Deafness in babies refers to a reduced ability to hear sounds, from mild to profound. This condition can arise from various factors, some present at birth and others developing shortly thereafter. Understanding the origins of infant hearing loss is important for early identification and intervention, which can influence a child’s development. This article explores the categories of factors contributing to deafness in infants.
Genetic Influences
Genetic factors frequently cause infant hearing loss, accounting for a substantial portion of cases. This type can be syndromic or non-syndromic. Non-syndromic hearing loss occurs when hearing impairment is the only symptom. Syndromic hearing loss is part of broader symptoms affecting multiple bodily systems, such as Usher syndrome (hearing loss with progressive vision impairment) or Waardenburg syndrome (hearing loss with changes in skin, hair, and eye pigmentation).
Genetic hearing loss is inherited through different patterns. Autosomal recessive inheritance is most common, where a child inherits a non-working gene copy from both parents, who are typically unaffected carriers. Autosomal dominant inheritance occurs when a child inherits a non-working gene copy from one parent, who usually also has hearing loss. Less commonly, X-linked inheritance involves genes on the X chromosome, affecting males more frequently.
Specific genes are frequently implicated in genetic hearing loss. The GJB2 gene, which provides instructions for making connexin 26 (a protein found in the inner ear), is a common cause of non-syndromic hearing loss, particularly in severe to profound deafness. Another gene, SLC26A4, is associated with Pendred syndrome and non-syndromic enlarged vestibular aqueduct, leading to fluctuating or progressive hearing loss. In some instances, hearing loss results from spontaneous genetic mutations, new changes in a gene that occur randomly and are not inherited.
Prenatal and Perinatal Factors
Factors occurring during pregnancy (prenatal) or around birth (perinatal) can contribute to deafness in babies. Maternal infections during pregnancy pose a notable risk. Cytomegalovirus (CMV) is the most common infectious cause of non-genetic hearing loss in newborns, potentially leading to progressive hearing loss months or years after birth. Other infections like rubella, toxoplasmosis, herpes simplex virus (HSV), and syphilis can also damage the developing auditory system of the fetus.
Maternal substance use during pregnancy, including alcohol or illicit drugs, can negatively impact fetal development, potentially affecting hearing. Certain prescription medications taken by the mother, if ototoxic, could pose a risk to the developing ear, though this is less common and carefully managed by healthcare providers. Uncontrolled maternal health conditions, such as severe diabetes or pre-eclampsia, may also affect fetal development, including the auditory system.
Around birth, several perinatal factors can lead to hearing impairment. Prematurity and low birth weight are associated with a higher risk of hearing loss, often due to immature body systems. Birth complications, such as lack of oxygen (anoxia or hypoxia) during delivery, can damage the brain and auditory pathways. Severe jaundice (hyperbilirubinemia), if untreated, can lead to kernicterus, where high bilirubin levels damage the brain, including hearing areas. Medical interventions in the neonatal intensive care unit (NICU), such as ototoxic medications like aminoglycoside antibiotics (e.g., gentamicin) for life-saving treatment of severe infections, can sometimes result in permanent hearing damage.
Postnatal Causes
Deafness can develop after birth, stemming from various postnatal events. Infections are a frequent cause of acquired hearing loss in infants and young children. Bacterial meningitis, an infection of the membranes surrounding the brain and spinal cord, is a severe cause, as it can directly damage the cochlea. Other common childhood illnesses like measles, mumps, and chickenpox, while less common due to vaccinations, can also lead to hearing impairment.
Chronic ear infections (otitis media) are common in infants and can lead to temporary hearing loss due to fluid buildup behind the eardrum. If recurrent and persistent, prolonged fluid presence can sometimes cause permanent damage to middle ear structures or the eardrum, affecting hearing. Certain medications administered after birth can also be ototoxic, meaning they can damage the inner ear. These include specific antibiotics like aminoglycosides, loop diuretics, and some chemotherapy drugs, typically used for serious conditions but requiring careful monitoring for their potential impact on hearing.
Physical head trauma can also result in hearing loss in infants. Injuries directly affecting the ear or auditory pathways within the brain can disrupt delicate structures responsible for hearing. Exposure to excessively loud noises, even for short durations, can damage cochlear hair cells, leading to permanent hearing loss. This can occur from sources like loud toys, fireworks, or prolonged high-volume music. While less common in infants, certain autoimmune diseases can, in rare cases, lead to early onset hearing loss by causing the body’s immune system to attack inner ear tissues.
References
https://www.nidcd.nih.gov/health/hereditary-hearing-loss
https://www.cdc.gov/ncbddd/hearingloss/causes.html
https://www.chop.edu/conditions-diseases/hearing-loss/causes