A nonsense variant in KRT31 is associated with autosomal-dominant monilethrix.

BACKGROUND: Monilethrix is a rare hereditary hair disorder that is characterised by a beaded hair shaft structure and increased hair fragility. Patients may also present with keratosis pilaris and nail changes. Research has identified three genes for autosomal-dominant monilethrix (KRT81, KRT83, and KRT86), and one gene for the autosomal-recessive form (DSG4). OBJECTIVES: To investigate the genetic basis of autosomal-dominant monilethrix in families with no pathogenic variants in any of the known monilethrix genes, and to understand the mechanistic basis of variant pathogenicity using a cellular model. METHODS: Nine affected individuals from four unrelated families were included in this study. A clinical diagnosis of monilethrix was assigned based on clinical examination and/or trichoscopy. Exome sequencing (ES) was performed in six individuals to identify pathogenic variants, and Sanger sequencing was used for co-segregation and haplotype analyses. Cell culture experiments (immunoblotting, immunofluorescence, and reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) analyses) were used to confirm variant pathogenicity, to determine expression and subcellular localisation of proteins, and to identify a possible nonsense-mediated mRNA decay. RESULTS: In six affected individuals with clinically suggested monilethrix, ES led to the identification of the nonsense variant c.1081G>T; p.(Glu361*) in KRT31, which was subsequently identified in other affected members of these families by Sanger sequencing. This variant led to the abolition of both the last three amino acids of the 2B subdomain and the complete C-terminal tail domain of keratin 31. Immunoblotting demonstrated that when co-expressed with its binding partner keratin 85, the truncated keratin 31 was still expressed, albeit less abundantly than the wild type protein. Immunofluorescence revealed that p.(Glu361*) keratin 31 had an altered cytoskeletal localisation and formed vesicular-like structures in the cell cytoplasm near the cell membrane. RT-qPCR analysis did not generate evidence for a nonsense mediated decay of the mutant transcript. CONCLUSIONS: This study is the first to identify pathogenic variants in KRT31 as a cause of autosomal-dominant monilethrix. This highlights the importance of hair keratin proteins in hair biology, and will increase the molecular diagnostic yield for rare ectodermal phenotypes of hair and nail tissues.

Gene expression profiling in porocarcinoma indicates heterogeneous tumor development and substantiates poromas as precursor lesions.

BACKGROUND AND OBJECTIVES: Malignant sweat gland tumors are rare, with the most common being eccrine porocarcinoma (EP). Approximately 18% of benign eccrine poroma (EPO) transit to EP. Previous research has provided first insights into the mutational landscape of EP. However, only few studies have performed gene expression analyses. This leaves a gap in the understanding of EP biology and potential drivers of malignant transformation from EPO to EP. METHODS: Transcriptome profiling of 23 samples of primary EP and normal skin (NS). Findings from the EP samples were then tested in 17 samples of EPO. RESULTS: Transcriptome profiling revealed diversity in gene expression and indicated biologically heterogeneous sub-entities as well as widespread gene downregulation in EP. Downregulated genes included CD74, NDGR1, SRRM2, CDC42, ANXA2, KFL9 and NOP53. Expression levels of CD74, NDGR1, SRRM2, ANXA2, and NOP53 showed a stepwise-reduction in expression from NS via EPO to EP, thus supporting the hypothesis that EPO represents a transitional state in EP development. CONCLUSIONS: We demonstrated that EP is molecularly complex and that evolutionary trajectories correspond to tumor initiation and progression. Our results provide further evidence implicating the p53 axis and the EGFR pathway. Larger samples are warranted to confirm our findings.

Mutations in SREBF1, Encoding Sterol Regulatory Element Binding Transcription Factor 1, Cause Autosomal-Dominant IFAP Syndrome.

IFAP syndrome is a rare genetic disorder characterized by ichthyosis follicularis, atrichia, and photophobia. Previous research found that mutations in MBTPS2, encoding site-2-protease (S2P), underlie X-linked IFAP syndrome. The present report describes the identification via whole-exome sequencing of three heterozygous mutations in SREBF1 in 11 unrelated, ethnically diverse individuals with autosomal-dominant IFAP syndrome. SREBF1 encodes sterol regulatory element-binding protein 1 (SREBP1), which promotes the transcription of lipogenes involved in the biosynthesis of fatty acids and cholesterols. This process requires cleavage of SREBP1 by site-1-protease (S1P) and S2P and subsequent translocation into the nucleus where it binds to sterol regulatory elements (SRE). The three detected SREBF1 mutations caused substitution or deletion of residues 527, 528, and 530, which are crucial for S1P cleavage. In vitro investigation of SREBP1 variants demonstrated impaired S1P cleavage, which prohibited nuclear translocation of the transcriptionally active form of SREBP1. As a result, SREBP1 variants exhibited significantly lower transcriptional activity compared to the wild-type, as demonstrated via luciferase reporter assay. RNA sequencing of the scalp skin from IFAP-affected individuals revealed a dramatic reduction in transcript levels of low-density lipoprotein receptor (LDLR) and of keratin genes known to be expressed in the outer root sheath of hair follicles. An increased rate of in situ keratinocyte apoptosis, which might contribute to skin hyperkeratosis and hypotrichosis, was also detected in scalp samples from affected individuals. Together with previous research, the present findings suggest that SREBP signaling plays an essential role in epidermal differentiation, skin barrier formation, hair growth, and eye function.

