Forkhead transcription factors: key players in health and disease.

Forkhead box (FOX) proteins constitute an evolutionarily conserved family of transcription factors with a central role not only during development, but also in the adult organism. Thus, the misregulation and/or mutation of FOX genes often induce human genetic diseases, promote cancer or deregulate ageing. Indeed, germinal FOX gene mutations cause diseases ranging from infertility to language and/or speech disorders and immunological defects. Moreover, because of their central role in signalling pathways and in the regulation of homeostasis, somatic misregulation and/or mutation of FOX genes are associated with cancer. FOX proteins have undergone diversification in terms of their sequence, regulation and function. In addition to dedicated roles, evidence suggests that Forkhead factors have retained some functional redundancy. Thus, combinations of slightly defective alleles might induce disease phenotypes in humans, acting as quantitative trait loci. Uncovering such variants would be a big step towards understanding the functional interdependencies of different FOX members and their implications in complex pathologies.