Nonsyndromic deafness is hearing loss that is not associated with other signs and symptoms. In contrast, syndromic deafness involves hearing loss that occurs with abnormalities in other parts of the body. Genetic changes are related to the following types of nonsyndromic deafness.

- DFNA: nonsyndromic deafness, autosomal dominant

- DFNB: nonsyndromic deafness, autosomal recessive

- DFNX: nonsyndromic deafness, X-linked

- nonsyndromic deafness, mitochondrial

Each type is numbered in the order in which it was described. For example, DFNA1 was the first described autosomal dominant type of nonsyndromic deafness. Mitochondrial nonsyndromic deafness involves changes to the small amount of DNA found in mitochondria, the energy-producing centers within cells.

Most forms of nonsyndromic deafness are associated with permanent hearing loss caused by damage to structures in the inner ear. The inner ear consists of three parts: a snail-shaped structure called the cochlea that helps process sound, nerves that send information from the cochlea to the brain, and structures involved with balance. Loss of hearing caused by changes in the inner ear is called sensorineural deafness. Hearing loss that results from changes in the middle ear is called conductive hearing loss. The middle ear contains three tiny bones that help transfer sound from the eardrum to the inner ear. Some forms of nonsyndromic deafness involve changes in both the inner ear and the middle ear; this combination is called mixed hearing loss.

The severity of hearing loss varies and can change over time. It can affect one ear (unilateral) or both ears (bilateral). Degrees of hearing loss range from mild (difficulty understanding soft speech) to profound (inability to hear even very loud noises). The loss may be stable, or it may progress as a person gets older. Particular types of nonsyndromic deafness often show distinctive patterns of hearing loss. For example, the loss may be more pronounced at high, middle, or low tones.

Nonsyndromic deafness can occur at any age. Hearing loss that is present before a child learns to speak is classified as prelingual or congenital. Hearing loss that occurs after the development of speech is classified as postlingual.

Congenital hearing loss is a hearing loss present at birth. It can include hereditary hearing loss or hearing loss due to other factors present either in-utero (prenatal) or at the time of birth.

Sensorineural hearing loss (SNHL) is a type of hearing loss, or deafness, in which the root cause lies in the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve (cranial nerve VIII) or neural part. SNHL accounts for about 90% of hearing loss reported. SNHL is generally permanent and can be mild, moderate, severe, profound, or total. Various other descriptors can be used such as high frequency, low frequency, U-shaped, notched, peaked or flat depending on the shape of the audiogram, the measure of hearing.

"Sensory" hearing loss often occurs as a consequence of damaged or deficient cochlear hair cells. Hair cells may be abnormal at birth, or damaged during the lifetime of an individual. There are both external causes of damage, including noise trauma, infection and ototoxic drugs, as well as intrinsic causes, including genetic mutations. A common cause or exacerbating factor in sensory hearing loss is prolonged exposure to environmental noise, for example, being in a loud workplace without wearing protection, or having headphones set to high volumes for a long period. Exposure to a very loud noise such as a bomb blast can cause noise-induced hearing loss.

"Neural", or 'retrocochlear', hearing loss occurs because of damage to the cochlear nerve (CVIII). This damage may affect the initiation of the nerve impulse in the cochlear nerve or the transmission of the nerve impulse along the nerve into the brainstem.

Most cases of SNHL present with a gradual deterioration of hearing thresholds occurring over years to decades. In some the loss may eventually affect large portions of the frequency range. It may be accompanied by other symptoms such as ringing in the ears (tinnitus), dizziness or lightheadedness (vertigo). SNHL can be genetically inherited or acquired as a result from external causes like noise or disease. It may be congenital (present at birth) or develop later in life. The most common kind of sensorineural hearing loss is age-related (presbycusis), followed by noise-induced hearing loss (NIHL).

Frequent symptoms of SNHL are loss of acuity in distinguishing foreground voices against noisy backgrounds, difficulty understanding on the telephone, some kinds of sounds seeming excessively loud or shrill (recruitment), difficulty understanding some parts of speech (fricatives and sibilants), loss of directionality of sound, esp. high frequency sounds, perception that people mumble when speaking, and difficulty understanding speech. Similar symptoms are also associated with other kinds of hearing loss; audiometry or other diagnostic tests are necessary to distinguish sensorineural hearing loss.

