FLT3L governs the development of partially overlapping hematopoietic lineages in humans and mice.

FMS-related tyrosine kinase 3 ligand (FLT3L), encoded by FLT3LG, is a hematopoietic factor essential for the development of natural killer (NK) cells, B cells, and dendritic cells (DCs) in mice. We describe three humans homozygous for a loss-of-function FLT3LG variant with a history of various recurrent infections, including severe cutaneous warts. The patients' bone marrow (BM) was hypoplastic, with low levels of hematopoietic progenitors, particularly myeloid and B cell precursors. Counts of B cells, monocytes, and DCs were low in the patients' blood, whereas the other blood subsets, including NK cells, were affected only moderately, if at all. The patients had normal counts of Langerhans cells (LCs) and dermal macrophages in the skin but lacked dermal DCs. Thus, FLT3L is required for B cell and DC development in mice and humans. However, unlike its murine counterpart, human FLT3L is required for the development of monocytes but not NK cells.

DNA repair-related heritable photosensitivity syndromes: Mutation landscape in a multiethnic cohort of 17 multigenerational families with high degree of consanguinity.

Inherited photosensitivity syndromes are a heterogeneous group of genetic skin disorders with tremendous phenotypic variability, characterized by photosensitivity and defective DNA repair, especially nucleotide excision repair. A cohort of 17 Iranian families with heritable photosensitivity syndromes was evaluated to identify their genetic defect. The patients' DNA was analyzed with either whole-exome sequencing or RNA sequencing (RNA-Seq). The interpretations of the genomic results were guided by genome-wide homozygosity mapping. Haplotype analysis was performed for cases with recurrent mutations. RNA-Seq, in addition to mutation detection, was also utilized to confirm the pathogenicity. Thirteen sequence variants, including six previously unreported pathogenic variants, were disclosed in 17 Iranian families, with XPC as the most common mutated gene in 10 families (59%). In one patient, RNA-Seq, as a first-tier diagnostic approach, revealed a non-canonical homozygous germline variant: XPC:c.413-9 T > A. The Sashimi plot showed skipping of exon 4 with dramatic XPC down-expression. Haplotype analysis of XPC:c.2251-1 G>C and XPC:1243 C>T in four families showed common haplotypes of 1.7 Mb and 2.6 Mb, respectively, denoting a founder effect. Lastly, two extremely rare cases were presented in this report: a homozygous UVSSA:c .1990 C>T was disclosed, and ERCC2-related cerebro-oculo-facio-skeletal (COFS) syndrome with an early childhood death. A direct comparison of our data with the results of previously reported cohorts demonstrates the international mutation landscape of DNA repair-related photosensitivity disorders, although population-specific differences were observed.

Monogenic etiologies of persistent human papillomavirus infections: A comprehensive systematic review.

PURPOSE: Persistent human papillomavirus infection (PHPVI) causes cutaneous, anogenital, and mucosal warts. Cutaneous warts include common warts, Treeman syndrome, and epidermodysplasia verruciformis, among others. Although more reports of monogenic predisposition to PHPVI have been published with the development of genomic technologies, genetic testing is rarely incorporated into clinical assessments. To encourage broader molecular testing, we compiled a list of the various monogenic etiologies of PHPVI. METHODS: We conducted a systematic literature review to determine the genetic, immunological, and clinical characteristics of patients with PHPVI. RESULTS: The inclusion criteria were met by 261 of 40,687 articles. In 842 patients, 83 PHPVI-associated genes were identified, including 42, 6, and 35 genes with strong, moderate, and weak evidence for causality, respectively. Autosomal recessive inheritance predominated (69%). PHPVI onset age was 10.8 ± 8.6 years, with an interquartile range of 5 to 14 years. GATA2,IL2RG,DOCK8, CXCR4, TMC6, TMC8, and CIB1 are the most frequently reported PHPVI-associated genes with strong causality. Most genes (74 out of 83) belong to a catalog of 485 inborn errors of immunity-related genes, and 40 genes (54%) are represented in the nonsyndromic and syndromic combined immunodeficiency categories. CONCLUSION: PHPVI has at least 83 monogenic etiologies and a genetic diagnosis is essential for effective management.

