Genetics of Inherited Ichthyoses and Related Diseases (original) (raw)
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Molecular Genetics of Keratinization Disorders – What’s New About Ichthyosis
Acta Dermato Venereologica
Patients with ichthyosis manifest with dry and scaly skin, with considerable phenotypic variability. The heritable forms of ichthyosis are associated with mutations in over 60 different genes which encode proteins critical for normal physiological function of the skin. This overview highlights some of the new findings in the genetics of heritable forms of ichthyosis and emphasizes the connection of skin findings to extracutaneous manifestations, in some forms of the syndromic ichthyosis. The presentation also emphasizes the importance of determining the specific mutations in the underlying genes, which allows subclassification of the patients into distinct categories, with the capability to prognosticate the severity and the overall outcome of the disease in general terms. The knowledge of mutations in specific genes is also required for application of allele-specific therapies being developed for this group of disorders currently without specific treatments. The heritable forms of keratinization disorders, including various forms of ichthyosis and keratodermas, comprise a phenotypically heterogeneous group of diseases which can be divided into syndromic and nonsyndromic forms. In the non-syndromic forms, the clinical manifestations are limited to the cutaneous structures while the syndromic ones are associated with a spectrum of extracutaneous manifestations. The inheritance in different families can be autosomal dominant, autosomal recessive or either X-linked dominant or recessive. Currently at least 67 distinct genes have been associated with different forms of ichthyosis. These genes can be grouped on the basis of their physiological involvement, including genes encoding structural components of epidermis, those involved in epidermal lipid metabolism, or those critical for cell-cell adhesion, and keratinocyte differentiation. This overview highlights some of the recent progress made in understanding the molecular genetics of keratinization disorders, and presents selected, recently characterized cases as representative of different forms of heritable ichthyosis.
Inherited Nonsyndromic Ichthyoses: An Update on Pathophysiology, Diagnosis and Treatment
American Journal of Clinical Dermatology
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. Key Points Ichthyoses are the phenotypic results of gene mutations which-one way or another-lead to an imbalance of stratum corneum homeostasis and skin barrier failure. Depending on the type of ichthyosis, different severities of localized or generalized hyperkeratosis and scaling are seen, often accompanied by erythema, fissures, and erosions. Usual histopathologic findings are variable degrees of epidermal hyperkeratosis, hyperproliferation, and-more rarely-skin inflammation and superficial epidermolysis. Genetic testing to confirm the diagnosis and enable correct genetic counseling is becoming increasingly rapid, but also more complicated because of the multiple testing (multi-gene panels) and the interpretation of large datasets. On the basis of new knowledge about the pathophysiology of different types of ichthyoses, novel and more individualized treatment options will hopefully soon become available.
Biomedicines, 2024
Inherited ichthyoses are a group of clinically and genetically heterogeneous rare disorders of skin keratinization with overlapping phenotypes. The clinical picture and family history are crucial to formulating the diagnostic hypothesis, but only the identification of the genetic defect allows the correct classification. In the attempt to molecularly classify 17 unrelated Italian patients referred with congenital nonsyndromic ichthyosis, we performed massively parallel sequencing of over 50 ichthyosis-related genes. Genetic data of 300 Italian unaffected subjects were also analyzed to evaluate frequencies of putative disease-causing alleles in our population. For all patients, we identified the molecular cause of the disease. Eight patients were affected by autosomal recessive congenital ichthyosis associated with ALOX12B, NIPAL4, and TGM1 mutations. Three patients had biallelic loss-of-function variants in FLG, whereas 6/11 males were affected by X-linked ichthyosis. Among the 24 different disease-causing alleles we identified, 8 carried novel variants, including a synonymous TGM1 variant that resulted in a splicing defect. Moreover, we generated a priority list of the ichthyosis-related genes that showed a significant number of rare and novel variants in our population. In conclusion, our comprehensive molecular analysis resulted in an effective first-tier test for the early classification of ichthyosis patients. It also expands the genetic, mutational, and phenotypic spectra of inherited ichthyosis and provides new insight into the current understanding of etiologies and epidemiology of this group of rare disorders.