Identification of sensorineural hearing loss is usually made by performing a pure tone audiometry (an audiogram) in which bone conduction thresholds are measured. Tympanometry and speech audiometry may be helpful. Testing is performed by an audiologist.

There is no proven or recommended treatment or cure for SNHL; management of hearing loss is usually by hearing strategies and hearing aid. In cases of profound or total deafness, a cochlear implant is a specialised hearing aid which may restore a functional level of hearing. SNHL is at least partially preventable by avoiding environmental noise, ototoxic chemicals and drugs, and head trauma, and treating or inoculating against certain triggering diseases and conditions like meningitis.

SSHL is diagnosed via pure tone audiometry. If the test shows a loss of at least 30db in three adjacent frequencies, the hearing loss is diagnosed as SSHL. For example, a hearing loss of 30db would make conversational speech sound more like a whisper.

The hearing loss of Pendred syndrome is often, although not always, present from birth, and language acquisition may be a significant problem if deafness is severe in childhood. The hearing loss typically worsens over the years, and progression can be step-wise and related to minor head trauma. In some cases, language development worsens after head injury, demonstrating that the inner ear is sensitive to trauma in Pendred syndrome; this is as a consequence of the widened vestibular aqueducts usual in this syndrome. Vestibular function varies in Pendred syndrome and vertigo can be a feature of minor head trauma. A goitre is present in 75% of all cases.

There are four main types of hearing loss, conductive hearing loss, sensorineural hearing loss, central deafness and combinations of conductive and sensorineural hearing losses which is called mixed hearing loss. An additional problem which is increasingly recognised is auditory processing disorder which is not a hearing loss as such but a difficulty perceiving sound.

- Conductive hearing loss

Conductive hearing loss is present when the sound is not reaching the inner ear, the cochlea. This can be due to external ear canal malformation, dysfunction of the eardrum or malfunction of the bones of the middle ear. The ear drum may show defects from small to total resulting in hearing loss of different degree. Scar tissue after ear infections may also make the ear drum dysfunction as well as when it is retracted and adherent to the medial part of the middle ear.

Dysfunction of the three small bones of the middle ear – malleus, incus, and stapes – may cause conductive hearing loss. The mobility of the ossicles may be impaired for different reasons and disruption of the ossicular chain due to trauma, infection or ankylosis may also cause hearing loss.

- Sensorineural hearing loss

Sensorineural hearing loss is one caused by dysfunction of the inner ear, the cochlea or the nerve that transmits the impulses from the cochlea to the hearing centre in the brain. The most common reason for sensorineural hearing loss is damage to the hair cells in the cochlea. Depending on the definition it could be estimated that more than 50% of the population over the age of 70 has impaired hearing.

- Central deafness

Damage to the brain can lead to a central deafness. The peripheral ear and the auditory nerve may function well but the central connections are damaged by tumour, trauma or other disease and the patient is unable to hear.

- Mixed hearing loss

Mixed hearing loss is a combination of conductive and sensorineural hearing loss. Chronic ear infection (a fairly common diagnosis) can cause a defective ear drum or middle-ear ossicle damages, or both. In addition to the conductive loss, a sensory component may be present.

- Central auditory processing disorder

This is not an actual hearing loss but gives rise to significant difficulties in hearing. One kind of auditory processing disorder is King-Kopetzky syndrome, which is characterized by an inability to process out background noise in noisy environments despite normal performance on traditional hearing tests.

Hearing loss is sensory, but may have accompanying symptoms:

- pain or pressure in the ears

- a blocked feeling

There may also be accompanying secondary symptoms:

- hyperacusis, heightened sensitivity to certain volumes and frequencies of sound, sometimes resulting from "recruitment"

- tinnitus, ringing, buzzing, hissing or other sounds in the ear when no external sound is present

- vertigo and disequilibrium

- tympanophonia, abnormal hearing of one's own voice and respiratory sounds, usually as a result of a patulous eustachian tube or dehiscent superior semicircular canals

- disturbances of facial movement (indicating possible tumour or stroke)

Genetic factors are thought to cause more than 50% of all incidents of congenital hearing loss. Genetic hearing loss may be autosomal dominant, autosomal recessive, or X-linked (related to the sex chromosome).

Michel aplasia, also known as complete labyrinthine aplasia (CLA), is a congenital abnormality of the inner ear. It is characterized by the bilateral absence of differentiated inner ear structures and results in complete deafness (anacusis).

