Медицина/ 7.Клиническая медицина.

Zhaisakova D.E., Kaltayeva M.B.

Asfendiyarov Kazakh National Medical University, Department of Otorhinolaryngology, Kazakhstan.

The study of sensorineural hearing loss etiological structure.

The problem of hearing loss is still relevant in the medical and social terms, as it often leads not only to a significant life quality deterioration, but also causes disablement in a number of patients.

The identification of the hearing loss causes is the main stage on the way of solving problems related to the search for effective methods of inner ear diseases treatment. Whereas, genetic disorders were deemed to be the cause of 60% of all congenital and early pediatric hearing loss cases. [1; 2]. About 2/3 (66%) of nonsyndromic hearing impairments are of genetic origin, while 1/3 (33%) are associated with environmental factors [3, 5].

In 2005, R. Smith published an article, which contains the diagram demonstrating data on syndromic and nonsyndromic forms of hearing loss according to its share in the general group of congenital and prelingual pediatric hearing loss cases (Pic. 1) [24;5].

Picture 1. Summary of congenital and prelingual hearing loss genetic characteristics according to R.Smith and Guy Van Camp [24; 5].

According to Figure 1, created by R. Smith and Guy Van Camp, 50% of all congenital and prelingual hearing loss has an acquired character. The rest cases occur due to genetic changes. Hereditary hearing loss include up to 30% syndromic forms and 70% of nonsyndromic forms of hearing impairments. It is believed that the latter include 75% -85% autosomal recessive forms, 15% -24% autosomal dominant forms, 1-2% X-linked recessive forms, and 1% was associated with mitochondrial DNA mutations. Autosomal recessive nonsyndromic hearing loss forms in 50% of cases are linked with the DFNB1 locus (Cx26 and Cx30 genes). Thus, the Cx26 gene mutation amounts not less than 16% of all prelingual SNHL cases. The remaining 50% are associated with the other recessive loci [5].

The development of hearing pathology is influenced by various causes. It has been established that the causes include violations in the antenatal - prenatal period (marriage between close relatives, rubella, syphilis, metabolic disorders, drugs with ototoxic effect), perinatal period (birth trauma - anoxia, jaundice (hemolytic), drugs with ototoxic effect) and neonatal - postnatal period (otitis media, infectious diseases (meningitis, measles, parotitis), trauma of the cervical spine and head, drugs with ototoxic effect) (Yu.V. Kozyun, G.A. Tavartkiladze).

According to various authors, the acquired hearing loss in children most commonly occurs as a result of prenatal infections such as toxoplasmosis, rubella, cytomegalovirus, and herpes. In this regard, in recent years there has been a significant increase in interest in the problem of prenatal infections, among which a special attention has been paid to herpesvirus infections and, in particular, cytomegalovirus infection. Herpes and cytomegalovirus infections remain one of the leading causes of stillbirth, spontaneous miscarriages, premature births, neonatal morbidity and infant mortality. According to the data of domestic and foreign specialists, from 0.5 to 5% of children are born with congenital CMV (cytomegalovirus) infection, about 90% of which of are asymptomatic carriers children [8; 7]. At the same time, the subclinical form of CMV infection does not mean a guarantee of well-being, violations of central nervous system, hearing, vision, cerebral palsy, mental retardation, poor school performance are diagnosed in 5-15% of such children in the next 1-2 years and later [9;10]. And also high incidence of Down's disease is associated with congenital CMV infection [11]. Many surviving children have long-term and sometimes lifelong complications: 28% have a mental retardation, 58% have neuromuscular disorders, including cerebral palsy, as well as somatosensory insufficiency, 20% have hearing loss, 24% have visual impairment [11]. All this led the European Regional Bureau of the World Health Organization to the decision to include CMVI (cytomegalovirus infection) in a group of diseases that determine the future of infectious pathology in 1984 [11]. In addition, WHO included CMVI in intrauterine infectious disease syndrome called TORCH syndrome, which includes T-toxoplasmosis, O-syphilis, listeriosis and other infections, R-rubella, C-cytomegalovirus infection and chlamydia, H-herpes and hepatitis [11].

According to the large-scale study conducted by the researchers of the Research Institute of Obstetrics and Gynecology of the Republic of Kazakhstan, primary CMV infection was detected in 31.2% of women with threatened miscarriage, in 18.2% of women with a spontaneous abortion, in 39.5% of women with premature birth, at 53.4% of women with polyhydramnios, in 35,4% of women with missed miscarriage [11].

