Spinocerebellar Ataxia, Infantile-Onset
Patient Information
Characteristics
Background and History
This is a rare hereditary neurodegenerative condition in which there is an early-onset of brain and neurological damage with blindness, hearing loss, and seizures. It was first described in the 1980s.
Clinical Correlations
Most infants seem to develop normally in the first year of life but by 10-18 months of age muscle weakness and coordination difficulties appear. Youngsters seem ‘floppy’ and often slow purposeless movements are seen in the arms and in the face. Muscle dysfunction and weakness progress relentlessly and many patients are confined to wheelchairs by their teenage years. There is also a more severe form in which associated liver disease leads to death within 5 years. Hearing loss and seizures are part of the syndrome and many individuals experience profound deafness. The sense of touch may be diminished.
Abnormalities of eye movements with some degree of difficulty moving the eyes (ophthalmoplegia) become evident at some point in the first decade of life. At the same time, damage to the optic nerve (connecting the eye to the brain) may become evident leading to severe vision loss.
Genetics
Inheritance
This is an autosomal recessive condition requiring changes (mutations) in two copies of a gene. Both clinically normal parents carry one copy of the mutation and in one out of four pregnancies on average the child inherits both copies and expresses this disorder.
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
A neurologist or pediatrician is most likely to make this diagnosis, often with the collaboration of an ophthalmologist who notes the abnormal eye movements and the optic nerve damage. There is no effective treatment.
Mildly affected individuals can live to young adulthood whereas those with more severe disease may not live beyond childhood. Mobility aids and physical therapy could aid in minimizing ambulatory difficulties while assistive hearing devices and low vision aids early could be helpful for sensory stimulation.
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