Childhood hearing loss is a key feature of CAPOS syndrome: A case report

Is auditory neuropathy an appropriate term? A systematic literature review on its aetiology and pathogenesis

To clarify the aetio-pathogenesis of Auditory Neuropathy Spectrum Disorder (ANSD), a total of 845 papers were divided into four categories: Review, Audiology, Treatment and Aetiology. Aetiology was the topic analysed categorising papers as: Genetics, Histopathology, Imaging and Medical diseases. Isolated ANs were in relation to Otoferlin, Pejvakin and DIAPH3 deficiency, and the syndromes were mainly Charcot Marie Tooth, Friedreich Ataxia, mitochondrial disorders and those associated with optic neuropathies. In histopathology papers, important information was available from analyses on human premature newborns and on some syndromic neuropathies. From cochlear dysmorphism to cerebral tumours associated with ANs, these are described in what is identified as the Imaging area. Finally, the prevalent clinical pathology was bilirubinopathy, followed by diabetes. In conclusion, AN/ANSDs do not refer to a clear pathological condition, but to an instrumental pattern without any evidence of auditory nerve involvement, except in a few conditions. The terms AN/ANSD are misleading and should be avoided, including terms such as “synaptopathy” or “dis-synchrony”.

Auditory Neuropathy as the Initial Phenotype for Patients With ATP1A3 c.2452 G > A: Genotype-Phenotype Study and CI Management

Objective: The objective of this study is to analyze the genotype–phenotype correlation of patients with auditory neuropathy (AN), which is a clinical condition featuring normal cochlear responses and abnormal neural responses, and ATP1A3 c.2452 G > A (p.E818K), which has been generally recognized as a genetic cause of cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS) syndrome.

Methods: Four patients diagnosed as AN by clinical evaluation and otoacoustic emission and auditory brainstem responses were recruited and analyzed by next-generation sequencing to identify candidate disease-causing variants. Sanger sequencing was performed on the patients and their parents to verify the results, and short tandem repeat-based testing was conducted to confirm the biological relationship between the parents and the patients. Furthermore, cochlear implantation (CI) was performed in one AN patient to reconstruct hearing.

Results: Four subjects with AN were identified to share a de novo variant, p.E818K in the ATP1A3 gene. Except for the AN phenotype, patients 1 and 2 exhibited varying degrees of neurological symptoms, implying that they can be diagnosed as CAPOS syndrome. During the 15 years follow-up of patient 1, we observed delayed neurological events and progressive bilateral sensorineural hearing loss in pure tone threshold (pure tone audiometry, PTA). Patient 2 underwent CI on his left ear, and the result was poor. The other two patients (patient 3 and patient 4, who were 8 and 6 years old, respectively) denied any neurological symptoms.

Conclusion:ATP1A3 p.E818K has rarely been documented in the Chinese AN population. Our study confirms that p.E818K in the ATP1A3 gene is a multiethnic cause of AN in Chinese individuals. Our study further demonstrates the significance of genetic testing for this specific mutation for identifying the special subtype of AN with somewhat favorable CI outcome and offers a more accurate genetic counseling about the specific de novo mutation.

ATP1A3-Related Disorders: An Ever-Expanding Clinical Spectrum

The Na+/K+ ATPases are Sodium-Potassium exchanging pumps, with a heteromeric α-β-γ protein complex. The α3 isoform is required as a rescue pump, after repeated action potentials, with a distribution predominantly in neurons of the central nervous system. This isoform is encoded by the ATP1A3 gene. Pathogenic variants in this gene have been implicated in several phenotypes in the last decades. Carriers of pathogenic variants in this gene manifest neurological and non-neurological features in many combinations, usually with an acute onset and paroxysmal episodes triggered by fever or other factors. The first three syndromes described were: (1) rapid-onset dystonia parkinsonism; (2) alternating hemiplegia of childhood; and, (3) cerebellar ataxia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS syndrome). Since their original description, an expanding number of cases presenting with atypical and overlapping features have been reported. Because of this, ATP1A3-disorders are now beginning to be viewed as a phenotypic continuum representing discrete expressions along a broadly heterogeneous clinical spectrum.