Whole transcriptome-based skin virome profiling in typical epidermodysplasia verruciformis reveals α-, ß-, and γ-HPV infections.

HPVs are DNA viruses include approximately 450 types that are classified into 5 genera (α-, ß-, γ-, µ-, and ν-HPV). The γ- and ß-HPVs are present in low copy numbers in healthy individuals; however, in patients with an inborn error of immunity, certain species of ß-HPVs can cause epidermodysplasia verruciformis (EV), manifesting as recalcitrant cutaneous warts and skin cancer. EV presents as either typical or atypical. Manifestations of typical EV are limited to the skin and are caused by abnormal keratinocyte-intrinsic immunity to ß-HPVs due to pathogenic sequence variants in TMC6, TMC8, or CIB1. We applied a transcriptome-based computational pipeline, VirPy, to RNA extracted from normal-appearing skin and wart samples of patients with typical EV to explore the viral and human genetic determinants. In 26 patients, 9 distinct biallelic mutations were detected in TMC6, TMC8, and CIB1, 7 of which are previously unreported to our knowledge. Additionally, 20 different HPV species, including 3 α-HPVs, 16 ß-HPVs, and 1 γ-HPV, were detected, 8 of which are reported here for the first time to our knowledge in patients with EV (ß-HPV-37, -47, -80, -151, and -159; α-HPV-2 and -57; and γ-HPV-128). This study expands the TMC6, TMC8, and CIB1 sequence variant spectrum and implicates new HPV subtypes in the pathogenesis of typical EV.

Inherited human ITK deficiency impairs IFN-γ immunity and underlies tuberculosis.

Inborn errors of IFN-γ immunity can underlie tuberculosis (TB). We report three patients from two kindreds without EBV viremia or disease but with severe TB and inherited complete ITK deficiency, a condition associated with severe EBV disease that renders immunological studies challenging. They have CD4+ αß T lymphocytopenia with a concomitant expansion of CD4-CD8- double-negative (DN) αß and Vδ2- γδ T lymphocytes, both displaying a unique CD38+CD45RA+T-bet+EOMES- phenotype. Itk-deficient mice recapitulated an expansion of the γδ T and DN αß T lymphocyte populations in the thymus and spleen, respectively. Moreover, the patients' T lymphocytes secrete small amounts of IFN-γ in response to TCR crosslinking, mitogens, or forced synapse formation with autologous B lymphocytes. Finally, the patients' total lymphocytes secrete small amounts of IFN-γ, and CD4+, CD8+, DN αß T, Vδ2+ γδ T, and MAIT cells display impaired IFN-γ production in response to BCG. Inherited ITK deficiency undermines the development and function of various IFN-γ-producing T cell subsets, thereby underlying TB.

Interpretation of genomic sequence variants in heritable skin diseases: A primer for clinicians.

Over 1000 heritable disorders have cutaneous manifestations, some of which are syndromicin association with extracutaneous manifestations, whereas others are limited to the skin. The genetic basis of many of these conditions has been deciphered, and mutation analyses using next-generation sequencing approaches, including whole-exome sequencing, whole-genome sequencing, and whole-transcriptome analysis, are now increasingly becoming part of the diagnostic process. Besides confirming the diagnosis, information on the specific mutations can be used for subclassification with prognostication and identification of the carriers, leading to accurate genetic counseling. It also forms a basis for prenatal testing and preimplantation genetic diagnosis. Furthermore, the ongoing therapeutics developments for heritable skin diseases are often allele-specific, necessitating the knowledge of the specific genes and mutations. Although practicing clinicians increasingly employ molecular diagnostics for heritable skin diseases, they often lack the sufficient knowledge required to interpret the implications of the mutations with precision. The purpose of this primer is to provide an overview of mutation-detection strategies and how to interpret genetic information for improved diagnostics and the management of such patients.

Inherited ichthyosis as a paradigm of rare skin disorders: Genomic medicine, pathogenesis, and management.

