FGF5 is a crucial regulator of hair length in humans

Hair length varies dramatically on different body sites and also varies between individuals. Thus, hair length is a quantitative trait, suggesting inherited differences. In this study, we obtained DNA from families segregating excessively long eyelashes consistent with an autosomal recessive trait. We identified mutations in a single gene, fibroblast growth factor 5 (FGF5), which was homozygous in affected family members only. FGF5 has previously been implicated as a regulator of hair lengths in mammals, with mutations resulting in the well-described angora phenotype. However, until now a human counterpart to this phenotype remained elusive. Here, we present, to our knowledge, the first human counterpart of the angora phenotype, showing that FGF5 underlies trichomegaly and is a crucial regulator of hair growth in humans.