OMIM ID:
Spastic Paraplegia 11
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Gaze evoked nystagmus and pigmentation in the macula are components of this syndrome and adults have some degree of retinal degeneration with poor vision eventually. Optic atrophy and ptosis have been reported but rarely.
Systemic Features
his progressive condition nay have its onset in childhood or early adolescence although rarely it first appears in adulthood. Obesity is a component in older individuals. Loss of ambulation usually occurs within 10 years of the onset of gait difficulties. Hyperreflexia and spasticity develop early while ataxia, urinary sphincter disturbances, extensor plantar responses, and dysarthria appear later. Amyotrophy is frequently seen in the thenar and hypothenar muscles. Children have learning difficulties while cognitive decline and frank mental retardation occur somewhat later.
Peripheral nerve biopsy may reveal hypomyelination and loss of unmyelinated nerve fibers. MRI imaging in some individuals shows a thin or absent corpus callosum and cortical atrophy.
Genetics
Inheritance
Homozygous mutations in the gene SPG11 (15q21.1) encoding spatacsin are responsible for this disorder.
See spastic paraplegia 15 (Kjellin syndrome) (270700) and spastic paraplegia 7 (607259) for other disorders with retinal degeneration, optic atrophy, and nystagmus.
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.