Michel aplasia should not be confused with michel dysplasia. It may affect one or both ears.

"Aplasia" is the medical term for body parts that are absent or do not develop properly. In Michel aplasia, the undeveloped (anaplastic) body part is the bony labyrinth of the inner ear. Other nearby structures may be underdeveloped as well.

Audiometry (measuring ability to hear sounds of a particular pitch) is usually abnormal, but the findings are not particularly specific and an audiogram is not sufficient to diagnose Pendred syndrome. A thyroid goitre may be present in the first decade and is usual towards the end of the second decade. MRI scanning of the inner ear usually shows widened or large vestibular aqueducts with enlarged endolymphatic sacs and may show abnormalities of the cochleae that is known as Mondini dysplasia. Genetic testing to identify the pendrin gene usually establishes the diagnosis. If the condition is suspected, a "perchlorate discharge test" is sometimes performed. This test is highly sensitive, but may also be abnormal in other thyroid conditions. If a goitre is present, thyroid function tests are performed to identify mild cases of thyroid dysfunction even if they are not yet causing symptoms.

Abnormal development of the skeletal portions of the second arch

1. Nondifferentiation of the stapes, with resultant absence of round and oval window.

2. Abnormal course of the facial nerve.

Skull base abnormalities

1. Hypoplasia of the petrous temporal bone.

2. Hypoplastic and sclerotic petrous apex may mimic labyrinthitis ossificans.

3. Platybasia.

4. Aberrant course of jugular veins.

Symptoms vary from one type of the syndrome to another and from one patient to another, but they include:

- Very pale or brilliantly blue eyes, eyes of two different colors (complete heterochromia), or eyes with one iris having two different colors (sectoral heterochromia)

- A forelock of white hair ("poliosis"), or premature graying of the hair

- Appearance of wide-set eyes due to a prominent, broad nasal root ("dystopia canthorum")—particularly associated with Type I) also known as "telecanthus"

- Moderate to profound hearing loss (higher frequency associated with Type II);

- A low hairline and eyebrows that meet in the middle ("synophrys")

- Patches of white skin pigmentation, in some cases

- Abnormalities of the arms, associated with Type III

- neurologic manifestations, associated with Type IV

- Cleft lip, mostly associated with Type I

Waardenburg syndrome has also been associated with a variety of other congenital disorders, such as intestinal and spinal defects, elevation of the scapula and cleft lip and palate. Sometimes this is concurrent with Hirschsprung disease.

Tietz syndrome is characterized by profound hearing loss from birth, white hair and pale skin (hair color may darken over time to blond or red).

The hearing loss is caused by abnormalities of the inner ear (sensorineural hearing loss) and is present from birth. Individuals with Tietz syndrome often have skin and hair color that is lighter than those of other family members.

Tietz syndrome also affects the eyes. The iris in affected individuals is blue, and specialized cells in the eye called retinal pigment epithelial cells lack their normal pigment. The changes to these cells are generally detectable only by an eye examination; it is unclear whether the changes affect vision.

Post-lingual deafness is a deafness which develops after the acquisition of speech and language, usually after the age of six.

Post-lingual hearing impairments are far less common than prelingual deafness. Typically, hearing loss is gradual, and often detected by family and friends of the people so affected long before the patients themselves will acknowledge the disability.

Since Usher syndrome is incurable at present, it is helpful to diagnose children well before they develop the characteristic night blindness. Some preliminary studies have suggested as many as 10% of congenitally deaf children may have Usher syndrome. However, a misdiagnosis can have bad consequences.

The simplest approach to diagnosing Usher syndrome is to test for the characteristic chromosomal mutations. An alternative approach is electroretinography, although this is often disfavored for children, since its discomfort can also make the results unreliable. Parental consanguinity is a significant factor in diagnosis. Usher syndrome I may be indicated if the child is profoundly deaf from birth and especially slow in walking.

Thirteen other syndromes may exhibit signs similar to Usher syndrome, including Alport syndrome, Alstrom syndrome, Bardet-Biedl syndrome, Cockayne syndrome, spondyloepiphyseal dysplasia congenita, Flynn-Aird syndrome, Friedreich ataxia, Hurler syndrome (MPS-1), Kearns-Sayre syndrome (CPEO), Norrie syndrome, osteopetrosis (Albers-Schonberg disease), Refsum's disease (phytanic acid storage disease), and Zellweger syndrome (cerebrohepatorenal syndrome).