Auditory Neuropathy Spectrum Disorders: From Diagnosis to Treatment: Literature Review and Case Reports

Auditory neuropathy spectrum disorder (ANSD) refers to a range of hearing impairments characterized by deteriorated speech perception, despite relatively preserved pure-tone detection thresholds. Affected individuals usually present with abnormal auditory brainstem responses (ABRs), but normal otoacoustic emissions (OAEs). These electrophysiological characteristics have led to the hypothesis that ANSD may be caused by various dysfunctions at the cochlear inner hair cell (IHC) and spiral ganglion neuron (SGN) levels, while the activity of outer hair cells (OHCs) is preserved, resulting in discrepancies between pure-tone and speech comprehension thresholds. The exact prevalence of ANSD remains unknown; clinical findings show a large variability among subjects with hearing impairment ranging from mild to profound hearing loss. A wide range of prenatal and postnatal etiologies have been proposed. The study of genetics and of the implicated sites of lesion correlated with clinical findings have also led to a better understanding of the molecular mechanisms underlying the various forms of ANSD, and may guide clinicians in better screening, assessment and treatment of ANSD patients. Besides OAEs and ABRs, audiological assessment includes stapedial reflex measurements, supraliminal psychoacoustic tests, electrocochleography (ECochG), auditory steady-state responses (ASSRs) and cortical auditory evoked potentials (CAEPs). Hearing aids are indicated in the treatment of ANSD with mild to moderate hearing loss, whereas cochlear implantation is the first choice of treatment in case of profound hearing loss, especially in case of IHC presynaptic disorders, or in case of poor auditory outcomes with conventional hearing aids.

Cochlear Implantation in a Case of Auditory Neuropathy Spectrum Disorder with CAPOS Syndrome

Auditory neuropathy spectrum disorder (ANSD) is a hearing disorder which characterized with normal outer hair cell function but disrupted neural synchrony in the afferent auditory pathway. CAPOS (cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss) syndrome can manifest itself with ANSD and this rare situation and audiological rehabilitation outcomes have not well documented in the literature. We aim to present a cochlear implant user subject with CAPOS syndrome and ANSD. A 14-year-old girl diagnosed with ANSD and CAPOS syndrome. She received unilateral cochlear implant (CI). Her hearing sensitivity and speech perception abilities have been improved with CI. Also, she has a good music perception ability measured with the Turkish version of Clinical Assessment of Music Perception Test. After detailed audiological evaluations, CI could be a good option for patients who have ANSD and CAPOS syndrome.

Fever-related ataxia: a case report of CAPOS syndrome

Background

CAPOS (Cerebellar ataxia, Areflexia, Pes cavus, Optic atrophy and Sensorineural hearing loss) syndrome is caused by the heterozygous mutation, c.2452G > A, in the ATP1A3 gene. Other mutations in this gene can cause a spectrum of overlapping phenotypes including alternating hemiplegia of childhood, rapid onset dystonia parkinsonism, early infantile epileptic encephalopathy and fever induced paroxysmal weakness and encephalopathy. The phenotype is still mistaken for mitochondrial/metabolic disorders and follow up studies are scare.

Case presentation

We report a 20 year old Norwegian male with ataxia, sensorineural deafness and visual loss. Before the age of five he experienced three fever related episodes of acute neurological deterioration when he temporarily lost his acquired motor skills and developed persistent gait and limb ataxia. In childhood, he developed bilateral optic atrophy and bilateral sensorineural hearing loss. Motor skills improved and at age 20 the patient showed a mild ataxia, hearing loss and reduced vision. A c.2452G > A mutation in the ATP1A3 gene was identified and CAPOS syndrome was confirmed.

Conclusions

This is the first Norwegian patient reported with CAPOS syndrome. Our patient had a de novo, previously identified ATP1A3 mutation. The combination of recurrent episodes of fever related ataxia, loss of motor skills in early childhood, and early onset hearing and vision loss is typical of CAPOS syndrome. Previous reports suggest a gradual progression of the disease after the initial episodes, while this patient showed a good outcome with improvement of motor skills from adolescence long after the last deterioration episode.