Short anagen hair syndrome: association with mono- and biallelic variants in WNT10A and a genetic overlap with male pattern hair loss.

BACKGROUND: Short anagen hair (SAH) is a rare paediatric hair disorder characterized by a short anagen phase, an inability to grow long scalp hair and a negative psychological impact. The genetic basis of SAH is currently unknown. OBJECTIVES: To perform molecular genetic investigations in 48 individuals with a clinical phenotype suggestive of SAH to identify, if any, the genetic basis of this condition. METHODS: Exome sequencing was performed in 27 patients diagnosed with SAH or with a complaint of short, nongrowing hair. The cohort was screened for variants with a minor allele frequency (MAF) < 5% in the general population and a Combined Annotation Dependent Depletion (CADD) score > 15, to identify genes whose variants were enriched in this cohort. Sanger sequencing was used for variant validation and screening of 21 additional individuals with the same clinical diagnosis and their relatives. Genetic association testing of SAH-related variants for male pattern hair loss (MPHL) was performed using UK Biobank data. RESULTS: Analyses revealed that 20 individuals (42%) carried mono- or biallelic pathogenic variants in WNT10A. Rare WNT10A variants are associated with a phenotypic spectrum ranging from no clinical signs to severe ectodermal dysplasia. A significant association was found between WNT10A and SAH, and this was mostly observed in individuals with light-coloured hair and regression of the frontoparietal hairline. Notably, the most frequent variant in the cohort [c.682T>A;p.(Phe228Ile)] was in linkage disequilibrium with four common WNT10A variants, all of which have a known association with MPHL. Using UK Biobank data, our analyses showed that c.682T>A;p.(Phe228Ile) and one other variant identified in the SAH cohort are also associated with MPHL, and partially explain the known associations between WNT10A and MPHL. CONCLUSIONS: Our results suggest that WNT10A is associated with SAH and that SAH has a genetic overlap with the common phenotype MPHL. The presumed shared biologic effect of WNT10A variants in SAH and MPHL is a shortening of the anagen phase. Other factors, such as modifier genes and sex, may also play a role in the clinical manifestation of hair phenotypes associated with the WNT10A locus.

Identification of a novel sporadic U2HR pathogenic variant in a patient with Marie Unna hereditary hypotrichosis.

Marie Unna hereditary hypotrichosis (MUHH) is a rare autosomal dominant hair loss disorder characterized by coarse, wiry, and twisted hair developing during early childhood, and followed by progressive hair loss with puberty. We report a sporadic case of a 4-year-old boy with clinical features suggestive of MUHH, in whom we identified the new pathogenic variant c.67C>T; p.(Gln23*) in U2HR. This finding extends the known spectrum of U2HR variants underlying MUHH and increases genetic information for further genotype-phenotype correlation.

Selected genodermatoses - Status quo and future prospects.

Genodermatoses are monogenetic disorders, which may manifest with symptoms either exclusively on the skin or also involve other organs in the context of an associated syndrome. Over the past 30 years, numerous hereditary hair, tumor, blistering, and keratinization diseases have been characterized both clinically and genetically. This has resulted in the continuous development of disease-specific classifications as well as diagnostic algorithms and examination techniques, and has also led to new pathogenesis-based therapeutic approaches. While the deciphering of the underlying genetic defects of these diseases is already well advanced, there is still much room for the development of new translationally motivated treatment strategies.

Genomic variants reducing expression of two endocytic receptors in 46,XY differences of sex development.

Transporter-dependent steroid hormone uptake into target cells was demonstrated in genetically engineered mice and fruit flies. We hypothesized that mutations in such transporters may cause differences in sex development (DSD) in humans. Exome sequencing was performed in 16 genetically unsolved cases of 46,XY DSD selected from an anonymized collection of 708 lines of genital fibroblasts (GF) that were taken from individuals with incomplete virilization. Selection criteria were based on available biochemical characterization of GF compatible with reduced androgen uptake. Two unrelated individuals were identified with mutations in LDL receptor-related protein 2 (LRP2), a gene previously associated with partial sex steroid insensitivity in mice. Like Lrp2-/- mice, affected individuals had non-descended testes. Western blots on GF confirmed reduced LRP2 expression, and endocytosis of sex hormone-binding globulin was reduced. In three unrelated individuals, two with undescended testes, mutations in another endocytic receptor gene, limb development membrane protein 1 like (LMBR1L), were detected. Two of these individuals had mutations affecting the same codon. In a transfected cell model, mutated LMBR1L showed reduced cell surface expression. Our findings suggest that endocytic androgen uptake in complex with sex hormone-binding globulin is relevant in human. LMBR1L may play a similar role in androgen uptake.

