Frontotemporal Lobar Degeneration and HHV-6
"Circumscribed cerebral atrophy of the frontal and anterior temporal lobes, also called lobar atrophy, is the gross pathological hallmark of FTLD." http://www.dcmsonline.org/jax-medicine/2000journals/February2000/ftld.htm
Contrary to conventional wisdom, FTLD may not be primarily a genetic disorder:
"In one study about 45% of FTLD patients have family members with a similar disorder.7 Genetic mutations in the tau protein on chromosome 17 have been identified in several families. Most of these mutations have been shown to increase the proportion of an isoform of tau called 4-repeat tau.8 However, it is clear that most cases in clinical practice don't have one of these mutations on chromosome 17. In fact in more than 50 consecutive cases, we have identified none with a chromosome 17 mutation. Apolipoprotein E4 allele (which has been shown to be a risk factor for AD) does not appear to be associated with FTLD." http://www.dcmsonline.org/jax-medicine/2000journals/February2000/ftld.htm