Review: Molecular pathology of frontotemporal lobar degenerations

Frontotemporal lobar degeneration (FTLD) is a group of disorders that principally affect the frontal and temporal lobes of the brain. In many parts of the world, FTLD is rapidly becoming a serious health burden on society and, as a result, the molecular mechanisms that underlie its onset and development have been the target of intense research efforts in recent years. Nonetheless, despite crucial pathological and genetic discoveries in this area much is still uncertain about how the many genes associated with this disease cause the observed neurodegeneration. Moreover, it has not been easy to define the molecular mechanisms that account for the clinical and pathological heterogeneity of the various FTLD subtypes, characterized by aggregates of Tau, TAR-DNA-Binding Protein-43 (TDP-43), and less often Fused in Sarcoma (FUS) protein. In this review, we will examine some of the emerging discoveries in this field: from the recent importance of autoimmunity to the presence of substantial variations in the composition and localization of TDP-43 and FUS brain aggregates in patients, and how they might affect the course of the disease. All together, these new results demonstrate how the observed clinical heterogeneity underlies considerable complexity at both the molecular and the disease pathway level. A better characterization of all this complexity will be essential for a more accurate stratification of patient cohorts for further studies and, eventually, for trials of therapy.