Autosomal recessive hypotrichosis with loose anagen hairs associated with TKFC mutations.
Loose anagen hair is a rare form of impaired hair anchorage in which anagen hairs that lack inner and outer root sheaths can be gently and painlessly plucked from the scalp. Usually occurring in children and often self-limiting, a genetic basis to the disorder has been suggested but not proven. A better understanding the aetiology of loose anagen hair may improve prevention and treatment strategies.To identify a possible genetic basis to loose anagen hair using next generation DNA sequencing and functional analysis of variants identified.In this case study, whole-exome sequencing analysis of a pedigree with 1 affected individual with features of loose anagen hair was performed.The patient was found to be compound heterozygous for two single nucleotide substitutions in TKFC resulting in missense mutations: c.574G>C (p.Gly192Arg) and c.682C>T (p.Arg228Trp). Structural analysis of human TKFC showed that both mutations are located near the active site cavity. Kinetic assays of recombinant proteins bearing either of these amino acid substitutions showed almost no DHA kinase or GA kinase activity and FMN cyclase activity reduced to just 10% of wild-type catalytic activity.TKFC missense mutations may predispose to the development of loose anagen hairs. Identification of this new biochemical pathobiology expands the metabolic and genetic basis of hypotrichosis.