On the whole, hereditary neurological disorders with monogenic inheritance, like the ones described above, are relatively rare. In many of the more common neurological disorders, such as Alzheimer's disease, epilepsy, multiple sclerosis, or Parkinson's disease, genetic factors play an important role in the etiology, but the diseases are in most cases not passed on in a simple dominant or recessive pattern of inheritance. Instead, a more complex inheritance is assumed (although this has not been proved):
• Polygenic inheritance: Several different inherited traits must come together to cause development of a disease.
• Multifactorial development: In addition to a genetic vulnerability, other nongenetic factors play a role (e. g., toxic or immunological influences).
For many of these disorders, however, subgroups with monogenic causes have also been found (Table 8.1). Identification of the causative genes in these rare monogenic subforms of disease has already led to a much better understanding of the molecular pathogenesis of these disorders and will in future also play an important role in explaining the disease mechanisms. For molecular diagnostic testing, these subforms only play a role in exceptional cases, since they are mostly found only in patients with unusually early disease onset and/or a strongly positive family history.
Gasser T, Dichgans M, Jurkat-Rott K, et al. Molekulare Diagnostik erblicher neurologischer Erkrankungen. Positionspapier. Nervenarzt 2000;71:774
Statement of the Practice Committee Genetics Testing Task Force of the American Academy of Neurology. Practice parameter: genetic testing alert. Neurology 1996;47:1343