And also premature birth, low body weight, child asphyxia refer to important exogenous risk factors.

In the total population of newborns, the share of premature infants is becoming more and more significant and amounts to 5-10% of newborns [19]. According to studies conducted in France and the United States, the incidence of severe hearing impairment in the group of newborns with a body weight of less than 2000g is 15.5 per 1000, and in the group of small premature infants it is 4-5% [20]. In recent years, the importance of perinatal pathology has significantly increased as one of the causes of congenital hearing loss and deafness in children [22,23]. In addition, it is known that this pathology develops in the first year of life in 82% of children with hearing loss and deafness, and in 38.5% of them - in the perinatal and neonatal period [21].

Postnatal infections, in particular, bacterial meningitis caused by Neisseria meningitidis, Haemophilusinfluenzae, Streptococcus pneumoniae, are often complicated by total hearing loss, vestibular disorder [5].

Meningitis continues to be one of the most common forms of damage to the central nervous system (neuroinfections) in adults and children worldwide. Depending on the pathogens, all cases of diseases are usually subdivided into bacterial (purulent) and viral (serosal) meningitis [4]. According to the World Health Organization, around 1 million cases of bacterial purulent meningitis are registered worldwide annually, 200 thousand cases of which are fatal cases [12,13]. Meningitis is one of the most frequent clinical forms in the structure of the general pathology of the nervous system [13; 17].

In the Republic of Kazakhstan, meningococcal infection is more often diagnosed in children. According to official statistics of the Republic of Kazakhstan, the highest incidence rate was registered in Almaty city (1.58 per 100 thousand people in 2012) and in Astana city (1.38 per 100 thousand people in 2012) [18].

Currently, despite the reduction in morbidity, the level of lethality remains high. Children of Almaty were conducted a study on the clinical and epidemiological features of meningococcal infection at the present stage in 2009-2013, which goal was to assess the incidence of generalized forms of meningococcal infection in children at the age of 0-14 years, assess the distribution of Neisseria meningitides serogroups in children patients, estimate the proportion of meningococcal meningitis and meningitis of unclear etiology in the overall structure of bacterial meningitis and to estimate the frequency of treatment in the intensive care unit, the incidence of complications, mortality. The study revealed that within five years the incidence of meningococcal infection ranged from 5.7 per 100 thousand people to 14.7 cases per 100 thousand people. These data exceeded the official figures twice. The lowest incidence was observed in 2009, the highest in 2012. This demonstrates the wave character of the epidemiological process of meningococcal infection, which makes it possible to predict an increase in the incidence rate in the next two years [18].

The patients were mostly children under the age of 5, with the highest incidence rate in children under 1 year old. In general, if we speak about all purulent bacterial meningitis cases, then there is no tendency to reduce the incidence rate for the period 2009-2013. Meningococcal meningitis (32%) prevailed in the etiologic structure of the children's population of Almaty (1993-2007) and unfortunately a percentage of meningitis of unknown etiology was remaining high (39,8 %) [18]. There is a high mortality rate in purulent meningitis, reaching an average of 4-10%, which is due to the severity of the course and numerous complications of the disease. They include: toxic shock syndrome (TSS), hypertension-hydrocephalic syndrome (HHS), sensorineural hearing loss syndrome, development of paresis and paralysis, apallic syndrome. Persistent organic lesions of the central nervous system (CNS) in the residual period are observed in almost 1/3 of the children who have recovered from the disease [16, 14, 15, 13].

For a long time, hearing loss was considered to be acquired as a result of ototoxic antibiotics effect. The existence of a hereditary predisposition to the effects of the ototoxic drugs is no longer in doubt. Isolated hearing loss develops when there is a mutation in the gene encoding the 12S protein of ribosomal RNA of mitochondrial DNA. But, the onset of hearing loss with this mutation may also be related to the effect of ototoxic drugs. Carriers of the mutation in 12S gene of ribosomal RNA of isolated hearing loss development are enough smaller doses of aminoglycosides [5, 26].

Numerous studies indicate a significant contribution of genetic factors in violations of auditory perception. The absence of data on cases of hearing impairment among family members does not exclude the possibility of the genetic origin of hearing loss, but one can also expect the acquired character of the lesion in a child from deaf parents.

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