Pedigrees with familial Alzheimer's disease (AD) show considerable phenotypic variability. Spastic paraparesis (SP), or progressive spasticity of the lower limbs is frequently hereditary and exists either as uncomplicated (paraparesis alone) or complicated (paraparesis and other neurological features) disease subtypes. In some AD families, with presenilin-1 (PSEN1) mutations, affected individuals also have SP. These PSEN1 AD pedigrees frequently have a distinctive and variant neuropathology, namely large, non-cored plaques without neuritic dystrophy called cotton wool plaques (CWP). The PSEN1 AD mutations giving rise to CWP produce unusually high levels of the amyloid beta peptide (Abeta) ending at position 42 or 43, and the main component of CWP is amino-terminally truncated forms of amyloid beta peptide starting after the alternative beta-secretase cleavage site at position 11. This suggests a molecular basis for the formation of CWP and an association with both SP and AD. The SP phenotype in some PSEN1 AD pedigrees also appears to be associated with a delayed onset of dementia compared with affected individuals who present with dementia only, suggesting the existence of a protective factor in some individuals with SP. Variations in neuropathology and neurological symptoms in PSEN1 AD raise the prospect that modifier genes may underlie this phenotypic heterogeneity.

Pedigrees with familial Alzheimer's disease (AD) show considerable phenotypic variability. Spastic paraparesis (SP), or progressive spasticity of the lower limbs is frequently hereditary and exists either as uncomplicated (paraparesis alone) or complicated (paraparesis and other neurological features) disease subtypes. In some AD families, with presenilin-1 (PSEN1) mutations, affected individuals also have SP. These PSEN1 AD pedigrees frequently have a distinctive and variant neuropathology, namely large, non-cored plaques without neuritic dystrophy called cotton wool plaques (CWP). The PSEN1 AD mutations giving rise to CWP produce unusually high levels of the amyloid beta peptide (Abeta) ending at position 42 or 43, and the main component of CWP is amino-terminally truncated forms of amyloid beta peptide starting after the alternative beta-secretase cleavage site at position 11. This suggests a molecular basis for the formation of CWP and an association with both SP and AD. The SP phenotype in some PSEN1 AD pedigrees also appears to be associated with a delayed onset of dementia compared with affected individuals who present with dementia only, suggesting the existence of a protective factor in some individuals with SP. Variations in neuropathology and neurological symptoms in PSEN1 AD raise the prospect that modifier genes may underlie this phenotypic heterogeneity.

Early onset familial Alzheimer's disease (EOFAD) has been associated with mutations in three genes, of which presenilin 1 (PSEN1) mutations are the most frequent. Several families with an association of progressive dementia and spastic paraplegia caused by PSEN1 mutations have been described. Here we described a novel PSEN1 mutation that was associated with dementia and spastic paraplegia in a family with 5 affected individuals in three generations. The proband was a 44-year-old woman who presented with 5 years history of progressive difficulties in walking, cognition and visuospatial impairment. Her maternal grandmother, mother and two maternal aunts also had similar neurological presentation. Molecular genetic analysis showed a missense mutation predicted to substitute an arginine residue for a serine residue at position 278 in the PSEN1 polypeptide (Arg278Ser). The novel PSEN1 mutation identified in this patient adds to the diverse list of existing mutations causing EOFAD associated with spastic paraparesis.