OMIM ID:
Spastic Ataxia, Optic Atrophy, Mental Retardation
Defective Genes
Clinical Characteristics
Ocular Features
Optic atrophy is generally but not always present. Internuclear ophthalmoplegia and nystagmus have been reported.
Systemic Features
This progressive neurodegenerative disorder has its onset in early childhood with delayed psychomotor development, spastic ataxia of the limbs, and dysarthria. Tremor, dysmetria, and poor coordination of fine movements are often present. A sensorineural hearing loss has been found in several individuals. Peripheral neuropathy has been reported as well. The nature and degree of cognitive impairment has not been quantified.
Genetics
Inheritance
The presence of consanguinity in one family and affected sibs in another suggest autosomal recessive inheritance but nothing is known about the genotype. The signs and symptoms resemble those found in other spastic ataxias and this may not be a unique disorder.
Optic atrophy is also found in autosomal recessive SPAX4 (613672) and in autosomal dominant SPAX7 (108650).
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.