Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia

Differential requirement of the transcription factor HOXC13 for the stable maintenance of human papillomavirus genome among high-risk genotypes

The viral genome of the high-risk human papillomavirus (HPV), the causative agent of cervical cancer, is stably maintained as extrachromosomal episomes that establish persistent infection. We previously identified homeobox-transcription factor HOXC13 as an important host protein mediating the short-term retention of the HPV16 and HPV18 genomes in normal human immortalized keratinocytes (NIKS). Here, we used CRISPR-Cas9 technology to construct HOXC13 knockout (KO) NIKS cells to determine whether HOXC13 is required for the long-term maintenance of high-risk HPV genomes. HPV16, HPV18, HPV52, and HPV58 whole genomes were transfected into HOXC13 KO cells, and the copy number of viral genomes per cell was monitored over cell passages. Copy numbers of HPV16, HPV52, and HPV58 genomes decreased continuously in HOXC13 KO cells, whereas HPV18 genomes remained stable throughout passages. Thus, HOXC13 is critical for the stable maintenance of the viral genomes of HPV16, HPV52, and HPV58, but not HPV18.

High-throughput DNA sequence analysis elucidates novel insight into the genetic basis of adaptation in local sheep

Understanding how evolutionary factors related to climate adaptation and human selection have influenced the genetic architecture of domesticated animals is of great interest in biology. In the current study, by using 304 whole genomes from different geographical regions (including Europe, north Africa, Southwest Asia, east Asia, west Africa, south Asia, east Africa, Australia and Turkey), We evaluate global sheep population dynamics in terms of genetic variation and population structure. We further conducted comparative population analysis to study the genetic underpinnings of climate adaption to local environments and also morphological traits. In order to identify genomic signals under selection, we applied fixation index (FST) and also nucleotide diversity (θπ) statistical measurements. Our results revealed several candidate genes on different chromosomes under selection for local climate adaptation (e.g. HOXC12, HOXC13, IRF1, FGD2 and GNAQ), body size (PDGFA, HMGA2, PDE3A) and also morphological related traits (RXFP2). The discovered candidate genes may offer newel insights into genetic underpinning of regional adaptation and commercially significant features in local sheep.

Evolutionary origin of Hoxc13-dependent skin appendages in amphibians

Cornified skin appendages, such as hair and nails, are major evolutionary innovations of terrestrial vertebrates. Human hair and nails consist largely of special intermediate filament proteins, known as hair keratins, which are expressed under the control of the transcription factor Hoxc13. Here, we show that the cornified claws of Xenopus frogs contain homologs of hair keratins and the genes encoding these keratins are flanked by promoters in which binding sites of Hoxc13 are conserved. Furthermore, these keratins and Hoxc13 are co-expressed in the claw-forming epithelium of frog toe tips. Upon deletion of hoxc13, the expression of hair keratin homologs is abolished and the development of cornified claws is abrogated in X. tropicalis. These results indicate that Hoxc13-dependent expression of hair keratin homologs evolved already in stem tetrapods, presumably as a mechanism for protecting toe tips, and that this ancestral genetic program was coopted to the growth of hair in mammals.

Molecular Genetic Characteristics of the Hoxc13 Gene and Association Analysis of Wool Traits

Homobox C13 (Hoxc13) is an important transcription factor in hair follicle cycle development, and its deletion had been found in a variety of animals leading to abnormal hair growth and disruption of the hair follicle system. In this study, we used immunofluorescence, immunohistochemistry, real-time fluorescence quantitative PCR (RT-qPCR), and Kompetitive Allele-Specific PCR (KASP) genotyping to investigate molecular genetic characteristics of the Hoxc13 gene in Gansu alpine fine-wool sheep. The results revealed that Hoxc13 was significantly expressed during both the anagen and catagen phases (p < 0.05). It was found to be highly expressed predominantly in the dermal papillae and the inner and outer root sheaths, showing a distinct spatiotemporal expression pattern. Two single nucleotide polymorphisms (SNPs) in the exon 1 of Hoxc13, both the individual locus genotypes and the combined haplotypes were found to be correlated with wool length (p < 0.05). It was determined the mutations led to changes in mRNA expression, in which higher expression of this gene was related with longer wool length. In summary, this unique spatiotemporal expression pattern of the Hoxc13 gene may regulate the wool length of Gansu alpine fine-wool sheep, which can be used as a molecular genetic marker for wool traits and thus improve the breed.

Commonly Associated Disorders with Complete Scalp Alopecia in Early Childhood: A Review

Complete scalp hair loss can be a source of distress for affected children and their families. In addition to infectious and trauma-related causes of hair loss, infants and children may present with total scalp alopecia arising from a range of genetic predispositions. Our objective with this review was to identify the common genetic conditions in children with complete scalp alopecia. The PubMed Database was reviewed for all articles from 1962 to 2019 containing the search terms related to genetic alopecia. The conditions with at least five reported cases in the literature were considered for the inclusion. All clinical trials, retrospective studies, and cases on human subjects and written in English were included. Six genetic conditions related to complete scalp alopecia were included in this review. The most common genetic conditions associated with total scalp hair loss include: alopecia totalis/Alopecia universalis (AU), atrichia with papular lesions, AU congenita, hereditary Vitamin D-resistant rickets type IIA, alopecia with mental retardation, and pure hair and nail ectodermal dysplasia. In children presenting with total scalp hair loss, a myriad of genetic and environmental factors may be the underlying cause. Increased awareness of potential genetic conditions associated with total scalp hair loss may assist in diagnosis, with improved the prognosis for the children.

Molecular Pathway-Based Classification of Ectodermal Dysplasias: First Five-Yearly Update

To keep pace with the rapid advancements in molecular genetics and rare diseases research, we have updated the list of ectodermal dysplasias based on the latest classification approach that was adopted in 2017 by an international panel of experts. For this purpose, we searched the databases PubMed and OMIM for the term "ectodermal dysplasia", referring mainly to changes in the last 5 years. We also tried to obtain information about those diseases on which the last scientific report appeared more than 15 years ago by contacting the authors of the most recent publication. A group of experts, composed of researchers who attended the 8th International Conference on Ectodermal Dysplasias and additional members of the previous classification panel, reviewed the proposed amendments and agreed on a final table listing all 49 currently known ectodermal dysplasias for which the molecular genetic basis has been clarified, including 15 new entities. A newly reported ectodermal dysplasia, linked to the gene LRP6, is described here in more detail. These ectodermal dysplasias, in the strict sense, should be distinguished from syndromes with features of ectodermal dysplasia that are related to genes extraneous to the currently known pathways involved in ectodermal development. The latter group consists of 34 syndromes which had been placed on the previous list of ectodermal dysplasias, but most if not all of them could actually be classified elsewhere. This update should streamline the classification of ectodermal dysplasias, provide guidance to the correct diagnosis of rare disease entities, and facilitate the identification of individuals who could benefit from novel treatment options.

