Ichthyosis is a family of genetic skin disorders characterized by dry, thickened, scaly skin. The more than 20 types of ichthyosis range in severity of symptoms, outward appearance, underlying genetic cause and mode of inheritance (e.g., dominant, recessive, autosomal or X-linked). Ichthyosis comes , since dry, scaly skin is the defining feature of all forms of ichthyosis.

The severity of symptoms can vary enormously, from the mildest, most common, types such as ichthyosis vulgaris, which may be mistaken for normal dry skin, up to life-threatening conditions such as harlequin-type ichthyosis. Ichthyosis vulgaris accounts for more than 95% of cases.

Types Many types of ichthyoses exist, and an exact diagnosis may be difficult. Types of ichthyoses are classified by their appearance, if they are syndromic or not, and by mode of inheritance. For example, non-syndromic ichthyoses that are inherited recessively come under the umbrella term autosomal recessive congenital ichthyosis (ARCI).

Ichthyosis caused by mutations in the same gene can vary considerably in severity and symptoms. Some ichthyoses do not appear to fit exactly into any one type while mutations in different genes can produce ichthyoses with similar symptoms. Of note, X-linked ichthyosis is associated with Kallmann syndrome (close to the KAL1 gene). The most common or well-known types are:

Non-syndromic ichthyosis +NameOMIMMode Of InheritanceGene(s)Ichthyosis vulgarisAutosomal semi-dominantFLGX-linked recessive ichthyosisX-linked recessive STSHarlequin ichthyosisAutosomal recessiveABCA12Congenital ichthyosiform erythodermaAutosomal recessiveTGMI1, NIPAL4, ALOX12B, ALOXE3, ABCA12, CYP4F22, NIPAL4, LIPN, CERS3, PNPLA1, ST14, CASP14Lamellar ichthyosisAutosomal recessiveTGMI1, NIPAL4, ALOX12B, ALOXE3, ABCA12, CYP4F22, NIPAL4, LIPN, CERS3, PNPLA1, ST14, CASP14Self improving congenital ichthyosisAutosomal recessiveTGM1, ALOX12B, ALOXE3Bathing suit ichthyosisAutosomal recessiveTGMI1Epidermolytic ichthyosisAutosomal dominantKRT1, KRT10Superficial epidermolytic ichthyosisAutosomal dominantKRT2Annular epidermolytic ichthyosisAutosomal dominantKRT1, KRT10Ichthyosis Curth-MacklinAutosomal dominantKRT1Autosomal recessive epidermolytic ichthyosisAutosomal recessiveKRT10Congenital reticular ichthyosiform erythrodermaAutosomal dominantKRT1, KRT10Epidermolytic neviPostzygotic mosaicismKRT1, KRT10Loricrin keratodermaAutosomal dominantLORErythrokeratodermia variabilisAutosomal dominantGJB3, GJB4Peeling skin diseaseAutosomal recessiveCDSNKeratosis linearis with ichthyosis congenita and sclerosing keratodermaAutosomal recessivePOMP

Syndromic ichthyosis +NameOMIMMode Of InheritanceGene (s)X-linked recessive ichthyosis syndromic formsX-linked recessiveSTSIchthyosis follicularis with alopecia and photophobia syndromeX-linked recessiveMBTPS2Conradi-Hunermann-Happle syndromeX-linked dominantEBPNetherton syndromeAutosomal recessiveSPINK5Ichthyosis-hypotrichosis syndromeAutosomal recessiveST14TrichothiodystrophyAutosomal recessiveERCC2, ERCC3, GTF2H5Trichothiodystrophy (non-congenital forms)Autosomal recessiveC7Orf11, TTDN1Sjögren-Larsson syndromeAutosomal recessiveALDH3A2Refsum's diseaseAutosomal recessivePHYH, PEX7Mental retardation, enteropathy, deafness, neuropathy, ichthyosis, keratoderma syndromeAutosomal recessiveSNAP29Arthrogryposis, renal dysfunction, cholestasis syndromeAutosomal recessiveVPS33BKeratitis-ichthyosis-deafness syndromeAutosomal dominantGJB2Neutral lipid storage disease with ichthyosisAutosomal recessiveABHD5Ichthyosis prematurity syndromeAutosomal recessiveSLC27A4Neu–Laxova syndromeautosomal recessivePHGDH, PSAT1 and PSPH

Non-genetic ichthyosis Ichthyosis acquisita

Diagnosis A physician often can diagnose ichthyosis by looking at the skin. A family history is also useful in determining the mode of inheritance. In some cases, a skin biopsy is done to help to confirm the diagnosis while in others genetic testing may be helpful in making a diagnosis. Diabetes has not been definitively linked to acquired ichthyosis or ichthyosis vulgaris; however, there are case reports associating new onset ichthyosis with diabetes.

Ichthyosis has been found to be more common in Native American, Asian, Mongolian groups. There is no way to prevent ichthyosis.

Ichthyosis is a genetically and phenotypically heterogeneous disease that can be isolated and restricted to the skin manifestations or associated with extracutaneous symptoms, one of which is limb reduction defect known as CHILD syndrome, a rare inborn error of metabolism of cholesterol biosynthesis that is usually restricted to one side of the body. One case with symptoms matching CHILD syndrome has been described as having a likely-different cause.Shawky, R. M., Elsayed, S. M., & Amgad, H. (2016). Autosomal recessive ichthyosis with limb reduction defect: A simple association and not CHILD syndrome. Egyptian Journal of Medical Human Genetics, 17(3), 255-258.

Treatments Treatments for ichthyosis often take the form of topical application of creams and emollient oils, in an attempt to hydrate the skin. Creams containing a high percentage of urea or lactic acid have been shown to work exceptionally well in some cases. Application of propylene glycol is another treatment method. Retinoids are used for some conditions.

Exposure to sunlight may improve or worsen the condition. In some cases, excess dead skin sloughs off much better from wet tanned skin after bathing or a swim, although the dry skin might be preferable to the damaging effects of sun exposure.

There can be ocular manifestations of ichthyosis, such as corneal and ocular surface diseases. Vascularizing keratitis, which is more commonly found in congenital keratitis-ichythosis-deafness (KID), may worsen with isotretinoin therapy.

Other animals Ichthyosis or ichthyosis-like disorders exist for several types of animals, including cattle, chickens, llamas, mice, and dogs.Sundberg, John P., Handbook of Mouse Mutations with Skin and Hair Abnormalities, Page 333, Published by CRC Press, 1994, Ichthyosis of varying severity is well documented in some popular breeds of domestic dogs. The most common breeds to have ichthyosis are Golden Retrievers, American bulldogs, Jack Russell Terriers, and Cairn Terriers.Gross, Thelma Lee, Veterinary Dermatopathology, Page 174-179, Published by Blackwell Publishing, 2004,

In fiction Arthur Conan Doyle – "The Adventure of the Blanched Soldier" Michel Faber – The Crimson Petal and the White George R. R. Martin – A Song of Ice and Fire Bernard Minier – Sisters DC Comics - Killer Croc Osamu Tezuka - Black Jack The X-Files - "Humbug" (Season 2, Episode 20)

See also Skin disease Ichthyosis en confetti List of cutaneous conditions List of cutaneous neoplasms associated with systemic syndromes

References

External links

Ichthyosis Overview - US National Institute of Arthritis and Musculoskeletal and Skin Diseases European Network for Ichthyosis – International patients' network run by national European patients' associations