Introduction:
Congenital (inborn) hearing loss is one of the most common causes of hearing loss worldwide, and most of them are related to syndromes. Syndromic hearing loss in patients results in hearing loss accompanied by other medical abnormalities. Syndromic sensorineural hearing loss (SNHL) is associated with damage to the vestibulocochlear nerve (the eighth cranial nerve) that transmits electrical signals from the inner ear to the brain, which is perceived by the brain as a sound.
What Is the Prevalence of Syndromic Sensorineural Hearing Loss?
The prevalence of syndrome associated with hearing loss is around 15 percent of the total congenital (inborn) hearing loss worldwide.
What Are the Syndromes Associated With Sensorineural Hearing Loss?
Different syndromes that result in sensorineural hearing loss are:
1. Usher Syndrome: It is the most common syndrome associated with sensorineural hearing loss affecting the general population. It results in hearing loss accompanied by vision loss due to retinitis pigmentosa (eye disease in which the back wall of the eye is damaged). It is of three types:
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Type 1: Bilateral (both sides) hearing loss with balance loss (vestibular dysfunction).
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Type 2: Mild to moderate hearing loss with normal vestibular function (balance loss is not seen).
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Type 3: Normal hearing present at birth, with progressive sensorineural hearing loss seen in later stages. Vestibular dysfunction (balance loss) is present.
2. Pendred Syndrome: It is the second most common syndrome associated with sensorineural hearing loss along with thyroid gland (a butterfly-shaped organ present in the neck) enlargement (goiter). It results in sensorineural hearing loss in both ears, underdeveloped cochlea (snail-shaped sac present in the inner ear), and vestibular dysfunction (loss of balance). It is caused by a mutation in the pendred syndrome (PDS) gene on chromosome 7.
3. Jervell and Lange-Nielsen Syndrome: It is the third most common syndrome associated with sensorineural hearing loss. It presents with hearing loss in both ears since birth, accompanied by abnormal heart rhythm. It is a syndrome associated with both heart and inner ear conduction (transfer of electrical signals) abnormalities.
4. Waardenburg Syndrome: This syndrome results in sensorineural hearing loss in one or both ears. It is characterized by the presence of premature gray hairs, variation in eye color in two different eyes, fused eyebrows, and an underdeveloped nose tip. It is of three types:
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Type 1: Dual eye colors in two different eyes, white flocks of hair in front of the head, and increased distance between two eyes (hypertelorism) are the features present. Around 20 percent of these patients have sensorineural hearing loss.
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Type 2: All the features are similar to type 1 except hypertelorism (increased distance between two eyes), which is absent in these patients. Around 50 percent of these patients have sensorineural hearing loss.
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Type 3: It consists of all the features of type 1 in addition to small head (microcephaly), mental retardation, and skeletal abnormalities.
5. Branchio-Oto-Renal (BOR) Syndrome: It is associated with defects in the outer, middle, and inner ear accompanied by kidney disorders. It also results in sensorineural (hearing loss due to nerve damage), conductive (hearing loss due to obstruction in vibrational conduction of sound to the inner ear), or mixed hearing loss.
6. Stickler Syndrome: It is associated with defects in the formation of the palate (cleft palate), small jaw, middle ear bone defects, and hearing loss that may be sensorineural, conductive, or mixed.
7. Alport Syndrome: It presents with sensorineural hearing loss, kidney disorders, and abnormalities in near-vision.
How Can We Diagnose Syndromic Sensorineural Hearing Loss?
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History and Physical Examination: Complete history of the patient with any family history of hearing loss or genetic disorders is recorded. Prenatal history, maternal drug history (drugs taken while pregnancy), and gestational diabetes are noted. An entire head and neck examination are done to check for eye, ears, heart, and head abnormalities.
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Auditory Brainstem Response (ABR) Test: These tests are done to rule out sensorineural hearing loss by assessing the auditory nerve damage and checking for the defects in the auditory pathway by measuring the response of the brain to the sound produced by mini speakers connected to the electrodes that are placed on the scalp and behind the ears.
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Computed Tomography (CT) Scans: This scan is done for the temporal bone to rule out the inner, middle, and outer ear defects.
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Otoacoustic Emission (OAE) Test: The response of the cochlear (snail-shaped organ in the inner ear) hair cells in response to the sound produced by the earphones.
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Early Hearing Detection and Intervention Program: Screening programs for hearing assessment are recommended for newborns. Early assessment is done in the first month of life, hearing loss assessment is done by three months of age, and early intervention services by six months of age.
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Genetic Testing: It is done to confirm the associated gene and diagnose the syndrome related to the gene.
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Hearing Assessment: Assessment of hearing for infants and newborns is done by an audiologist (the doctor who specializes in treating hearing and balance loss disorder) to evaluate the middle ear reflex.
What Is the Treatment for Syndromic Sensorineural Hearing Loss?
Treatment modalities for syndromic sensorineural hearing loss are:
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Hearing Aids: A suitable hearing aid (small artificial electronic device) like a hearing headband is given in the first month of life.
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Bone Anchored Hearing Aids: These are the hearing aids that help to hear clear sound through bone conduction.
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Cochlear Implants: These are prosthetic devices (artificial devices) that are surgically implanted in the bone of the inner ears and skull to help in clear and sound hearing. This surgery is done after five to seven years of age.
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Assisted Listening Devices (ALD): Different types of assisted listening devices, like infrared system and hearing loop system, helps to listen to clear sounds even with a lot of background noise.
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Speech and Language Pathologist: A speech and language pathologist helps to train the child in learning communications skills or speech and language development.
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Genetic Counseling: Genetic counseling is done for parents and their families. Prenatal counseling and tests are advised for pregnant females if any family member has a history of hearing loss.
Conclusion:
Syndromic sensorineural hearing loss occurs due to inborn defects of the inner ear due to alteration in one or more genes resulting in hearing loss accompanied by other symptoms. Early diagnosis and management of syndromic sensorineural hearing loss are crucial for preventing delays in the growth and development of the child. Prenatal tests are advised in pregnant women with a family history of hearing loss for early detection of syndromes associated with hearing loss.
