Profiling Immune Expression to Consider Repurposing Therapeutics for the Ichthyoses

Hair follicles modulate skin barrier function

Our skin provides a protective barrier that shields us from our environment. Barrier function is typically associated with the interfollicular epidermis; however, whether hair follicles influence this process remains unclear. Here, we utilize a potent genetic tool to probe barrier function by conditionally ablating a quintessential epidermal barrier gene, Abca12, which is mutated in the most severe skin barrier disease, harlequin ichthyosis. With this tool, we deduced 4 ways by which hair follicles modulate skin barrier function. First, the upper hair follicle (uHF) forms a functioning barrier. Second, barrier disruption in the uHF elicits non-cell-autonomous responses in the epidermis. Third, deleting Abca12 in the uHF impairs desquamation and blocks sebum release. Finally, barrier perturbation causes uHF cells to move into the epidermis. Neutralizing IL-17a, whose expression is enriched in the uHF, partially alleviated some disease phenotypes. Altogether, our findings implicate hair follicles as multi-faceted regulators of skin barrier function.

Challenges and progress related to gene editing in rare skin diseases

Genodermatoses represent a large group of inherited skin disorders encompassing clinically-heterogeneous conditions that manifest in the skin and other organs. Depending on disease variant, associated clinical manifestations and secondary complications can severely impact patients' quality of life and currently available treatments are transient and not curative. Multiple emerging approaches using CRISPR-based technologies offer promising prospects for therapy. Here, we explore current advances and challenges related to gene editing in rare skin diseases, including different strategies tailored to mutation type and structural organization of the affected gene, considerations for in vivo and ex vivo applications, the critical issue of delivery into the skin, and immune aspects of therapy. Against the backdrop of a landmark FDA approval for the first re-dosable gene replacement therapy for a rare genetic skin disorder, gene editing approaches are inching closer to the clinics and the possibility of a local permanent cure for patients affected by these disorders.

Compound heterozygous ABCA12 variants identified in a Chinese patient with congenital ichthyosiform erythroderma: Advancing genotype-phenotype correlations and literature review

BACKGROUND

Ichthyosis is a common keratotic skin disease with high clinical, etiological and genetic heterogeneity. There are four types of non-syndromic hereditary ichthyoses, among which autosomal recessive congenital ichthyosis (ARCI) is a heterogeneous group of recessive Mendelian disorders. ARCI present with different phenotypes and ABCA12 pathogenic variants have been shown to cause complex ARCI phenotypes, including harlequin ichthyosis (HI), lamellar ichthyosis (LI) and congenital ichthyosiform erythroderma (CIE).

METHODS

A sporadic male patient, clinically diagnosed with CIE, was enrolled in this study. Exome sequencing was combined with Sanger sequencing to confirm the diagnosis and identify the pathogenic variants. In silico predictions were made using multiple software programs, and the identified variants were interpreted using the ACMG guidelines. A review of all literature reported ABCA12 variants was performed to explore genotype-phenotype correlations.

RESULTS

Compound heterozygous ABCA12 variants [c.5381+1G>A and c.5485G>C (p.Asp1829His)] (NM_173076) were identified. The two variants were not detected in the public database. c.5381+1G>A is predicted to affect ABCA12 mRNA splicing and Asp1829 is highly conserved among various species. In silico analysis suggested that these two variants were responsible for the phenotype of the patient. Genotype-phenotype correlation analysis showed that biallelic truncation variants and/or exon/amino acid deletions in ABCA12 are the most common causes of HI. Biallelic missense variants are most common in LI and CIE.

CONCLUSIONS

The compound heterozygous ABCA12 variants caused the CIE phenotype observed in the patient. The spectrum of ABCA12 pathogenic variants were broaden. Genotype-phenotype correlation analysis provided detailed evidence which can be used in future prenatal diagnosis and can inform the need for genetic counselling for patients with ABCA12-related ARCIs.

Hair follicles modulate skin barrier function

Our skin provides a protective barrier that shields us from our environment. Barrier function is typically associated with interfollicular epidermis; however, whether hair follicles influence this process remains unclear. Here, we utilize a potent genetic tool to probe barrier function by conditionally ablating a quintessential epidermal barrier gene, Abca12 , which is mutated in the most severe skin barrier disease, harlequin ichthyosis. With this tool, we deduced 4 ways by which hair follicles modulate skin barrier function. First, the upper hair follicle (uHF) forms a functioning barrier. Second, barrier disruption in the uHF elicits non-cell autonomous responses in the epidermis. Third, deleting Abca12 in the uHF impairs desquamation and blocks sebum release. Finally, barrier perturbation causes uHF cells to move into the epidermis. Neutralizing Il17a, whose expression is enriched in the uHF, partially alleviated some disease phenotypes. Altogether, our findings implicate hair follicles as multi-faceted regulators of skin barrier function.

