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.

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.

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.

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.

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.

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.

The clinical presentation is variable but includes

- developmental and growth delay

- athletic muscular built

- skeletal anomalies

- joint stiffness

- characteristic facial appearance

- deafness

- variable cognitive deficits

- tracheal stenosis

- aortic stenosis

- pyloric stenosis

The facial abnormalities include:

- blepharophimosis (an abnormally narrow gap between the upper and lower eyelids)

- maxillary hypoplasia (underdevelopment of the upper jaw)

- prognathism (prominent lower jaw)

The skeletal abnormalities include:

- short stature

- square body shape

- broad ribs

- iliac hypoplasia

- brachydactyly

- flattened vertebrae

- thickened calvaria

Congenital heart disease and undescended testes have also been reported in association with this 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.

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.

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.

DOOR (deafness, onychdystrophy, osteodystrophy, and mental retardation) syndrome is a genetic disease which is inherited in an autosomal recessive fashion. DOOR syndrome is characterized by mental retardation, sensorineural deafness, abnormal nails and phalanges of the hands and feet, and variable seizures. A similar deafness-onychodystrophy syndrome is transmitted as an autosomal dominant trait and has no mental retardation. Some authors have proposed that it may be the same as Eronen Syndrome, but since both disorders are extremely rare it is hard to make a determination.

BVVL is marked by a number of cranial nerve palsies, including those of the motor components involving the 7th and 9th-12th cranial nerves, spinal motor nerves, and upper motor neurons. Major features of BVVL include facial and neck weakness, fasciculation of the tongue, and neurological disorders from the cranial nerves. The neurological manifestations develop insidiously: they usually begin with sensorineural deafness, progress inexorably to paralysis, and often culminate in respiratory failure. Most mortality in patients has been from either respiratory infections or respiratory muscle paralysis. Pathological descriptions of BVVL include injury and depletion of 3rd-7th cranial nerves, loss of the spinal anterior horn cells, degeneration of Purkinje cells, as well as degeneration of the spinocerebellar and pyramidal tracts. The first symptoms in nearly all cases of BVVL is progressive vision loss and deafness, and the first initial symptoms are seen anywhere from one to three years.

Most cases of deafness are followed by a latent period that can extend anywhere from weeks to years, and this time is usually marked by cranial nerve degeneration. Neurological symptoms of BVVL include optic atrophy, cerebellar ataxia, retinitis pigmentosa, epilepsy and autonomic dysfunction. Non-neurological symptoms can include diabetes, auditory hallucinations, respiratory difficulties, color blindness, and hypertension.

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.

TBS patients may have the following symptoms:

- Abnormalities of the external ears (unusually large or small, unusually shaped, sometimes with sensorineural hearing loss or deafness due to lesions or dysfunctions of part of the internal ear or its nerve tracts and centers or conductive hearing loss from the external or middle ear), dysplastic ears, lop ear (over-folded ear helix), preauricular tags or pits (a rudimentary tag of ear tissue typically located just in front of the ear).

- Anorectal malformations, including imperforate anus/absence of an anal opening, rectovaginal fistula, anal stenosis, unusually placed anus.

- Renal abnormalities, sometimes leading to impaired renal function or renal failure, including hypoplastic kidneys (underdeveloped), multicystic kidneys, dyspastic kidneys.

- Heart abnormalities, including tetralogy of fallot and defects of the ventricular septum.

- Hand and foot abnormalities, such as hypoplastic thumbs, fingerlike thumbs, syndactyly (webbed fingers/toes), fusion of the wrist bones, overlapping foot and/or toe bones.

Learning difficulties have been reported in some children with TBS. For others, intelligence is within the normal range.

These abnormalities, which are present prenatally, can range from minor to severe, and as with similar disorders, most individuals with this condition have some, but not all, of these traits.

Robinow noted the resemblance of affected patients' faces to that of a fetus, using the term "fetal facies" to describe the appearance of a small face and widely spaced eyes. Clinical features also may include a short, upturned nose, a prominent forehead, and a flat nasal bridge. The upper lip may be "tented", exposing dental crowding, "tongue tie", or gum hypertrophy.

Though the eyes do not protrude, abnormalities in the lower eyelid may give that impression. Surgery may be necessary if the eyes cannot close fully. In addition, the ears may be set low on the head or have a deformed pinna.

Patients suffer from dwarfism, short lower arms, small feet, and small hands. Fingers and toes may also be abnormally short and laterally or medially bent. The thumb may be displaced and some patients, notably in Turkey, experience ectrodactyly. All patients often suffer from vertebral segmentation abnormalities. Those with the dominant variant have, at most, a single butterfly vertebra. Those with the recessive form, however, may suffer from hemivertebrae, vertebral fusion, and rib anomalies. Some cases resemble Jarcho-Levin syndrome or spondylocostal dysostosis.

