Modeling of pigmentation disorders associated with MITF mutation in Waardenburg syndrome revealed an impaired melanogenesis pathway in iPS-derived melanocytes.

Waardenburg Syndrome (WS) is a rare genetic disorder that leads to congenital hearing loss and pigmentation defects. Microphthalmia-associated transcription factor (MITF) is one of its significant pathogenic genes. Despite the comprehensive investigation in animal models, the pathogenic mechanism is still poorly described in humans due to difficulties accessing embryonic tissues. In this work, we used induced pluripotent stem cells derived from a WS patient carrying a heterozygous mutation in the MITF gene c.626A>T (p.His209Leu), and differentiated toward melanocyte lineage, which is the most affected cell type involved in WS. Compared with the wild-type cell line, the MITFmut cell line showed a reduced expression of the characteristic melanocyte-related genes and a lesser proportion of mature, fully pigmented melanosomes. The transcriptome analysis also revealed widespread gene expression changes at the melanocyte stage in the MITFmut cell line. The differentially expressed genes were enriched in melanogenesis and cell proliferation-related pathways. Interestingly, ion transport-related genes also showed a significant difference in MITFmut -induced melanocytes, indicating that the MITF mutant may lead to the dysfunction of potassium channels and transporters produced by intermediate cells in the cochlea, further causing the associated phenotype of deafness. Altogether, our study provides valuable insights into how MITF mutation affects WS patients, which might result in defective melanocyte development and the related phenotype based on the patient-derived iPSC model.

Uncovering a new SASH1 mutation associated with dyschromatosis universalis hereditaria using whole-exome-sequencing: A case report.

RATIONALE: Dyschromatosis universalis hereditaria (DUH) is an uncommon form of pigmented genodermatosis that is typically inherited autosomally and dominantly. In the previous study, the pathogenic genes of DUH have been identified in ATP-binding cassette subfamily B, member 6 and SASH1. However, the mutational screening of the causative gene remains incomplete and still lacks sufficient proof in the etiology. PATIENT CONCERNS: A 2-generation Chinese family clinically diagnosed with DUH were enrolled. They showed pigmented spots from their childhood and came to the hospital for medical advice and genetic analysis. We found a novel mutation c.1757T > C (p.I586T) of SASH1 in 3 affected family members by whole-exome sequencing. DIAGNOSES: Genetic outcomes and clinical examinations confirmed the diagnosis of DUH in 3 family members with lentiginous syndrome. INTERVENTIONS AND OUTCOMES: Using whole-exome sequencing and sanger sequencing technologies, we identified a novel mutation c.1757T > C (p.I586T) of SASH1 that co-segregated in 3 afflicted family members but not in the normal individuals. Significantly, c.1757T > C (p.I586T) is a novel mutation which had not been previously reported. The same codon position in SASH1 (c.1758C > G, p.I586M) has been reported in a Japanese man, and he showed identical phenotype compared to our study participants. LESSONS: Our study broadens the spectrum of DUH mutations and provides more genetic characteristics of DUH in understanding its etiology. Furthermore, we demonstrated the diagnostic accuracy of whole-exome sequencing for inherited skin diseases and provided new information for etiological study.

Low rates of neurological abnormalities in patients with pigmentary mosaicism: A retrospective cohort study from a tertiary dermatology center.

BACKGROUND: Pigmentary mosaicism (PM) is a descriptive term encompassing a range of hyper- and hypo-pigmented phenotypes in various patterns. Information from the neurology literature initially noted neurological abnormalities (NA) in up to 90% of children with PM. The dermatology literature suggests lower associated rates (15%-30%) of NA. Variations in terminology, inclusion criteria, and small population sizes makes interpreting existing PM literature complicated. We aimed to assess rates of NA in children presenting to dermatology with PM. METHODS: We included patients <19 years, diagnosed with PM, nevus depigmentosus and/or segmental café au lait macules (CALM) seen in our dermatology department between 1 January 2006 and 31 December 2020. Patients with neurofibromatosis, McCune-Albright syndrome, and non-segmental CALM were excluded. Data collected included pigmentation, pattern, site(s) affected, presence of seizures, developmental delay, and microcephaly. RESULTS: One hundred fifty patients were included (49.3% female), with a mean age at diagnosis of 4.27 years. Patterns of mosaicism were ascertained for 149 patients and included blaschkolinear (60/149, 40.3%), blocklike (79/149, 53.0%), or a combination of both patterns (10/149, 6.7%). Patients with a combination of patterns were more likely to have NA (p < .01). Overall, 22/149 (14.8%) had NA. Nine out of twenty-two patients with NA had hypopigmented blaschkolinear lesions (40.9%). Patients with ≥4 body sites affected were more likely to have NA (p < .01). DISCUSSION: Overall, our population had low rates of NA in PM patients. A combination of blaschkolinear and blocklike patterns, or ≥4 body sites involved were associated with higher rates of NA.

