Are the children born of cousin marriages in Asian community at a higher risk of developing a hearing loss due to gene mutations compared to other Asian children in the same community?
the main aim of this research proposal is to discover if the connexin 26 (Cx26) gene mutation that occurs due to cousin marriage among Asian communities is the largest contributor of permanent childhood hearing impairment (PCHI). A group of patients under the age of 18 diagnosed with an autosomal receive sensorineural hearing will be elected for this study.
The data will be collected from all hospitals in the region of west London to increase the chances of finding patients with the Cx26 mutation.
The patients hearing as well as their genetic background will be recorded at the start of the study, to identify the cause of their impairment.
Identifying the cause of mutation will help spread awareness among communities to prevent passing on mutations due to cultural traditions and believes.
If the mutation among Asian communities is found to be significantly increasing the number of PCHI, this will need to have an important public health awareness to manage genetic diseases and optimize public health.
Hearing impairment is one of the causes of human sensory defects, it effects one in 1000 children approximately at birth or during their early childhood (ear disorders related to Connexin 26, 2012). The cause of the impairment that are genetically and clinically heterogenous can be related to a genetic factor in more than half of the cases (Cohn and Kelly, 2012).
Congenital hearing loss is divided into two groups, syndromic form and non-syndromic form. The syndromic form accounts for over 400 genetic syndrome including hearing loss, as 30% of genetic deafness are caused by syndromic form. The non-syndromic form accounts for autosomal recessive as well as autosomal dominant and x-linked hearing losses (Owen, 2005). Autosomal recessive hearing loss display a severe to profound loss across all frequencies, compared to autosomal dominant where the hearing loss ranges from moderate to severe (Kelsell et al, 2008).
Some genes are known to cause mutations responsible of autosomal recessive sensorineural hearing loss, the most common reported mutations were in GJB2. GJB2 provides instructions to form a protein called gap junction beta 2, commonly known as Connexin 26 (Smith et al, 2014). Connexin 26 is found in the inner ear, in a snail shaped hearing organ called the cochlear, its responsible of forming multiple channels called gap junctions that allows the transport of potassium ions between the adjacent cells, any defects in this gene can possibly lead to congenital hearing loss or deafness know sometimes as connexin 26 deafness (Lench et al, 2014).
Some studies reported that mutations in the gene GJB2 are genetically linked to chromosome 13q11. The study identified a link between mutations in the CX26 gene and chromosome 13q11 in three Pakistani families, confirming that the gene is big contributor to prelingual deafness in Caucasian communities. The occurrence of these mutations in this specific populations resulting in carriers between 1 in 30 to 1 in 75 (Davis et al, 2015).
In London the population is estimated at 9,176,530 and it is continually increasing (London population, 2019). Since 1991 the ethnic minority population has dramatically increased especially the Asian population consisting of Indian, Pakistani and Bangladesh. Compared to other local authorities in England, Asians are making 20.9% of London populace (Regional ethnic diversity, 2019).
The number of children diagnosed with a childhood hearing loss has also dramatically increased in London. A particularly high number of children diagnosed with a childhood hearing impairment (PCHI) were among Asian families, where some of the marriages are between cousins, resulting in children 10 times more likely to suffer from a genetic disorder including hearing impairments (Mytton and Machenzie, 2013).
According to a research conducted by an Oxford University anthropologist the number of cousin marriages has dramatically risen in the UK over the past 30 years, specifically among Pakistanis and Bangladeshi communities, estimating the average national risk of genetic disorders at about two in every 100 new born, with the possibility of doubling the risk in marriages between first cousins (Chinthapalli, 2013).
Connexin 26 mutations are genetically recessive and transmitted from parent to a child. The child must inherit one copy of the non-functioning gene from each parent to be affected (Shaw, 2016). Children who only have a single copy of the non-functioning gene and a normal gene do not present signs of haring loss, but the have an increased risk of 1 in 2 of passing on the mutated gene to their offspring (Smith et al, 2014). The effect of the mutation will often produce a pre-lingual hearing loss due to the effect of the mutation taking place before the child can develop speech.
The sense of hearing is accomplished by a process known as the auditory transduction. The ear converts sounds wave in the air into electrical impulses that can be interpreted by the brain. When sound enters the ear, it passes through the external auditory canal, where the tympanic membrane is located (Lefort, 2010). The tympanic membrane will vibrate in response to the sound that is present in the external ear canal. Sounds of low pitch or frequency will produce a slow vibration and high frequency sounds will produce faster vibrations (How hearing works, 2017).
The tympanic membrane is cone shaped structure that is connected to a chain of three bones (malleus, incus and stapes) known as the auditory ossicles. As the tympanic membrane vibrates, it will also vibrate the ossicles, passing on information of frequency and amplitude (Welling, 2017). The information will then be transferred from the tympanic membrane through the ossicles to the stapes footplate. Vibrations produced by the stapes are then passed into a spiral system know as the cochlear which is filled with fluid known as the endolymph (Welling, 2017).
The vibrations in the cochlear causes the fluid to also vibrate, causing the hair cells found in the cochlear to bend. When the hair cells start to bend, the organ of Corti will be stimulated. nerve impulses will be generated and passed on to the brain via the cochlear nerve. The nerve impulses are generated by the hair cells within the organ of Corti (Gelfand, 2016).
There are two types of hair cells in the cochlear, inner hairs cells consisting of one row and out hair cells consisting of three rows. The inner hair cells are responsible of delivering clarity of the sound therefore they detect low pitch sounds while the outer hair cells are responsible of detecting high pitched sounds (audiology, 2017). The hair cells convert mechanical energy to electrical energy that can be transferred to the brain so speech and sounds can be understood. If any damage occurs to the hair cells, the ability to hear will be affected (Delk, 1983).
