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15 Facts about Pathology of Ichthyoses

Dr Sampurna Roy MD   







Ichthyosis Vulgaris: Epidermis is slightly thinned with loss of rete ridges. The stratum corneum is thickened and laminated. Granular layer is inconspicuous.




(1) Ichthyoses, also known as disorders of keratinization, encompass a heterogeneous group of hereditary and acquired skin diseases, characterized by the presence of visible scales on the skin surface.


(2) The word ichthyosis comes from the Greek word ichthys, meaning fish, referring to the cutaneous scaling that is characteristic of these disorders, which is said to resemble the scales of a fish.


(3) Although ichthyoses are primarily inherited disorders with onset at or shortly after birth, rare acquired forms have been reported in the setting of malignancy, nutritional deficiency, and autoimmune or infectious disease.


(4) Mutations in over 50 genes have been reported to cause ichthyoses.


(5) Ichthyosis vulgaris and X-linked recessive ichthyosis are classified as the "common ichthyoses".


(6) It is the most common form of nonsyndromic inherited ichthyosis, with an estimated incidence of 1 in 250 births.


(7) Clinical findings usually appear at around 2 months of age and include generalized xerosis and fine white to gray scale that is most prominent on the abdomen, chest, and extensor surfaces of the extremities.


(8) It is caused by autosomal dominant mutations in the filaggrin gene (FLG), which plays an essential role in epidermal differentiation and formation of the skin barrier.


(9) X-linked recessive ichthyosis is the second most common form of inherited ichthyosis, with a prevalence of 1:2000 to 1:6000 in males.


(10) Autosomal recessive congenital ichthyosis is a genetically and phenotypically heterogeneous group of disorders that includes harlequin ichthyosis, lamellar ichthyosis  and congenital ichthyosiform erythroderma. It's incidence has been approximated at 1 in 200,000 births.

(11) Harlequin ichthyosis is caused by loss-of-function mutations in ABCA12. Neonates present with thick, armor-like scale with severe ectropion (eversion of the eyelids), eclabium (eversion of the lips), and flattening of the ears.

There is massive hyperkeratosis in all biopsies.


(12) Lamellar Ichthyosis is characterized by large plate-like scales of ichthyosis. It may present as "collodion baby". The palms and soles are often involved. An increased incidence of skin cancer has been reported in this variant.


(13) Keratinopathic ichthyosis is a group of disorders caused by mutations in the keratin family of genes. The major variant of keratinopathic ichthyosis is epidermolytic ichthyosis.


(14) Epidermolytic ichthyosis is caused by autosomal dominant mutations in the keratin 1 ( KRT1) and keratin10 (KRT10) genes, which play an essential role in maintaining structural integrity in suprabasal keratinocytes.  


(15) In addition to cutaneous involvement, syndromic ichthyoses affect at least one other organ or system. Many causative genes have been identified for syndromic ichthyoses, including NSDHL (CHILD syndrome), EBP (Conradi-Hunermann-Happle syndrome, CHILD Syndrome) and ALDH3A2 (Sjögren-Larsson syndrome).






Marukian NV, Choate KA. Recent advances in understanding ichthyosis pathogenesis. F1000Research. 2016;5:F1000 Faculty Rev-1497. 


Craiglow BG. Ichthyosis in the Newborn. Seminars in perinatology. 2013;37(1):26-31
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