NF2 Gene

Neurofibromatosis type 2 is a disorder characterized by the growth of noncancerous tumors in the nervous system. The most common tumors associated with neurofibromatosis type 2 are called vestibular schwannomas or acoustic neuromas. These growths develop along the nerve that carries information from the inner ear to the brain (the auditory nerve). Tumors that occur on other nerves are also commonly found with this condition.

The signs and symptoms of neurofibromatosis type 2 usually appear during adolescence or in a person's early twenties, although they can begin at any age. The most frequent early symptoms of vestibular schwannomas are hearing loss, ringing in the ears (tinnitus), and problems with balance. In most cases, these tumors occur in both ears by age 30. If tumors develop elsewhere in the nervous system, signs and symptoms vary according to their location. Complications of tumor growth can include changes in vision, numbness or weakness in the arms or legs, and fluid buildup in the brain. Some people with neurofibromatosis type 2 also develop clouding of the lens (cataracts) in one or both eyes, often beginning in childhood.

MN1 C-terminal truncation (MCTT) syndrome is a condition characterized by intellectual disability, developmental delay, distinctive facial features, and brain abnormalities.

Most people with MCTT syndrome have mild to moderate intellectual disability. Many affected individuals are nonverbal, but some have speech limited to one or two words or communicate using sign language. Most children with this condition have delayed development of motor skills, such as crawling or walking, but are able to walk by age 2 or 3. However, they often need help with fine-motor skills, such as getting dressed or using a fork when eating.

Individuals with MCTT syndrome often have distinctive facial features that include a sunken appearance of the middle of the face (midface hypoplasia); a high arch in the roof of the mouth (high-arched palate); outside corners of the eyes that point downward (downslanting palpebral fissures); widely spaced eyes (hypertelorism ); shallow and bulging eyes (exophthalmos); a short, upturned nose; and small, low-set ears. Some affected individuals have dental abnormalities, such as cone-shaped (conical ), jagged, or crowded teeth. Rarely, people with MCTT syndrome have premature fusion of certain skull bones (craniosynostosis).

People with MCTT syndrome often have characteristic brain abnormalities. The surface of the brain normally has many ridges or folds, called gyri. A common brain abnormality in people with MCTT syndrome is called perisylvian polymicrogyria, in which an area of the brain called the perisylvian region develops too many gyri, and the folds are irregular and unusually small. Individuals with MCTT syndrome can also have a malformation of the part of the brain that coordinates movement (the cerebellum ). This malformation, called atypical rhombencephalosynapsis, is characterized by tissue loss in the central part of the cerebellum (known as the vermis) and fusion of the two sides of the cerebellum. These brain abnormalities likely contribute to the movement problems and intellectual disability that are common in MCTT syndrome. 

Less common features of MCTT syndrome include hearing loss, seizures, abnormal curvature of the spine, and heart abnormalities.

Nonsyndromic hearing loss is a partial or total loss of hearing that is not associated with other signs and symptoms. In contrast, syndromic hearing loss occurs with signs and symptoms affecting other parts of the body.

Nonsyndromic hearing loss can be classified in several different ways. One common way is by the condition's pattern of inheritance: autosomal dominant (DFNA), autosomal recessive (DFNB), X-linked (DFNX), or mitochondrial (which does not have a special designation). Each of these types of hearing loss includes multiple subtypes. DFNA, DFNB, and DFNX subtypes are numbered in the order in which they were first described. For example, DFNA1 was the first type of autosomal dominant nonsyndromic hearing loss to be identified.

The characteristics of nonsyndromic hearing loss vary among the different types. Hearing loss 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 term "deafness" is often used to describe severe-to-profound hearing loss. Hearing loss can be stable, or it may be progressive, becoming more severe as a person gets older. Particular types of nonsyndromic hearing loss show distinctive patterns of hearing loss. For example, the loss may be more pronounced at high, middle, or low tones.

Most forms of nonsyndromic hearing loss are described as sensorineural, which means they are associated with a permanent loss of hearing caused by damage to structures in the inner ear. The inner ear processes sound and sends the information to the brain in the form of electrical nerve impulses. Less commonly, nonsyndromic hearing loss is described as conductive, meaning it results from changes in the middle ear. The middle ear contains three tiny bones that help transfer sound from the eardrum to the inner ear. Some forms of nonsyndromic hearing loss, particularly a type called DFNX2, involve changes in both the inner ear and the middle ear. This combination is called mixed hearing loss.

Depending on the type, nonsyndromic hearing loss can become apparent at any time from infancy to old 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.