Genetics of human isolated hereditary hair loss disorders

Novel pathogenic variants in HR underlie atrichia with papular lesions in a cohort of 10 families

Atrichia with papular lesions (APL) is a hair abnormality characterized by loss of hair on the scalp and rest of the body. In a few cases, hair loss is accompanied by the appearance of keratotic papules on the body. It is inherited in an autosomal recessive manner. Sequence variants in the HR (hairless) gene are responsible for this hair abnormality. Here, we present nine consanguineous families and one nonconsanguineous family with clinical manifestations of APL. Whole exome followed by Sanger sequencing and/or direct Sanger sequencing was performed to identify pathogenic variants. The study revealed seven novel pathogenic variants c.794del;p.(Pro265Argfs*98), c.2921-2936del;p.(Tyr974Leufs*16), c.2889C>A;p.(Cys963*), c.2689C>T;p.(Gln897*), c.3186_3187dup;p.(Gln1063Profs*43), c.560dup;p.(Tyr188Ilefs*131), c.2203+5G>C, c.2776+5G>A, and the previously reported variant c.1837C>T;p.(Arg613*) in HR in these families. The study not only expands the mutational spectrum in the HR gene but also highlights the unusual phenotypic findings and will facilitate genetic counseling of families with members showing various types of hair loss disorders in the local population.

JAM-A facilitates hair follicle regeneration in Alopecia Areata through functioning as ceRNA to protect VCAN expression in dermal papilla cells

The dermal papilla cells in hair follicles function as critical regulators of hair growth. In particular, alopecia areata (AA) is closely related to the malfunctioning of the human dermal papilla cells (hDPCs). Thus, identifying the regulatory mechanism of hDPCs is important in inducing hair follicle (HF) regeneration in AA patients. Recently, growing evidence has indicated that 3′ untranslated regions (3′ UTR) of key genes may participate in the regulatory circuitry underlying cell differentiation and diseases through a so-called competing endogenous mechanism, but none have been reported in HF regeneration. Here, we demonstrate that the 3′ UTR of junctional adhesion molecule A (JAM-A) could act as an essential competing endogenous RNA to maintain hDPCs function and promote HF regeneration in AA. We showed that the 3′ UTR of JAM-A shares many microRNA (miRNA) response elements, especially miR-221–3p, with versican (VCAN) mRNA, and JAM-A 3′ UTR could directly modulate the miRNA-mediated suppression of VCAN in self-renewing hDPCs. Furthermore, upregulated VCAN can in turn promote the expression level of JAM-A. Overall, we propose that JAM-A 3′ UTR forms a feedback loop with VCAN and miR-221–3p to regulate hDPC maintenance, proliferation, and differentiation, which may lead to developing new therapies for hair loss.

Isolated autosomal recessive woolly hair/hypotrichosis: genetics, pathogenesis and therapies

Isolated autosomal recessive woolly hair/hypotrichosis (ARWH) is a rare hereditary hair disease characterized by tightly curled sparse hair at birth or in early infancy. Patients with ARWH consist of genetically heterogeneous groups. Woolly hair autosomal recessive 1 (ARWH1) (MIM #278150), woolly hair autosomal recessive 2 (ARWH2) (MIM #604379) and woolly hair autosomal recessive 3 (ARWH3) (MIM #616760) are caused by mutations in LPAR6, LIPH and KRT25, respectively. In addition, nonsense variants in C3ORF52 (*611956) were identified in ARWH patients. The frequencies of the mutations in the causative genes in ARWH patients are thought to differ by ethnicity and country/geographical area. Large numbers of ARWH families with LIPH mutations have been described only in populations from Japan, Pakistan and the Volga-Ural region of Russia. In that region of Russia, most ARWH families have an extremely prevalent founder mutation, the deletion of exon 4, in LIPH. In the Pakistani population, 47.2% of ARWH families had the disease due to LIPH mutations and 52.8% of them carried LPAR6 mutations. The prevalent, recurrent LIPH mutation c.659_660delTA (p.Ile220Argfs*29) was found in more than half of Pakistani ARWH families with LIPH mutations. Most Japanese ARWH families (98.7%) harbour LIPH mutations, including the two highly prevalent, recurrent LIPH mutations c.736T>A (p.Cys246Ser) and c.742C>A (p.His248Asn). In ARWH patients whose disease was due to LIPH, LPAR6 or C3ORF52 mutations, the loss of function of LIPH, LPAR6 or C3ORF52 leads to reduced LIPH-LPA-LPAR6 signalling, resulting in the decreased transactivation of EGFR signalling and the phenotype of underdeveloped hairs. Our recent prospective interventional study suggests that topical minoxidil might be a promising treatment for ARWH due to LIPH mutations, although sufficiently effective treatments have not been established for ARWH yet.

Epistatic interactions between at least three loci determine the "rat-tail" phenotype in cattle

BACKGROUND

The "rat-tail" syndrome (RTS) is an inherited hypotrichosis in cattle, which is exclusively expressed in diluted coloured hair. The affected animals also suffer from disturbed thermoregulation, which impairs their health and growth performance. Phenotypic features that are similar to RTS are observed in dogs with black hair follicle dysplasia.

RESULTS

We used a resource cross population between German Holstein and Charolais cattle breeds to prove that epistatic interactions between at least three independent genetic loci are required for the expression of the RTS phenotype. In this population, the RTS is exclusively expressed in animals with a eumelanic background that is due to the dominant E (D) allele at the melanocortin 1 receptor gene located on Bos taurus autosome (BTA) 18. In addition, only the individuals that are heterozygous at the dilution locus on BTA5 that corresponds to the premelanosome protein or silver gene variant c.64G>A were classified as displaying a RTS phenotype. Linkage and whole-genome association analyses using different models and different pedigrees allowed us to map a third locus (hereafter referred to as the RTS locus) that is essential for the expression of the RTS phenotype to the chromosomal region between 14 and 22 Mb on BTA5. Our findings clearly demonstrate that the RTS and dilution loci are distinct loci on BTA5.

CONCLUSIONS

Our study provides evidence that the RTS locus has effects on hair conformation and coat colour dilution and that the effect on coat colour dilution is clearly independent from that of the dilution locus. Finally, our results excluded several other loci that were previously reported to be associated with or to underlie hair conformation or pigmentation traits as the causal mutations of RTS and also several major functional candidate genes that are associated with hypotrichosis in humans. Our finding on the identification of a three-locus interaction that underlies RTS provides a prime example of epistatic interaction between several independent loci that is required for the expression of a distinct phenotype.