Pure hereditary spastic paraparesis: an exclusion map covering more than 40% of the autosomal genome

Molecular genetics of familial spastic paraplegia: a multitude of responsible genes

Familial spastic paraplegia (FSP or SPG) is a genetically heterogeneous group of upper motor neuron syndromes. To date, two distinct loci for X-linked recessive type (SPG1 and SPG2), three loci for autosomal dominant type (FSP1, FSP2 and FSP3), and one locus for autosomal recessive type have been reported. SPG1 and SPG2 have been mapped to Xq28 and Xq21-q22, respectively. SPG1 shows a mutation in the gene for neural cell adhesion molecule L1 (LICAM), which is an axonal glycoprotein involved in neuronal migration and differentiation. Different mutations of the same L1 gene also cause. MASA (mental retardation, aphasia, spastic paraplegia, adducted thumbs) syndrome and X-linked hydrocephalus. SPG2 shows mutations in one of the major myelin proteins, the proteolipid protein (PLP) gene, and is allelic to Pelizaeus-Merzbacher disease. Thus, mutations in two functionally distinct genes manifest the phenotype of X-linked spastic paraparesis. Three dominantly inherited spastic paraplegia genes have been genetically mapped to regions of chromosomes, yet no specific genes or mutations have been identified. FSP1 is mapped to a region of 7 cM on chromosome 14q12-q23 (approximately 20% of dominant FSP families) and FSP2 to 4 cM on chromosome 2p21-p24 (approximately 70% of dominant FSP families). Anticipation (increasing clinical severity in successive generations) has been observed in both FSP1 and FSP2 families. Another autosomal dominant FSP (FSP3) has been mapped in the centromeric region of chromosome 15q (< 10% of dominant FSP families). An autosomal recessive FSP has been mapped to chromosome 8q. The definite genetic heterogeneity in FSP indicates that a multitude of genes/proteins can cause spastic paraplegia. Clinical features of each of the loci which may permit differential diagnosis are discussed. We also present pedigrees of two new FSP families.

Infantile onset of hereditary ascending spastic paralysis with bulbar involvement

Primary lateral sclerosis and hereditary spastic paraparesis are both rare neurodegenerative disorders characterized by progressive weakness and spasticity of the lower limbs, with involvement of the corticospinal tracts and sparing of anterior horn cells. We describe a consanguineous family in which three sons developed progressive paralysis of the lower extremities in infancy with subsequent involvement of the upper extremities and bulbar muscles but cognitive sparing. This family presents the nosologic difficulty of distinguishing between hereditary spastic paraparesis and primary lateral sclerosis. We suggest that the diagnosis in this family is hereditary primary lateral sclerosis. This is the first instance of familial occurrence of primary lateral sclerosis.

Clinically silent dysfunction of dorsal columns and dorsal spinocerebellar tracts in hereditary spastic paraparesis

Hereditary spastic paraparesis (HSP) is a neurodegenerative disorder, of which progressive spastic paraparesis is the clinical hallmark. Given the neuropathological evidence of degeneration of pyramidal tracts, dorsal columns, and dorsal spinocerebellar tracts, it is surprising that sensory symptoms are so indistinct compared to motor symptoms. We investigated the involvement of peripheral conduction and spinal proprioceptive pathways by nerve conduction studies, somatosensory evoked potentials of the median and tibial nerves, and quantitative assessment of the vibration perception thresholds of the hands and feet respectively in 32 patients suffering from HSP and healthy control groups. We did not find peripheral conduction abnormalities in HSP patients. Log-transformed vibration perception thresholds of the feet were abnormal in 13/32 HSP patients and in 0/64 controls (p < 0.00001), while tibial nerve somatosensory evoked potentials were abnormal in 20/32 patients and in 1/17 controls (p = 0.00001). The values for the upper extremities were within normal limits for nearly all subjects. In the HSP group, the neurophysiological disturbances did not correlate significantly with duration or severity of the disease, when age was controlled for, except for median nerve SSEP latency, which was affected by severity (p = 0.0072). We conclude that neurophysiological methods detected proprioceptive, subclinical abnormalities in several HSP patients, which may reflect degeneration of the dorsal columns, and/or dorsal spinocerebellar tracts. Since we found no correlation with several disease variables, the fact that not all HSP patients displayed these abnormalities may be caused by anatomical variations in proprioceptive pathways, rather than by phenotypical heterogeneity.