GJB2 is responsible of manufacturing Connexin 26 protein, also know as gap junction protein, which allows communication between the cells (Al-Sebeih et al, 2013).
The absence of connexin 26 causes a disruption in the flow of potassium from the hair cells located in the cochlear, resulting in the accumulation of potassium in the organ of Corti. the excessive potassium in the organ or Corti will lead to a profound Sensorineural hearing loss (Connexin 26 and hearing loss, 2018). The cause of sensorineural hearing loss lies in the inner ear, the cochlear or the vestibulocochlear nerve.
Although there is little research into this growing issue, there has been studies conducted to investigate the effect of Cx26 gene mutations among other ethic minorities. Some of the information gathered for the study can be useful to investigate whether Asian families are more prone to gene mutations that causes congenital hearing loss due to cousins marriage. Therefore, the aim of the proposed research is to evaluate whether cousin marriage among Asian communities is a big contributor to the increased number of diagnosis of congenital hearing loss in children compared to Asian children diagnosed with PICH from non-consanguineous marriages.
Due to the nature of the study and the involvement of the children below the consenting age of 18, it is important to follow a strict ethical protocol when gathering data for the study. Since all the patient involved in the study are below the age of 18 year, an informed consent must be obtained from the parents of the children after describing the study to them. The gathered information must also be kept confidential and no personal identifiable details must be included.
A participant information sheet will also be giving to the parents to provide an adequate understanding of the aim and the benefits of the proposal and the planned purpose of the collected data.
Ethics approval will also be obtained from the NHS and each hospital in the region where the data will be collected from. A permission will also be obtained from each hospital to allow the use of the data in the study.
the parents must also be informed that their children participation in the study is not obligatory, and it will not affect the treatment their child is receiving. Parents will also be informed that if at any point during the study they would like to withdraw, they are able to do so, and their data will be correctly disposed of.
case control study is conducted by comparing two factors, one that have the medical condition and the other one does not have it. The study is done to identify which factor contribute to the condition (Introduction to study design, 2017).
When gathering data for the research proposal, it is important to implement an inclusion criterion to determine the safety and the accuracy of the study. The criteria must ensure all the patients are under the age of 18 years from Asian parents. The patients must also be carriers of the mutations and their tests should confirm the diagnosis of an autosomal receive sensorineural hearing loss.
Exclusion criteria must also be put in place to ensure all the selected patients are reliable and valid for the research. Children with other type of hearing loss, and those which a syndromic or non-congenital hearing loss will be excluded from the research, as including those patients in the study could influence the results. Patients who are carriers of one copy of the gene will also be excluded from the study, as they will not have the mutation that causes the sensorineural hearing loss.
The information needed for the study will be gathered from the paediatric audiology department in hospitals in west London. Patients referred to the audiology department (a team of healthcare professionals trained to test and diagnosis hearing loss and other related disorders) () from ENT and paediatrics clinics will be elected for this study based on the type of hearing loss they have acquired, the degree of their loss, their genetic history and parents origin. Patients will be from both genders, aged from 6 months to 18 years. patients history will need be obtained including, family history, genetic evaluation, pedigree study and a battery of diagnostic tests. The patients acquired hearing loss will need to be confirmed as non-syndromic autosomal recessive sensorineural loss
The number of the patients chosen for the study should be large enough to enable adequate comparison. Therefore, the data will be collected from more than one hospital in London. Choosing only one hospital to collect the data from will strict the study as the patients might not fit the inclusion criteria, or they might not be comfortable volunteering for the research.
For each patient an information sheet must be filled out to include their gender, age, their parents age and consanguinity, history of their birth and pregnancy, delivery type and other clinical background.
The patients that meet the inclusion criteria will have a full battery of audiological test including an otoscopic examination, which is necessary to check the outer ear and the external auditory canal for any abnormalities. pure tone audiometry (for children above the age of 2.5) and behavioural observational audiometry (for children below the age of 2.5) is needed to measure the hearing sensitivity for each patient (Debroah, 2017). Tympanometry to measure the mobility of the tympanic membrane. The graph produced from tympanometry test will represent the how air pressure in the ear canal effect the movement of the tympanic membrane (What is tympanometry, 2018). Conducting a PTA along with tympanometry test will enable diagnosing the type of loss each patient has.
Other tests will be conducted including acoustical reflex threshold to assess the neural pathway surrounding the stapedial reflex. Auditory brainstem response to identify any neurological abnormalities in the 8th nerve or the brainstem. Finally, transient evoked otoacoustic emission for threshold estimation and hearing loss confirmation.
Blood samples will also be drawn from each patient to check the DNA using the appropriate testing tool for the Cx26 mutation.
The information collected will produce categorical data. Statistical analysis will be used to define the data characteristics. The null hypothesis of the data is true therefore, Chai-square test will be used to evaluate the connections among the giving variable and to determine if there is a significant different between the variables. Depending on the p value of the variables, if more than 0.05 the finding will be considered significantly high.
The main outcome of the statistical analysis is to determine whether cousin marriage is a larger contributor of congenital hearing loss compared to other marriages.
If the number of children with congenital hearing loss found is greater in cousin marriages among Asian communities, this will need a significant public health awareness, as if it is prevented it could reduce the number of children born with permanent hearing loss and other congenital conditions. Families from Asian communities will also need to have enough information to make an informed decision regarding their family planning and understand the risk associated with consanguineous marriages. Awareness can also be spread by providing genetic counselling to help families make a more informed choice to minimise the risk of passing on mutations.