What causes frontotemporal lobe dementia with motor neuron disease (FTD/MND)?

Updated: Apr 11, 2017
  • Author: Jasvinder Chawla, MD, MBA; Chief Editor: Jasvinder Chawla, MD, MBA  more...
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Answer

Answer

Worldwide, frontotemporal lobe dementia with motor neuron disease (FTD/MND) is a sporadic condition with an unknown etiology. It is characterized by pyramidal cell loss in the frontal and temporal lobes and degeneration of motor neurons in the hypoglossal nucleus and spinal motor neurons. Pyramidal neurons in the premotor cortex usually are preserved. [8]

Takeda et al have shown that ALS pathology initiated by cytoplasmic inclusions and neuronal loss in layer II-III of the transentorhinal cortex (TEC)–molecular dentate gyrus (DG) projection and subiculum is specific to ALS. [9] This is different from the neurofibrillary tangles of Alzheimer disease, dominant in layer II-III of the entorhinal cortex. This may provide a basis for clinical characterization of memory deficits of ALS, which may be distinct from those of Alzheimer disease.

TDP-43 has been identified as the major pathologic protein in sporadic ALS and has also been found in the most common pathologic subtype of FTD (ie, frontotemporal lobar degeneration with ubiquitinated inclusions). Data now suggest that delocalization, accumulation, and ubiquitination of TDP-43 in the cytoplasm of motor neurons are early dysfunctions in the cascade of the events leading to motor neuron degeneration in ALS. [4, 5, 6, 7, 10, 11]

Signs and symptoms reflect frontal and temporal lobe dysfunction with lower motor neuron–type weakness, muscle atrophy, and fasciculations.


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