Consanguinity and Hearing Impairment in a Deaf School

Objective: To find out the frequency of consanguinity and positive family history of hearing impairment among deaf children in a deaf school in Bangladesh. Methods: This was a retrospective study were included 150 patients. They were subjected to complete audiological examinations. These pupils were collected from Integrated Pre-school for Hearing Impaired children (IPSHIC) of SAHIC, Mohakhali, Dhaka, Bangladesh. Results: The results showed that out of 150 Hearing impaired (HI ) children 30.0% (45) were from the consanguineous parents and 70.0% (105) from nonconsanguineous parents. Also found 22.0% (33) had positive family history of hearing impairment. Conclusion: Prevention is only means to reduce the prevalence of Congenital hearing impairment.


Introduction
Deafness is the hidden disability of childhood, and leads to poor educational and employment prospects.Hearing impairment has debilitating effects on children as it can retard individual's language acquisition skills and impair the overall development. 1 UK approximately one child in 1000 is born with a bilateral permanent childhood hearing impairment (PCHI).This is defined as confirmed permanent bilateral hearing impairment exceeding 40dBHL(Hearing level) (average of pure tone thresholds at 0.5, 1, 2 and 4 KHz in the better hearing ear).About 60% of these children have a moderate (41-60dBHL) Hearing loss, while the remainder have a severe (61-80dBHL) or profound (>81dBHL) loss.WHO estimated in 2005 that there were 278 million people worldwide with bilateral moderate to profound hearing loss of whom 62 million had deafness that begin in child hood.2/3 rd of people with moderate to severe hearing impairment live in developing countries. 2 Bangladesh, deafness is a major public health problem.The country has a population of over 130 million and about 13 million people are suffering from variable degree of hearing loss which 3 million are suffering from severe to profound hearing loss leading to disability. 3 In nearly half of children in the world with permanent hearing impairment the cause is genetic. 4Of the genetic causes of hearing loss, syndromic form of deafness accounts 30% and non-syndromic hearing loss accounts for nearly 70% cases. 5Major causes of deafness among children are genetic.Approximately 70-80% is autosomal recessive,15-20% autosomal dominant and 2-3% are x-linked or mitochondrial. 6,7It is already established that 50 percent of the causes of deafness are preventable. 8There is evidence that profound hearing impairment is more prevalent in countries where consanguineous marriages are common. 9nsanguinity refers to marriages between individuals who share at least one common ancestor and is conventionally applied to persons related as first or second cousins or to relatives within the extended family or same tribe. 10nsanguineous marriages are traditional in many Asian, African and South American communities.Consanguineous marriages are most prevalent in Arab countries, followed by India, Japan, Brazil and Israel.This is most common in lower educational and socioeconomic groups, among the traditionally religious, and in those marrying young.Particularly in the Muslim community, 20-50 percent of all marriages are consanguineous. 11e most recent consanguinity estimate indicated that some 10.4% of the world population are either married to a biological relative or are the progeny of a consanguineous union.There is no prescription that Muslims marry within the family, and first cousin marriage is freely permissible in the Jewish, Christian protestant, Buddhist and Zoroastrian / parsi religions.Also seen in the Dravidian Hindu populations of southern India preference is for a first cousin marriage between a man and his mother's brother's daughter, or more often marriage between an uncle and niece. 12 Pakistan, the prevalence of consanguinity is reported to be 60 percent. 13Many studies have shown that the off spring of consanguineous marriages have a greater incidence of autosomal recessive diseases, including hearing impairment. 14In addition ,the great majority of hereditary deafness is caused by single gene, autosomal recessive inheritance. 15n-syndromic hearing impairment accounts for 80 percent of cases of hereditary deafness.Mutations in the same single gene have been shown to be responsible for both autosomal dominant and autosomal recessive forms of hearing impairment(e,g-connexin26). 16A single locus, DFNB1, has been found to contribute to the majority of cases of autosomal recessive, non-syndromic hearing impairment. 17e study shows, the prevalence of deafness in children of Bangladeshi origin resident in East London up to 16 years of age was calculated to be at least 3.86 per 1000 which is 2.3 times higher the national average of 1.65/1000.In this study, the excess of childhood deafness was also attributed to genetic cause secondary to the practice of consanguineous marriage.One analysis suggests that consanguinity contributes to the raised prevalence of deafness in British Bangladeshi population.The distribution of causes of deafness has been genetic causes in 60%, acquired/ environment in 18%, and unknown in 22% of the 134 subjects in the study carried in East London Bangladeshi population.Amongst the genetic causes, most of the children (58%) had non-syndromic deafness.Even after genetic analysis, the cause of deafness remains undetermined in 22% patient. 18 developing countries, the WHO recommends that children's hearing should be screened at least at school entry, using simple audiometer, and that the external ear be inspected for the presence of discharge.Earlier detection with universal neonatal screening is now practiced in developed countries.
In Bangladesh, the government runs seven deaf schools, where education is given free of cost.In the non-government sector there are about thirty schools for deaf. 3Special teaching should be given by teachers of the deaf and available for deaf and partially hearing children.

Methods
This Retrospective study was carried out in Integrated pre-school for hearing impaired children (IPSHIC) of SAHIC, Mohakhali, Dhaka-1212.
Study period of February 2012 to July 2012 (6 months).
One Hundred and fifty (150) children was Purposely selected on single random method.The patient selected on the basis of Non probability purposive sampling method (Judgment sampling) who are admitted student in the IPSHIC.The parents or guardians of the patients were informed about the study and their consent was obtained.

Discussion
In this study 150 deaf children aged below 12 years have been studied.Emphasis was given on history, clinical examination and audiological investigation.Although this study had been carried out within a limited period of time and with a limited number of patients yet this may in some extent reflex the overall situation of the society as the patient had been collected from a referral from different areas of the country.In this series, age distribution of the children presented to the deaf school showed that maximum number patients (60.0%) were in the age group between 5-8 years.
This study reflected parents were consanguineous in 30.0%(1 st cousin 22.0% and 2 nd cousin 8.0%), which is supported by the study Bajaj Y et al. 18 who also found consanguinal marriage in 33% in British-Bangladeshi community.Various other studies conducted amongst children born to consanguineous parents reveal a much higher incidence of hearing loss in this group. 9,10,11 s study also reveals a family history of deafness in 22. 0%, this is supported by the study J.O. Hara et al 19  In this study population, Consanguinity 30% was observed.This high percentage of consanguinity indicating that the consanguinity is a risk factor for hereditary hearing loss, but this is not overall focus in Bangladesh.
This subject also needs further investigation to rule out genetic causes such as GJB2 gene (connexin 26) mutation etc. 23 .However such testing was beyond the purview of the present study.This protocol should include both, audiological diagnostic test as well as suitable immunological and genetic studies to establish the causes of the condition.

Conclusion
Condition such as Consanguinity require more research to establish or discredit them as potential causes of childhood hearing loss.Prevention is only means to reduce the prevalence of congenital hearing impairment.This can be achieved by genetic counseling of individually and families at risk.Further large number of hearing impaired babies gave history of conditions that are preventable, such as Low birth weight, Birth asphyxia, meningitis etc.This suggest that a large number of babies could be prevented from developing hearing loss.

Table - IV
Distribution of Degree of hearing loss (n=150)