Familial auditory neuropathy spectrum disorder – A case report

Auditory neuropathy is a disorder where the transmission of the auditory signals from the inner ear to the auditory nerve and auditory brainstem is distorted. Auditory neuropathy is characterized by normal outer hair cell function within the cochlea. However auditory nerve function is disrupted [1]. Patients with the characteristics of auditory neuropathy were initially reported as early as the 1970’s [2]. Patients with normal pure-tone audiograms and absent Auditory Brainstem Responses (ABR) who reported to have difficulty in understanding speech especially in the presence of background noise were reported [3-9]. The audiometric results in patients with auditory neuropathy can vary greatly anywhere from normal hearing to severe hearing loss [10]. Research suggests that auditory neuropathy is due to an abnormality or lesion at the level of the inner hair cells, the synapse between the inner hair cells and auditory nerve, or at the auditory nerve itself [11]. The lesion could be anywhere from the inner hair cells in the cochlea up to the auditory cortex [12]. Recently, authors [11], suggested that any pathological mechanism that impairs temporal encoding and neural synchrony might be responsible for auditory neuropathy.


Introduction
Auditory neuropathy is a disorder where the transmission of the auditory signals from the inner ear to the auditory nerve and auditory brainstem is distorted. Auditory neuropathy is characterized by normal outer hair cell function within the cochlea. However auditory nerve function is disrupted [1]. Patients with the characteristics of auditory neuropathy were initially reported as early as the 1970's [2]. Patients with normal pure-tone audiograms and absent Auditory Brainstem Responses (ABR) who reported to have difficulty in understanding speech especially in the presence of background noise were reported [3][4][5][6][7][8][9]. The audiometric results in patients with auditory neuropathy can vary greatly anywhere from normal hearing to severe hearing loss [10]. Research suggests that auditory neuropathy is due to an abnormality or lesion at the level of the inner hair cells, the synapse between the inner hair cells and auditory nerve, or at the auditory nerve itself [11]. The lesion could be anywhere from the inner hair cells in the cochlea up to the auditory cortex [12]. Recently, authors [11], suggested that any pathological mechanism that impairs temporal encoding and neural synchrony might be responsible for auditory neuropathy.

Case presentation
A Case aged 60 years male [CASE 1] and another 31 years old Abstract Auditory Neuropathy Spectrum Disorder (ANSD) is a hearing disorder where outer hair cell function inside the cochlea is typical, but inner hair cell and/or the auditory nerve function is disrupted. It is a heterogeneous disorder which can have any congenital or acquired causes. Additionally, the etiology of auditory neuropathy is immense, which may comprise prematurity, hyperbilirubinaemia, anoxia, hypoxia, congenital brain anomalies, ototoxic drug exposure, and genetic actors. It is projected that roughly 40% of cases have an underlying genetic origin, which can be inherited in both syndromic and non-syndromic conditions. The below case report serves as an extra evidence for the underlying genetic trait in ANSD. The study presents two cases where, both father and daughter were diagnosed as ANSD.

Case Report
Familial auditory neuropathy spectrum disorder -A case report Aravinda HR 1 *, Shalini A 2 and Prasad CM 2 Hearing aid trail was conducted for both father and daughter with high gain, super power hearing aids (Oticon Dynamo SP 4) and was not found to be benefi cial in speech understanding.

Discussion
A study [13], reported that patients with characteristics of non-syndromic hereditary auditory neuropathy were identifi ed in one large and three smaller Chinese families.
Pedigree analysis suggested an X-linked, recessive hereditary pattern in one pedigree and autosomal recessive inheritances in the other three pedigrees. The phenotypes in the study were typical of auditory neuropathy; they were transmitted in different inheritance patterns, indicating clinical and genetic heterogeneity of this disorder. Another study [14], discovered that mutation with some of the genes and/or loci to be the cause for auditory neuropathy spectrum disorders (ANSDs). A study conducted by [15], concluded that sixtysix percent of patients with auditory neuropathy spectrum disorder were born of consanguineous marriages. Genetic alterations were investigated in 47 patients with hearing loss and clinical diagnosis of auditory neuropathy, and the c.35delG mutation in the GJB2 gene was identifi ed in three homozygous patients, and the heterozygous parents of one of these cases.
Additionally, OTOF gene mutations were tracked by complete sequencing of 48 exons [16]. A study [17], result showed that collectively, the de novo ATP1A3 variant can cause post lingualonset auditory synaptopathy, making this gene a signifi cant contributor to sporadic progressive ANSD. The above studies are in agreement with the fi ndings of the current study which indicates a familial trait of ANSD.

Conclusion
The fi ndings of the above case report serve as an extra evidence for the already existing studies which defi nes a familial trait of ANSD. It is also important to report such cases so that the genetic factor resulting in ANSD is deeply understood and researched.

Author note
Informed Patient consent was taken before collecting data and publication.

Confl ict of interest statement:
The authors of this article certify that they have NO affi liations with or involvement in any organization or entity with any fi nancial interest (such as honoraria; educational grants; participation in speakers' bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-fi nancial interest (such as personal or professional relationships, affi liations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.