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Since first described by Kossard in 1994, frontal fibrosing alopecia (FFA) has been something of an enigma. The clinical heterogeneity of FFA, its apparent rarity and investigators' suboptimal access to phenotypically consistent patient cohorts may all have had a negative impact on delineating disease pathogenesis. Moreover, there is a relative paucity of epidemiological, interventional and basic research studies, and there have been no advances in translational therapeutics, unlike for other inflammatory dermatoses, such as alopecia areata (AA). Dermatologists anecdotally describe an increasing incidence in FFA over the last decade, which has led to the notion that the disorder may be induced by unknown environmental triggers. On the other hand, segregation of FFA in some families lends support to an unexplored genetic element implicated in disease pathogenesis. We herein review what is known about the pathobiology of FFA and formulate working hypotheses to advance insight into this intriguing hair disorder.

Frontal fibrosing alopecia (FFA) is a recently described inflammatory and scarring type of hair loss affecting almost exclusively women. Despite a dramatic recent increase in incidence the aetiopathogenesis of FFA remains unknown. We undertake genome-wide association studies in females from a UK cohort, comprising 844 cases and 3,760 controls, a Spanish cohort of 172 cases and 385 controls, and perform statistical meta-analysis. We observe genome-wide significant association with FFA at four genomic loci: 2p22.2, 6p21.1, 8q24.22 and 15q2.1. Within the 6p21.1 locus, fine-mapping indicates that the association is driven by the HLA-B*07: 02 allele. At 2p22.1, we implicate a putative causal missense variant in CYP1B1 , encoding the homonymous xenobiotic- and hormone-processing enzyme. Transcriptomic analysis of affected scalp tissue highlights overrepresentation of transcripts encoding components of innate and adaptive immune response pathways. These findings provide insight into disease pathogenesis and characterise FFA as a genetically predisposed immuno-inflammatory disorder driven by HLA-B*07: 02.