Congenital deafness is a hearing loss that is present at birth. It differs from progressive hearing impairment which occurs at birth but gradually progresses. Congestive deafness affects every 1 to 2 per 1000 infants.
Congestive Deafness Overview
Hearing loss is measured in decibels (dB). A person with normal hearing is able to identify sounds at 0-20 (dB). An individual who cannot detect sounds of less than 40 dB is considered to have bilateral hearing impairment. Bilateral congenital hearing loss means that both ears are affected and this condition is more common than unilateral congenital hearing loss.
There are different grades of hearing loss. Mild hearing loss (20-40 dB HL) refers to inability to detect whispers, moderate hearing loss (41-70 dB HL) means a person cannot detect normal speech while severe hearing loss (71-95 dB HL) refers to difficulty detecting shouting. Profound hearing loss is the condition in which a person cannot detect sounds of less than 95 dB HL.
Also, deafness can be categorized into sensorineural and conductive hearing loss. Sensorineral hearing loss (SNHL) is the most common type of hearing loss and occurs due to damage or abnormalities in the sensory cells and nerve fibers of the inner ear. Conductive hearing loss develops when the sound waves fail to reach the inner ear via normal channels of the outer and middle ear.
Causes of Congestive Deafness
The most common form of congenital deafness is caused by a genetic condition passed in autosomal recessive manner. In fact, autosomal recessive inheritance accounts for more than 75% of all congenital deafness.
The remaining percentage of congenital deafness is associated with syndromic deafness. Syndromic deafness includes over 100 different syndromes that lead to sensorineural hearing loss.
This includes Alport’s syndrome, Branchio-oto-renal syndrome, X-linked Charcot-Marie-Tooth syndrome, Goldenhar’s syndrome, Jervell and Lange-Nielsen syndrome, Mohr-Tranebjaerg syndrome, Norrie’s disease, Pendred’s syndrome, Stickler’s syndrome, Treacher Collin’s syndrome, Waardenburg’s syndrome, Usher’s syndrome and mitochondrial disorders.
Congenital deafness can also have non-genetic causes and arise from malformations of parts of the ear. The most common non-inherited cause of congenital deafness is Mondini dysplasia or Mondini malformation which is characterized by misshapen cochlea.
Other non-genetic causes of congenital deafness include enlarged vestibular aqueduct syndrome, cleft palate, ossicular malformation, ossicular fixation, external auditory canal atresia and congenital cholesteatoma.
Risk factors for congenital deafness include family history of the condition, prenatal infection (TORCH), premature delivery, low birth weight, fetal distress during delivery, head malformation, jaundice, treatment with ototoxic drugs and infections such as bacterial meningitis.