Variant PADI3 in Central Centrifugal Cicatricial Alopecia.

BACKGROUND: Central centrifugal cicatricial alopecia (CCCA) is the most common form of scarring alopecia among women of African ancestry. The disease is occasionally observed to affect women in families in a manner that suggests an autosomal dominant trait and usually manifests clinically after intense hair grooming. We sought to determine whether there exists a genetic basis of CCCA and, if so, what it is. METHODS: We used exome sequencing in a group of women with alopecia (discovery set), compared the results with those in a public repository, and applied other filtering criteria to identify candidate genes. We then performed direct sequencing to identify disease-associated DNA variations and RNA sequencing, protein modeling, immunofluorescence staining, immunoblotting, and an enzymatic assay to evaluate the consequences of potential etiologic mutations. We used a replication set that consisted of women with CCCA to confirm the data obtained with the discovery set. RESULTS: In the discovery set, which included 16 patients, we identified one splice site and three heterozygous missense mutations in PADI3 in 5 patients (31%). (The approximate prevalence of the disease is up to 5.6%.) PADI3 encodes peptidyl arginine deiminase, type III (PADI3), an enzyme that post-translationally modifies other proteins that are essential to hair-shaft formation. All three CCCA-associated missense mutations in PADI3 affect highly conserved residues and are predicted to be pathogenic; protein modeling suggests that they result in protein misfolding. These mutations were found to result in reduced PADI3 expression, abnormal intracellular localization of the protein, and decreased enzymatic activity - findings that support their pathogenicity. Immunofluorescence staining showed decreased expression of PADI3 in biopsy samples of scalp skin obtained from patients with CCCA. We then directly sequenced PADI3 in an additional 42 patients (replication set) and observed genetic variants in 9 of them. A post hoc analysis of the combined data sets showed that the prevalence of PADI3 mutation was higher among patients with CCCA than in a control cohort of women of African ancestry (P = 0.002 by the chi-square test; P = 0.006 by Fisher's exact test; and after adjustment for relatedness of persons, P = 0.03 and P = 0.04, respectively). CONCLUSIONS: Mutations in PADI3, which encodes a protein that is essential to proper hair-shaft formation, were associated with CCCA. (Funded by the Ram Family Foundation and others.).

A new de novo heterozygous missense mutation in the desmoplakin gene, causing Naxos and Carvajal disease, associating oligodontia and nail fragility.

A new de novo heterozygous mutation in the desmoplakin gene, causing Naxos and Carvajal disease, has been reported in a 13-year-old Caucasian girl, with expanded clinical phenotype. In addition to woolly hair, palmoplantar keratoderma and cardiomyopathy, she had oligodontia and nail fragility. These additional clinical features may help in the diagnosis of Naxos and Carvajal disease, known to be severe on the cardiac level.

Bi-allelic Mutations in LSS, Encoding Lanosterol Synthase, Cause Autosomal-Recessive Hypotrichosis Simplex.

Hypotrichosis simplex (HS) is a rare form of hereditary alopecia characterized by childhood onset of diffuse and progressive scalp and body hair loss. Although research has identified a number of causal genes, genetic etiology in about 50% of HS cases remains unknown. The present report describes the identification via whole-exome sequencing of five different mutations in the gene LSS in three unrelated families with unexplained, potentially autosomal-recessive HS. Affected individuals showed sparse to absent lanugo-like scalp hair, sparse and brittle eyebrows, and sparse eyelashes and body hair. LSS encodes lanosterol synthase (LSS), which is a key enzyme in the cholesterol biosynthetic pathway. This pathway plays an important role in hair follicle biology. After localizing LSS protein expression in the hair shaft and bulb of the hair follicle, the impact of the mutations on keratinocytes was analyzed using immunoblotting and immunofluorescence. Interestingly, wild-type LSS was localized in the endoplasmic reticulum (ER), whereas mutant LSS proteins were localized in part outside of the ER. A plausible hypothesis is that this mislocalization has potential deleterious implications for hair follicle cells. Immunoblotting revealed no differences in the overall level of wild-type and mutant protein. Analyses of blood cholesterol levels revealed no decrease in cholesterol or cholesterol intermediates, thus supporting the previously proposed hypothesis of an alternative cholesterol pathway. The identification of LSS as causal gene for autosomal-recessive HS highlights the importance of the cholesterol pathway in hair follicle biology and may facilitate novel therapeutic approaches for hair loss disorders in general.