Journey toward unraveling the molecular basis of hereditary hair disorders

Investigating the morphology and genetics of scalp and facial hair characteristics for phenotype prediction

Microscopic traits and ultrastructure of hair such as cross-sectional shape, pigmentation, curvature, and internal structure help determine the level of variations between and across human populations. Apart from cosmetics and anthropological applications, such as determining species, somatic origin (body area), and biogeographic ancestry, the evidential value of hair has increased with rapid progression in the area of forensic DNA phenotyping (FDP). Individuals differ in the features of their scalp hair (greying, shape, colour, balding, thickness, and density) and facial hair (eyebrow thickness, monobrow, and beard thickness) features. Scalp and facial hair characteristics are genetically controlled and lead to visible inter-individual variations within and among populations of various ethnic origins. Hence, these characteristics can be exploited and made more inclusive in FDP, thereby leading to more comprehensive, accurate, and robust prediction models for forensic purposes. The present article focuses on understanding the genetics of scalp and facial hair characteristics with the goal to develop a more inclusive approach to better understand hair biology by integrating hair microscopy with genetics for genotype-phenotype correlation research.

Update of recent findings in genetic hair disorders

Genetic hair disorders, although unusual, are not very rare, and dermatologists often have opportunities to see patients. Significant advances in molecular genetics have led to identifying many causative genes for genetic hair disorders, including the recently identified causative genes, such as LSS and C3ORF52. Many patients have been detected with autosomal recessive woolly hair/hypotrichosis in the Japanese population caused by founder mutations in the LIPH gene. Additionally, many patients with genetic hair disorders caused by other genes have been reported in East Asia including Japan. Understanding genetic hair disorders is essential for dermatologists, and the findings obtained from analyzing these diseases will contribute to revealing the mechanisms of hair follicle morphogenesis and development in humans.

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.

Basmanav FB, Mohungoo J, Pasternack-Ziach SM, Mattheisen M, Oprisoreanu AM, Humbatova A, Wolf S, Messenger A, Betz RC. Autosomal-dominant hypotrichosis with woolly hair: Novel gene locus on chromosome 4q35.1-q35.2

Hypotrichosis simplex (HS) with and without woolly hair (WH) comprises a group of rare, monogenic disorders of hair loss. Patients present with a diffuse loss of scalp and/or body hair, which usually begins in early childhood and progresses into adulthood. Some of the patients also show hair that is tightly curled. Approximately 10 genes for autosomal recessive and autosomal dominant forms of HS have been identified in the last decade, among them five genes for the dominant form. We collected blood and buccal samples from 17 individuals of a large British family with HS and WH. After having sequenced all known dominant genes for HS in this family without the identification of any disease causing mutation, we performed a genome-wide scan, using the HumanLinkage-24 BeadChip, followed by a classical linkage analysis; and whole exome-sequencing (WES). Evidence for linkage was found for a region on chromosome 4q35.1-q35.2 with a maximum LOD score of 3.61. WES led to the identification of a mutation in the gene SORBS2, encoding sorbin and SH3 domain containing 2. Unfortunately, we could not find an additional mutation in any other patient/family with HS; and in cell culture, we could not observe any difference between cloned wildtype and mutant SORBS2 using western blotting and immunofluorescence analyses. Therefore, at present, SORBS2 cannot be considered a definite disease gene for this phenotype. However, the locus on chromosome 4q is a robust and novel finding for hypotrichosis with woolly hair. Further fine mapping and sequencing efforts are therefore warranted in order to confirm SORBS2 as a plausible HS disease gene.

Bald thigh syndrome in sighthounds-Revisiting the cause of a well-known disease

Bald thigh syndrome is a common hair loss disorder in sighthounds. Numerous possible causes, including environmental conditions, trauma, stress, endocrinopathies and genetic components have been proposed, but only endocrinopathies have been ruled out scientifically. The overall goal of our study was to identify the cause of bald thigh syndrome and the pathological changes associated with it. We approached this aim by comparing skin biopsies and hair shafts of affected and control dogs microscopically as well as by applying high-throughput technologies such as genomics, transcriptomics and proteomics. While the histology is rather unspecific in most cases, trichogram analysis and scanning electron microscopy revealed severe structural abnormalities in hair shafts of affected dogs. This finding is supported by the results of the transcriptomic and proteomic profiling where genes and proteins important for differentiation of the inner root sheath and the assembly of a proper hair shaft were downregulated. Transcriptome profiling revealed a downregulation of genes encoding 23 hair shaft keratins and 51 keratin associated proteins, as well as desmosomal cadherins and several actors of the BMP signaling pathway which is important for hair shaft differentiation. The lower expression of keratin 71 and desmocollin 2 on the mRNA level in skin biopsies corresponded with a decreased protein expression in the hair shafts of affected dogs. The genetic analysis revealed a missense variant in the IGFBP5 gene homozygous in all available Greyhounds and other sighthounds. Further research is required to clarify whether the IGFBP5 variant represents a predisposing genetic risk factor. We conclude from our results that structural defects in the hair shafts are the cause for this well-known disease and these defects are associated with a downregulation of genes and proteins essential for hair shaft formation. Our data add important knowledge to further understand the molecular mechanisms of HF morphogenesis and alopecia in dogs.

Computational derivation of a molecular framework for hair follicle biology from disease genes

Knowledge about genetic drivers of disease increases the efficiency of interpreting patient DNA sequence and helps to identify and prioritize biological points of intervention. Discoveries of genes with single mutations exerting substantial phenotypic impact reliably provide new biological insight, although such approaches tend to generate knowledge that is disjointed from the complexity of biological systems governed by elaborate networks. Here we sought to facilitate diagnostic sequencing for hair disorders and assess the underlying biology by compiling an archive of 684 genes discovered in studies of monogenic disorders and identifying molecular annotations enriched by them. To demonstrate utility for this dataset, we performed two data driven analyses. First, we extracted and analyzed data implicating enriched signaling pathways and identified previously unrecognized contributions from Hippo signaling. Second, we performed hierarchical clustering on the entire dataset to investigate the underlying causal structure of hair disorders. We identified 35 gene clusters representing genetically derived biological modules that provide a foundation for the development of a new disease taxonomy grounded in biology, rather than clinical presentations alone. This Resource will be useful for diagnostic sequencing in patients with diseases affecting the hair follicle, improved characterization of hair follicle biology, and methods development in precision medicine.