Spastic Ataxia 6, Charlevoix-Saguenay Type
Patient Information
Characteristics
Background and History
This is a progressive degenerative disorder of the neurological system that begins in early childhood (12-18 months of age). It was first described in the Charlevoix-Saguenay region of Quebec, Canada in 1978 where the greatest number of cases is found but it has also been seen in families in Asia and Europe.
Clinical Correlations
Early signs include difficulties in balance and motor function leading to difficulties in walking and in speech. The limbs are stiff and reflexes are often hyperreactive. Wasting of muscles in the limbs becomes evident later along with slurring of speech and some loss of sensation. The course of disease is slow but relentless. Most patients eventually are unable to walk but many live until the sixth decade. Mental function remains intact. Striated white or yellowish-white patches of nerves can be seen in the retina but these do not seem to be of functional significance.
Genetics
Inheritance
This is an autosomal recessive disorder that results from changes (mutations) in a specific gene. Two copies of the mutation are necessary for the disease to develop. Carrier parents with only one copy are clinically normal but each of their children has a 25% risk of inheriting this condition.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
The diagnosis of this type of spastic ataxia is most likely to be made by a neurologist but an ophthalmologist is most likely to be the one to see the patches in the retina. The latter is not diagnostic though since some otherwise normal individuals may have similar patches. Nerve conduction studies (EMG) and brain imaging can help to confirm the diagnosis. Longevity is only mildly impacted.
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