25 November 2009

Hereditary factors associated with FTLD

The heritability and genetics of frontotemporal lobar degeneration
Dementia News (Alzheimer’s Australia): 23 November 2009
There are many forms of dementia and some of these forms fall into the category of frontotemporal lobar degeneration. These disorders are genetically and pathologically diverse but all cause degeneration of the brain.

A group of researchers from the Institute of Neurology, London, undertook research examining whether different forms of frontotemporal lobar degeneration are heritable, and if so, which ones are heritable and to what degree. Two hundred and twenty-five people who had been diagnosed with frontotemporal lobar degeneration spectrum were included in the study.

The researchers collected blood samples for genetic examination and took each person’s family history to determine whether any first-degree relatives (e.g. mother, father, sister, brother) had been diagnosed with frontotemporal lobar degeneration. Each participant was given a score from 1 to 4, depending on his or her family history. A score of 1 indicated a clear autosomal dominant history of frontotemporal lobar degeneration. (A genetic trait is autosomal dominant when only one copy of the gene from one parent is needed in order for an individual to show the characteristic that is coded for by that gene. For example, genes that code for brown eyes are dominant over genes that code for any other eye colour). A score of 4 was given to individuals who had no family history of dementia. Of the 225 study participants, 41.8% had some family history of dementia, although only 10.2% had a clear score of 1.

The researchers also looked for mutations in each of the five known disease-causing genes: MAPT, GRN, VCP, CHMP2B, and TARDP, and the FUS gene, which is known to cause motor neuron disease. Mutations were found in the MAPT gene in 8.9% of study participants, and in the GRN gene in 8.4% of study participants. Both the MAPT and GRN genes are associated with frontotemporal lobar degeneration. No mutations were found in any of the other genes.

Degrees of heritability were found to vary across the different types of frontotemporal lobar degeneration. The “behavioral variant” was found to be the most heritable form. The least heritable forms were found to be frontotemporal dementia-motor neuron disease and the language syndromes, particularly semantic dementia, which refers to a progressive loss of the ability to remember the meaning of words, faces, and objects.

Reference: Rohrer JD, Guerreiro R, Vandrovcova J, Uphill J, et al. 2009. The heritability and genetics of frontotemporal lobar degeneration. Neurology, 73(18):1451-6.

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