Genital defects characteristically seen in males include a micropenis with a normally developed scrotum and testes. Sometimes, testicles may be undescended, or the patient may suffer from hypospadias. Female genital defects may include a reduced size clitoris and underdeveloped labia minora. Infrequently, the labia majora may also be underdeveloped. Some research has shown that females may experience vaginal atresia or haematocolpos.

The autosomal recessive form of the disorder tends to be much more severe. Examples of differences are summarized in the following table:

The combination of muscular hypotonia and fixed dilated pupils in infancy is suspicious of Gillespie syndrome. Early onset partial aniridia, cerebellar ataxia, and mental retardation are hallmark of syndrome. The iris abnormality is specific and seems pathognomonic of Gillespie syndrome. The aniridia consisting of a superior coloboma and inferior iris hypoplasia, foveomacular dysplasia.

Atypical Gillespie syndrome associated with bilateral ptosis, exotropia, correctopia, iris hypoplasia, anterior capsular lens opacities, foveal hypoplasia, retinal vascular tortuosity, and retinal hypopigmentation.

Neurological signs ar nystagmus, mild craniofacial asymmetry, axial hypotonia, developmental delay, and mild mental retardation. Mariën P did not support the prevailing view of a global mental retardation as a cardinal feature of Gillespie syndrome but primarily reflect cerebellar induced neurobehavioral dysfunctions following disruption of the cerebrocerebellar anatomical circuitry that closely resembles the "cerebellar cognitive and affective syndrome" (CeCAS).

Congenital pulmonary stenosis and helix dysplasia can be associated.

Fountain syndrome is an autosomal recessive congenital disorder characterized by mental retardation, deafness, skeletal abnormalities and a coarse face with full lips. The abnormal swelling of the cheeks and lips are due to the excessive accumulation of body fluids under the skin. The deafness is due to malformation of the cochlea structure within the inner ear.

Oculodentodigital syndrome (ODD syndrome) is an extremely rare genetic condition that typically results in small eyes, underdeveloped teeth, and syndactyly and malformation of the fourth and fifth fingers. It has also been called oculo-dento-digital syndrome, oculodentodigital dysplasia (ODDD), and oculodentoosseous dysplasia (ODOD). It is considered a kind of ectodermal dysplasia.

Weissenbacher–Zweymuller syndrome (WZS), also called Pierre-Robin syndrome with fetal chondrodysplasia, is an autosomal recessive congenital disorder, linked to mutations (955 gly -> glu) in the "COL11A2" gene (located on chromosomal position 6p21.3), which codes for the α strand of collagen type XI. It is a collagenopathy, types II and XI disorder.

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."

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.

Myhre syndrome is a rare genetic disorder inherited in an autosomal dominant fashion. It is caused by mutation in SMAD4 gene.

Gordon syndrome is an extremely rare disorder that belongs to a group of genetic disorders known as the distal arthrogryposes. These disorders typically involve stiffness and impaired mobility of certain joints of the lower arms and legs (distal extremities) including the knees, elbows, wrists, and/or ankles. These joints tend to be permanently fixed in a bent or flexed position (contractures). Gordon syndrome is characterized by the permanent fixation of several fingers in a flexed position (camptodactyly), abnormal bending inward of the foot (clubfoot or talipes), and, less frequently, incomplete closure of the roof of the mouth (cleft palate). In some cases, additional abnormalities may also be present. The range and severity of symptoms may vary from case to case. Gordon syndrome is inherited as an autosomal dominant trait.

Björnstad syndrome is an autosomal recessive congenital condition involving pili torti and nerve deafness and hair abnormalities.

It was first characterized in 1965, in Oslo, by prof. Roar Theodor Bjørnstad (1908–2002).

It has been mapped to BCS1L. Hearing disabilities related to Björnstad syndrome are congenital, and the severity of the deafness varies from person to person. Pili torti is recognized in early childhood and is characterised by twisted hair shafts and brittle hair.

Brown-Vialetto-Van-Laere syndrome (BVVL), sometimes known as Brown's Syndrome, is a rare degenerative disorder often initially characterized by progressive sensorineural deafness.

The syndrome most often affects children, adolescents, and young adults. As knowledge of BVVL grows some adult patients have now been diagnosed. There is no known cure, however with prompt treatment the prognosis may be positive with some patients stabilizing and even minor improvements noted in certain cases.