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Cogan type ocular motor apraxia is a rare congenital disorder characterized by a defect in side-to-side (horizontal) eye movements. The eyes do not move properly in response to stimuli or voluntarily. When affected infants are asked to fixate on an object to the side, their eyes will lag and then move in the opposite direction. In order to compensate for this, the infants will sharply jerk their heads past the desired object in an effort to bring the eyes to a position where they can view the object. When the eyes fixate on the object, the head will return to its normal position. These jerking head movements are the most noticeable sign of Cogan type ocular motor apraxia and are usually recognized three to four months after birth. Before these head jerkings occur, an infant's inability to fixate on an object may sometimes be mistaken for blindness.
Infants with Cogan type ocular motor apraxia will also be unable to follow rapid movements across their fields of vision, such as focusing on a moving train (opticokinetic nystagmus). The disorder can also be associated with mild developmental delay and speech difficulties.
In other rare cases of Cogan type ocular motor apraxia, individuals exhibit an inability to fixate on objects to one particular side of the body (unilateral ocular motor apraxia). In some of these cases, individuals may demonstrate improper eye movements and/or an inability to track an object with the other eye.
Cogan type ocular motor apraxia is not progressive and many affected individuals eventually learn to compensate for the disorder by overshooting the eyes instead of jerking the head. The number and severity of symptoms varies widely among affected individuals.
Some individuals with Cogan type ocular motor apraxia have a brain abnormality such as underdevelopment (hypoplasia) of the corpus callosum, hypoplasia of the cerebellum, or an abnormality in the grey matter. (For more information on agenesis of corpus callosum, see the Related Disorders section of this report.)
Cogan type ocular motor apraxia is a genetic condition for which the inheritance pattern has not been well established. It is not clear if it is inherited as an autosomal recessive genetic trait or an autosomal dominant genetic trait.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
Cogan type ocular motor apraxia affects males approximately twice as often as females. Symptoms are present at birth (congenital). The jerking-head movements associated with this disorder usually appear by the third or fourth month of life. Approximately 50 cases have been reported in the medical literature.
Symptoms of the following disorders can be similar to those of Cogan type ocular motor apraxia. Comparisons may be useful for a differential diagnosis:
Balint's syndrome is a rare eye disorder characterized by the inability to voluntarily look at objects to the side (peripherally). An affected individual may also have trouble grasping objects due to difficulties with hand-to-eye coordination and may be unable to follow objects across the eyes' field of vision. Although the exact cause of Balint's syndrome is not known, it is thought that symptoms may be caused by improper development of part of the brain.
Ataxia-telangiectasia is a rare inherited form of cerebellar ataxia that usually begins during infancy. It is characterized by loss of coordination of the limbs, the head, and the eyes, and a lower than normal immune response against infections. Rapid eye blinking, abnormal eye movements, and head thrusting may develop gradually. Ataxia-telangiectasia may be confused with Cogan type ocular motor apraxia prior to the development of visible widened (dilated) blood vessels (telangiectasias). However, unlike individuals with Cogan type ocular motor apraxia, individuals with ataxia-telangiectasia have defective up-and-down (vertical) as well as side-to-side (horizontal) eye movements. Ocular telangiectasias, which lead to a bloodshot appearance, usually begin between three and six years of age but may occur earlier. Ataxia-telangiectasia is inherited as an autosomal recessive genetic trait. (For more information on this disorder, choose "ataxia-telangiectasia" as your search term in the Rare Disease Database.)
The following disorder may precede the development of Cogan type ocular motor apraxia. It can be useful in identifying an underlying cause of some forms of this disorder:
Agenesis of corpus callosum (ACC) is a rare neurological disorder that is present at birth (congenital). It is characterized by a partial or complete absence (agenesis) of the area of the brain that connects the two cerebral hemispheres. Symptoms of this disorder include seizures and delays in the ability to properly sit, stand, or walk (developmental delays). Agenesis of corpus callosum is usually inherited as either an autosomal recessive trait or an X-linked dominant trait. (For more information on this disorder, choose "agenesis of corpus callosum" as your search term in the Rare Disease Database.)
Diagnosis of Cogan type ocular motor apraxia may be made upon observing the jerking-head movements that an infant will make in order to view an object to the side. Infants who exhibit jerking-head movements and the inability to fixate on an object should have a thorough eye examination by a qualified physician. Magnetic Resonance Imaging (MRI), CT Scan, or Positron Emission Tomography (PET) may be used to determine whether any associated brain abnormalities (i.e., underdevelopment of the corpus callosum or improper development of the cerebellar vermis) are present.
A supportive team approach for children with ocular motor apraxia may be of benefit and may include special education services, physical therapy, speech therapy, and other medical, social, or vocational services.
Cogan type ocular motor apraxia has been associated with progressive kidney failure (nephronophthisis) in some individuals. It has been suggested that affected individuals have routine screening to determine if their kidneys are functioning normally.
Genetic counseling may be of benefit for patients and their families. Other treatment is symptomatic and supportive.
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FROM THE INTERNET
McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore, MD. The Johns Hopkins University; Entry No. 257550; Last Update: 3/19/04.
Report last updated: 2008/05/25 00:00:00 GMT+0