Congenital deafness is a hearing loss that exists at birth. 80% are genetic. However, not all genetic deafness is congenital. Congenital deafness affects 1 in 1000 to 1 in 2000 births.
They can be :
• Severe, making it impossible to acquire language;
• Progressive, evolving over the years.
Deafness of genetic origin
Genetic deafness is a deafness linked to an abnormality in a gene (segment of DNA conditioning the synthesis of one or more proteins and therefore the expression of predisposed hereditary characteristics). Many genes responsible for sensorineural deafness (sensorineural deafness) have been located on human chromosomes and may be responsible for this genetic deafness.
Genetic deafness can be syndromic (associated with other symptoms or malformations in 10% of cases).
In the case of syndromic deafness, this deafness may initially be the only symptom found.
If most congenital deafnesses are sensorineural deafnesses (inner ear), there are also congenital conductive deafnesses, progressive, sometimes asymmetric (tympanic or outer ear anomalies). These transmissional, genetic deafnesses are transmitted according to the autosomal recessive mode, i.e. they are linked to the non-sexual chromosomes and are of variable penetrance. More generally :
- 85% of genetic deafness are transmitted according to an autosomal recessive mode,
- 10 to 15% are transmitted according to an autosomal dominant mode (non-sexual chromosome, all affected, identical penetrance),
- 1% of deafness is transmitted according to a mode linked to the X chromosome (sexual). The presence of two paired X chromosomes in the female and absent in the male (XY) means that only the male is affected (the female would have to have both loci on her deficient X chromosomes to be affected).
Non-genetic congenital deafness
Within the framework of acquired deafness, we classify them according to their date of onset :
- Acquired ante natal deafness
Linked to a viral infection, most often in the mother, which leaves sequels in the child (rubella, toxoplasmosis, cytomegalovirus infection in particular, taking ototoxic drugs during pregnancy ;
- Neonatal acquired deafness
This can be caused by a bacterial infection, especially in the vaginal canal, or by neonatal suffering (by anoxia) ;
- Early postnatal deafness
Can be linked to a pathology contracted just after birth (meningitis for example) but a severe post-natal jaundice of the newborn can also lead to deafness at birth.
These three types of deafness can, more or less, be considered as congenital deafness. We now tend to speak of pre-lingual deafness, that is to say that we speak of a deafness discovered or revealed by the non-acquisition of language or revealed before the theoretical acquisition of language. Let us specify that the systematic screening of deafness is done, since 2012, in the first days of life and by various tests, in all neonatal centers; a doubt on the examination requiring further investigations by more invasive examinations.
Prevention is essential :
- Vaccination verification against certain viruses, if the woman wishing to be pregnant is not immune,
- Make sure that there is no fetomaternal blood incompatibility (Rhesus group),
- No ototoxic drugs,
- Prevention of severe infections in the mother, etc.
Diabetes and deafness
Ear damage with deafness in diabetics is not well known to the medical profession and is quite common. It is customary to classify diabetes :
- Type I diabetes
Classically occurring very early in life, linked to an almost complete destruction of the pancreatic cells secreting insulin (islets of Langerhans) and resulting essentially from genetic factors. This diabetes will quickly require the intake of missing insulin which will stabilize the blood sugar level;
- Type II diabetes.
It appears later in life and is linked to a dysfunction of insulin regulation of the blood sugar level. It is most common in people who are overweight or obese.
A recent study included 90 diabetic patients without occupational exposure to noise, with an average age of 32 years and a predominance of women. The diabetes was divided into :
- Type I diabetes (28% of cases),
- Type 2 diabetes (70% of cases).
The average duration of diabetes was 8 years (1 to 19 years).
- 94% of the patients studied had no complaints of hearing loss,
- 10% of the patients had a bilateral sensorineural hearing loss on audiogram, mild in 5 cases and moderate in the remaining 4 cases.
This loss was significantly different from a normal population of the same age and not subjected to repeated sound aggression.
What is the genesis of this loss?
It is known that diabetes, whatever its type, presents early complications, all the more rapidly as it remains poorly balanced (poorly adapted treatment, unstable diabetes, poorly respected diet).
A well-balanced diabetic throughout his life does not present a higher morbidity than a normal person. Two major complications occur in poorly controlled diabetes.
- Diabetic neuropathy
Linked to a destruction of the myelin that surrounds the nerves, playing a major role in the conduction of nerve impulses. It is the consequence of the chronic increase of sugar in the blood. It results in diabetic polyneuritis with sensitivity disorders in the terminal part of the nerves.
- Diabetic microangiopathy
The chronic increase of sugar in the blood causes, over time, a thickening of the basal membrane of the capillaries (small peripheral vessels) and a chronic damage of the endothelial cells (cells that line the inner side of the vessels, in direct contact with the blood) altering the peripheral vessels. Over time, this leads to chronic damage to these vessels, resulting in diabetic retinopathy, with the possibility of blindness in severe cases (particularly in type II diabetes), kidney damage, and even damage to the distal vessels of the lower limbs, which can lead to repeated amputations of the extremities (particularly the toes).
These two conditions are certainly involved in the neuro-sensory damage to the cochlea in the ear, resulting in sensorineural deafness.
The prevention is simply based on the rigor of the treatment of diabetes which must be perfectly balanced and this, in a constant way (value of the dosage of the glycated hemoglobin).
Diabetes and obesity
In 2013, researchers from Columbia University in New York conducted a study on 1,500 American adolescents (ages 12 to 19). These young people, not subjected to a particularly noisy environment, underwent hearing assessments. In this study, the most obese adolescents showed a more marked hearing loss than normal weight or slightly overweight adolescents.
The most affected frequencies were the low frequencies (frequencies below 2000Hz).
15% of these adolescents had a unilateral hearing loss compared to 8% in the normal weight or slightly overweight population. This is a neuro-sensory loss, particularly in the hair cells of the inner ear.
The hypothesis put forward is that the excess fatty tissue releases inflammatory molecules that alter the hair cells. These lesions are quite different from presbycusis lesions which preferentially affect the high frequencies from 4000Hz and lesions by sound trauma which affect the same frequencies as presbycusis.
However, 80% of these adolescents are not aware of this damage and these obese adolescents should benefit from an ENT follow-up and a regular audiometric assessment, knowing that prevention remains the specific treatment.
However, obesity is not exclusively linked to a sedentary lifestyle or “junk food”: 70% of obese people have at least one parent in the same situation. We currently know the FTO (Fat Mass and Obesity associated protein) gene, a gene located on chromosome 16 that promotes obesity. Lack of sleep remains a major factor (less than 5 hours of regular sleep would increase the risk of obesity by 60%)
It is not surprising, here as elsewhere, that a sedentary lifestyle, junk food, and the absence of regular exercise, promote diabetes and obesity, which contribute, along with our environment, to early hearing impairment.
Our world is aggressive in more ways than one.
Good health, in terms of blood pressure, cardiovascular health, physical health and now audiometry, requires awareness of the aggressive factors that surround us, both nutritional and acoustic, as well as sports activity associated with a healthy diet.
But this plea for hygienic-dietary rules goes, of course, far beyond the audiometric consequences mentioned here.
• Medical Press-
Vol. 46, issue 11, Nov. 2017, p.1089 to 1096
• “Ear and diabetes: a little-known microangiopathic complication?”
Department of endocrinology, diabetology and metabolic diseases, CHU MohammedVI, Marrakech.
• Diabetes and Metabolism-
Vol. 41, suppl. I, March 95, p. A94
• “Obesity is associated with neurosensorial hearing loss in adolescents”
The laryngoscope, June 11, 2013
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