What is hereditary ataxia?
Hereditary ataxia is not a single disorder, but a group of disorders which have in common that they cause ataxia and that they run in families. Physicians and researchers usually separate out from this category patients whose ataxia is caused by a known metabolic defect (e.g. hexosaminidase deficiency) or whose symptoms fit a more specific, named disorder (such as Friedreich's ataxia), although these too are hereditary diseases that cause ataxia.
Scientists have used a number of different methods to categorize and name the hereditary, adult-onset ataxias, none of which have been entirely satisfactory. Here are some of the terms you may see or hear used in describing hereditary ataxia:
hereditary OPCA (olivopontocerebellar atrophy)
spinocerebellar ataxia (SCA)
SCA-1, SCA-2, SCA-3
"slow-eye movement" ataxia
"pure" cerebellar ataxia
OPCA I, OPCA II, OPCA III, OPCA IV
ataxia with ophthalmoplegia
ataxia with retinopathy
How does a physician diagnose hereditary ataxia?
In most cases, the physician bases a diagnosis of hereditary ataxia on:
- The presence of neurologic symptoms and signs that are usually seen in ataxia
- The presence of other similarly affected family members
- The absence of other diseases (such as multiple sclerosis or stroke) which could account for the symptoms
It is virtually impossible to diagnose HEREDITARY ataxia in someone who has no similarly affected relatives; in these cases, the diagnosis of "sporadic ataxia" is usually made. As the genes which cause hereditary ataxia are identified, simple blood tests to diagnose some forms of ataxia will become available.
The symptoms that are often present in patients with hereditary ataxia include:
- ataxia, or incoordination of the hands, arms, feet, or legs;
- slowness, stiffness, or clumsiness of movement;
- thick or slurred speech (dysarthria) or choking (dysphagia).
These symptoms are usually due to abnormal function of the cerebellum, the coordination center of the brain. As the disease progresses, patients may develop additional symptoms related to other parts of the brain or nervous system, such as inability to move the eyes, weakness, tremor, spasticity, dementia, or loss of feeling in the feet or hands (neuropathy). Even within the same family, the severity of one or another symptom may vary from one person to the next. Occasionally, the symptoms NOT related to the cerebellum are so much more prominent than the ataxic symptoms that a person may receive a diagnosis of another disorder, such as Parkinson's disease, when in fact, she/he has hereditary ataxia.
Because the symptoms of hereditary ataxia may also be seen in a number of other neurologic disorders, individuals suspected of having hereditary ataxia may be asked to undergo a number of tests to "rule out" other conditions, and to look for the changes in the cerebellum that are present in most individuals with hereditary ataxia. These tests might include blood or urine tests; a CT or CAT (computerized axial tomography) or MRI (magnetic resonance imaging) scan of the brain or spinal cord; an EMG (electromyogram) to access the function of the nerves and muscles; and sometimes an EEG (electroencephalogram) or spinal tap. THe PET (positron emission tomography) scan is used in some centers to access the function of the cerebellum and other parts of the brain.
What should I do if I have hereditary ataxia?
A person who suspects that he or she has hereditary ataxia should first consult a neurologist or other physician for a thorough neurologic evaluation, to make sure there are no other possible medical or neurologic causes for the symptoms, and to make a proper diagnosis.
All of the hereditary ataxias tend to progress over time, so that a person diagnosed with ataxia can be expected to have increasing needs; however, how fast the disease progresses varies widely from one individual to the next. Many patients with ataxia live normal lifespans. Because this is a chronic disease with many potential complications, the person who has hereditary ataxia should identify a medical caregiver who understands ataxia and is able to coordinate the necessary services, which may include social services, speech pathology, genetic counseling, psychological or family counseling, and rehabilitation medicine (physical therapy and occupational therapy), among others. Because many physicians and other medical professionals are not knowledgeable about ataxia, it is important for the affected person and his family to become knowledgeable themselves, so that they can assist their caregivers in providing appropriate care and services.
How is hereditary ataxia passed on in a family?
Because there are several different types of hereditary ataxia, there are different ways that the disease may be passed on in the family. It is important to know that ataxia is not contagious, so there is no reason to avoid a person who has ataxia for fear of "catching" it.
Most of the time, ataxia in families with adult onset of symptoms is passed on in an "autosomal dominant" fashion. The word "autosomal" means that the sex of the person does not matter; ataxia can strike men or women in the family with equal likelihood. The word "dominant" means that the disease-causing ataxia gene can't hide; anyone who has the altered gene will eventually develop symptoms of ataxia. Thus, the disease does not skip generations; in the family tree anyone who has ataxia has a parent who also had ataxia. Two other facts are important to know about autosomal dominant inheritance. A person who does not have the altered ataxia gene will not develop ataxia and cannot pass ataxia on to his or her children. A person who DOES have the altered ataxia gene CAN pass ataxia on to his or her children whether or not he or she had SYMPTOMS of ataxia at the time that the children were born.
Another way that ataxia can be passed on in families is in an "autosomal recessive" fashion. Friedreich's ataxia is an example of a form of ataxia that is autosomal recessive. Autosomal recessive diseases affect men and women equally, but a recessive gene can be passed on by an "asymptomatic carrier", that is, a person who has no symptoms of ataxia. It takes a double dose of an altered recessive gene to result in a disease; in other words, both parents have to be carriers of an altered gene in order to have a child or children with the disease. Although all human beings carry a few genes which are altered in some way, it is uncommon to bear children with another person who carries the same altered gene (unless the other person is a blood relative or the two individuals live in a socially or geographically isolated area). Thus, autosomal recessive forms of ataxia are uncommon, but do occur.
A geneticist or physician can usually tell by looking at the family tree whether ataxia is dominant or recessive or inherited in some other way. It may be very important, then, for the family history to be explored.
Please note: this information is Copyright 1993 by the National Ataxia Foundation, Inc. All rights reserved. - Find their site: http://www.ataxia.org