Filaggrin null mutations are not a protective factor for acne vulgaris

Revisiting the Roles of Filaggrin in Atopic Dermatitis

The discovery in 2006 that loss-of-function mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris and can predispose to atopic dermatitis (AD) galvanized the dermatology research community and shed new light on a skin protein that was first identified in 1981. However, although outstanding work has uncovered several key functions of filaggrin in epidermal homeostasis, a comprehensive understanding of how filaggrin deficiency contributes to AD is still incomplete, including details of the upstream factors that lead to the reduced amounts of filaggrin, regardless of genotype. In this review, we re-evaluate data focusing on the roles of filaggrin in the epidermis, as well as in AD. Filaggrin is important for alignment of keratin intermediate filaments, control of keratinocyte shape, and maintenance of epidermal texture via production of water-retaining molecules. Moreover, filaggrin deficiency leads to cellular abnormalities in keratinocytes and induces subtle epidermal barrier impairment that is sufficient enough to facilitate the ingress of certain exogenous molecules into the epidermis. However, although FLG null mutations regulate skin moisture in non-lesional AD skin, filaggrin deficiency per se does not lead to the neutralization of skin surface pH or to excessive transepidermal water loss in atopic skin. Separating facts from chaff regarding the functions of filaggrin in the epidermis is necessary for the design efficacious therapies to treat dry and atopic skin.

Contact dermatitis to topical acne drugs: a review of the literature

Acne vulgaris is a chronic dermatological disorder that affects the majority of teenagers in the Western world. Topical therapy is widely used to treat mild-moderate acne and is known as well-tolerated thanks to its low systemic toxicity, although associated to skin adverse effects. Acne seems to be associated also to an intrinsic alteration of the epidermal barrier, regarding both the upper and the follicular stratum corneum that promotes the onset of such local side effects. The commonest one is irritant contact dermatitis, an event of frequent observation occurring with erythema, burning, dryness, scaling, and itching, usually characterized by low severity and limited duration. Among topical acne drugs, retinoids are the most irritating ones. Another side effect is allergic contact dermatitis: it is rare and mainly associated to benzoyl peroxide.

The role of filaggrin in the skin barrier and disease development

Filaggrin is a structural protein that is fundamental in the development and maintenance of the skin barrier. The function of filaggrin and its involvement in various cutaneous and extracutaneous disorders has been the subject of considerable research in recent years. Mutations in FLG, the gene that encodes filaggrin, have been shown to cause ichthyosis vulgaris, increase the risk of atopic dermatitis and other atopic diseases, and exacerbate certain conditions. The present article reviews the current knowledge on the role of filaggrin in the skin barrier, FLG mutations, and the consequences of filaggrin deficiency.

Ichthyosis vulgaris: the filaggrin mutation disease

Ichthyosis vulgaris is caused by loss-of-function mutations in the filaggrin gene (FLG) and is characterized clinically by xerosis, scaling, keratosis pilaris, palmar and plantar hyperlinearity, and a strong association with atopic disorders. According to the published studies presented in this review article, FLG mutations are observed in approximately 7·7% of Europeans and 3·0% of Asians, but appear to be infrequent in darker-skinned populations. This clinical review article provides an overview of ichthyosis vulgaris epidemiology, related disorders and pathomechanisms. Not only does ichthyosis vulgaris possess a wide clinical spectrum, recent studies suggest that carriers of FLG mutations may have a generally altered risk of developing common diseases, even beyond atopic disorders. Mechanistic studies have shown increased penetration of allergens and chemicals in filaggrin-deficient skin, and epidemiological studies have found higher levels of hand eczema, irritant contact dermatitis, nickel sensitization and serum vitamin D levels. When relevant, individuals should be informed about an increased risk of developing dermatitis when repeatedly or continuously exposed to nickel or irritants. Moreover, with our current knowledge, individuals with ichthyosis vulgaris should be protected against neonatal exposure to cats to prevent atopic dermatitis and should abstain from smoking to prevent asthma. Finally, they should be advised against excessive exposure to factors that decrease skin barrier functions and increase the risk of atopic dermatitis.

Acne Vulgaris and the Epidermal Barrier: Is Acne Vulgaris Associated with Inherent Epidermal Abnormalities that Cause Impairment of Barrier Functions? Do Any Topical Acne Therapies Alter the Structural and/or Functional Integrity of the Epidermal Barrier?

Acne vulgaris is a common dermatological disorder that predominantly affects teenagers, but can also affect preadolescents and post-teen individuals. Despite the fact that acne vulgaris is the most common skin disorder encountered in ambulatory dermatology practice in the United States, there has been limited research on the epidermal permeability barrier in untreated skin of people with acne vulgaris and also after use of acne therapies. This article reviews the research results and discusses the available literature on this subject area. The importance of proper skin care as a component of the management of acne vulgaris is supported by the information that is currently available.

One remarkable molecule: filaggrin

The discovery, in 2006, that loss-of-function mutations in the filaggrin (FLG) gene are the cause of ichthyosis vulgaris-the most common disorder of keratinization-and also a strong genetic risk factor for atopic eczema, marked a significant breakthrough in the understanding of eczema pathogenesis. Subsequent investigations of the role of FLG-null mutations have identified a series of significant associations with atopic disease phenotypes, including atopic asthma, allergic rhinitis, and peanut allergy. However, many questions remain to be answered in relation to the precise mechanisms by which deficiency of an intracellular protein expressed primarily in the differentiating epidermis may contribute to the development of cutaneous and systemic pathology. This review aims to highlight the key milestones in filaggrin research over the past 25 years, to discuss the mechanistic, clinical, and therapeutic implications, and to consider possible future directions for ongoing investigation.

Wide spectrum of filaggrin-null mutations in atopic dermatitis highlights differences between Singaporean Chinese and European populations

BACKGROUND

Null mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris (IV) and predispose to atopic dermatitis (AD). Cohort studies in Europe and Japan have reported an FLG mutation carrier frequency of between 14% and 56%, but the prevalent European FLG mutations are rare or absent in Chinese patients with IV and AD.

OBJECTIVES

To investigate further the spectrum of FLG-null mutations in Chinese patients and to compare it with that in other populations.

METHODS

We conducted comprehensive FLG genetic analysis in a discovery cohort of 92 Singaporean Chinese individuals with IV and/or moderate-to-severe AD. All detected FLG mutations were then screened in a cohort of 425 patients with AD and 440 normal controls. Results In total, 22 FLG-null mutations, of which 14 are novel, were identified in this study; the combined null FLG genotype of 17 mutations detected in cases and controls showed strong association with AD [Fisher's exact test; P = 5·3 × 10⁻⁹; odds ratio (OR) 3·3], palmar hyperlinearity (Fisher's exact test; P = 9·0 × 10⁻¹⁵; OR 5·8), keratosis pilaris (Fisher's exact test; P = 0·001; OR 4·7) and with increased severity of AD (permutation test; P = 0·0063).

CONCLUSIONS

This study emphasizes the wider genetic landscape of FLG-null mutations in Asia that is slowly emerging.