Heterozygous KRT32 variant is responsible for autosomal dominant loose anagen hair syndrome

Loose anagen hair syndrome is a form of childhood-onset non-scarring alopecia marked by easily and painlessly plucking terminal hair during its active growth, or anagen, phase. It is believed to result from poor hair shaft anchoring within the follicle due to premature keratinization. Our study identified a plausibly pathogenic variant in KRT32 (c.296C>T; p.Thr99Ile) that co-segregates with the phenotype in a large family. This study aimed to explore the role of KRT32, previously unassociated with loose anagen hair, in hair anchorage and assess the functional impact of its p.Thr99Ile variant. We hypothesized that the p.Thr99Ile variant reduces the binding affinity of KRT32 to KRT82, disrupting the intermediate filament structure in the hair shaft cuticle and leading to weak anagen hair anchorage. To test this hypothesis, we conducted a protein-protein interaction assay using far-western blotting and performed in silico intermediate filament network segmentation analysis on high-resolution fluorescent microscopy images. Our results showed a decreased binding affinity of KRT32^Thr99Ile to KRT82 when compared to KRT32^WT. There were significant differences in segment count and filament thickness, as measured by brightness, between the KRT32^Thr99Ile and the KRT32^WT. We conclude that the c.296C>T variant of KRT32 is associated with loose anagen hair phenotype.