Other Autosomal Recessive Ataxias
Autosomal recessive ataxias are now classified using a similar system to the autosomal dominant SCA’s. The ataxias are numbered by the order of their discovery. The acronym “SCAR” is used rather than “SCA,” which is used for dominant ataxias. The acronym SCAR stands for Spinocerebellar ataxia autosomal recessive. Many of these ataxias are quite rare and have only been reported in one family in the world. To make matters more confusing, some autosomal recessive ataxias used to be named with the acronym ARCA (Autosomal Recessive Cerebellar Ataxia). SCAR1 (AOA2)
SCAR 1 is now used to indicate ataxia with oculomotor apraxia type 2 (AOA2). Usually has a later age of onset as compared to AOA1. Onset is still usually before 20 years of age. Individuals often have a high level of a protein called “Alpha Feto Protein or AFP” in their blood. Individuals with AOA2 may have problems with abnormal posture (dystonia), twitching movements (chorea), in addition to ataxia. Neuropathy is often found in this condition. AOA2 is an autosomal recessive condition caused by sequence changes in a gene called “SETX.” In order to confirm a diagnosis of AOA2, sequence changes must be found in both copies of the gene. Carrier testing for family members may be available if sequence changes are identified in the individual with ataxia.
SCAR2
This is a severe form of recessive ataxia that is also associated with mental subnormality. Affected individuals may not survive until adulthood. Families from Italy and Lebanon have been reported. The gene that causes this type of ataxia has not been discovered. Therefore, no gene testing is available. SCAR3
This type of ataxia is also associated with blindness and deafness. Two families have been reported, one of which was from Israel. The gene that causes this type of ataxia has not been identified. No gene testing is available. SCAR4
SCAR4 was originally called SCA24. Because the pattern of inheritance is autosomal recessive, the name was changed to SCAR4. This type of ataxia has been described in a single family from Slovenia. There is no gene testing for SCAR4. SCAR5
SCAR5 has been described in a single family from Lebanon. There is no gene testing for this type of ataxia. Affected family members often have problems with the optic nerve in the eye (optic atrophy). SCAR6
This type of ataxia begins in infancy and is slowly progressive. The one family described is from Norway. There is no gene testing available. SCAR7
SCAR7 is a slowly progressive form of ataxia described in a single Dutch family. There is no gene testing available. SCAR8 (ARCA1)
SCAR8 has been described in some French Canadian families. This condition is also called ARCA1 (autosomal recessive ataxia 1) or Ataxia of Beauce. Beauce is the region of Quebec where this ataxia is seen. SCAR8 is caused by sequence changes in a gene called SYNE1. Four different sequence changes in the SYNE1 gene have been found in this part of Canada. Genetic testing for these four sequence changes is available. These sequence changes appear to be specific to the French Canadian population. SCAR9
This type of ataxia was identified in a family from Algeria. The symptoms begin in childhood and in some cases, there may be mental subnormailty or learning difficulties. This type of ataxia is caused by sequence changes in a gene called CABC1. Gene testing is not available in the United States. This type of ataxia has also been called ARCA2 (autosomal recessive cerebellar ataxia type 2). Ataxia with vitamin E deficiency (AVED)
Ataxia with vitamin E deficiency has symptoms that resemble Friedreich ataxia. This type of ataxia can be non-genetic or genetic. Individuals with non-genetic AVED either lack vitamin E in their diet, or they don’t absorb vitamin E from their diet. Individuals with the genetic form of AVED have sequence changes in a gene called TTPA. This genetic instruction normally tells the body how to process and use vitamin E. Symptoms often begin around puberty and often involve problems with sensation. Affected individuals have difficulty sensing where their joints, arms, legs, feet etc. are in space. This makes it very difficult for them to coordinate movements. AVED often responds to treatment with vitamin E. Because this type of ataxia is treatable, neurologists should screen all ataxia patients to make sure they have normal vitamin E levels. If the levels are low, patients must be evaluated to see if the vitamin E deficiency is due to dietary reasons or genetic reasons. IOSCA
IOSCA stands for Infantiale Onset SpinoCerebellar Ataxia. This type of ataxia has only been identified in people from Finland. Symptoms often begin around the age of 2 and include ataxia, muscle weakness, abnormal twisting movements, hearing loss, vision loss, and paralysis of the muscles that move the eyes. Females often have problems with hormones that may affect their fertility. Later in the disease, seizures may develop. These seizures can be severe and life-threatening. This type of ataxia is caused by sequence changes in a gene called C10ORf2. IOSCA has not yet been found in people without Finnish ancestry. Marinesco-Sjogren Syndrome
This type of ataxia usually begins in early childhood. The first symptoms include ataxia, muscle weakness, mental retardation, and cataracts. Adults with Marinesco Sjogren syndrome often have significant mental retardation, but usually have a normal life-span. Marinesco Sjogren syndrome is caused by sequence changes in a gene called SIL1. Genetic testing for Marinesco Sjogren syndrome is available. Coenzyme Q10 deficiency
Coenzyme Q10 is a very important chemical in the body. It is critical in the process that our body uses to make energy. Some individuals with ataxia have very low levels of coenzyme Q10 in their muscle tissue. There are many different genes that can cause coenzyme Q10 deficiency. All of the different forms of coenzyme Q10 deficiency appear to be inherited in an autosomal recessive manner. The clinical findings in people with coenzyme Q10 deficiency are extremely variable and can include ataxia, infertility, blindness, seizures, muscle disease, kidney disease, and other symptoms. The diagnosis is initially suspected by finding low hormones in the blood and confirmed by measuring coenzyme Q10 on a muscle biopsy. If there is a deficiency, genetic testing for some genes that cause coenzyme Q10 deficiency is available. Coenzyme Q10 is available as a medication in the form of pills (anti-oxidant).
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