People with Usher I are usually born deaf and often have difficulties in maintaining their balance owing to problems in the vestibular system. Babies with Usher I are usually slow to develop motor skills such as walking. Worldwide, the estimated prevalence of Usher syndrome type I is 3 to 6 per 100,000 people in the general population.

Usher syndrome type I can be caused by mutations in any one of several different genes: "CDH23, MYO7A, PCDH15, USH1C", and "USH1G". These genes function in the development and maintenance of inner ear structures such as hair cells (stereocilia), which transmit sound and motion signals to the brain. Alterations in these genes can cause an inability to maintain balance (vestibular dysfunction) and hearing loss. The genes also play a role in the development and stability of the retina by influencing the structure and function of both the rod photoreceptor cells and supporting cells called the retinal pigmented epithelium. Mutations that affect the normal function of these genes can result in retinitis pigmentosa and resultant vision loss.

Type I has been found to be more common in people of Ashkenazi Jewish ancestry (central and eastern European) and in the French-Acadian populations (Louisiana).

Tietz syndrome, also called Tietz albinism-deafness syndrome or albinism and deafness of Tietz, is an autosomal dominant congenital disorder characterized by deafness and leucism. It is caused by a mutation in the microphthalmia-associated transcription factor (MITF) gene. Tietz syndrome was first described in 1963 by Walter Tietz (1927–2003) a German Physician working in California.

In some cases, the loss is extremely sudden and can be traced to specific diseases, such as meningitis, or to ototoxic medications, such as Gentamicin. In both cases, the final degree of loss varies. Some experience only partial loss, while others become profoundly deaf. Hearing aids and cochlear implants may be used to regain a sense of hearing, with different people experiencing differing degrees of success. It is possible that the affected person may need to rely on speech-reading and/or sign language for communication.

In most cases the loss is a long term degradation in hearing loss. Discrediting earlier notions of presbycusis, Rosen demonstrated that long term hearing loss is usually the product of chronic exposure to environmental noise in industrialized countries (Rosen, 1965). The U.S. Environmental Protection Agency has asserted the same sentiment and testified before the U.S. Congress that approximately 34 million Americans are exposed to noise pollution levels (mostly from roadway and aircraft noise) that expose humans to noise health effects including the risk of hearing loss (EPA, 1972).

Certain genetic conditions can also lead to post-lingual deafness. In contrast to genetic causes of pre-lingual deafness, which are frequently autosomal recessive, genetic causes of post-lingual deafness tend to be autosomal dominant.

It causes facial abnormalities, skeletal malformation and occasionally neural tube defects; the skeletal disfigurements resolve to a degree in the course of development.

Mutations in different parts of the gene may lead to deafness or Stickler syndrome type III (eye problems: myopia, retinal detachment and skeletal abnormalities).

Infants and children: Infants that are born with Weissenbacher-Zweymüller syndrome usually have short bones in their arms and legs. The thigh and upper arm bones are wider than usual resulting in a dumbbell-shape while the bones of the vertebrae may be abnormal. Typical abnormal facial features can be wide-set protruding eyes (hypertelorism), a small and upturned nose with a flat bridge, small jaw (micrognathia) and a cleft palate. Some infants have high-frequency hearing loss. Infants may also exhibit a psychomotor delay. After the period of growth deficiency the individual makes improvements in bone growth leading to a normal physical development around age 5 or 6.

Adults: Many with Weissenbacher-Zweymüller syndrome have a catch-up growth phase causing the adults to not be unusually short. Many adults still will have hearing loss and typical abnormal facial features of Weissenbacher-Zweymüller syndrome.

It is a genetic developmental disorder with clinical diversity characterized by hypoparathyroidism, sensorineural deafness and renal disease. Patients usually present with hypocalcaemia, tetany, or afebrile convulsions at any age. Hearing loss is usually bilateral and may range from mild to profound impairment. Renal disease includes nephrotic syndrome, cystic kidney, renal dysplasia, hypoplasia or aplasia, pelvicalyceal deformity, vesicoureteral reflux, chronic kidney disease, hematuria, proteinuria and renal scarring.

Not all of the DOOR symptoms are consistently present. They can vary in severity, and additional features can be noted in individuals affected by DOOR syndrome.