Great advances have been made in the field of heritable skin disorders using next-generation sequencing (NGS) technologies (ie, whole-genome sequencing, whole-exome sequencing, whole-transcriptome sequencing, and disease-targeted multigene panels). When NGS first became available, the cost and lack of access to these technologies were limiting factors; however, with decreasing sequencing costs and the expanding knowledge base of genetic skin diseases, fundamental awareness of NGS has become prudent. The heritable ichthyoses comprise a genotypically and phenotypically heterogeneous group of monogenic keratinization disorders characterized by persistent scaling, with at least 55 distinct genes currently implicated in causing nonsyndromic and syndromic forms of the disease. By providing a simplified overview of available NGS techniques and applying them in the context of ichthyosis, one of the most common genodermatoses, we hope to encourage dermatologists to offer, when appropriate, genetic testing earlier in patients with unsolved presentations. With the aid of NGS, dermatologists can provide diagnostic certainty in cases of suspected genodermatoses and offer potentially life-changing genome-guided and targeted therapies as they become available.

Acquired ichthyosis, asteatotic dermatitis or xerosis? An update on pathoetiology and drug-induced associations.

Acquired ichthyosis (AI) is a relatively rare cutaneous entity characterized by transient, generalized scaling and pruritus in the absence of family history of ichthyosis or atopic disease. The hyperkeratosis in AI can range from the mild, white-to-brown scaling resembling that in ichthyosis vulgaris (IV) to the more prominent dark brown scaling phenotype, similar to that found in lamellar ichthyosis. The disease can wax and wane in relation to endogenous and/or exogenous factors. Histopathology of AI is similar to that found in IV. AI is usually of cosmetic concern to patients but can, in some cases, reflect the presence of more serious conditions, including malignancies, autoimmune diseases or metabolic disorders. In some cases, AI can be an adverse effect of a medication or the cutaneous symptom of a toxic exposure. Other conditions, such as severe xerosis or eczema, can present with clinical findings similar to AI, making diagnosis a challenge. Furthermore, cases of AI are sporadic throughout the literature and have been documented across a wide variety of medical settings distinct from dermatology, which often contribute to misdiagnosis of this disease. Definitive management requires prompt identification and treatment of the inciting factors combined with conservative therapies, which can include topical emollients, keratolytics, retinoids or corticosteroids, and in rare cases, oral retinoids.

Mutation update: The spectra of PLEC sequence variants and related plectinopathies.

Plectin, encoded by PLEC, is a cytoskeletal linker of intermediate filaments expressed in many cell types. Plectin consists of three main domains that determine its functionality: the N-terminal domain, the Rod domain, and the C-terminal domain. Molecular defects of PLEC correlating with the functional aspects lead to a group of rare heritable disorders, plectinopathies. These multisystem disorders include an autosomal dominant form of epidermolysis bullosa simplex (EBS-Ogna), limb-girdle muscular dystrophy (LGMD), aplasia cutis congenita (ACC), and an autosomal recessive form of EBS, which may associate with muscular dystrophy (EBS-MD), pyloric atresia (EBS-PA), and/or congenital myasthenic syndrome (EBS-MyS). In this study, genotyping of over 600 Iranian patients with epidermolysis bullosa by next-generation sequencing identified 15 patients with disease-causing PLEC variants. This mutation update analyzes the clinical spectrum of PLEC in our cohort and in the literature and demonstrates the relationship between PLEC genotype and phenotypic manifestations. This study has integrated our seven novel PLEC variants and phenotypic findings with previously published data totaling 116 variants to provide the most complete overview of pathogenic PLEC variants and related disorders.

Pathomechanisms of epidermolysis bullosa: Beyond structural proteins.

