Download The European Response to Congenital Hearing Loss

THE EUROPEAN RESPONSE TO CONGENITAL HEARING LOSS
Ferdinando Grandori, Director, CNR Center of Biomedical Engineering, Polytechnic of Milan, Italy
[email protected]
We are entering a new era in the care of infants with hearing loss.
The most important period for speech, language, cognitive and mental development is generally
regarded as the first 1 to 2 years of life and crucially appropriate input is needed at this time, while
the average age of identification of hearing losses, in the vast majority of the European countries
still remains close to three years (about 31 months).
Etiology of congenital hearing loss is still a matter of epidemiological research, but increasing
evidence indicates that over than 50% have a genetic cause, 70% being non syndromal, with 75%
being due to a mutation in an autosomal recessive gene. Up to 100 genes are responsible for nonsyndromal sensorineural hearing impairment. In the past years 28 autosomal recessive, 30
autosomal dominant and 5 X-linked loci have been mapped. It is now possible to offer mutation
testing of babies affected with non-syndromal sensorineural hearing impairment to determine
whether their hearing impairment is due to a genetic cause allowing precise Mendelian recurrence
risk advice to be provided for couples where a mutation is identified.
The number of newborns with hearing losses is about 2 per thousand, while it can be as high as
some 5 per cent for those babies who are admitted into the Neonatal Intensive Care Unit (NICU) or
belong to at-risk categories for hearing loss.
The result is that for many hearing-impaired children, much of the crucial period for language and
speech learning is lost and they shall never enjoy full social development.
On the other hand, all available scientific results from pilot integrated newborn screening and
intervention programmes unequivocally show that babies who are technically severely impaired, if
treated at a few months of age (i.e. less than 6), are not distinguishable from normal hearing babies
at about 2 to 3 years, for speech and language development, width of vocabulary, emotional
stability, behaviour and vestibular responses.
Very early detection of hearing impairment in newborns and subsequent habilitation/intervention at
a few months of age has been recently considered the focus of health care systems all over the
World (NIH Consensus Statement on Universal Hearing Screening in Infants, 1994; World Health
Organisation, Resolution 48.9, 1995; European Consensus Statement on Neonatal Hearing
Screening, May 1998; American Academy of Pediatrics Position Statement, 1999; Joint Committee
on Infant Hearing Position Statement, 2000).
The 1998 European Consensus Statement on Neonatal Hearing Screening is the result of the
European Consensus Development Conference organised by the Biomed2 Concerted Action
AHEAD, and it has been reported in its full version by more than 18 journals in the area of
Audiology, Otolaryngology, Pediatrics and Neonatology.
It was the development of technology for recording Otoacoustic Emissions (OAEs) that made
feasible the implementation of objective, reliable, fast (few seconds) and low cost (<10 Euro per
baby) methods of universal newborn hearing screening.
These technologies were entirely developed in Europe and are being applied by European
manufacturers who still maintain the technical leadership in the field.
Research in hearing has advanced dramatically over the most recent years.
The advance began with the startling realisation that existing knowledge could not explain the
acoustic response of the peripheral ear to sound and particularly Otoacoustic Emissions.
The very understanding of both the physical basis for hearing and the nature of hearing impairment
were challenged. Contractile properties of the cochlear receptors (similar to those responsible for
muscular contraction) were shown to be present in the outer hair cells. Different types of OAEs
were discovered: spontaneous, click-evoked, distortion product otoacoustic emissions. The action of
the cochlear efferent system was demonstrated objectively in humans. The presence of these active
mechanisms is now known to represent the process by which the whole response of the cochlea to
sounds comes to be actually under the control of physiological processes, thus linking together
haircell motility, OAEs, sensory hearing loss, and the influence of high cerebral functions on the
auditory periphery.
On more practical grounds, recording methods based on OAEs do provide an objective and reliable
assessment of even mild sensory hearing loss, by far the type of permanent losses with the highest
incidence in infants, children and adults. OAE recording is being considered as the method of
choice to assess hearing in neonates.
In those areas – still quite few and scattered all over Europe – in which early detection is currently
done by means of mass screening programs, the average age of identification of hearing losses has
dropped to about 3 to 6 months, so that the remediation process can start very soon, thus helping to
ensure early language and speech development.
The penetration of such programmes differs greatly from country to country, and within the same
country it varies from area to area. For example, Austria has enacted legislation mandating newborn
hearing screening and early intervention in 1997, as a direct result of a previous European Project
form the Biomed 2 (Project AHEAD), and at present about 65% of all newborns are screened (the
coverage was lower than 1% in 1996) and the intervention starts at 3 to 4 months of age, much like
in the Flanders (mandatory, current coverage of about 90%) and in a few regions, or hospitals, in
France, Germany, Greece, Italy, Lithuania, The Netherlands, Poland, Russia, Spain and United
Kingdom. In other countries of the EU the level of awareness among pediatricians and audiologists
is still rather low.
In the USA newborn screening and extremely early intervention is now mandatory in more than 28
States and legislation is pending in other 11 States (in 1996 screening programmes were
implemented only in a few centres), and it is estimated that by the end of Year 2000 about 20 to
25% of all newborns in the US will be screened for hearing.
A new European Project (AHEAD II, 2000-03, a Thematic Network) will provide a framework for
developing in the European area well integrated systems of universal hearing screening, diagnosis
and intervention.
The main objectives of Project AHEAD II are:
i) make significant contribution to the technical progress for recording, processing, interpreting
and scoring OAE responses;
ii) advance the whole field of OAEs and validate the clinical applications of the new techniques
mainly in newborn hearing screening and assessment programmes;
iii) establish agreed common protocols for testing and educate the clinical community with the
realisable applications achieved todate in the area of screening and intervention;
iv) demonstrate practical feasibility of universal newborn hearing screening programmes and of
extremely early intervention at a few months of age;
v) provide full assistance to the creation of new integrated programmes of hearing assessment and
early intervention;
vi) publicise the achievable results among audiologists and otolaryngologists, neonatologists,
pediatricians, speech-language pathologists, teachers of the deaf and primary health care
providers.