Post-lingual, acquired or adventitious deafness is a deafness developed following the acquisition of speech and language, and is usually classified in patients over the age of 6.  People deafened post-lingually are more likely to communicate well in their native language as they do not rely on auditory feedback to communicate with people differing from Prelingual deafness. Patients are only diagnosed with post-lingual deafness if they have acquired auditory and spoken language prior to deafness as neural connections have been stimulated sufficiently passed the sensitive period of language. The sensitive period of language acquisition is crucial in the development of audition, due to it's role in the development of the synapses in the Broca's area. If this area is stimulated sufficiently and the area is does not deteriorate drastically following deafness, the patient suffers from post-lingual deafness. This shows whether or not spoken language has been acquired and can be interpreted, which usually only occurs in post-lingual sufferers. Post-lingual deafness can affect patients unilaterally or through bilateral deafness.
- 1 Causes
- 2 Social impact
- 3 Treatment
- 4 References
Post-lingual hearing impairments affects around 10% of the general population for 60 year old, 50% by 80 years old showing age related effects in the degradation of hearing loss. Presbycusis is similar in that deafness affects hearing and occurs after the onset of language, thus causing a communication problem which does not affect their language processing capabilities, i.e. they are still able to read or write, but affects the patients auditory and psychologically processing. 
Environmental hearing loss
Rosen (1965) demonstrated that long-term hearing loss is usually the product of chronic exposure to environmental noise in industrialised countries . The U.S. Environmental Protection Agency has asserted the same sentiment and testified before the U.S. Congress that approximately 34 million Americans are exposed to noise pollution levels that expose humans to noise health effects including the risk of hearing loss . Acquired hearing loss in adults is most likely caused by susceptibility although susceptibility is most likely to be caused by environmental-genetic effects. Age related and noise related hearing loss is most commonly the result of environmental-genetic effects of post-lingual deafness.
Genetic conditions can also lead to post-lingual deafness. In contrast to genetic causes of pre-lingual deafness, which are frequently autosomal recessive, post-lingual deafness tends to be autosomal dominant which account for 10-20% of deaf prognosis, although autosomal recessive and x linked non-syndromic (carried on the x chromosome) hearing loss is also diagnosed. with 30% of all deafness diagnosis being in syndromic.  . Otosclerosis is a genetic factor which is correlated with post-lingual deafness within the population, as are Alport syndrome, Alström syndrome and Refsum syndrome  . Recent research suggests that gene sequencing in DNA is responsible for some deafness and can be traced before the onset of deafness through gene mutation. Mucopolysaccharidosis is used to screen monogenic genes efficiently, outlining genes which could account for this disorder .
Autosomal Dominant Syndromic Hearing Impairment
Mitochondrial DNA mutations may cause hearing loss in adults in a variety of disease conditions from neuromuscular syndromes like Kearns-Sayre syndrome, to more general conditions including diabetes mellitus, Parkinson disease and Alzheimer disease causing a MTTL1 mutation, after the onset of the disease .  This form of syndromic mutation affects the ossicles, Eustachian tube and the tympanic membrane of the ear
Autosomal Dominant non syndromic hearing Impairment
This occurs in the inner ear and is usually progressive. Most post-lingual hearing loss occurs within this category with many genetic mutations accounting for this. As it is a dominant factor, it means only one defected allele is needed in order to cause the onset of deafness.
|Autosomal Dominant non-syndromic genes|
Autosomal Recessive non syndromic
|Autosomal Recessive non syndromic hearing impairment genes|
This is when a defected gene is present on the sex chromosome and results in the phenotype being expressed. In males, this would be only on hemizygous as only one X chromosome is in their DNA, and females heterozygous. Only PRPS1 is linked to post-lingual deafness at present.  
Post-lingual deafened patients who develop the disorder later in life become at risk of developing behavioural problems including social isolation, as the Andersen model has found significant evidence suggesting a correlation between age and health services in the older generation  The likeliness of this effect is significantly higher in people of a language minority and are deafened, correlating with being less likely to visit a medical practitioner due to a language barrier and are more susceptible to social isolation from seeing an expert.  Generally post-lingually deafened adults have a significantly higher health service utilisation compared to the general adult population although other research suggest that the general post-lingually deaf patients report more social isolation and depression, although not as severe as the patients who develop the illness later in life neither the minorities.
Higher doctor visits have been found in native language speakers suffering from post-lingual deafness as compared to pre-lingual deafness patients, correlating with doctors not sufficiently addressing the medical issues affecting the post-lingual deafness patients. A similar finding to patients with a chronic illness visiting the doctor. This is accounted by the communication barrier between patient and doctor resulting in a misdiagnosis in relation to their medical illness.
Age of Onset
Research suggests that age of onset can still have language development issues even after the sensitive period of language development. Previous research into the field found that children who become deaf pre-puberty adversely affected their language skills more than adults deafened in their middle age, which accounts for their language experience.  Patient with the onset of post-lingual deafness show deviations in speech patterns due to no auditory feedback, while onset after puberty shows a more profound effect towards phonetic deviations in speech, although some patients show no significant deterioration following the onset of post-lingual deafness, unilaterally or bilaterally 
Cochlear Implant, Hearing Aid and Electric Acoustic Stimulation
Patient variability will effect the treatment they will receive relating to their deafness, whether it is environmental factors, genetic mutations or a hereditary illness. In order to decide which treatment would best suit their patients needs, testing should be commenced. One test would be a MAC test, to decide if the patient would benefit more a Cochlear Implant or a hearing aid. Although the treatments target structurally different regions (Hearing aids amplify the sound through the ossicles and tympanic membranes, Cochlear implantation (CI) sends the information straight into the cochlear) no significant phoneme score differences can be found when testing hearing aid users or CI users. A vast amount of research suggests that CI users have a the availability to improve their speech understanding and their quality of life, and is much more effective in treating patients and decreasing the risk of developing emotional problems as compared to hearing aids. However, it is important that if a patient does opt to have a CI operation, then they must understand the invasiveness of the procedure and the importance to participate in speech therapy and hearing rehabilitation post-op in order to receive the full benefits of the CI.  Additionally, audiologists and researchers suggest that patients receive the CI operation as soon as possible due to shorter hearing deprivation being singled out as a factor in the outcome of the implant. An additional treatment is electric acoustic stimulation (EAS) involving the use of both a CI and a hearing aid together unilaterally. This method of treatment is sensitive to patient variability.
Mucopolysaccharidosis (MPS) can also be used as a diagnostic tool, it is used in order to screen monogenic genes efficiently as many cases of post-lingual deafness are caused by gene mutations. Following gene screening, audiologists can then decide which treatment would be most effective for that patient. 
|Mutated Gene||Recommended Treatment|
Some research disputes the effectiveness of these treatments and effective they can be. Early research finding CI effective in overall treatment for patients with TMRRSS3 mutation although this is disputed due to it’s effect on the spinal ganglion.  MPS screening is also effective in estimating the best tuning for EAS/CI surgery and the most effective electrode selection to be inserted, resulting in optimal performance prior to surgery. Additionally, due to the inheritance of gene’s relatives can be screened and monitored if they have inherited the defective gene, resulting in a shorter period in treatment when the gene begins to mutate and result in early treatment.
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