Canine coat pigmentation genetics: a review.

Our understanding of canine coat colour genetics and the associated health implications is developing rapidly. To date, there are 15 genes with known roles in canine coat colour phenotypes. Many coat phenotypes result from complex and/or epistatic genetic interactions among variants within and between loci, some of which remain unidentified. Some genes involved in canine pigmentation have been linked to aural, visual and neurological impairments. Consequently, coat pigmentation in the domestic dog retains considerable ethical and economic interest. In this paper we discuss coat colour phenotypes in the domestic dog, the genes and variants responsible for these phenotypes and any proven coat colour-associated health effects.

Equine vitiligo-like depigmentation in grey horses is related to genes involved in immune response and tumor metastasis.

BACKGROUND: In horses, the autoimmune disease vitiligo is characterized by the loss of melanocytes and results in patchy depigmentation of the skin around the eyes, muzzle and the perianal region. Vitiligo-like depigmentation occurs predominantly in horses displaying the grey coat colour and is observed at a prevalence level of 26.0-67.0% in grey horses compared with only 0.8-3.5% in non-grey horses. While the polygenetic background of this complex disease is well documented in humans, the underlying candidate genes for this skin disorder in horses remain unknown. In this study we aim to perform a genome-wide association study (GWAS) for identifying putative candidate loci for vitiligo-like depigmentation in horses. METHODS: In the current study, we performed a GWAS analysis using high-density 670 k single nucleotide polymorphism (SNP) data from 152 Lipizzan and 104 Noriker horses, which were phenotyped for vitiligo-like depigmentation by visual inspection. After quality control 376,219 SNPs remained for analyses, the genome-wide Bonferroni corrected significance level was p < 1.33e-7. RESULTS: We identified seven candidate genes on four chromosomes (ECA1, ECA13, ECA17, ECA20) putatively involved in vitiligo pathogenesis in grey horses. The highlighted genes PHF11, SETDB2, CARHSP1 and LITAFD, are associated with the innate immune system, while the genes RCBTB1, LITAFD, NUBPL, PTP4A1, play a role in tumor suppression and metastasis. The antagonistic pathogenesis of vitiligo in relation to cancer specific enhanced cell motility and/or metastasis on typical melanoma predilection sites underlines a plausible involvement of RCBTB1, LITAFD, NUBPL, and PTP4A1. CONCLUSIONS: The proposed candidate genes for equine vitiligo-like depigmentation, indicate an antagonistic relation between vitiligo and tumor metastasis in a horse population with higher incidence of melanoma. Further replication and expression studies should lead to a better understanding of this skin disorder in horses.

MYO5A Frameshift Variant in a Miniature Dachshund with Coat Color Dilution and Neurological Defects Resembling Human Griscelli Syndrome Type 1.

A 1-month-old, female, smooth-haired miniature Dachshund with dilute color and neurological defects was investigated. The aim of this study was to characterize the clinical signs, histopathological changes and underlying genetic defect. The puppy had visible coat color dilution and was unable to hold its head on its own or to remain in a stable prone position for an extended period. Histopathological examination revealed an accumulation of clumped melanin and deposition of accumulated keratin within the hair follicles, accompanied by dermal pigmentary incontinence. These dermatological changes were compatible with the histopathology described in dogs with an MLPH-related dilute coat color. We sequenced the genome of the affected dog and compared the data to 795 control genomes. MYO5A, coding for myosin VA, was investigated as the top functional candidate gene. This search revealed a private homozygous frameshift variant in MYO5A, XM_022412522.1:c.4973_4974insA, predicted to truncate 269 amino acids (13.8%) of the wild type myosin VA protein, XP_022268230.1:p.(Asn1658Lysfs*28). The genotypes of the index family showed the expected co-segregation with the phenotype and the mutant allele was absent from 142 additionally genotyped, unrelated Dachshund dogs. MYO5A loss of function variants cause Griscelli type 1 syndrome in humans, lavender foal in horses and the phenotype of the dilute mouse mutant. Based on the available data, together with current knowledge on other species, we propose the identified MYO5A frameshift insertion as a candidate causative variant for the observed dermatological and neurological signs in the investigated dog.

