|Year : 2016 | Volume
| Issue : 4 | Page : 280-283
Auditory neuropathy spectrum disorder in a child with albinism
Mayur Bhat, G Archana, M Ayas
Department of Speech and Hearing, School of Allied Health Science, Manipal University, Manipal, Karnataka, India
|Date of Web Publication||13-Oct-2016|
Department of Speech and Hearing, School of Allied Health Science, Manipal University, Manipal, Karnataka
Source of Support: None, Conflict of Interest: None
Albinism is a congenital disorder characterized by complete or partial absence of pigments in the skin, eyes, and hair due to the absence or defective melanin production. As a result of that, there will be disruption seen in auditory pathways along with other areas. Therefore, the aim of the present study is to highlight the underlying auditory neural deficits seen in albinism and discuss the role of audiologist in these cases.
Keywords: Albinism, Auditory neuropathy, Melanin
|How to cite this article:|
Bhat M, Archana G, Ayas M. Auditory neuropathy spectrum disorder in a child with albinism. Indian J Otol 2016;22:280-3
| Introduction|| |
Auditory neuropathy (AN) is defined as a clinical syndrome characterized by normal outer hair cell (OHC) functioning and abnormal or absent auditory pathway transduction.  It affects the normal synchronous activity in the auditory nerve, without affecting the amplification function in the OHCs. The potential sites of dysfunction include inner hair cells, synaptic dysfunction between nerve and hair cells, and auditory nerve fiber itself. Hence, the term AN spectrum disorder (ANSD) was coined to cover various sites of dysfunctions. It was initially thought to be a rare disorder, but later studies estimated that approximately 7%-10% of children diagnosed with permanent hearing loss had AN.  It is also reported that 10% of the patients with deafness may have AN. 
Common signs and symptoms include hearing loss (variable), speech understanding difficulty, particularly in noisy environments, tinnitus, and temporal deficits.  The output from the subjective evaluation in individual with AN includes pure tone thresholds ranging from normal to profound. Audiogram patterns include 82% - an asymmetrical hearing loss, 14% - an asymmetrical hearing loss, 4% - a unilateral hearing loss, 43% - flat audiogram pattern, 28% - raising audiogram pattern,  poor speech recognition abilities for their degree of hearing loss. Yellin et al. 1989 compared speech discrimination score (SDS) in patients with ANSD to those SDS scores expected by particular degree of hearing loss of patient with sensory loss.  They inferred that when the pure tone average exceeds about 30 dB, the SDS of AN patient falls significantly below the expected level.
The objective evaluation leads to following results in the case of AN, which includes the absence or elevated acoustic reflex,  normal outer hair cells functioning which is indicated by the presence of otoacoustic emissions (OAEs)  and cochlear microphonics, abnormal auditory nerve response as observed by absent or markedly abnormal auditory brainstem response (ABR) and the presence of higher cortical potentials.
Common causes of AN are genetic factor which contributes to more than 40% of the patients with ANSD. Other causes include tumors of vestibulocochlear nerve -acoustic neuroma, cerebellopontine angle tumor; degeneration of nerve - aging, Frederic's ataxia, multiple sclerosis; infections - mumps, rubella, cytomegalovirus, etc.; birth-related conditions - hyperbilirubinemia, anoxia, and hypoxia; metabolic and immune disorder - albinism; syndrome mitochondrial syndromes, Friedreich's ataxia, Stevens-Johnson syndrome More Details, Ehlers-Danlos syndrome More Details, Charcot-Marie-Tooth syndrome, etc.; idiopathic. 
Albinism is a congenital disorder characterized by the complete or partial absence of pigments in the skin, hair, and eyes due to the absent or defective copper-containing enzyme involved in the production of melanin. According to the National Organization for Albinism and Hypopigmentation, one in every 17,000 people in the United States has some type of albinism. Researchers have identified five genes which on mutation may cause albinism. In normals, these five genes are responsible for the production of melanin. These five genes code for an amino acid called tyrosine which helps in the production of melanin in humans. They are tyrosinase, oculocutaneous albinism (OCA) 2, tyrosine-related protein 1, solute carrier family 45 member 2, and melanocortin 1 receptor.
General characteristics of albinism can be grouped under three major headings. They are visual characteristics, skin characteristics, and other characteristics. Visual characteristics Include miss routing in retinogeniculate projection resulting in the abnormal decussation of optic nerve, photophobia with decreased visual acuity, foveal hypoplasia; nystagmus: Irregular, rapid movement of the eye back and forth; astigmatism: Irregular-shaped cornea; amblyopia: Decrease in visual acuity due to reduced transmission to the brain; optic nerve hypoplasia: Poorly developed optic nerve. Skin characteristics include white and pale in color, more prone to skin cancer and other skin disorder. Another characteristics include hearing problem - retrocochlear pathology (RCP), blood clotting problem; red/pink eye - lack of pigmentation, sensitivity to bright light, "slowness to see" in infancy. 
