Ichthyosis

Ichthyosis^[1] is a family of genetic skin disorders characterized by dry, thickened, scaly skin.^[2] 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 from Greek ἰχθύς (ichthys) 'fish', since dry, scaly skin is the defining feature of all forms of ichthyosis.^[3]

Ichthyosis
Other names	Ichthyoses
Ichthyosis is characterized by generalised, scaly skin.
Specialty	Dermatology

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.^[4]

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.^[5] 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:^[5]

Non-syndromic ichthyosis

Name	OMIM	Mode Of Inheritance	Gene(s)
Ichthyosis vulgaris	146700	Autosomal semi-dominant	FLG
X-linked recessive ichthyosis	308100	X-linked recessive	STS
Harlequin ichthyosis	242500	Autosomal recessive	ABCA12
Congenital ichthyosiform erythoderma	242100	Autosomal recessive	TGMI1, NIPAL4, ALOX12B, ALOXE3, ABCA12, CYP4F22, NIPAL4, LIPN, CERS3, PNPLA1, ST14, CASP14
Lamellar ichthyosis	242300	Autosomal recessive	TGMI1, NIPAL4, ALOX12B, ALOXE3, ABCA12, CYP4F22, NIPAL4, LIPN, CERS3, PNPLA1, ST14, CASP14
Self improving congenital ichthyosis	242300	Autosomal recessive	TGM1, ALOX12B, ALOXE3
Bathing suit ichthyosis	242300	Autosomal recessive	TGMI1
Epidermolytic ichthyosis	113800	Autosomal dominant	KRT1, KRT10
Superficial epidermolytic ichthyosis	146800	Autosomal dominant	KRT2
Annular epidermolytic ichthyosis	607602	Autosomal dominant	KRT1, KRT10
Ichthyosis Curth-Macklin	146590	Autosomal dominant	KRT1
Autosomal recessive epidermolytic ichthyosis	113800	Autosomal recessive	KRT10
Congenital reticular ichthyosiform erythroderma	609165	Autosomal dominant	KRT1, KRT10
Epidermolytic nevi	113800	Postzygotic mosaicism	KRT1, KRT10
Loricrin keratoderma	604117	Autosomal dominant	LOR
Erythrokeratodermia variabilis	133200	Autosomal dominant	GJB3, GJB4
Peeling skin disease	270300	Autosomal recessive	CDSN
Keratosis linearis with ichthyosis congenita and sclerosing keratoderma	601952	Autosomal recessive	POMP

Syndromic ichthyosis

Name	OMIM	Mode Of Inheritance	Gene (s)
X-linked recessive ichthyosis syndromic forms	308700 300500 300533	X-linked recessive	STS
Ichthyosis follicularis with alopecia and photophobia syndrome	308205	X-linked recessive	MBTPS2
Conradi-Hunermann-Happle syndrome	302960	X-linked dominant	EBP
Netherton syndrome	256500	Autosomal recessive	SPINK5
Ichthyosis-hypotrichosis syndrome	610765	Autosomal recessive	ST14
Trichothiodystrophy	601675	Autosomal recessive	ERCC2, ERCC3, GTF2H5
Trichothiodystrophy (non-congenital forms)	275550 211390 601675	Autosomal recessive	C7Orf11, TTDN1
Sjögren-Larsson syndrome	270200	Autosomal recessive	ALDH3A2
Refsum's disease	266500	Autosomal recessive	PHYH, PEX7
Mental retardation, enteropathy, deafness, neuropathy, ichthyosis, keratoderma syndrome	609528	Autosomal recessive	SNAP29
Arthrogryposis, renal dysfunction, cholestasis syndrome	208085	Autosomal recessive	VPS33B
Keratitis-ichthyosis-deafness syndrome	602450 148210	Autosomal dominant	GJB2
Neutral lipid storage disease with ichthyosis	275630	Autosomal recessive	ABHD5
Ichthyosis prematurity syndrome	608649	Autosomal recessive	SLC27A4
Neu–Laxova syndrome	256520 616038	autosomal recessive	PHGDH, 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.^[6]

Ichthyosis has been found to be more common in Native American, Asian, Mongolian groups.^{[citation needed]} 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.^[7]

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.^[8] Application of propylene glycol is another treatment method. Retinoids are used for some conditions.

Exposure to sunlight may improve^{[citation needed]} 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.^[9] 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.^[10][11]

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

See also

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