Epidermolysis bullosa (EB), a phenotypically and genetically heterogeneous disorder, has been linked to mutations in the genes encoding structural proteins that reinforce skin integrity via dermal-epidermal adhesion. Breakdowns in these adhesion mechanisms result in four different subtypes of EB classified on the basis of the level of tissue separation within the cutaneous basement membrane zone (BMZ). Mutations in as many as 17 distinct genes that encode structural proteins in the BMZ have been linked to EB. Despite the clinical and histopathological confirmation of EB, many cases remain genetically unsolved. Technical advancements in next-generation sequencing have paved the way for the identification of genes involved in the pathophysiology of EB. Structural proteins have long been identified as the candidate molecules altered in EB, however, recently non-structural proteins, encoded for example by PLOD3, USB1, EXPH5, and KLHL24, involved in enzymatic modification or migration of structural proteins have been implicated. In this overview, we discuss recent work regarding these proteins vis-à-vis their function, associated clinical manifestations, and involvement in the pathogenesis of EB.

Ichthyosis follicularis syndromes in patients with mutations in GJB2.

Ichthyosis follicularis (IF) manifests as generalized spiny follicular projections found in syndromic diseases secondary to SREBF1 and MBTPS2 mutations. We sought the genetic cause of IF in two distinct families from a cohort of 180 patients with ichthyosis. In Family 1, the proband (Patient 1) presented with IF, bilateral sensorineural hearing loss and punctate palmoplantar keratoderma. Using DNA from peripheral blood lymphocytes, two compound heterozygous mutations, c.526A>G and c.35delG, were discovered in GJB2. In Family 2, the proband (Patient 2) presented with a previously unreported IF phenotype in the context of keratitis-ichthyosis-deafness syndrome, and whole-exome sequencing found a de novo heterozygous mutation, c.148G>A in GJB2. Histopathology was consistent with porokeratotic eccrine ostial and dermal duct naevus (PEODDN) and IF in Patients 1 and 2, respectively. Our findings add to the clinical and histopathological spectrum of IF and emphasize the association of PEODDN-like entities with GJB2 variants.

Losartan treatment improves recessive dystrophic epidermolysis bullosa: A case series.

Recessive dystrophic epidermolysis bullosa (RDEB) manifests with blistering and erosions of the skin and mucous membranes due to mutations in COL7A1. The repetitive wound healing processes lead to extensive cutaneous scarring. The scarring is driven by inflammatory processes, particularly the TGF-ß signaling pathways, resulting in excess synthesis and deposition of the extracellular matrix, especially collagen. There is currently no effective or specific treatment for RDEB. Losartan, an angiotensin II type 1 receptor antagonist, is an inhibitor of TGF-ß activity. Previous preclinical studies with hypomorphic Col7a1 mice recapitulating features of RDEB have suggested that losartan may improve the clinical features of RDEB. In this case series, we assessed the effects of losartan on the clinical and histopathologic features in seven patients with RDEB; three females and four males; aged 18.1 ± 9.1 years. The diagnosis was based on characteristic clinical features and the presence of biallelic loss-of-function mutations in COL7A1. Daily oral administration of losartan (0.7 mg/kg) for six weeks resulted in subjective improvement of the clinical features, as judged by the treating physicians and the patients, and the severity of the disease objectively improved based on Birmingham Epidermolysis Bullosa Severity (BEBS) score (30.1 ± 12.8 versus 23.3 ± 10.4, before and after treatment, p = 0.018), accompanied by improvement of quality of life, as determined by the EB-QoL questionnaire (24.0 ± 8.1 versus 17.7 ± 5.5, p = 0.018). Histopathology of the selected lesions revealed after treatment increased number of mast cells, and enhanced microvasculature in the mid and lower dermis. The width of collagen bundles in dermis was suggested to be decreased in four samples and changed from dense to loose in appearance. In summary, this case series reports beneficial effects of losartan on RDEB as a potentially novel treatment.

ENPP1 variants in patients with GACI and PXE expand the clinical and genetic heterogeneity of heritable disorders of ectopic calcification.