Albinism as a cause for developing ANSD in children is not extensively studied and reported in the literature. In the current scenario with increasing incidence of ANSD in children as well as in adults, there is a need for documenting and studying all possible causes that can lead to ANSD. Albinism can be considered as one of the conditions, which has to be studied comprehensively so that other than the general clinical manifestation, audiological manifestations can also be studied broadly. Hence, the present case study highlights the audiological profile of a child with albinism who was diagnosed as having ANSD.
| Case Report|| |
A 6-month-old male child came to the Department of Pediatrics of the study center on September 15, 2012, with a complaint of respiratory distress. The child was kept on continuous positive air pressure and was weaned off after 7 days. The preterm child (34 weeks) was referred to an ophthalmologist and was diagnosed with ocular albinism with foveal hypoplasia. Depigmentation was seen in skin, hair, and eye. Hence, the final diagnosis of OCA was given. The child was referred to the Department of Speech and Hearing on September 17, 2012, for a detailed audiological evaluation. Oral consent was taken from the parents before starting the test. Initially, audiologist took a detailed case history, which included the demographic details, onset of the problem, medical history, family history of hearing loss, consanguinity, and auditory behaviors of the child. Tests carried out include ABR and OAE. A provisional diagnosis of RCP was given. The child visited the Department of Speech and Hearing for follow-up evaluation on March 2, 2013. Tests carried out include, ABR, OAE, electrocochleography (EcochG), and late latency response (LLR). Protocol for ABR, LLR, and EcochG is given in [Table 1],[Table 2] and [Table 3].
|Table 1: Recording parameters for auditory brainstem response generation|
Click here to view
| Results|| |
According to the case history, the parent does not suspect hearing loss and there is no family history of hearing loss as well as consanguinity. History also revealed that child exhibits poor auditory behavior, even for loud sounds. Initial assessment revealed the presence of bilateral transient-evoked OAE (TEOAEs), which indicated that OHCs were functioning normally. ABR findings indicated that there was no identifiable fifth peak at 90 dBnHL. A provisional diagnosis of RCP was given and the child was called for follow-up after 1 month to do further analysis. Parents were counseled about the importance of speech and language stimulation at home and also observations of auditory responses. During the second visit, bilateral TEOAEs were absent. ABR findings indicated bilateral fifth peak absent at 90 dBnHL [Graph 1 [Additional file 1]]. To confirm the diagnosis, EcochG was done. Cochlear microphonics were present which indicated normal hair cell functioning. LLR revealed that P1 was identified at a latency of 182 ms bilaterally which indicated that the signal is reaching the cortex. Hence, the final diagnosis was given as auditory dyssynchrony. Parents were counseled to observe auditory responses at home and follow-up after 2 months.
| Discussion|| |
AN in the pediatric population is a very rare condition.  Even though several cases have been reported in the literature for auditory dyssynchrony, there is a lack of evidence with regard to albinism as a cause of Alzheimer's disease (AD). Because of this, there is a lack of awareness among parents and physicians regarding the same, and thereby such children went unidentified and intervened at an early age. Hence, it is of importance to perform some clinical studies to confidently state that albinism may be a causative factor for AD. This case report is an initial step for this purpose and is the only report of its kind in the literature which reports the audiological profile of a child with albinism as previous studies have been done only in animals and lacks support.  Previous studies reported that the human cochlea and auditory brainstem hold place for any amount of melanin and it can be hypothesized that any alteration in this pigment level might affect the normal physiology of the cochlea as well as auditory brainstem. 
In the current case, the results of TEOAE and EcochG support the notion that the OHC functioned normally in the child even though the TEOAEs were absent on the second visit which can be associated with the presence of upper respiratory tract infection. This indicates that the change in the metabolic activity which is resulting in the variation of melanin level has not altered the cochlear function in the present case scenario. However, ABR results revealed that there was no identifiable fifth peak at 90 dBnHL. This made us confident enough to state that the problem is not in the cochlea rather it is somewhere beyond the cochlea. Alterations in the melanin pigment in the ABR may be the reason why there was an absent ABR in this case since all other possibilities were excluded from the list. This finding supports Creel et al., who stated that there could be anomalies of decussating auditory pathways in albinism.  In addition to this, the presence of P1 which is the component of the LLR was obtained at 102 ms which indicates that the stimulus is reaching the cortex and the pathology lies between the cochlea and the cortex.
The result obtained from this case can be used to make an assumption that alteration of melanin pigment in albinism may not have an effect on the functioning of the cochlea and the central auditory cortex rather it affects the functioning of the auditory brainstem alone. This hypothesis should be proved on a larger number of participants in future researches. This evidence can be used to make awareness among parents and physicians regarding the importance of early identification and intervention of these individuals so that they can have near normal speech and language skills.
| Conclusion|| |
From this case study, it can be concluded that albinism can be a causative factor for AN. Thus, albinism also should be included as one of the high-risk factors which lead to hearing loss
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]