Monoallelic and biallelic variants in LEF1 are associated with a new syndrome combining ectodermal dysplasia and limb malformations caused by altered WNT signaling

PURPOSE

LEF1 encodes a transcription factor acting downstream of the WNT-β-catenin signaling pathway. It was recently suspected as a candidate for ectodermal dysplasia in 2 individuals carrying 4q35 microdeletions. We report on 12 individuals harboring LEF1 variants.

METHODS

High-throughput sequencing was employed to delineate the genetic underpinnings of the disease. Cellular consequences were characterized by immunofluorescence, immunoblotting, pulldown assays, and/or RNA sequencing.

RESULTS

Monoallelic variants in LEF1 were detected in 11 affected individuals from 4 unrelated families, and a biallelic variant was detected in an affected individual from a consanguineous family. The phenotypic spectrum includes various limb malformations, such as radial ray defects, polydactyly or split hand/foot, and ectodermal dysplasia. Depending on the type and location of LEF1 variants, the inheritance of this novel Mendelian condition can be either autosomal dominant or recessive. Our functional data indicate that 2 molecular mechanisms are at play: haploinsufficiency or loss of DNA binding are responsible for a mild to moderate phenotype, whereas loss of β-catenin binding caused by biallelic variants is associated with a severe phenotype. Transcriptomic studies reveal an alteration of WNT signaling.

CONCLUSION

Our findings establish mono- and biallelic variants in LEF1 as a cause for a novel syndrome comprising limb malformations and ectodermal dysplasia.

miR-129-5p Participates in Hair Follicle Growth by Targeting HOXC13 in Rabbit

Mammalian hair formation is critically determined by the growth of hair follicles (HF). MiRNAs are crucial in the periodic development of hair follicles; they maintain epidermal homeostasis by targeting genes and influencing the activity of signaling pathways and related regulators. Our study discovered miR-129-5p to be overexpressed in the skin of Angora rabbits during catagen, and was negatively correlated with HOXC13 expression (Pearson’s R = −0.313, p < 0.05). The dual-Luciferase reporter gene detection system and Western blotting confirmed that miR-129-5p targeted HOXC13. In addition, miR-129-5p overexpression was found to significantly inhibit the expression of hair follicle development-related genes (HFDRGs), such as BCL2, WNT2, CCND1, and LEF1 (p < 0.01), and promoted the expression of SFRP2, TGF-β1, and FGF2 (p < 0.01), which was the same as the knockdown of HOXC13. In contrast, the knockout of miR-129-5p was the opposite, and it demonstrated similar results to the overexpression of HOXC13. CCK8 and flow cytometry demonstrated that miR-129-5p mimics significantly promoted the apoptosis of dermal papilla cells (DPCs) and inhibited proliferation (p < 0.01), while the inhibitor was found to reduce the apoptosis of DPCs and promote proliferation (p < 0.01). These results showed that miR-129-5p can participate in the periodic development of HF by targeting HOXC13, and it can induce apoptosis and inhibit proliferation of DPCs. These results will help to understand the role and mechanism of miR-129-5p in the periodic development of HF, and will provide support for subsequent studies, not only providing a theoretical basis for genetically improving the quality of hair in animals in the future, but also a new theory and method for diagnosing and treating hair loss in humans.

Hair follicle stem cells feel the pressure

The number of hair follicle stem cells decreases during aging and in hair-loss disorders, such as alopecia. In this issue of Cell Stem Cell, Xie et al. (2021) discover that the hair shaft serves as a physical niche component for the preservation of hair follicle stem cells.

Complementary evolution of coding and noncoding sequence underlies mammalian hairlessness

Body hair is a defining mammalian characteristic, but several mammals, such as whales, naked mole-rats, and humans, have notably less hair. To find the genetic basis of reduced hair quantity, we used our evolutionary-rates-based method, RERconverge, to identify coding and noncoding sequences that evolve at significantly different rates in so-called hairless mammals compared to hairy mammals. Using RERconverge, we performed a genome-wide scan over 62 mammal species using 19,149 genes and 343,598 conserved noncoding regions. In addition to detecting known and potential novel hair-related genes, we also discovered hundreds of putative hair-related regulatory elements. Computational investigation revealed that genes and their associated noncoding regions show different evolutionary patterns and influence different aspects of hair growth and development. Many genes under accelerated evolution are associated with the structure of the hair shaft itself, while evolutionary rate shifts in noncoding regions also included the dermal papilla and matrix regions of the hair follicle that contribute to hair growth and cycling. Genes that were top ranked for coding sequence acceleration included known hair and skin genes KRT2, KRT35, PKP1, and PTPRM that surprisingly showed no signals of evolutionary rate shifts in nearby noncoding regions. Conversely, accelerated noncoding regions are most strongly enriched near regulatory hair-related genes and microRNAs, such as mir205, ELF3, and FOXC1, that themselves do not show rate shifts in their protein-coding sequences. Such dichotomy highlights the interplay between the evolution of protein sequence and regulatory sequence to contribute to the emergence of a convergent phenotype.

Genotype-phenotype correlation in clubfoot (talipes equinovarus)

Clubfoot (talipes equinovarus) is a congenital malformation affecting muscles, bones, connective tissue and vascular or neurological structures in limbs. It has a complex aetiology, both genetic and environmental. To date, the most important findings in clubfoot genetics involve PITX1 variants, which were linked to clubfoot phenotype in mice and humans. Additionally, copy number variations encompassing TBX4 or single nucleotide variants in HOXC11, the molecular targets of the PITX1 transcription factor, were linked to the clubfoot phenotype. In general, genes of cytoskeleton and muscle contractile apparatus, as well as components of the extracellular matrix and connective tissue, are frequently linked with clubfoot aetiology. Last but not least, an equally important element, that brings us closer to a better understanding of the clubfoot genotype/phenotype correlation, are studies on the two known animal models of clubfoot-the pma or EphA4 mice. This review will summarise the current state of knowledge of the molecular basis of this congenital malformation.

