Hearing loss in children can be frightening and confusing to parents. Children with otitis media (ear infection) or otitis media with effusion (OME) (fluid in the ear), may have temporary hearing loss due to the fluid in the middle ear. Upon removal of the fluid, hearing usually returns to normal.
This is known as conductive hearing loss. This usually means that sound waves which hit the ear drum have a difficult time being transmitted from the eardrum into the inner ear (hearing nerve). Sensorineural hearing loss means the sound reaches the inner ear, but some defect in the hearing organ (cochlea), nerve, or brain is the cause of the hearing loss.
A less common form of hearing loss is known as mixed hearing loss. In this form of hearing loss, there are components of both conductive hearing loss and sensorineural (nerve) hearing loss.
Sensorineural hearing loss is present in about 40,000 newborns each year. It is estimated that one in every 1,000 newborns has significant hearing loss. Fifty percent of these children with hearing loss have hereditary hearing loss. Of these, one-third have a syndrome associated with their hearing loss and usually have identifiable physical features which may alert the parents or physician to seek evaluation. The remaining two-thirds of these children have a hearing loss for which a cause cannot be discovered.
The joint committee on infant hearing has identified ten risk factors for newborn hearing loss:
- Family history of hearing loss,
- In utero infection,
- Craniofacial anomalies,
- Hyperbilirubinemia requiring exchange transfusion,
- Birth weight less than 1500 grams,
- Bacterial meningitis,
- Apgar scores of 0 to 4 at one minute or 0 to 6 at five minutes,
- Ototoxic medications,
- Mechanical ventilation (greater than five days),
- Physical appearance of the known syndrome.
Of those children with hearing loss associated with a known syndrome, advancements in the fields of genetics and molecular biology have allowed us to identify many of these syndromes. Sixty to seventy percent of these children have an autosomal recessive hearing impairment, making it the most common pattern of transmission. In these cases, the parents have normal hearing but carry the recessive gene, and there is a 25% chance of the children being affected. The next mode of transmission is autosomal dominant inheritance, which accounts for the other 20 – 30% of cases. In this instance, one parent usually has a hearing impairment and carries the abnormal gene, and there is a 50% chance that their children will be affected. A small percentage of hereditary hearing impairment is due to x-linked abnormalities. Because girls have two x chromosomes and boys only have one, x-linked disorders are “carried” by girls and “show up” in boys. Hearing loss can also be linked to mitochondrial mutations.
The terms hereditary and familial are sometimes confusing to many parents. When a disorder is hereditary, we mean to say that there is an identifiable genetic basis for the disorder. There is usually an inheritance pattern that is recognizable by examining the family history and seeing a definite pattern. However, when a disorder appears to be more common in a certain family but shows no definitive pattern of inheritance, we call this familial. In hereditary disorders, a percentage of affected children can be predicted. In familial disorders, affected individuals appear randomly and cannot be predicted.
Common Types of Hereditary Hearing Impairment
- Autosomal Recessive
- Usher syndrome
- Pendred syndrome
- Jervell and Lang-Nielson syndrome
- Autosomal Dominant
- Treacher-Collins syndrome
- Goldenhar syndrome
- Waardenburg syndrome
- branchio-oto-renal syndrome
- neurofibromatosis type II
- Alport syndrome
- autosomal dominant delayed (late) progressive sensorineural hearing impairment.
- X-linked Disorders
- Alport syndrome
- X-linked mixed hearing impairment with stapes fixation and perilymphatic gusher.
Hereditary causes of hearing loss are suspected in all cases of hearing impairment. Two factors that increase levels of suspicion are U-shaped audiograms and the consanguinity of the parents (parents related before marriage). In general, the younger the child upon diagnosis and the less apparent the alternative causes, the more likely the diagnosis is of hereditary hearing impairment. A hereditary cause, however, must be considered even in adolescents and young adults because hereditary hearing impairment can occur with delayed onset. When hereditary hearing impairment is suspected, parents and siblings of the affected patient should also have audiologic testing.