Pseudoxanthoma elasticum (PXE) and generalized arterial calcification of infancy (GACI) are clinically distinct genetic entities of ectopic calcification associated with differentially reduced circulating levels of inorganic pyrophosphate (PPi), a potent endogenous inhibitor of calcification. Variants in ENPP1, the gene mutated in GACI, have not been associated with classic PXE. Here we report the clinical, laboratory, and molecular evaluations of ten GACI and two PXE patients from five and two unrelated families registered in GACI Global and PXE International databases, respectively. All patients were found to carry biallelic variants in ENPP1. Among ten ENPP1 variants, one homozygous variant demonstrated uniparental disomy inheritance. Functional assessment of five previously unreported ENPP1 variants suggested pathogenicity. The two PXE patients, currently 57 and 27 years of age, had diagnostic features of PXE and had not manifested the GACI phenotype. The similarly reduced PPi plasma concentrations in the PXE and GACI patients in our study correlate poorly with their disease severity. This study demonstrates that in addition to GACI, ENPP1 variants can cause classic PXE, expanding the clinical and genetic heterogeneity of heritable ectopic calcification disorders. Furthermore, the results challenge the current prevailing concept that plasma PPi is the only factor governing the severity of ectopic calcification.

Whole-transcriptome sequencing identifies postzygotic ATP2A2 mutations in a patient misdiagnosed with herpes zoster, confirming the diagnosis of very late-onset segmental Darier disease.

An 82-year-old female patient presented with a recent onset of painful skin lesions in unilateral distribution on the abdominal area following the lines of Blaschko; the initial diagnosis of Varicella-Zoster infection was made. However, because the individual lesions appeared as hyperkeratotic papules and were unresponsive to antiviral therapy, a skin biopsy was performed, which revealed hyperkeratosis, suprabasal acantholysis and dyskeratosis with corps ronds and grains, consistent with acantholytic dyskeratotic acanthoma. Since this entity has been associated with Darier disease, whole-transcriptome sequencing by RNA-Seq was performed on RNA isolated from a lesion and from adjacent normal appearing skin, and a recently developed bioinformatics pipeline that can identify both genomic sequence variants and the presence of any of 926 viruses was applied. Two pathogenic missense mutations in the ATP2A2 gene were identified in the lesional but not in normal appearing skin, and no evidence of Varicella-Zoster infection was obtained. These findings confirm the diagnosis of segmental Darier disease due to postzygotic mutations in the ATP2A2 gene, and attest to the power of a novel single-step application of RNA-Seq in providing correct diagnosis in this rare genodermatosis.

Evaluation of neurodevelopmental symptoms in 10 cases of neonatal ichthyosis and sclerosing cholangitis syndrome.

Neonatal ichthyosis and sclerosing cholangitis (NISCH) syndrome is an extremely rare entity with only 19 patients described in the literature. We report an extended family with the disorder and investigate the association of neurodevelopmental symptoms. Patients with CLDN1 mutations, and specifically « the Moroccan¼ c.200_201delTT deletion, may be an increased risk for neurodevelopmental symptoms such as learning disabilities, mental retardation, and language delay.

Whole-transcriptome sequencing-based concomitant detection of viral and human genetic determinants of cutaneous lesions.

Severe viral infections of the skin can occur in patients with inborn errors of immunity (IEI). We report an all-in-one whole-transcriptome sequencing-based method by RNA-Seq on a single skin biopsy for concomitantly identifying the cutaneous virome and the underlying IEI. Skin biopsies were obtained from healthy and lesional skin from patients with cutaneous infections suspected to be of viral origin. RNA-Seq was utilized as the first-tier strategy for unbiased human genome-wide rare variant detection. Reads unaligned to the human genome were utilized for the exploration of 926 viruses in a viral genome catalog. In 9 families studied, the patients carried pathogenic variants in 6 human IEI genes, including IL2RG, WAS, CIB1, STK4, GATA2, and DOCK8. Gene expression profiling also confirmed pathogenicity of the human variants and permitted genome-wide homozygosity mapping, which assisted in identification of candidate genes in consanguineous families. This automated, online, all-in-one computational pipeline, called VirPy, enables simultaneous detection of the viral triggers and the human genetic variants underlying skin lesions in patients with suspected IEI and viral dermatosis.

Pathogenic DST sequence variants result in either epidermolysis bullosa simplex (EBS) or hereditary sensory and autonomic neuropathy type 6 (HSAN-VI).