Human Mutation, 2018
Autosomal recessive congenital ichthyosis (ARCI), a phenotypically heterogeneous group of nonsyndromic Mendelian disorders of keratinization, is caused by mutations in as many as 13 distinct genes. We examined a cohort of 125 consanguineous families with ARCI for underlying genetic mutations. The patients' DNA was analyzed with a gene-targeted next generation sequencing panel comprising 38 ichthyosis associated genes. The interpretations of results of genomic data was assisted by genome-wide homozygosity mapping and transcriptome sequencing. Sequence data analysis identified biallelic mutations in 106 families out of a total of 125 (85%), most of them (102, 96.2%) being homozygous, reflecting consanguinity in these families. Among the 85 distinct mutations in 10 different genes, 45 (53%) were previously unreported. Phenotype-genotype correlations allowed assignment of specific genes in the majority of the families to a specific subtype of ARCI, lamellar ichthyosis (LI) vs. congenital ichthyosiform erythroderma (CIE). Interestingly, mutations in several genes could give rise to an overlapped phenotype consistent with either LI or CIE. Also, this is the third report for SDR9C7, SULT2B1 and fourth report for CERS3 mutations. Direct comparison of our results with previously published regional cohorts highlights the global mutation landscape of ARCI, however, population specific differences were noted.
Mosaic and Generalized Forms of Keratinopathic Ichthyoses
Mutations in KRT1 (keratin 1) or KRT10 (keratin 10) underlie a spectrum of diseases known as keratinopathic ichthyoses. Epidermolytic ichthyosis (EI) is caused by heterozygous missense mutations in the genes KRT1 or KRT10, mutations in the gene KRT2 (keratin 2) lead to superficial epidermolytic ichthyosis, and congenital reticular ichthyosiform erythroderma is caused by frameshift mutations in the genes KRT10 or KRT1, which lead to the phenomenon of revertant mosaicism. Epidermolytic ichthyosis is also present in a mosaic pattern known as epidermolytic (acantholytic) nevus, isolated or diffuse. In the latter case, gonadic involvement is possible, leading to a rare pedigree in which a parent with diffuse epidermolytic nevus (linear EI) gives birth to a child affected by EI. We present here an update on the phenotypic presentations of keratinopathic ichthyoses and their molecular mechanisms.
Acta dermato-venereologica, 2016
Autosomal recessive congenital ichthyosis (ARCI) represents a heterogeneous group of rare disorders of cornification with 3 major subtypes: harlequin ichthyosis (HI), lamellar ichthyosis (LI) and congenital ichthyosiform erythroderma (CIE). A 4th subtype has also been proposed: pleomorphic ichthyosis (PI), characterized by marked skin changes at birth and subsequently mild symptoms. In nationwide screenings of suspected cases of ARCI in Denmark and Sweden, we identified 132 patients (age range 0.1-86 years) classified as HI (n = 7), LI (n = 70), CIE (n = 17) and PI (n = 38). At birth, a collodion membrane or similar severe hyperkeratosis was reported in almost all patients with HI and LI, and in nearly half of patients with CIE and PI. Persistent ectropion was more common in HI (85%) and LI (57%), than in CIE (35%) and PI (5%). Anhidrosis was a frequent problem in all 4 groups (58-100%). A scoring (0-4) of ichthyosis/ery-thema past infancy showed widely different mean values in the ...
BMC Medical Genomics, 2022
Background Ichthyosis is a heterogeneous group of Mendelian cornification disorders that includes syndromic and non-syndromic forms. Autosomal Recessive Congenital Ichthyosis (ARCI) and Ichthyosis Linearis Circumflexa (ILC) belong to non-syndromic forms. Syndromic ichthyosis is rather a large group of heterogeneous diseases. Overlapping phenotypes and genotypes between these disorders is a major characteristic. Therefore, determining the specific genetic background for each form would be necessary. Methods A total of 11 Tunisian patients with non-syndromic (8 with ARCI and 2 with ILC) and autosomal syndromic ichthyosis (1 patient) were screened by a custom Agilent HaloPlex multi-gene panel and the segregation of causative mutations were analyzed in available family members. Results Clinical and molecular characterization, leading to genotype–phenotype correlation in 11 Tunisian patients was carried out. Overall, we identified 8 mutations in 5 genes. Thus, in patients with ARCI, we i...