Loose Anagen Hair Associated with Wooly Hair Caused by a Heterozygous, Intronic KRT71 Variant

Abstract

Background: Loose anagen hair syndrome is a recently described genetic form of non-scarring alopecia that occurs in children and is due to poorly anchored hair shafts during the anagen phase. It can occur alone or in association with hair pathology or complex systemic phenotypes.

Methods: We report a mother and daughter with loose anagen hair syndrome that is associated with wooly hair, although it shows variable expressivity. We studied the family using genomic sequencing and identified an intronic variant in their KRT71 that segregates in an autosomal dominant pattern and is suspected to affect splicing in the tail domain of this hair follicle keratin. We studied this variant with a minigene experimental approach.

Results: We provide experimental evidence that the identified intronic variant affects splicing in the tail domain, which is critical to the biomechanical properties of the keratin intermediate filaments. We demonstrate that it affects splicing by adding 12 bases to the mature transcript and consequently four amino acids to the peptide.

Conclusion: We suspect that this variant is responsible for the poorly anchored and finely curled hair in the mother and daughter, which leads to a proposed diagnosis of autosomal dominant wooly hair, as well as loose anagen hair syndrome. We thus expand the variant spectrum of KRT71 and its associated phenotypes to include both disorders.

Keywords: KRT71; Keratin71; keratin intermediate filament; loose anagen hair syndrome; minigene; wooly hair.

Figure 2

(A) Schematic of the minigene design. The intronic variant is indicated with a red diamond. (B) Agarose gel of cDNA products using total RNA as a template. RT-PCR of RNA from all transfections produced a GAPDH band of a size confirming the presence of mRNA template from each condition. No minigene products were detected in the mock transfection, and bands of a different size were detected in the cells transfected with the WT and mutant vector. (C) Sanger results of minigene cDNA products sequenced with the same primers that were used to amplify them. The mutant sequence includes 12 bp from the intron that are not present in the natively spliced product. (D) Predicted tertiary structure based on amino acid sequence generated with the SWISS model workspace. The mutant and reference predicted structures are overlaid and colored green where the models agree. The inset highlights the introduced residues of the tail domain, which add a small loop structure in this region which can be seen in white overlaying the reference structure which is colored from olive to red where the models deviate, with red denoting more extreme deviation. Created with BioRender.com.

Figure 1

(A) Proband’s hair at age 6 (B) and age 16. The reddened patches on her temples are a reaction to the glue used for her wig and the hair near her nape is intentionally shaved. (C) Pedigree of the family suggesting an autosomal dominant pattern of inheritance. (D) Hairs from mother and proband under 50X magnification, tape mount. The proband’s hair lacks root sheath and is in anagen phase with tapered, dysmorphic root. The mother’s hair is normal telogen-phase club hair. There is no curl present in the mother’s hair owing to chemical treatment for cosmetic straightening. Created with BioRender.com.