French national protocol for the management of congenital ichthyosis

Congenital ichthyoses (CI) comprise a heterogeneous group of monogenic genetic skin diseases characterized by diffuse scaling, often associated with skin inflammation. Diagnosis of the individual form of ichthyosis is complex and is guided by clinical expertise. CI usually has a major impact on quality of life (QOL) and thus requires lifelong treatment. To date, there are no curative therapies, although various symptomatic treatment options exist. The present protocol for the management of CI has been drawn up in accordance with the recommendations published in 2012 by the French National Authority for Health, based on a literature review, with the help and validation of members of the French network for rare skin diseases (FIMARAD). It provides a summary of evidence and expert-based recommendations and is intended to help clinicians with the management of these rare and often complex diseases.

Advances in the treatment of autosomal recessive congenital ichthyosis, a look towards the repositioning of drugs

Autosomal recessive congenital ichthyoses (ARCI) are a skin pathology due to genetic causes characterized by a variable degree of desquamation, accompanied by erythema. The degree of symptoms is variable, different altered genes are involved, and the symptoms drastically affect patients' quality of life. Topical treatments are a first-choice strategy due to their ease of application and cost; however, enteral administration of retinoids offers greater efficacy, although with certain limitations. Despite the treatment alternatives, ARCI will persist throughout life, disabling people. Therefore, the search for new treatments always remains necessary. Especially repositioning drugs could be a short-term alternative to new affordable treatments for patients. Taking advantage of extensive knowledge of known drugs or biologics could ensure more accessible and possibly lower-cost treatments. This review briefly and concisely addresses possible repositioning strategies with drugs and biologics for ichthyosis.

Ichthyosis

The ichthyoses are a large, heterogeneous group of skin cornification disorders. They can be inherited or acquired, and result in defective keratinocyte differentiation and abnormal epidermal barrier formation. The resultant skin barrier dysfunction leads to increased transepidermal water loss and inflammation. Disordered cornification is clinically characterized by skin scaling with various degrees of thickening, desquamation (peeling) and erythema (redness). Regardless of the type of ichthyosis, many patients suffer from itching, recurrent infections, sweating impairment (hypohidrosis) with heat intolerance, and diverse ocular, hearing and nutritional complications that should be monitored periodically. The characteristic clinical features are considered to be a homeostatic attempt to repair the skin barrier, but heterogeneous clinical presentation and imperfect phenotype-genotype correlation hinder diagnosis. An accurate molecular diagnosis is, however, crucial for predicting prognosis and providing appropriate genetic counselling. Most ichthyoses severely affect patient quality of life and, in severe forms, may cause considerable disability and even death. So far, treatment provides only symptomatic relief. It is lifelong, expensive, time-consuming, and often provides disappointing results. A better understanding of the molecular mechanisms that underlie these conditions is essential for designing pathogenesis-driven and patient-tailored innovative therapeutic solutions.

Transcriptomic Analysis of the Major Orphan Ichthyosis Subtypes Reveals Shared Immune and Barrier Signatures

Preliminary work suggested upregulation of inflammatory pathways in patients with common forms of ichthyosis. However, a comprehensive characterization of skin from various ichthyosis subtypes is unavailable, precluding the development of targeted treatments. Thus, we sought to characterize the immune and barrier profiles of common and subtype-specific skin transcriptomes in a large group of patients with ichthyosis. We performed a global RNA-sequencing analysis in 54 patients with ichthyosis (7 with Netherton syndrome, 13 with epidermolytic ichthyosis, 16 with lamellar ichthyosis, and 18 with congenital ichthyosiform erythroderma) and 40 healthy controls. Differentially expressed genes were defined on the basis of fold changes > 2 and false discovery rate < 0.05 criteria. We found robust and significant T helper (Th) 22/Th17 skewing in all subtypes (e.g., IL-17A/C/F, S100A7/8/9/12; P < 0.001) with modest changes in Th2 pathway, primarily in Netherton syndrome, and Th1 skewing in congenital ichthyosiform erythroderma. Across all subtypes (less evident in epidermolytic ichthyosis), lipid metabolism and barrier junction markers were downregulated (e.g., FA2H, CDH10/11/12/2; P < 0.05), whereas epidermal cornification and proliferation measures were upregulated (e.g., SPRR1A/1B/2C/2G, EREG; P < 0.05). Our findings suggest that the common ichthyosis variants share aberrations in Th17/Th22 and barrier function, with minimal Th2 modulation. This may help to elucidate the pathogeneses of these subtypes and inform the development of subtype-specific treatments.