DST encodes bullous pemphigoid antigen-1 (BPAG1), a protein with eight tissue-specific isoforms expressed in the skin, muscle, brain and nerves. Accordingly, mutations in this gene are associated with epidermolysis bullosa simplex (EBS) and hereditary sensory and autonomic neuropathy type 6 (HSAN-VI). The genotypic spectrum is attested to by 19 distinct mutations but genotype-phenotype correlation for both disorders is not well established. In this study, we performed next-generation sequencing (NGS) on two families with different phenotypic presentations, one foetus (P1) with musculoskeletal and neurological malformations established by prenatal ultrasound and family history, and a 15-year-old female patient (P2) with skin blistering. P1 had a novel homozygous nonsense mutation, DST: NM_001144769, c.3805C>T, p.R1269* within a region of genetic homozygosity (ROH). This mutation resides within the plakin domain of BPAG1 and ablates all isoforms of this protein, leading to novel extracutaneous phenotypes consistent with HSAN-VI in P1. P2 had a recurrent homozygous mutation DST: NM_001723.7, c.3370C>T, p.Gln1124* that presented with giant, trauma-induced skin blisters without extracutaneous involvement. This mutation is located within the coiled-coil domain present in the skin isoform of DST, BPGA1-e, associated with EBS. In summary, we report two families with pathogenic DST variants and expand the spectrum of DST genotype and phenotypes.

Recalcitrant Cutaneous Warts in a Family with Inherited ICOS Deficiency.

Recalcitrant warts, caused by human papillomaviruses (HPVs), can be a cutaneous manifestation of inborn error of immunity. This study investigated the clinical manifestations, immunodeficiency, single-gene susceptibility, and HPV repertoire in a consanguineous family with severe sinopulmonary infections and recalcitrant warts. Clinical and immunologic evaluations, including FACS and lymphocyte transformation test, provided evidence for immunodeficiency. Combined whole-exome sequencing and genome-wide homozygosity mapping were utilized to disclose candidate sequence variants. Whole-transcriptome sequencing was used to concomitantly investigate the HPV genotypes and the consequences of detected sequence variants in the host. The proband, a male aged 41 years, was found to be homozygous for the c.6delG, p.Lys2Asnfs∗17 variant in ICOS, encoding the inducible T-cell costimulator. This variant was located inside the 5 megabase of runs of homozygosity on 2q33.2. RNA sequencing confirmed the deleteriousness of the ICOS variant in three skin biopsies revealing significant downregulation of ICOS and its ligand, ICOSLG. Reads unaligned to the human genome were applied to 926 different viruses, and α-HPV57, ß-HPV107, ß-HPV14, and ß-HPV17 were detected. Collectively, we describe a previously unrecognized inborn error of T-cell immunity to HPVs, indicating that autosomal recessive ICOS deficiency can underlie recalcitrant warts, emphasizing the immunologic underpinnings of recalcitrant warts at the nexus of human and viral genomic variation.

Recalcitrant Warts, Epidermodysplasia Verruciformis, and the Tree-Man Syndrome: Phenotypic Spectrum of Cutaneous Human Papillomavirus Infections at the Intersection of Genetic Variability of Viral and Human Genomes.

Human papillomavirus (HPV) infections can cause common warts, which usually resolve spontaneously or become recalcitrant, resistant to multiple treatments. In rare cases, they transform into cutaneous giant horns resulting in the tree-man syndrome (TMS). Defective ß-HPVs can cause flat warts in epidermodysplasia verruciformis (EV), a genetic disorder. In typical EV, limited to the skin, the mutated genes are critical for keratinocyte-intrinsic immunity, whereas atypical, syndromic EV involves genes controlling T cells. Inborn errors of immunity due to mutations in distinct genes underlying recalcitrant warts and the α-HPV2‒driven TMS have been identified, all disrupting T-cell immunity. Collectively, these observations attest to the wide phenotypic spectrum of cutaneous infections caused by different HPV types at the intersection of the genetic diversity of the viral and human genomes.