Audiological profile of a patient with MPS type IVA

Abstract

Mucopolysaccharidosis IVA is a rare metabolic disorder caused by the deficiency of N-acetylgalatosamine-6-sulfate-sulfatase, which is helpful in the degradation of keratan sulfate. Hearing loss is common in these individuals, which may be conductive, mixed or sensorineural. The disorder has a manifestation mainly in the skeletal and visceral organs; however, the presence of subtle neurological abnormalities has also been reported. Thus, a detailed audiological evaluation for differentiating sensory pathology with the neural pathology is warranted. The present case highlights the audiological characteristics of a 14 year old male child diagnosed with MPS IVA. Immitance audiometry, Pure tone audiometry, Speech audiometry, Otoacoustic emission and Auditory brainstem responses (ABR) (for threshold estimation) indicated mild sensorineural hearing loss in right ear and moderate mixed hearing loss in the left ear. However, lack of replicability in the ABR waveforms, and difference in the absolute latency for ABR peaks with different rate of stimulus presentation (11.1/sec and 90.1/sec) signifies the presence of retrocochlear pathology. The findings were further strengthened by the absence of speech ABR and the presence of late latency responses. The findings have a direct implication on the audiological rehabilitation of such individuals and the prescription of hearing aid should be made with caution.