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.

Naked (N) mutant mice carry a nonsense mutation in the homeobox of Hoxc13

Loss of function mutations in HOXC13 have been associated with Ectodermal Dysplasia-9, Hair/Nail Type (ECTD9) in consanguineous families, characterized by sparse to complete absence of hair and nail dystrophy. Here we characterize the spontaneous mouse mutation Naked (N) as a terminal truncation in the Hoxc13 (homeobox C13) gene. Similar to previous reports for homozygous Hoxc13 knock-out (KO) mice, homozygous N/N mice exhibit generalized alopecia with abnormal nails and a short lifespan. However, in contrast to Hoxc13 heterozygous KO mice, N/+ mice show generalized or partial alopecia, associated with loss of hair fibres, along with normal lifespan and fertility. Our data point to a lack of nonsense-mediated Hoxc13 transcript decay and the presence of the truncated mutant protein in N/N and N/+ hair follicles, thus suggesting a dominant-negative mutation. To our knowledge, this is the first report of a semi-dominant and potentially dominant-negative mutation affecting Hoxc13/HOXC13. Furthermore, recreating the N mutant allele in mice using CRISPR/Cas9-mediated genome editing resulted in the same spectrum of deficiencies as those associated with the spontaneous Naked mutation, thus confirming that N is indeed a Hoxc13 mutant allele. Considering the low viability of the Hoxc13 KO mice, the Naked mutation provides an attractive new model for studying ECTD9 disease mechanisms.

Hair shaft miniaturization causes stem cell depletion through mechanosensory signals mediated by a Piezo1-calcium-TNF-α axis

In aging, androgenic alopecia, and genetic hypotrichosis disorders, hair shaft miniaturization is often associated with hair follicle stem cell (HFSC) loss. However, the mechanism causing this stem cell depletion in vivo remains elusive. Here we show that hair shaft loss or a reduction in diameter shrinks the physical niche size, which results in mechanical compression of HFSCs and their apoptotic loss. Mechanistically, cell compression activates the mechanosensitive channel Piezo1, which triggers calcium influx. This confers tumor necrosis factor alpha (TNF-α) sensitivity in a hair-cycle-dependent manner in otherwise resistant HFSCs and induces ectopic apoptosis. Persistent hair shaft miniaturization during aging and genetic hypotrichosis disorders causes long-term HFSC loss by inducing continuous ectopic apoptosis through Piezo1. Our results identify an unconventional role of the inert hair shaft structure as a functional niche component governing HFSC survival and reveal a mechanosensory axis that regulates physical-niche-atrophy-induced stem cell depletion in vivo.

Mammalian-specific ectodermal enhancers control the expression of Hoxc genes in developing nails and hair follicles

Vertebrate Hox genes are critical for the establishment of structures during the development of the main body axis. Subsequently, they play important roles either in organizing secondary axial structures such as the appendages, or during homeostasis in postnatal stages and adulthood. Here, we set up to analyze their elusive function in the ectodermal compartment, using the mouse limb bud as a model. We report that the HoxC gene cluster was co-opted to be transcribed in the distal limb ectoderm, where it is activated following the rule of temporal colinearity. These ectodermal cells subsequently produce various keratinized organs such as nails or claws. Accordingly, deletion of the HoxC cluster led to mice lacking nails (anonychia), a condition stronger than the previously reported loss of function of Hoxc13, which is the causative gene of the ectodermal dysplasia 9 (ECTD9) in human patients. We further identified two mammalian-specific ectodermal enhancers located upstream of the HoxC gene cluster, which together regulate Hoxc gene expression in the hair and nail ectodermal organs. Deletion of these regulatory elements alone or in combination revealed a strong quantitative component in the regulation of Hoxc genes in the ectoderm, suggesting that these two enhancers may have evolved along with the mammalian taxon to provide the level of HOXC proteins necessary for the full development of hair and nail.

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.

Meta-analysis of genome-wide association studies identifies 8 novel loci involved in shape variation of human head hair

Shape variation of human head hair shows striking variation within and between human populations, while its genetic basis is far from being understood. We performed a series of genome-wide association studies (GWASs) and replication studies in a total of 28 964 subjects from 9 cohorts from multiple geographic origins. A meta-analysis of three European GWASs identified 8 novel loci (1p36.23 ERRFI1/SLC45A1, 1p36.22 PEX14, 1p36.13 PADI3, 2p13.3 TGFA, 11p14.1 LGR4, 12q13.13 HOXC13, 17q21.2 KRTAP, and 20q13.33 PTK6), and confirmed 4 previously known ones (1q21.3 TCHH/TCHHL1/LCE3E, 2q35 WNT10A, 4q21.21 FRAS1, and 10p14 LINC00708/GATA3), all showing genome-wide significant association with hair shape (P < 5e-8). All except one (1p36.22 PEX14) were replicated with nominal significance in at least one of the 6 additional cohorts of European, Native American and East Asian origins. Three additional previously known genes (EDAR, OFCC1, and PRSS53) were confirmed at the nominal significance level. A multivariable regression model revealed that 14 SNPs from different genes significantly and independently contribute to hair shape variation, reaching a cross-validated AUC value of 0.66 (95% CI: 0.62–0.70) and an AUC value of 0.64 in an independent validation cohort, providing an improved accuracy compared with a previous model. Prediction outcomes of 2504 individuals from a multiethnic sample were largely consistent with general knowledge on the global distribution of hair shape variation. Our study thus delivers target genes and DNA variants for future functional studies to further evaluate the molecular basis of hair shape in humans.

The inconsistent regulation of HOXC13 on different keratins and the regulation mechanism on HOXC13 in cashmere goat (Capra hircus)

Background

During hair growth, cortical cells emerging from the proliferative follicle bulb rapidly undergo a differentiation program and synthesize large amounts of hair keratin proteins. In this process, HOXC13 is one critical regulatory factor, proved by the hair defects in HOXC13 mutant mice and HOXC13 mutant patients. However, inconsistent conclusions were drawn from previous researches regarding the regulation of HOXC13 on different keratins. Whether HOXC13 has extensive and unified regulatory role on these numerous keratins is unclear.