Terminal osseous dysplasia with pigmentary defects and cardiomyopathy caused by a novel FLNA variant.

Terminal osseous dysplasia with pigmentary defects (TODPD), also known as digitocutaneous dysplasia, is one of the X-linked filaminopathies caused by a variety of FLNA-variants. TODPD is characterized by skeletal defects, skin fibromata and dysmorphic facial features. So far, only a single recurrent variant (c.5217G>A;p.Val1724_Thr1739del) in FLNA has found to be responsible for TODPD. We identified a novel c.5217+5G>C variant in FLNA in a female proband with skeletal defects, skin fibromata, interstitial lung disease, epilepsy, and restrictive cardiomyopathy. This variant causes mis-splicing of exon 31 predicting the production of a FLNA-protein with an in-frame-deletion of 16 residues identical to the miss-splicing-effect of the recurrent TODPD c.5217G>A variant. This mis-spliced transcript was explicitly detected in heart tissue, but was absent from blood, skin, and lung. X-inactivation analyses showed extreme skewing with almost complete inactivation of the mutated allele (>90%) in these tissues, except for heart. The mother of the proband, who also has fibromata and skeletal abnormalities, is also carrier of the FLNA-variant and was diagnosed with noncompaction cardiomyopathy after cardiac screening. No other relevant variants in cardiomyopathy-related genes were found. Here we describe a novel variant in FLNA (c.5217+5G>C) as the second pathogenic variant responsible for TODPD. Cardiomyopathy has not been described as a phenotypic feature of TODPD before.

SIRT7 gene knockout using CRISPR/Cas9 system enhances melanin production in the melanoma cells.

Melanin is a prominent pigment of skin and hair, and its deficiency can cause various disorders such as hair graying and albinism. The improvement of melanin production at a genetic level could offer an effective and permanent solution. Recently, SIRT7 has evoked an interest in the study of hair follicle stem cells, but its role in melanin synthesis remains unclear. In the present study, we have first successfully developed SIRT7 gene KO melanoma cells using the CRISPR/Cas9 system. It was found that the SIRT7 gene KO enhanced melanin production in melanoma cells. To validate the role of SIRT7 in melanin production, RT-PCR, western blot, and immunofluorescence staining assays were performed. The expression levels of melanin-producing genes and proteins (MITF, TRP1, TRP-2, TYR, TH) were significantly increased in SIRT7 gene KO cells compared to normal cells. In addition, melanin production was increased in KO cells higher than in normal cells through the image analysis. All these results suggest that SIRT7 could play an essential role in regulating melanin production, providing an alternative drug target to treat pigmentary disorders.

microRNAs in the Regulation of Melanogenesis.

Melanogenesis is the process leading to the synthesis of melanin, the main substance that influences skin color and plays a pivotal role against UV damage. Altered melanogenesis is observed in several pigmentation disorders. Melanogenesis occurs in specialized cells called melanocytes, physically and functionally related by means of autocrine and paracrine interplay to other skin cell types. Several external and internal factors control melanin biosynthesis and operate through different intracellular signaling pathways, which finally leads to the regulation of microphthalmia-associated transcription factor (MITF), the key transcription factor involved in melanogenesis and the expression of the main melanogenic enzymes, including TYR, TYRP-1, and TYRP-2. Epigenetic factors, including microRNAs (miRNAs), are involved in melanogenesis regulation. miRNAs are small, single-stranded, non-coding RNAs, of approximately 22 nucleotides in length, which control cell behavior by regulating gene expression, mainly by binding the 3' untranslated region (3'-UTR) of target mRNAs. This review collects data on the miRNAs involved in melanogenesis and how these miRNAs can modulate target gene expression. Bringing to light the biological function of miRNAs could lead to a wider understanding of epigenetic melanogenesis regulation and its dysregulation. This knowledge may constitute the basis for developing innovative treatment approaches for pigmentation dysregulation.

Two novel SASH1 mutations in Chinese families with dyschromatosis universalis hereditaria.

