Expanding the Mutation Spectrum of Ichthyosis with Confetti

Clinical and genetic findings in 13 Chinese children with keratinopathic ichthyosis

Importance

Keratinopathic ichthyosis (KPI) represents a group of predominantly autosomal dominant genodermatoses resulting from mutations in the KRT1, KRT2, or KRT10 genes. In KPI, the relationship between genotype and phenotype is complex.

Objective

To analyze the clinical manifestations and gene mutations in Chinese patients with KPI.

Methods

Clinical data were collected from 13 children diagnosed with KPI, and peripheral blood DNA samples were extracted from both the patients and their parents Next-generation sequencing was performed using a congenital ichthyosis multi-gene panel, and the selected variants in the patients and their parents were further validated using the Sanger sequencing method.

Results

Genetic analysis identified missense mutations in either KRT1 or KRT10 in ten patients exhibiting varying degrees of severity and distinct features of epidermolytic ichthyosis. A missense hotspot mutation in KRT2 was identified in one patient with superficial epidermolytic ichthyosis. Additionally, two truncation mutations in KRT10 were detected, leading to the development of generalized ichthyosiform erythroderma. Ear malformation and ectropion at birth, scalp involvement, and palmoplantar hyperkeratosis were observed as early signs of ichthyosis with confetti.

Interpretation

We analyzed the genotype-phenotype correlations in KPI, revealing that the types and locations of different mutations are associated with distinct phenotypic characteristics. Oral acitretin could be considered a treatment option for severe patients at an appropriate dosage and timing.

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.

A novel frameshift truncation mutation in the V2 tail domain of KRT1 causes mild ichthyosis hystrix of Curth-Macklin

Ichthyosis hystrix, Curth-Macklin type (IHCM) is an extremely rare autosomal dominant dermatosis caused by mutations in the keratin genes, KRT1 or KRT10, which often manifests as extensive, dark, spiky or verrucous plaques and severe palmoplantar keratoderma. We report a novel frameshift truncation mutation, c.1596_1597insAT (p.Gly533Metfs*82) in exon 7 (V2 tail domain) of KRT1, which, by replacing the glycine-serine-rich tail of KRT1 with a series of 75 alanine-rich amino acids, produces a mild IHCM phenotype. The patient with the mutation presented with localized ichthyosis and progressive hyperkeratosis of the palms and soles with no history of blistering.

Mosaicism in Cutaneous Disorders

Genetic mosaicism arises when a zygote harbors two or more distinct genotypes, typically due to de novo, somatic mutation during embryogenesis. The clinical manifestations largely depend on the differentiation status of the mutated cell; earlier mutations target pluripotent cells and generate more widespread disease affecting multiple organ systems. If gonadal tissue is spared-as in somatic genomic mosaicism-the mutation and its effects are limited to the proband, whereas mosaicism also affecting the gametes, such as germline or gonosomal mosaicism, is transmissible. Mosaicism is easily appreciated in cutaneous disorders, as phenotypically distinct mutant cells often give rise to lesions in patterns determined by the affected cell type. Genetic investigation of cutaneous mosaic disorders has identified pathways central to disease pathogenesis, revealing novel therapeutic targets. In this review, we discuss examples of cutaneous mosaicism, approaches to gene discovery in these disorders, and insights into molecular pathobiology that have potential for clinical translation.

Inherited Nonsyndromic Ichthyoses: An Update on Pathophysiology, Diagnosis and Treatment

Hereditary ichthyoses are due to mutations on one or both alleles of more than 30 different genes, mainly expressed in the upper epidermis. Syndromic as well as nonsyndromic forms of ichthyosis exist. Irrespective of etiology, virtually all types of ichthyosis exhibit a defective epidermal barrier that constitutes the driving force for hyperkeratosis, skin scaling, and inflammation. In nonsyndromic forms, these features are most evident in severe autosomal recessive congenital ichthyosis (ARCI) and epidermolytic ichthyosis, but to some extent also occur in the common type of non-congenital ichthyosis. A correct diagnosis of ichthyosis-essential not only for genetic counseling but also for adequate patient information about prognosis and therapeutic options-is becoming increasingly feasible thanks to recent progress in genetic knowledge and DNA sequencing methods. This paper reviews the most important aspects of nonsyndromic ichthyoses, focusing on new knowledge about the pathophysiology of the disorders, which will hopefully lead to novel ideas about therapy.

Revertant mosaicism in genodermatoses

Inherited monogenic skin disorders include blistering disorders, inflammatory disorders, and disorders of differentiation or development. In most cases, the skin is broadly involved throughout the affected individual's lifetime, but rarely, appearance of normal skin clones has been described. In these cases of revertant mosaicism, cells undergo spontaneous correction to ameliorate the effects of genetic mutation. While targeted reversion of genetic mutation would have tremendous therapeutic value, the mechanisms of reversion in the skin are poorly understood. In this review, we provide an overview of genodermatoses that demonstrate widespread reversion and their corrective mechanisms, as well as the current research aimed to understand this "natural gene therapy".