 Current measures to prevent SNHL in children should be focused on decreasing the incidence of genetic SNHL through educational programmes and prevention of acquired SNHL
Conclusion
The prevalence of SNHL is decreasing as a result of improvements in health care and the expansion of immunisation programmes around the world. At the same time, advances and discoveries in human genetics have improved our ability to diagnose genetic SNHL. Current habilitation options centre on hearing aids and cochlear implants, the latter being the foremost treatment for children with severe to profound SNHL. In the coming decades, novel habilitation options will become available for specific
Search strategy and selection criteria
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