BACKGROUND: Dyschromatosis universalis hereditaria (DUH) is a rare genodermatosis characterized by hyper- and hypo-pigmented macules on the face, trunk, and extremities. The condition causes severe cosmetic problem which can lead to significant psychological distress to the patients and bear a negative impact on society. DUH is a condition with genetic heterogeneity. The SASH1 gene was recently identified as pathogenic genes in DUH patients. METHODS: Two families clinically diagnosed with dyschromatosis universalis hereditaria were enrolled. Whole-exome sequencing combined with Sanger sequencing and bioinformatics analysis was performed in the probands. MutationTaster, CADD, SIFT, PolyPhen-2, and LRT software, and The American College of Medical Genetics and Genomics Standards and Guidelines were employed to assess the pathogenicity of detected missense mutations. One hundred healthy unrelated Chinese individuals were used as controls. All participants signed an informed consent form. RESULTS: Genetic screening revealed a heterozygous SASH1 c.1547G>A (p.Ser516Asn) mutation for patients in family 1, and SASH1 c.1547G>T (p.Ser516Ile) for family 2. Both such de novo mutations are located in a highly conserved SLY domain in SASH1, have not been previously reported in any publication, and were not detected in any control databases. CONCLUSIONS: The novel heterozygous mutations, SASH1 c.1547G>A and c.1547G>T, are likely responsible for the DUH phenotype in these two families. Our study expands the mutation spectrum of DUH. Whole-exome sequencing showed its efficiency in the diagnostic of hereditary skin disorders.

Decoupling expression and editing preferences of ADAR1 p150 and p110 isoforms.

Human adenosine deaminase acting on RNA 1 (ADAR1) catalyzes adenosine-to-inosine deamination reactions on double-stranded RNA molecules to regulate cellular responses to endogenous and exogenous RNA. Defective ADAR1 editing leads to disorders such as Aicardi-Goutières syndrome, an autoinflammatory disease that manifests in the brain and skin, and dyschromatosis symmetrica hereditaria, a skin pigmentation disorder. Two ADAR1 protein isoforms, p150 (150 kDa) and p110 (110 kDa), are expressed and can edit RNA, but the contribution of each isoform to the editing landscape remains unclear, largely because of the challenges in expressing p150 without p110. In this study, we demonstrate that p110 is coexpressed with p150 from the canonical p150-encoding mRNA due to leaky ribosome scanning downstream of the p150 start codon. The presence of a strong Kozak consensus context surrounding the p110 start codon suggests the p150 mRNA is optimized to leak p110 alongside expression of p150. To reduce leaky scanning and translation initiation at the p110 start codon, we introduced synonymous mutations in the coding region between the p150 and p110 start codons. Cells expressing p150 constructs with these mutations produced significantly reduced levels of p110. Editing analysis of total RNA from ADAR1 knockout cells reconstituted separately with modified p150 and p110 revealed that more than half of the A-to-I edit sites are selectively edited by p150, and the other half are edited by either p150 or p110. This method of isoform-selective editing analysis, making use of the modified p150, has the potential to be adapted for other cellular contexts.

Telomere Dynamics and Telomerase in the Biology of Hair Follicles and their Stem Cells as a Model for Aging Research.

In this review, we propose that telomere length dynamics play an important but underinvestigated role in the biology of the hair follicle (HF), a prototypic, cyclically remodeled miniorgan that shows an intriguing aging pattern in humans. Whereas the HF pigmentary unit ages quickly, its epithelial stem cell (ESC) component and regenerative capacity are surprisingly aging resistant. Telomerase-deficient mice with short telomeres display an aging phenotype of hair graying and hair loss that is attributed to impaired HF ESC mobilization. Yet, it remains unclear whether the function of telomerase and telomeres in murine HF biology translate to the human system. Therefore, we propose new directions for future telomere research of the human HF. Such research may guide the development of novel treatments for selected disorders of human hair growth or pigmentation (e.g., chemotherapy-induced alopecia, telogen effluvium, androgenetic alopecia, cicatricial alopecia, graying). It might also increase the understanding of the global role of telomeres in aging-related human disease.

Mitochondrial DNA-depleter mouse as a model to study human pigmentary skin disorders.

Pigmentation abnormalities are reported in the spectrum of phenotypes associated with aging and in patients with mitochondrial DNA depletion syndrome (MDS). Yet, a relevant animal model that mimics these effects and would allow us to evaluate the detrimental aspects of mtDNA depletion on melanocyte function has not been described. Here, we characterize the pigmentary changes observed in the ears of a mtDNA-depleter mouse, which phenotypically includes accentuation of the peri-adnexal pseudonetwork, patchy hyper- and hypopigmentation, and reticular pigmentation. Histologically, these mice show increased epidermal pigmentation with patchy distribution, along with increased and highly dendritic melanocytes. These mtDNA-depleter mice mimic aspects of the cutaneous, pigmentary changes observed in humans with age-related senile lentigines as well as MDS. We suggest that this mouse model can serve as a novel resource for future interrogations of how mitochondrial dysfunction contributes to pigmentary skin disorders. The mtDNA-depleter mouse model also serves as a useful tool to identify novel agents capable of treating pigmentary changes associated with age-related mitochondrial dysfunction in humans.

