The Molecular Genetics and Neuropathology of Frontotemporal Lobar Degeneration: Recent Developments

The past year has seen a number of significant advances in our understanding of the neuropathological and molecular genetic basis of frontotemporal lobar degeneration (FTLD). Whereas, in the past, most attention focused on FTLD associated with tau-based pathology and microtubule associated protein tau gene (MAPT) mutations, there has recently been greater attention paid to non-tau FTLD. FTLD with tau-negative, ubiquitinated inclusions (FTLD-U) is now recognized as the most common pathology associated with clinical FTLD. Mutations in the progranulin gene (PGRN) have been identified as the cause of FTLD-U linked to chromosome 17. A rapidly growing number of PGRN mutations have been identified, and to date, all appear to cause FTLD by reducing the amount of functional PGRN protein (haploinsufficiency). The neuropathology associated with each of the known non-MAPT FTLD genes and loci (PGRN, valosin-containing protein gene, CHMP2B and 9p), has been shown to be a specific subtype of FTLD-U. The ubiquitinated pathological protein in FTLD-U has been identified as TAR deoxyribonucleic acid-binding protein with M (r) 43 kDa (TDP-43). Immunohistochemical and biochemical studies of TDP-43 have helped to clarify the relationship between different sub-types of FTLD-U and related conditions. It is anticipated that these discoveries will facilitate the development of new diagnostic tests and therapeutics.