New developments in the molecular treatment of ichthyosis: review of the literature

Ichthyosis covers a wide spectrum of diseases affecting the cornification of the skin. In recent years, new advances in understanding the pathophysiology of ichthyosis have been made. This knowledge, combined with constant development of pathogenesis-based therapies, such as protein replacement therapy and gene therapy, are rather promising for patients with inherited skin diseases. Several ongoing trials are investigating the potency of these new approaches and various studies have already been published. Furthermore, a lot of case series report that biological therapeutics are effective treatment options, mainly for Netherton syndrome and autosomal recessive congenital ichthyosis. It is expected that some of these new therapies will prove their efficacy and will be incorporated in the treatment of ichthyosis.

Loricrin at the Boundary between Inside and Outside

Cornification is a specialized mode of the cell-death program exclusively allowed for terrestrial amniotes. Recent investigations suggest that loricrin (LOR) is an important cornification effector. As the connotation of its name (“lorica” meaning an armor in Latin) suggests, the keratin-associated protein LOR promotes the maturation of the epidermal structure through organizing covalent cross-linkages, endowing the epidermis with the protection against oxidative injuries. By reviewing cornification mechanisms, we seek to classify ichthyosiform dermatoses based on their function, rather than clinical manifestations. We also reviewed recent mechanistic insights into the Kelch-like erythroid cell-derived protein with the cap “n” collar homology-associated protein 1/nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway in skin health and diseases, as LOR and NRF2 coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of cross-talking between keratinocytes and epidermal resident leukocytes, dissecting an LOR immunomodulatory function.

Stratum corneum as polymer sheet: concept and cornification processes

The skin barrier protects our body from external insults and water loss through a specialized layer, the stratum corneum. The stratum corneum, an accumulation of dead keratinocytes (corneocytes), comprises lipids and supporting cell bodies. We propose a framework of lipid-filled polymer sheet of corneocytes, a unique structure that achieves flexibility and robustness, updating the rigid image of the historical bricks-and-mortar model. The polymerization of polymer sheet (cornification) by cell death of keratinocytes (corneoptosis) is delicately and dynamically controlled by cytoplasmic calcium ion and pH. Understanding the structure and formation of the stratum corneum can lead to better treatments for skin diseases and a better understanding of the evolution of the stratum corneum.

Challenges in Treating Genodermatoses: New Therapies at the Horizon

Genodermatoses are rare inherited skin diseases that frequently affect other organs. They often have marked effects on wellbeing and may cause early death. Progress in molecular genetics and translational research has unravelled many underlying pathological mechanisms, and in several disorders with high unmet need, has opened the way for the introduction of innovative treatments. One approach is to intervene where cell-signaling pathways are dysregulated, in the case of overactive pathways by the use of selective inhibitors, or when the activity of an essential factor is decreased by augmenting a molecular component to correct disequilibrium in the pathway. Where inflammatory reactions have been induced by a genetically altered protein, another possible approach is to suppress the inflammation directly. Depending on the nature of the genodermatosis, the implicated protein or even on the particular mutation, to correct the consequences or the genetic defect, may require a highly personalised stratagem. Repurposed drugs, can be used to bring about a "read through" strategy especially where the genetic defect induces premature termination codons. Sometimes the defective protein can be replaced by a normal functioning one. Cell therapies with allogeneic normal keratinocytes or fibroblasts may restore the integrity of diseased skin and allogeneic bone marrow or mesenchymal cells may additionally rescue other affected organs. Genetic engineering is expanding rapidly. The insertion of a normal functioning gene into cells of the recipient is since long explored. More recently, genome editing, allows reframing, insertion or deletion of exons or disruption of aberrantly functioning genes. There are now several examples where these stratagems are being explored in the (pre)clinical phase of therapeutic trial programmes. Another stratagem, designed to reduce the severity of a given disease involves the use of RNAi to attenuate expression of a harmful protein by decreasing abundance of the cognate transcript. Most of these strategies are short-lasting and will thus require intermittent life-long administration. In contrast, insertion of healthy copies of the relevant gene or editing the disease locus in the genome to correct harmful mutations in stem cells is more likely to induce a permanent cure. Here we discuss the potential advantages and drawbacks of applying these technologies in patients with these genetic conditions. Given the severity of many genodermatoses, prevention of transmission to future generations remains an important goal including offering reproductive choices, such as preimplantation genetic testing, which can allow selection of an unaffected embryo for transfer to the uterus.

Juvenile idiopathic arthritis in Harlequin ichthyosis, a rare combination or the clinical spectrum of the disease? Report of a child treated with etanercept and review of the literature

BACKGROUND

Harlequin ichthyosis (HI) is the most severe phenotype of autosomal recessive congenital ichthyosis. Juvenile Idiopathic Arthritis (JIA) represents a heterogenous group of disorders all sharing the clinical manifestation of chronic arthritis. Association of HI and chronic arthritis has been reported in few cases.