Results

In this study, firstly, RNA-seq was performed to reveal the molecular mechanism of cashmere cycle including anagen and telogen. Subsequently, combining the sequencing with qRT-PCR and immunofluorescent staining results, we found that HOXC13 showed similar expression pattern with a large proportion of keratins except for KRT1 and KRT2, which were higher in anagen compared with telogen. Then, the regulatory role of HOXC13 on different keratins was investigated using dual-luciferase reporter system and keratin promoter-GFP system by overexpressing HOXC13 in HEK 293 T cells and dermal papilla cells. Our results demonstrated that HOXC13 up-regulated the promoter activity of KRT84 and KRT38, while down-regulated the promoter activity of KRT1 and KRT2, which suggested HOXC13 had an ambivalent effect on the promoters of different KRTs. Furtherly, the regulation on HOXC13 itself was investigated. At transcriptional level, the binding sites of HOXC13 and LEF1 were found in the promoter of HOXC13. Then, through transfecting corresponding overexpression vector and dual-luciferase reporter system into dermal papilla cells, the negative-feedback regulation of HOXC13 itself and positive regulation of LEF1 on HOXC13 promoter were revealed. In addition, melatonin could significantly increase the promoter activity of HOXC13 under the concentration of 10 μM and 25 μM by adding exogenous melatonin into dermal papilla cells. At post-transcriptional level, we investigated whether chi-miR-200a could target HOXC13 through dual-luciferase reporter system. At epigenetic level, we investigated the methylation level of HOXC13 promoter at different stages including anagen, telogen and 60d of embryonic period. As a result, miR-200a and methylation were not regulatory factors of HOXC13. Interestingly, we found two SNPs (c.812A > G and c.929A > C) in the homeodomain of HOXC13 that could deprive the regulatory function of HOXC13 on keratins without changing its protein expression.

Conclusion

HOXC13 had an inconsistent effect on the promoters of different keratins. Two SNPs (c.812A > G and c.929A > C) in the homeodomain of HOXC13 deprived its function on keratin regulation. Besides, the negative-feedback regulation by HOXC13 itself and positive regulation by LEF1 and melatonin on HOXC13 promoter were revealed. This study will enrich the function of HOXC13 on keratin regulation and contribute to understand the mechanism of hair follicle differentiation.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5011-4) contains supplementary material, which is available to authorized users.

The disrupted balance between hair follicles and sebaceous glands in Hoxc13-ablated rabbits

Pure hair and nail ectodermal dysplasia 9 (ECTD-9) is an autosomal recessive genetic disease caused by mutation of HOXC13 and is characterized by hypotrichosis and nail dystrophy in humans. Unlike patients with ECTD-9, Hoxc13-mutated mice and pigs do not faithfully recapitulate the phenotype of hypotrichosis, so there is a limited understanding of the molecular mechanism of Hoxc13-mediated hypotrichosis in animal models and clinically. Here, the homozygous Hoxc13^-/- rabbits showed complete loss of hair on the head and dorsum, whereas hypotrichosis in the limbs and tail were determined in the Hoxc13^-/- rabbits. In addition, reduced hair follicles (HFs) while the enlarged and increased number of sebaceous glands (SGs) were also found in the Hoxc13^-/- rabbits, showing that the disrupted balance between HFs and SGs may respond to hypotrichosis of ECTD-9 in an animal model and clinically. Therefore, our findings demonstrate that Hoxc13^-/- rabbits can be used as a model for human ECTD-9, especially to understand the pathologic mechanism of hypotrichosis. Moreover, the disrupted balance between HFs and SGs, especially in the Hoxc13^-/- rabbits, can be used as an ideal animal model for dermatology ailments, such as acne and hypotrichosis, in preclinical studies.-Deng, J., Chen, M., Liu, Z., Song, Y., Sui, T., Lai, L., Li, Z. The disrupted balance between hair follicles and sebaceous glands in Hoxc13-ablated rabbits.

Transcription and microRNA Profiling of Cultured Human Tympanic Membrane Epidermal Keratinocytes

The human tympanic membrane (TM) has a thin outer epidermal layer which plays an important role in TM homeostasis and ear health. The specialised cells of the TM epidermis have a different physiology compared to normal skin epidermal keratinocytes, displaying a dynamic and constitutive migration that maintains a clear TM surface and assists in regeneration. Here, we characterise and compare molecular phenotypes in keratinocyte cultures from TM and normal skin. TM keratinocytes were isolated by enzymatic digestion and cultured in vitro. We compared global mRNA and microRNA expression of the cultured cells with that of human epidermal keratinocyte cultures. Genes with either relatively higher or lower expression were analysed further using the biostatistical tools g:Profiler and Ingenuity Pathway Analysis. Approximately 500 genes were found differentially expressed. Gene ontology enrichment and Ingenuity analyses identified cellular migration and closely related biological processes to be the most significant functions of the genes highly expressed in the TM keratinocytes. The genes of low expression showed a marked difference in homeobox (HOX) genes of clusters A and C, giving the TM keratinocytes a strikingly low HOX gene expression profile. An in vitro scratch wound assay showed a more individualised cell movement in cells from the tympanic membrane than normal epidermal keratinocytes. We identified 10 microRNAs with differential expression, several of which can also be linked to regulation of cell migration and expression of HOX genes. Our data provides clues to understanding the specific physiological properties of TM keratinocytes, including candidate genes for constitutive migration, and may thus help focus further research.

Generation of Hoxc13 knockout pigs recapitulates human ectodermal dysplasia-9

Atrichia and sparse hair phenotype cause distress to many patients. Ectodermal dysplasia-9 (ED-9) is a congenital condition characterized by hypotrichosis and nail dystrophy without other disorders, and Hoxc13 is a pathogenic gene for ED-9. However, mice carrying Hoxc13 mutation present several other serious disorders, such as skeletal defects, progressive weight loss and low viability. Mouse models cannot faithfully mimic human ED-9. In this study, we generated an ED-9 pig model via Hoxc13 gene knockout through single-stranded oligonucleotides (c.396C > A) combined with CRISPR/Cas9 and somatic cell nuclear transfer. Eight cloned piglets with three types of biallelic mutations (five piglets with Hoxc13c.396C > A/c.396C > A, two piglets with Hoxc13c.396C > A/c.396C > A + 1 and one piglet with Hoxc13Δ40/Δ40) were obtained. Hoxc13 was not expressed in pigs with all three mutation types, and the expression levels of Hoxc13-regulated genes, namely, Foxn1, Krt85 and Krt35, were decreased. The hair follicles displayed various abnormal phenotypes, such as reduced number of follicles and disarrayed hair follicle cable without normal hair all over the body. By contrast, the skin structure, skeleton phenotype, body weight gain and growth of Hoxc13 knockout pigs were apparently normal. The phenotypes of Hoxc13 mutation in pigs were similar to those in ED-9 patients. Therefore, Hoxc13 knockout pigs could be utilized as a model for ED-9 pathogenesis and as a hairless model for hair regeneration research. Moreover, the hairless pigs without other major abnormal phenotypes generated in this study could be effective models for other dermatological research because of the similarity between pig and human skins.

