Genetic heterogeneity in the hereditary spastic paraplegias
Genetic heterogeneity is defined by the presence of multiple genetic causes leading to a similar phenotype or the same disease.
This phenomenon is common to many human diseases.
Examples of neurologic diseases with marked genetic heterogeneity include spinocerebellar ataxia and hereditary spastic paraplegia (HSP).
Clinically, HSP is a group of disorders characterized by progressive spasticity and weakness of the lower limbs associated with length-dependent distal axonal degeneration of the corticospinal tracts.
Autosomal dominant, autosomal recessive, X-linked, and maternal inheritance have been described, and to date over 70 spastic gait disease loci and at least 55 spastic paraplegia genes have been identified.
Moreover, a clinical and genetic overlap has been described between forms of HSP and other motor neuron diseases.