CASE PRESENTATION

We report the case of a child with HI who developed a severe form of chronic polyarthritis during the first years of life, treated with repeated multiple joint injections, methotrexate and etanercept with good response and without any adverse events.

CONCLUSION

The reported case and the literature review highlighted the presence of a peculiar severe seronegative polyarthritis with early onset in a series of patients with HI, suggesting that polyarthritis may be a specific manifestation of HI, rather than a rare combination of two separate conditions.

Efficacy and safety of secukinumab for the treatment of severe ABCA12 deficiency-related ichthyosis in a child

Background

Patients with severe autosomal recessive congenital ichthyosis (ARCI) show a T helper 17/interleukin 17 (Th17/IL17) skewing in their skin and serum, resembling the inflammatory profile of psoriatic patients. Secukinumab, an IL-17A inhibitor, has shown clinical efficacy in patients with moderate-to-severe plaque psoriasis.

Aims

To test the clinical efficacy and safety of secukinumab in a paediatric patient with ATP-binding cassette subfamily A member 12 deficiency-related severe erythrodermic ARCI.

Materials & Methods

6-months therapeutic trial. During the first 4-weeks induction period, the patient received weekly subcutaneous injections of 150 mg secukinumab (five injections in total). During the following 20-weeks maintenance period, the patient was given a subcutaneous injection of 150 mg secukinumab every 4 weeks.

Result & Discussion

After the 6-months therapy period, there was a 48% reduction from the baseline Ichthyosis-Area-Severity-Index (-Erythema/-Scaling) score. The treatment was well tolerated. Moreover, cytokine analysis revealed a reduction of keratinocyte-derived proinflammatory cytokines and an abrogation of Th17-skewing during therapy.

Conclusion

Further studies are needed to evaluate the effects of the use of IL-17A inhibition in ARCI patients.

Uncrossed corticospinal tracts in a patient with ichthyosis and hemiparesis: a case report

Background

Anomalies of pyramidal tract decussation are rare phenomena that can be caused by ectodermal dysplasia. Herein, we describe a patient with ichthyosis who exhibited ipsilateral hemiparesis after stroke and whose neuroimaging results showed evidence of motor control being provided by the ipsilateral motor cortex.

Case presentation

A 24-year-old right-handed man presented with skin abnormalities, sudden-onset left hemiparesis, and dysarthria. He exhibited a mild-to-moderate left-sided weakness (grade 4 on the Medical Research Council scale). Magnetic resonance imaging revealed an acute infarct in the left corona radiata. Diffusion tensor imaging revealed uncrossed corticospinal tracts. Next-generation sequencing identified heterozygous FLG mutations. The patient was diagnosed with cerebral infarction and ichthyosis vulgaris and was treated with aspirin (100 mg/d). His symptoms gradually dissipated.

Conclusions

This case suggests that pyramidal decussation anomalies can be associated with ichthyosis. Patients with ichthyosis should therefore be evaluated for nerve involvement.

Reduced stratum corneum acylceramides in autosomal recessive congenital ichthyosis with a NIPAL4 mutation

BACKGROUND

NIPAL4, encoding the NIPA-like domain containing 4 protein (NIPAL4), is one of the causative genes of autosomal recessive congenital ichthyosis (ARCI). The physiological role of NIPAL4 and the pathogenetic mechanisms of ARCI caused by NIPAL4 mutations remain unclear.

OBJECTIVE

To clarify the changes of ceramide components in the lesional stratum corneum (SC) and the gene expression profile in the lesional skin of an ARCI patient with a novel frameshift mutation in NIPAL4.

METHODS

We performed ultrastructural and immunohistochemical analyses of the skin. We used RNA sequencing to determine the mRNA expression in the skin of the patient and healthy individuals. We investigated ceramide components using tape stripped SC samples from the patient.

RESULTS

mRNA expression profiling in the patient's skin showed significant upregulation of IL-17/TNFα-related genes (IL17C, IL36A, IL36G, S100A7A, S100A9) and psoriasis hallmark genes (VNN3, LCE3D, PLA2G4D), and significant downregulation of lipid-associated genes (GAL, HAO2, FABP7). Ceramide analysis in the patient's SC revealed amounts of CER[NS] with carbon chain-length (C) 32-52 were increased, while amounts of most acylceramide with C66:2 - C72:2 were reduced relatively to those in healthy individuals. After the retinoid treatment, CER[NS] with carbon chains C46-54, CER[EOH] and CER[EOP] increased.

CONCLUSION

IL-17C and IL-36 family cytokines might be involved in the pathogenetic process of ARCI with NIPAL4 mutations. Reduced amounts of the acylceramides in the SC are associated with the skin phenotype due to NIPAL4 mutations. Efficacy of the oral retinoid treatment might be due to restored amounts of CER[EOH] and CER[EOP] in the SC.