A novel mutation in homeobox DNA binding domain of HOXC13 gene underlies pure hair and nail ectodermal dysplasia (ECTD9) in a Pakistani family

Background

Pure hair and nail ectodermal dysplasia (PHNED) is a congenital disorder of hair abnormalities and nail dysplasia. Both autosomal recessive and dominant inheritance fashion of PHNED occurs. In literature, to date, five different forms of PHNED have been reported at molecular level, having three genes known and two loci with no gene yet.

Methods

In this study, a four generations consanguineous family of Pakistani origin with autosomal recessive PHNED was investigated. Affected members exhibited PHNED phenotypes with involvement of complete hair loss and nail dysplasia. To screen for mutation in the genes (HOXC13, KRT74, KRT85), its coding exons and exons-intron boundaries were sequenced. The 3D models of normal and mutated HOXC13 were predicted by using homology modeling.

Results

Through investigating the family to known loci, the family was mapped to ectodermal dysplasia 9 (ECTD9) loci with genetic address of 12q13.13. Mutation screening revealed a novel missense mutation (c.929A > C; p.Asn310Thr) in homeobox DNA binding domain of HOXC13 gene in affected members of the family. Due to mutation, loss of hydrogen bonding and difference in potential energy occurs, which may resulting in alteration of protein function.

Conclusion

This is the first mutation reported in homeodomain, while 5^th mutation reported in HOXC13 gene causing PHNED.

A Novel Homozygous Missense Mutation in HOXC13 Leads to Autosomal Recessive Pure Hair and Nail Ectodermal Dysplasia

Pure hair and nail ectodermal dysplasia (PHNED) is a rare disorder that presents with hypotrichosis and nail dystrophy while sparing other ectodermal structures such as teeth and sweat glands. We describe a homozygous novel missense mutation in the HOXC13 gene that resulted in autosomal recessive PHNED in a Hispanic child. The mutation c.812A>G (p.Gln271Arg) is located within the DNA-binding domain of the HOXC13 gene, cosegregates within the family, and is predicted to be maximally damaging. This is the first reported case of a missense HOXC13 mutation resulting in PHNED and the first reported case of PHNED identified in a North American family. Our findings illustrate the critical role of HOXC13 in human hair and nail development.

Identification of LCK mutation in a family with atypical epidermodysplasia verruciformis with T-cell defects and virus-induced squamous cell carcinoma

BACKGROUND

Inherited epidermodysplasia verruciformis (EV) is a rare skin disorder characterized by susceptibility to specific types of human papilloma virus (HPV) and is strongly associated with skin carcinomas. Inactivating mutations in EVER1/EVER2 account for most cases of EV. However, more phenotypes related to but distinct from EV have been reported with an immunodeficiency state but without EVER1/EVER2 mutation, and the genetic basis for these atypical EV cases is poorly understood.

OBJECTIVES

To identify the causative gene responsible for three siblings affected by atypical EV but without EVER1/EVER2 mutation.

METHODS

Whole-exome sequencing followed by Sanger sequencing was performed to identify the gene responsible for the patients with atypical EV enrolled in our study.

RESULTS

A homozygous splicing mutation was detected in LCK (c.188-2A>G). This mutation resulted in an exon 3 deletion T lymphocyte-specific protein tyrosine kinase isoform, which further led to frameshift mutation and subsequent mRNA decay.

CONCLUSIONS

We demonstrate a novel mutation in LCK in a family affected by atypical EV with T-cell defects, HPV infection and virus-induced malignancy, providing new clues in the understanding of host defences against HPV and better genetic counselling of patients with the EV phenotype.

HOX genes: Major actors in resistance to selective endocrine response modifiers

Long term treatment with therapies aimed at blocking the estrogen- (ER) or androgen receptor (AR) action often leads to the development of resistance to selective modulators of the estrogen receptor (SERMs) in ERα-positive breast cancer, or of the androgen receptor (SARMs) in AR-positive prostate cancer. Many underlying molecular events that confer resistance are known, but a unifying theme is yet to be revealed. Receptor tyrosine kinases (RTKs) such EGFR, ERBB2 and IGF1R are major mediators that can directly alter cellular response to the SERM, tamoxifen, but the mechanisms underlying increased expression of RTKs are not clear. A number of HOX genes and microRNAs and non-coding RNAs residing in the HOX cluster, have been identified as important independent predictors of endocrine resistant breast cancer. Recently, convincing evidence has accumulated that several members belonging to the four different HOX clusters contribute to endocrine therapy resistant breast cancer, but the mechanisms remain obscure. In this article, we have reviewed recent progress in understanding of the functioning of HOX genes and regulation of their expression by hormones. We also discuss, in particular, the contributions of several members of the HOX gene family to endocrine resistant breast cancer.

Deletions of 5' HOXC genes are associated with lower extremity malformations, including clubfoot and vertical talus

BACKGROUND

Deletions of the HOXC gene cluster result in variable phenotypes in mice, but have been rarely described in humans.

OBJECTIVE

To report chromosome 12q13.13 microdeletions ranging from 13 to 175 kb and involving the 5' HOXC genes in four families, segregating congenital lower limb malformations, including clubfoot, vertical talus and hip dysplasia.

METHODS

Probands (N=253) with clubfoot or vertical talus were screened for point mutations and copy number variants using multiplexed direct genomic selection, a pooled BAC targeted capture approach. SNP genotyping included 1178 probands with clubfoot or vertical talus and 1775 controls.