Some of these additional features are:

- Polyhydramnios (increased amniotic fluid during pregnancy) and increased nuchal fold during pregnancy

- Specific facial features such as a large nose

- Severe and sometimes refractory seizures, abnormalities on the magnetic resonance imaging of the brain

- Increased 2-oxoglutaric acid in the blood and urine - this compound is made or used by several enzymes

- Finger-like thumbs

- Visual impairment

- Peripheral neuropathy (nerves conducting sensation from extremities to the brain) and insensivity to pain

Intellectual impairment is present in all reported cases, but the severity can vary widely. The prognosis in terms of survival also varies greatly from early childhood till adulthood.

Although genetic testing positively identifies nearly two thirds of children with CHARGE syndrome, diagnosis is still largely clinical. The following signs were originally identified in children with this syndrome, but are no longer used in to make the diagnosis alone.

- C - Coloboma of the eye, central nervous system anomalies

- H - Heart defects

- A - Atresia of the choanae

- R - Retardation of growth and/or development

- G - Genital and/or urinary defects (Hypogonadism, undescended testicles, besides hypospadias.)

- E - Ear anomalies and/or deafness and abnormally bowl-shaped and concave ears, known as "lop ears".

Treatment is supportive and consists of management of manifestations. User of hearing aids and/or cochlear implant, suitable educational programs can be offered. Periodic surveillance is also important.

In the beginning, medical officials defined ABCD syndrome by the four key characteristics of the syndrome. In the first case study of the Kurdish girl, researches described her as having "albinism and a black lock at the right temporo-occipital region along Blaschko lines, her eyelashes and brows were white, the irises in her eyes appeared to be blue, she had spots of retinal depigmentation, and she did not react to noise." The albinism is interesting in this diagnosis because the skin of an affected individual is albino pale besides the brown patches of mispigmented skin. The "black locks" described and seen in clinical pictures of the infants are thick patches of black hair above the ears that form a half circle reaching to the other ear to make a crest shape.

As identified in this first case study and stated in a dictionary of dermatologic syndromes, ABCD syndrome has many notable features, including "snow white hair in patches, distinct black locks of hair, skin white except brown macules, deafness, irises gray to blue, nystagmus, photophobia, poor visual activity, normal melanocytes in pigmented hair and skin, and absent melanocytes in areas of leukoderma." Individuals have the blue/gray irises typical of people affected by blindness. The C of ABCD syndrome is what distinguishes this genetic disorder from BADS and it involves cell migration disorder of the neurocytes of the gut. This characteristic occurs when nerve cells do not function correctly in the gut, which results in aganglionosis: The intestines’ failure to move food along the digestive tract. Deafness or being unresponsive to noise due to very low quality of hearing was reported in every case of ABCD syndrome. The characteristics of ABCD syndrome are clearly evident in an inflicted individual.

No longer considered a separate syndrome, ABCD syndrome is today considered to be a variation of Shah-Waardenburg type IV. Waardenburg syndrome (WS) is described as "the combination of sensorineural hearing loss, hypopigmentation of skin and hair, and pigmentary disturbances of the irides." Hearing loss and deafness, skin mispigmentation and albinism, and pigmentary changes in irises are the similarities between WS and ABCD. According to a dictionary of dermatologic syndromes, Waardenburg syndrome has many notable features, including "depigmentation of hair and skin – white forelock and premature graying of hair, confluent thick eyebrows, heterochromic irides or hypopigmentation of iris, laterally displaced inner canthi, congenital sensorineural deafness, broad nasal root, autosomal dominant disorder, and other associated findings, including black forelocks."

People with ODD syndrome often have a characteristic appearance. Visible features of the condition include:

- small teeth that are prone to caries because of underdeveloped tooth enamel;

- a long, thin nose;

- unusually small eyes; and

- type III syndactyly of the fourth and fifth fingers.

Iris atrophy and glaucoma are more common than average. The size of the eyes often interferes with learning to read; special eyeglasses may be required. Hair may be fine, thin, dry, or fragile; in some families, it is curly.

Neurologic abnormalities may be seen in adults. The neurologic changes may appear earlier in each subsequent generation and can include abnormal white matter, conductive deafness, and various kinds of paresis, including ataxia, spastic paraplegia, difficulty controlling the eyes, and bladder and bowel disturbances.