The hereditary spastic paraplegias are classified according to the mode of inheritance (autosomal dominant, autosomal recessive, and X-linked) and whether progressive spasticity occurs in isolation ("uncomplicated HSP") or with other neurologic abnormalities ("complicated HSP"), such as optic neuropathy, retinopathy, extrapyramidal disturbance, dementia, ataxia, ichthyosis, mental retardation, deafness and epilepsy. Harding (Harding, 1981) reviewed 19 families with autosomal dominant, uncomplicated HSP and classified the disease as Type I if spasticity exceeded weakness, onset occurred before age 35, and progression was slow, and as Type II if onset occurred after age 35 and patients had weakness in addition to spasticity, mild distal sensory loss, urinary bladder disturbance, and faster progression (Holmes and Shaywitz, 1977; Harding, 1981; Opjordsmoen et al., 1980). In HSP families reported by the Hereditary Spastic Paraplegia Working Group (Fink et al., 1996) autosomal dominant HSP kindreds linked to chromosomes 2p, 14q, and 15q showed an overlap of the range of ages at which symptoms began. Assuming that kindreds linked to these loci were represented among those Harding (Harding, 1981) classified as Type I and Type II, there does not appear to be a genetic basis for HSP classification based entirely on age of symptom onset.
Classification schemes based entirely on clinical features (such as age of onset and the presence of other neurologic deficits) will be revised as the underlying molecular genetic and biochemical features of HSP become known. Presently, though it is useful to distinguish between "uncomplicated" and "complicated" HSP (defined above). Instead of sub-classifying autosomal dominant HSP as early (type I) or late onset (type II), it is preferable to refer to HSP subtypes by the mode of inheritance and chromosome (and eventually genetic mutation) to which patients were linked (e.g. "autosomal dominant, chromosome 2p linked, uncomplicated HSP"). Similarly, kindreds with X-linked HSP should be designated by their locus (if possible), e.g., uncomplicated Xq22-linked HSP. Alternatively, Genome Database designation for X-linked HSP loci (SPG1 and SPG2), and autosomal HSP loci (SPG3: chromosome 14q; SPG4: chromosome 2p; SPG5A: chromosome 8q: SPG6: chromosome 15q) may be used when the chromosomal locus is known.
Adapted with permission from (Fink et al., 1996) and (Fink, 1997).