RESULTS

The microdeletions share a minimal non-coding region overlap upstream of HOXC13, with variable phenotypes depending upon HOXC13, HOXC12 or the HOTAIR lncRNA inclusion. SNP analysis revealed HOXC11 p.Ser191Phe segregating with clubfoot in a small family and enrichment of HOXC12 p.Asn176Lys in patients with clubfoot or vertical talus (rs189468720, p=0.0057, OR=3.8). Defects in limb morphogenesis include shortened and overlapping toes, as well as peroneus muscle hypoplasia. Finally, HOXC and HOXD gene expression is reduced in fibroblasts from a patient with a 5' HOXC deletion, consistent with previous studies demonstrating that dosage of lncRNAs alters expression of HOXD genes in trans.

CONCLUSIONS

Because HOXD10 has been implicated in the aetiology of congenital vertical talus, variation in its expression may contribute to the lower limb phenotypes occurring with 5' HOXC microdeletions. Identification of 5' HOXC microdeletions highlights the importance of transcriptional regulators in the aetiology of severe lower limb malformations and will improve their diagnosis and management.

Hoxc13 is a crucial regulator of murine hair cycle

Hair follicles undergo cyclical growth and regression during postnatal life. Hair regression is an apoptosis-driven process strictly controlled by micro- and macro-environmental signals. However, how these signals are controlled remains largely unknown. Hoxc13, a member of the Hox gene family, is reported to play an important role in hair follicle differentiation. In the present study, we observed that Hoxc13 was highly expressed in the outer root sheath, matrix, medulla and inner root sheath of hair follicles in a hair cycle-dependent manner. We therefore investigated the role of Hoxc13 in hair follicle cycling. Injection of ShRNA (ShHoxc13) to suppress Hoxc13 in early anagen promoted premature catagen entry, shown by significantly decreased hair length and hair bulb size, increased percentage of catagen hair follicles, hair cycle score and TUNEL+ cells and inhibited proliferation. In contrast, local injection of recombinant Hoxc13 polypeptide (rhHoxc13) during the late anagen phase prolonged the anagen phase. Additionally, rhHoxc13 injections during the telogen phase significantly promoted hair growth and induced the anagen progression. At the molecular level, the expression of phosphorylated smad2 (p-smad2), a key factor of active TGF-β1 signaling, was up-regulated in the ShHoxc13-treated hair follicles and down-regulated in rhHoxc13-treated hair follicles, suggesting that Hoxc13 might block anagen-catagen transition by inhibiting the TGF-β1 signaling. Taken together, our data strongly suggest that Hoxc13 is a novel and crucial regulator of the hair cycle. This might also provide an understanding of the mechanism of the 'hair cycle clock' and the development of alopecia treatments.

A Novel Locus for Ectodermal Dysplasia of Hair, Nail and Skin Pigmentation Anomalies Maps to Chromosome 18p11.32-p11.31

Ectodermal dysplasias (EDs) are a large heterogeneous group of inherited disorders exhibiting abnormalities in ectodermally derived appendages such as hair, nails, teeth and sweat glands. EDs associated with reticulated pigmentation phenotype are rare entities for which the genetic basis and pathophysiology are not well characterized. The present study describes a five generation consanguineous Pakistani family segregating an autosomal recessive form of a novel type of ectodermal dysplasia. The affected members present with sparse and woolly hair, severe nail dystrophy and reticulate skin pigmentation. After exclusion of known gene loci related with other skin disorders, genome-wide linkage analysis was performed using Illumina HumanOmniExpress beadchip SNP arrays. We linked this form of ED to human chromosome 18p11.32-p11.31 flanked by the SNPs rs9284390 (0.113Mb) and rs4797100 (3.14 Mb). A maximum two-point LOD score of 3.3 was obtained with several markers along the disease interval. The linkage interval of 3.03 Mb encompassed seventeen functional genes. However, sequence analysis of all these genes did not discover any potentially disease causing-variants. The identification of this novel locus provides additional information regarding the mapping of a rare form of ED. Further research, such as the use of whole-genome sequencing, would be expected to reveal any pathogenic mutation within the disease locus.

Exome sequencing reveals novel BCS1L mutations in siblings with hearing loss and hypotrichosis

As a powerful tool to identify the molecular pathogenesis of Mendelian disorders, exome sequencing was used to identify the genetic basis of two siblings with hearing loss and hypotrichosis and clarify the diagnosis. No pathogenic mutations in GJB2, GJB3 and GJB6 genes were found in the siblings. By analysis of exome of the proband, we identified a novel missense (p.R306C) mutation and a nonsense (p.R186*) mutation in the BCS1L gene. Mutations were confirmed by Sanger sequencing. The siblings were compound heterozygotes, and the inheritance mode of autosomal recessive was postulated. BCS1L is the causative gene of Björnstad syndrome, which is characterized by sensorineural hearing loss and pili torti. The longitudinal gutters along the hair shaft were found by scanning electron microscopy in our patient. Therefore the diagnosis of Björnstad syndrome was eventually made for the patients. Our study extends the phenotypic spectrum of Björnstad syndrome and highlights the clinical applicability of exome sequencing as a diagnostic tool for atypical Mendelian disorders.

YAP regulates the expression of Hoxa1 and Hoxc13 in mouse and human oral and skin epithelial tissues

Yes-associated protein (YAP) is a Hippo signaling transcriptional coactivator that plays pivotal roles in stem cell proliferation, organ size control, and tumor development. The downstream targets of YAP have been shown to be highly context dependent. In this study, we used the embryonic mouse tooth germ as a tool to search for the downstream targets of YAP in ectoderm-derived tissues. Yap deficiency in the dental epithelium resulted in a small tooth germ with reduced epithelial cell proliferation. We compared the gene expression profiles of embryonic day 14.5 (E14.5) Yap conditional knockout and YAP transgenic mouse tooth germs using transcriptome sequencing (RNA-Seq) and further confirmed the differentially expressed genes using real-time PCR and in situ hybridization. We found that YAP regulates the expression of Hoxa1 and Hoxc13 in oral and dental epithelial tissues as well as in the epidermis of skin during embryonic and adult stages. Sphere formation assay suggested that Hoxa1 and Hoxc13 are functionally involved in YAP-regulated epithelial progenitor cell proliferation, and chromatin immunoprecipitation (ChIP) assay implies that YAP may regulate Hoxa1 and Hoxc13 expression through TEAD transcription factors. These results provide mechanistic insights into abnormal YAP activities in mice and humans.

