Inherited ichthyoses: a review of the histology of the skin

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.

Ocular Manifestations of Congenital Lamellar Ichthyosis

PURPOSE

To describe the ophthalmic manifestations in a series of children with congenital lamellar ichthyosis. These cases presented with varying types of eyelid abnormality associated with the systemic disease. The clinical features and ophthalmic management were studied.

METHODS

The case histories of three children presenting to the oculoplastic clinic were reviewed. All were diagnosed with congenital lamellar ichthyosis and under the care of the Dermatology department. Family history and pedigree analysis was performed to determine mode of genetic inheritance. Ocular examination for visual acuity, eyelid and eyelash malposition, lid function and closure were carried out. Corneal examination including tests for exposure was also done.

RESULTS

All three patients had eyelid position abnormalities from the systemic disease. There was no clinical evidence of conjunctival involvement. One patient required full thickness skin grafts to treat corneal exposure secondary to lower lid ectropion. One had mild lower lid ectropion but without corneal exposure. The third case had the unusual finding of inward turning of the anterior lamella of the upper eyelid with a marked lash ptosis and only mild ectropion of the lower lid.

CONCLUSIONS

Congenital lamellar ichthyosis is a heterogeneous disorder with phenotypic variability. The most common eyelid abnormality is cicatricial ectropion of the upper and mainly lower eyelids. Most cases are managed conservatively although in severe cases secondary corneal exposure may require surgical correction. In this condition, to the best of our knowledge, the tendency for the eyelids to turn inwards has not previously been described.

Inherited ichthyoses/generalized Mendelian disorders of cornification

Inherited ichthyoses, defined as the generalized form of Mendelian disorders of cornification, are characterized by visible scaling and/or hyperkeratosis of most or all of the skin. This etiologically and phenotypically heterogenous group of conditions is caused by mutations in various different genes important for keratinocyte differentiation and epidermal barrier function. Diagnosing a specific entity is a particular challenge for the nonspecialist presented with the common clinical scaling. For the clinician, this review outlines an algorithmic approach for utilizing diagnostic clues to narrow down the differential diagnosis and to guide further testing and treatment options.

Spink5-deficient mice mimic Netherton syndrome through degradation of desmoglein 1 by epidermal protease hyperactivity

Mutations in SPINK5, encoding the serine protease inhibitor LEKTI, cause Netherton syndrome, a severe autosomal recessive genodermatosis. Spink5(-/-) mice faithfully replicate key features of Netherton syndrome, including altered desquamation, impaired keratinization, hair malformation and a skin barrier defect. LEKTI deficiency causes abnormal desmosome cleavage in the upper granular layer through degradation of desmoglein 1 due to stratum corneum tryptic enzyme and stratum corneum chymotryptic enzyme-like hyperactivity. This leads to defective stratum corneum adhesion and resultant loss of skin barrier function. Profilaggrin processing is increased and implicates LEKTI in the cornification process. This work identifies LEKTI as a key regulator of epidermal protease activity and degradation of desmoglein 1 as the primary pathogenic event in Netherton syndrome.

Homozygosity mapping of a locus for a novel syndromic ichthyosis to chromosome 3q27-q28

Ichthyosis is a heterogeneous group of skin disorders characterized by abnormal epidermal scaling. Occasionally, extracutaneous features are associated. A novel autosomal recessive ichthyosis syndrome is described here with scalp hypotrichosis, scarring alopecia, sclerosing cholangitis, and leukocyte vacuolization in two inbred kindreds of Moroccan origin. We also report the mapping of the diseased gene to a 21.2 cM interval of chromosome 3q27-q28. Homo zygosity for polymorphic markers has enabled us to reduce the genetic interval to a 16.2 cM region. Furthermore, comparison of mutant chromosomes in the two families has suggested a common ancestral mutant haplotype. This linkage disequilibrium has reduced the genetic interval encompassing the diseased gene to less than 9.5 cM maximum. Further study of additional families from the same geographic area will hopefully reduce the genetic interval as well as help in the cloning of the gene involved in this rare disorder.

Omenn's syndrome: differential diagnosis in infants with erythroderma and immunodeficiency

The clinical differential diagnosis of erythroderma plus immunodeficiency and failure to thrive in neonates includes graft-versus-host-disease (GVHD), Omenn's syndrome (OS), and Netherton's syndrome (NS). In addition to immunological investigations, skin biopsy is an important part of the diagnostic work-up. We reviewed biopsies from 25 patients that were retrieved from the archives of the Department of Histopathology at Great Ormond Street, of which 9 were OS, 11 were GVHD, and 5 were NS. Five patients had two biopsy specimens. Both OS and GVHD show dyskeratosis and basal vacuolation. OS always shows acanthosis and almost always parakeratosis. GVHD shows a flat epidermis and rarely parakeratosis. OS and GVHD can be distinguished after immunohistochemistry for LCA and CD68 by the relative proportions of lymphocytes and macrophages in the dermal infiltrate (predominantly lymphocytes in OS, relatively more macrophages in GVHD). Skin biopsy diagnosis of OS is difficult before 6 weeks of age because the features are poorly developed. NS can be distinguished by psoriasiform acanthosis, thickening of the basement membrane, prominent dermal blood vessels, absence of dyskeratosis, and basal layer vacuolation, and a dermal infiltrate in which lymphocytes and macrophages are equally represented. Thus, the main difference between GVHD and OS is in the proportion of lymphocytes and macrophages in the infiltrate on immunohistochemical staining for LCA and CD68, while OS and NS may be distinguished on H&E morphology alone.