Co-occurrence of Aicardi-Goutières syndrome type 6 and dyschromatosis symmetrica hereditaria due to compound heterozygous pathogenic variants in ADAR1: a case series from India.

Aicardi-Goutières syndrome type 6 (AGS6) and dyschromatosis symmetrica hereditaria (DSH) are allelic disorders caused respectively by biallelic and heterozygous pathogenic variants in ADAR1. We report three unrelated children presenting with features of both AGS6 and DSH, two of whom had compound heterozygous pathogenic variants in ADAR1. We also describe the novel genetic variants in our cases and review the literature on association of ADAR1-related AGS6 and DSH with these phenotypes.

Heterocromia de íris: uma revisão das condições que podem afetar a pigmentação iridiana / Heterochromia: a review of conditions that may affect iris pigmentation

RESUMO A íris é responsável pela cor dos olhos. Ela ainda realiza o controle da quantidade de luz que penetra no olho pela pupila. Variações nos genes de cada indivíduo, além da quantidade e da qualidade de melanina na íris, determinam a cor dos olhos. A heterocromia é caracterizada por diferenças na coloração da íris de um mesmo indivíduo, sendo, na maioria das vezes, benigna. Existem basicamente três tipos de heterocromia de íris: central, setorial e completa. A heterocromia de íris pode ter como causa alterações genéticas e congênitas, relacionadas ou não a síndromes específicas, como a de Sturge-Weber, a de Waardenburg, a de Parry-Romberg e a de Horner congênita. Há também causas adquiridas, como doenças ou lesões, trauma ocular e corpos estranhos intraoculares, uso de certas medicações tópicas, siderose ocular, irites ou uveítes como a síndrome uveítica de Fuchs, dentre outras. Diante de um paciente com heterocromia de íris, deve-se entender o contexto e o curso clínico desse sinal, pois pode se tratar de uma alteração de pigmentação benigna ou existir uma doença base em curso, que requer terapêutica específica. Este artigo de revisão de literatura visa abordar as principais etiologias relacionadas à heterocromia de íris, além de discorrer sobre a anatomia e a fisiologia da coloração iridiana e sobre a fisiopatologia de suas possíveis alterações.

ABSTRACT The iris is responsible for eye color and controls the amount of light that enters the eye through the pupil. Variation in each individual's genes, besides the quantity and quality of melanin in the iris, determine eye color. Heterochromia is characterized by different colors of irises in the same individual, and it is benign in most cases. There are basically three types of heterochromia: central, partial and complete. Heterochromia can be caused by genetic and congenital alterations, which may or may not be related to specific conditions, such as Sturge-Weber syndrome, Waardenburg syndrome, Parry-Romberg syndrome and congenital Horner syndrome. It may be associated to acquired causes like diseases or injuries, such as eye trauma and intraocular foreign bodies, use of some topical medications, ocular siderosis, iritis or uveitis, such as Fuchs´ uveitis, among others. When assessing a patient with heterochromia, one must understand the context and clinical course of this signal, since it may be a benign pigmentation disorder or there may be an underlying disease, which requires specific therapy. This literature review article was set out to address the main etiologies related to heterochromia, in addition to describing the anatomy and physiology of the iris color and the pathophysiology of possible alterations.

[Analysis of ADAR1 gene variants in two pedigrees affected with dyschromatosis symmetrica hereditaria].

OBJECTIVE: To detect variants of ADAR1 gene in two Chinese pedigrees affected with dyschromatosis symmetrica hereditaria (DSH). METHODS: Clinical data and peripheral blood samples of the pedigrees were collected. All exons of the ADAR1 gene were amplified by PCR and subjected to Sanger sequencing. Suspected pathogenic variants were validated among other members of the pedigrees and 100 unrelated healthy controls. RESULTS: For pedigree 1, Sanger sequencing has identified a heterozygous missense variant c.3002G>C (p.Asp968His) in exon 11 of the ADAR1 gene in the proband and his father. For pedigree 2, a novel nonsense variant c.3145C>T (p.Gln1049Ter) was identified in exon 12 of the ADAR1 gene in the proband and his son, which were previously unreported and absent among the healthy controls. CONCLUSION: The c.3002G>C (p.Asp968His) and c.3145C>T (p.Gln1049Ter)variants of the ADAR1 gene probably underlay the DSH in the two pedigrees.