Expression of human skin-specific genes defined by transcriptomics and antibody-based profiling

To increase our understanding of skin, it is important to define the molecular constituents of the cell types and epidermal layers that signify normal skin. We have combined a genome-wide transcriptomics analysis, using deep sequencing of mRNA from skin biopsies, with immunohistochemistry-based protein profiling to characterize the landscape of gene and protein expression in normal human skin. The transcriptomics and protein expression data of skin were compared to 26 (RNA) and 44 (protein) other normal tissue types. All 20,050 putative protein-coding genes were classified into categories based on patterns of expression. We found that 417 genes showed elevated expression in skin, with 106 genes expressed at least five-fold higher than that in other tissues. The 106 genes categorized as skin enriched encoded for well-known proteins involved in epidermal differentiation and proteins with unknown functions and expression patterns in skin, including the C1orf68 protein, which showed the highest relative enrichment in skin. In conclusion, we have applied a genome-wide analysis to identify the human skin-specific proteome and map the precise localization of the corresponding proteins in different compartments of the skin, to facilitate further functional studies to explore the molecular repertoire of normal skin and to identify biomarkers related to various skin diseases.

Discovery in genetic skin disease: the impact of high throughput genetic technologies

The last decade has seen considerable advances in our understanding of the genetic basis of skin disease, as a consequence of high throughput sequencing technologies including next generation sequencing and whole exome sequencing. We have now determined the genes underlying several monogenic diseases, such as harlequin ichthyosis, Olmsted syndrome, and exfoliative ichthyosis, which have provided unique insights into the structure and function of the skin. In addition, through genome wide association studies we now have an understanding of how low penetrance variants contribute to inflammatory skin diseases such as psoriasis vulgaris and atopic dermatitis, and how they contribute to underlying pathophysiological disease processes. In this review we discuss strategies used to unravel the genes underlying both monogenic and complex trait skin diseases in the last 10 years and the implications on mechanistic studies, diagnostics, and therapeutics.

Walking the interactome for candidate prioritization in exome sequencing studies of Mendelian diseases

Motivation: Whole-exome sequencing (WES) has opened up previously unheard of possibilities for identifying novel disease genes in Mendelian disorders, only about half of which have been elucidated to date. However, interpretation of WES data remains challenging.

Results: Here, we analyze protein–protein association (PPA) networks to identify candidate genes in the vicinity of genes previously implicated in a disease. The analysis, using a random-walk with restart (RWR) method, is adapted to the setting of WES by developing a composite variant-gene relevance score based on the rarity, location and predicted pathogenicity of variants and the RWR evaluation of genes harboring the variants. Benchmarking using known disease variants from 88 disease-gene families reveals that the correct gene is ranked among the top 10 candidates in ≥50% of cases, a figure which we confirmed using a prospective study of disease genes identified in 2012 and PPA data produced before that date. We implement our method in a freely available Web server, ExomeWalker, that displays a ranked list of candidates together with information on PPAs, frequency and predicted pathogenicity of the variants to allow quick and effective searches for candidates that are likely to reward closer investigation.

Availability and implementation: http://compbio.charite.de/ExomeWalker

Contact: peter.robinson@charite.de

Etiology and pathogenesis of ectodermal dysplasias

Ectodermal dysplasias are a large group of heterogeneous heritable conditions characterized by congenital defects of one or more ectodermal structures and their appendages. The skin and its appendages are mainly composed by ectodermal components but development initiation of appendages is orchestrated by signals of the mesoderm with the help of placodes. A complex network of signaling pathways coordinates the formation and function of ectodermal structures. In recent years much has been discovered regarding the molecular mechanisms of ectodermal embryogenesis and this facilitates a rational basis for classification of ectodermal dysplasia. Interestingly, not only complex ectodermal syndromes but also mono- or oligosymptomatic ectodermal malformations may result from a mutation in a gene that is critical for ectodermal development. Mesodermal, and occasionally endodermal malformations may coexist. Embryogenesis occurs in distinct tissue organizational fields and specific interactions among the germ layers exist that may lead to a wide range of ectodermal dysplasias. Of the approximately 200 different ectodermal dysplasias, about 80 have been characterized at the molecular level with identification of the genes that are mutated in these disorders. Modern molecular genetics will increasingly elucidate the basic defects of these distinct syndromes and shed more light into the regulatory mechanisms of embryology. The upcoming classification of ectodermal dysplasias will combine detailed clinical and molecular knowledge.

Autosomal recessive transmission of a rare KRT74 variant causes hair and nail ectodermal dysplasia: allelism with dominant woolly hair/hypotrichosis

Pure hair and nail ectodermal dysplasia (PHNED) comprises a heterogeneous group of rare heritable disorders characterized by brittle hair, hypotrichosis, onychodystrophy and micronychia. Autosomal recessive (AR) PHNED has previously been associated with mutations in either KRT85 or HOXC13 on chromosome 12p11.1-q14.3. We investigated a consanguineous Pakistani family with AR PHNED linked to the keratin gene cluster on 12p11.1 but without detectable mutations in KRT85 and HOXC13. Whole exome sequencing of affected individuals revealed homozygosity for a rare c.821T>C variant (p.Phe274Ser) in the KRT74 gene that segregates AR PHNED in the family. The transition alters the highly conserved Phe274 residue in the coil 1B domain required for long-range dimerization of keratins, suggesting that the mutation compromises the stability of intermediate filaments. Immunohistochemical (IHC) analyses confirmed a strong keratin-74 expression in the nail matrix, the nail bed and the hyponychium of mouse distal digits, as well as in normal human hair follicles. Furthermore, hair follicles and epidermis of an affected family member stained negative for Keratin-74 suggesting a loss of function mechanism mediated by the Phe274Ser substitution. Our observations show for the first time that homozygosity for a KRT74 missense variant may be associated with AR PHNED. Heterozygous KRT74 mutations have previously been associated with autosomal dominant woolly hair/hypotrichosis simplex (ADWH). Thus, our findings expand the phenotypic spectrum associated with KRT74 mutations and imply that a subtype of AR PHNED is allelic with ADWH.

