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How is the TOMM40 gene used to estimate the age of Alzheimer disease onset?
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Alzheimer disease
Histopathologic image of neuritic plaques in the cerebral cortex in a patient with Alzheimer disease of presenile onset (onset before age 65).
Genetic screening for the TOMM40 (translocase of outer mitochondrial membrane 40 homolog) gene helps estimate the age of onset for Alzheimer disease by analyzing variations in the gene's length.1
These variations are determined by the number of repeats of a specific base-pair segment within the gene sequence. The risk and predicted timing of disease onset are assessed as follows:1
- Long forms: When an individual inherits a long form of TOMM40 in conjunction with either the APOE3 or APOE4 variants, it correlates with an earlier onset of the disease, typically before age 80.1
- Short forms: Conversely, the presence of short forms of TOMM40 is associated with a later onset of the disease, occurring after age 80.1
By identifying these specific genetic variants, researchers can provide additional insight into an individual's risk profile and the likely timing of disease development.1