Spastic Ataxia 4, mtPAP Deficiency
Patient Information
Characteristics
Background and History
This is a very rare congenital neurological disorder affecting balance, speech, movement of the arms, legs, and tongue. It is associated with abnormalities of the optic nerve that carries visual signals to the brain.
Clinical Correlations
Children with this condition have difficulty with balance almost from birth. They also are slow to walk and talk which becomes more of a problem as they grow older. The arms and legs seem stiff, speech sounds slurred, and swallowing may become a problem. Balance as in sitting and walking is a special problem. Children in grade school require special education assistance but there is no evidence that there is deterioration of mental capabilities. Nothing is known about the level of vision but in spite of evidence for damage to the optic nerve that transmits visual images from the eye to the brain, individuals seem to function well at home and in school. However, some children have 'dancing eyes', which is often associated with some decrease of vision.
Genetics
Inheritance
Two families with multiple affected sibs have been reported with a pattern consistent with autosomal recessive inheritance. Mutations (changes) in both copies of a specific gene are responsible. Parents who carry a single copy are clinically normal but they can expect a risk of 25% of each of their children having 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 is likely to be made by a neurologist or pediatrician in a child who is slow to walk and speak. No treatment is available but children can benefit from speech and physical therapy as well as from special education assistance. There is no evidence of deterioration in mental function. Motor functions, especially gait and balance, however, become progressively more difficult. Adults remain able to ambulate and care for themselves with minimal assistance.
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