Absence of skeletal anomalies in siblings with a maternally inherited 12q13.13-q13.2 microdeletion partially involving the HOXC gene cluster

Microdeletions (12q13.13-q13.2) involving the HOXC gene cluster are rare. Only three patients with this contiguous deletion have been reported, all resulting in phenotypic features that include skeletal anomalies, facial dysmorphism, and intellectual disability. The deletion of the HOXC gene cluster is thought to result in skeletal anomalies in these patients. We report on siblings with a 969 kb deletion in the 12q13.13-q13.2 region detected by array comparative genomic hybridization (aCGH). This deletion spans seven of nine HOXC cluster genes. FISH analysis confirmed the siblings and mother were carriers of the 12q13.13-q13.2 deletion. Although minor facial dysmorphic features were present in both siblings, no skeletal anomalies were present in the siblings or the mother. The proband had autistic-like features and mild developmental delay, while the sibling and mother are of normal intelligence. The absence of skeletal anomalies in our family suggests that deletion of the entire HOXC gene cluster may be required to result in an abnormal skeletal phenotype, or those skeletal anomalies in previously reported patients may be attributed to other genes within the deletion interval.

Exome sequencing greatly expedites the progressive research of Mendelian diseases

The advent of whole-exome sequencing (WES) has facilitated the discovery of rare structure and functional genetic variants. Combining exome sequencing with linkage studies is one of the most efficient strategies in searching disease genes for Mendelian diseases. WES has achieved great success in the past three years for Mendelian disease genetics and has identified over 150 new Mendelian disease genes. We illustrate the workflow of exome capture and sequencing to highlight the advantages of WES. We also indicate the progress and limitations of WES that can potentially result in failure to identify disease-causing mutations in part of patients. With an affordable cost, WES is expected to become the most commonly used tool for Mendelian disease gene identification. The variants detected cumulatively from previous WES studies will be widely used in future clinical services.

Human HOX gene disorders

The Hox genes are an evolutionarily conserved family of genes, which encode a class of important transcription factors that function in numerous developmental processes. Following their initial discovery, a substantial amount of information has been gained regarding the roles Hox genes play in various physiologic and pathologic processes. These processes range from a central role in anterior-posterior patterning of the developing embryo to roles in oncogenesis that are yet to be fully elucidated. In vertebrates there are a total of 39 Hox genes divided into 4 separate clusters. Of these, mutations in 10 Hox genes have been found to cause human disorders with significant variation in their inheritance patterns, penetrance, expressivity and mechanism of pathogenesis. This review aims to describe the various phenotypes caused by germline mutation in these 10 Hox genes that cause a human phenotype, with specific emphasis paid to the genotypic and phenotypic differences between allelic disorders. As clinical whole exome and genome sequencing is increasingly utilized in the future, we predict that additional Hox gene mutations will likely be identified to cause distinct human phenotypes. As the known human phenotypes closely resemble gene-specific murine models, we also review the homozygous loss-of-function mouse phenotypes for the 29 Hox genes without a known human disease. This review will aid clinicians in identifying and caring for patients affected with a known Hox gene disorder and help recognize the potential for novel mutations in patients with phenotypes informed by mouse knockout studies.

To grow or not to grow: hair morphogenesis and human genetic hair disorders

Mouse models have greatly helped in elucidating the molecular mechanisms involved in hair formation and regeneration. Recent publications have reviewed the genes involved in mouse hair development based on the phenotype of transgenic, knockout and mutant animal models. While much of this information has been instrumental in determining molecular aspects of human hair development and cycling, mice exhibit a specific pattern of hair morphogenesis and hair distribution throughout the body that cannot be directly correlated to human hair. In this mini-review, we discuss specific aspects of human hair follicle development and present an up-to-date summary of human genetic disorders associated with abnormalities in hair follicle morphogenesis, structure or regeneration.

[Genetic hair diseases. An update]

Patients suffering from hair loss or undesirable excessive hair growth are a challenge for dermatologists because the pathogenesis of most hair diseases is not well understood and therapeutic options are limited. This particularly holds true for genetic hair disorders, in which all current treatment attempts are unsuccessful. Furthermore, these diseases also pose a diagnostic challenge due to a broad range of clinical and genetic heterogeneity. However, the enormous progress in molecular biology over the past 20 years, in particular the availability of different new techniques such as whole exome and genome sequencing, has enabled us to elucidate the genetic basis of most monogenic hair disorders, given the availability of suitable index patients and families as well as adequate technical equipment and sufficient financial resources. In this review we provide an update on clinical and genetic aspects of selected monogenic and polygenic hair diseases manifesting with hypertrichosis and hypotrichosis.

Adaptive evolution of Hoxc13 genes in the origin and diversification of the vertebrate integument

The problem of origination and diversification of integument derivatives in vertebrates is still a challenge. The homeobox (Hox) genes Hoxc13 control integument formation in vertebrate. Hoxc13 show strong expression in the integument development, are highly conserved across vertebrates, and show mutations that are associated with skin and appendages. To test whether the evolution of the integument is associated with positive selection or relaxation of Hoxc13, we obtained these genes in a wide range of vertebrates. In Hoxc13, we found evidence of diversifying selection after speciation during the origin of vertebrates. In addition, we found the glycine-rich regions in Hoxc13 protein in mammals, but not among non-mammalian taxa. Our results strongly implicate that Hoxc13 genes could have played an important role in the evolution of integument structure.

A homozygous frameshift mutation in the HOXC13 gene underlies pure hair and nail ectodermal dysplasia in a Syrian family

Pure hair and nail ectodermal dysplasia (PHNED) is a rare genetic disorder characterized by hypotrichosis or complete alopecia, as well as nail dystrophy. Mutations in the type II hair keratin gene KRT85 and the HOXC13 gene on chromosome 12q have recently been identified in families with autosomal-recessive PHNED. In the present study, we have analyzed a consanguineous Syrian family with an affected girl having complete alopecia and nail dystrophy since birth. The family clearly showed linkage to chromosome 12q13.13-12q14.3, which excluded the KRT85 gene. Sequencing of another candidate gene HOXC13 within the linkage interval identified a homozygous frameshift mutation (c.355delC; p.Leu119Trpfs*20). Expression studies in cultured cells revealed that the mutant HOXC13 protein mislocalized within the cytoplasm, and failed to upregulate the promoter activities of its target genes. Our results strongly suggest crucial roles of the HOXC13 gene in the development of hair and nails in humans.