Testing for hearing loss
The testing for hearing loss is at an exciting and dynamic period. Because of advances in molecular genetics we now have identified specific causes of hearing loss. Identification of this genetic cause (mutation) helps us manage your child’s care, prevents further expensive and invasive tests, and gives us information on long-term prognosis. As you can imagine, knowing about genetic mutation can help families make decisions as parents and help identify other family members who may be at risk.
One of our favorite sites for hearing loss is The Hearing and Deafness Center at Cincinnati Children’s Medical Center. This site will allow you to read their material as a further reference.
In our practice, we follow their algorithm for testing as they continually update their processes as new information becomes available- (many times through research done there!).
Testing as follows: If your child has sensorineural hearing loss that affects both ears a Connexin 26 test is ordered if positive, patients are clinically followed and genetic testing is ordered. If negative, a mitochondrial screen is ordered. If heterozygous, a Connexin 30 test is ordered. If either of these are negative, a CT of the temporal bone (ear) is ordered. If an abnormality is found a SLCZ6A4 gene mutation test is ordered to rule out Pendred Syndrome (hearing loss, temporal bone anomalies, and thyroid abnormalities). If your child has sensorineural hearing loss that affects one ear, a CT scan is ordered to see if the ear was not formed correctly on that side.
Your physician will probably order a hearing assessment by audiogram or ABR (auditory brain stem response). In addition, vestibular testing (testing of the balance system) may also be recommended. Although no specific blood test may identify hearing loss, some testing may be suggested by your physician and may include urinalysis (Alport syndrome), thyroid function studies (Pendred syndrome), EKG (JLN syndrome), ophthalmologic exam (Usher syndrome), computerized tomography (CT scan) or magnetic resonance imaging (MRI).
Otosclerosis – Otosclerosis is an autosomal dominant inherited disorder. It is a relatively common progressive disease of the middle ear. It may first become apparent with conductive hearing loss due to stapes (stirrup bone) fixation but may progress to include sensorineural hearing loss. Hearing can usually be restored by surgery.
Treacher-Collins Syndrome – Treacher-Collins is an autosomal dominant disorder. There is a characteristic appearance in this syndrome, and usually, one parent will closely resemble the child. Abnormalities of the ear may include a small external ear, ear tag, or narrowing and/or complete absence of the external ear canal. Other findings may include malformed middle ear bones. Conductive hearing loss is the most common hearing problem.
Goldenhar Syndrome – Physical findings, in this case, may be one-sided and may include the jawbone, ear, palate, and the voice box. Hearing loss is usually conductive.
Waardenburg Syndrome – This syndrome is an autosomal dominant disorder with some facial findings as well as hair hypopigmentation (white forelock or early graying of the hair). Hearing loss in Waardenburg syndrome may range from mild to profound and may be one-sided or affects both ears. It is usually sensorineural.
Branchio-Oto-Renal Syndrome – This syndrome is an autosomal dominant syndrome with an association between ear deformity (40%), hearing impairment, and renal dysplasia. Mixed hearing loss (nerve and conductive) is most common.
Usher syndrome – Usher syndrome is autosomal recessive. This disorder usually is characterized by fairly profound congenital deafness and may or may not have abnormal balance function. These patients may eventually also suffer severe visual impairment and suffer from rhinitis pigmentosa.
Pendred Syndrome – Pendred syndrome is an autosomal recessive disorder characterized by thyroid enlargement and sensorineural type hearing loss. In more than half the patients, hearing loss is severe to profound, progressive, and involves both ears.
Jervell and Lang-Nielsen Syndrome – In this syndrome which is also autosomal recessive, there may be a history of syncopal episodes in a congenitally deaf child. Associated abnormalities on an EKG would be diagnostic.
Alport syndrome – Alport syndrome is an x-link disorder that usually involves congenital sensorineural hearing impairment and nephritis. Because it is x-linked, mothers are usually carriers without the disease, and the syndrome is more severe in males.
The diagnoses of these hereditary hearing loss syndromes, as well as non-hereditary hearing loss, involve careful history taking and physical examination as well as testing. Your physician will suggest selected laboratory and x-ray studies based on the physical examination and history involving your particular child. Only some of the laboratory or x-ray studies listed above will be done on your child as not all of these tests may be appropriate in your situation. Therefore, the selection of these particular studies is best decided on an individual basis.