Biology and Genetics of Hair

The document from 2010 provides a comprehensive review of the biology and genetics of hair, particularly focusing on the mammalian hair follicle (HF) and its self-renewal capabilities through the hair cycle. It discusses the critical roles of stem cells in the bulge region of the HF and dermal papilla cells in regulating hair cycles. The paper identifies key genes and pathways involved in HF morphogenesis and cycling, including the Wnt signaling pathway and mutations in WNT10A and APCDD1 genes associated with hereditary hair diseases. It also explores the role of cadherin switching during HF induction and the impact of mutations in the P-cadherin (CDH3) gene on syndromic hair diseases. The document further examines the Eda-A1/Edar/Edaradd signaling pathway and its significance in HF morphogenesis, with mutations leading to conditions like hypohidrotic ectodermal dysplasia (HED). It describes the hair cycle, hair follicle stem cells, and hereditary hair diseases such as atrichia with papular lesions (APL) and Marie Unna hypotrichosis (MUH), both associated with mutations in the hairless (HR) gene. Additionally, the LIPH/LPA/LPAR6 signaling pathway's role in hair growth is highlighted, with mutations in these genes linked to hair disorders like autosomal recessive woolly hair (ARWH) and/or hypotrichosis. The importance of hair keratins and desmosomal components in hair structure and disorders, such as monilethrix and localized autosomal recessive hypotrichosis (LAH), is also discussed. Lastly, the document touches on polygenic hair diseases like androgenetic alopecia (AGA) and alopecia areata (AA), noting identified susceptibility loci and genes, and emphasizes the need for further research to understand human-specific HF morphogenesis and hair growth for potential new treatments for hair diseases.