Ichthyosis is a family of rare genetic skin disorders characterized by dry, thickened, scaly skin.

There are more than 20 types of ichthyosis which range in severity of symptoms, outward appearance, underlying genetic cause, and mode of inheritance (e.g., whether the abnormal gene inherited is dominant, recessive, autosomal, or X-linked). Ichthyosis comes from the , 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, type 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.

There are many types of ichthyoses and an exact diagnosis may be difficult. Types of ichthyoses are classified by their appearance and their genetic cause. Ichthyosis caused by the same gene can vary considerably in severity and symptoms. Some ichthyoses do not appear to fit exactly into any one type. Different genes can produce ichthyoses with similar symptoms. Of note, X-linked ichthyosis is associated with Kallmann syndrome (close to "KAL1" gene). The most common or well-known types are as follows:

An extremely rare disease of which only a few isolated cases are known.

Congenital Ichthyosiform Erythroderma (CIE), also known as Nonbullous congenital ichthyosiform erythroderma is a rare type the ichthyosis family of skin diseases which occurs in 1 in 200,000 to 300,000 births.

Ichthyosis hystrix is a group of rare skin disorders in the ichthyosis family of skin disorders characterized by massive hyperkeratosis with an appearance like spiny scales. This term is also used to refer to a type of epidermal nevi with extensive bilateral distribution.

Large and especially giant congenital nevi are at higher risk for malignancy degeneration into melanoma. Because of the premalignant potential, it is an acceptable clinical practice to remove congenital nevi electively in all patients and relieve the nevocytic overload.

CIE has symptoms very similar to Lamellar ichthyosis (LI) but milder and is considered by many scientists to be a variant of that disease, so both diseases are grouped under the title autosomal recessive congenital ichthyosis (ARCI).

The baby is often born in a collodion membrane, a shiny, wax outer layer on the skin and usually with ectropion, having the lower eyelid turned outwards. When the membrane is shed the skin is red with a generalized white scale. Palms, soles and areas on the joints are often affected with hyperkeratosis, a thickening of the layer of dead skin cells on the surface of the skin. In classical CIE (unlike LI) there is little eclabion (eversion of the lips), ectropion and alopecia (hair loss).

Many people with ACRI don't fit neatly into the definition of LI or CIE but have characteristics of both diseases. The definitions of CIE and LI describe the extremes of the range of ACRI.

The appearance can be caused by several skin diseases, and it is most often not associated with other birth defects. In most cases, the baby develops an ichthyosis or ichthyosis-like condition or other rare skin disorder.

Most cases (approximately 75%) of collodion baby will go on to develop a type of autosomal recessive congenital ichthyosis (either lamellar ichthyosis or congenital ichthyosiform erythrodema).

In around 10% of cases the baby sheds this layer of skin and has normal skin for the rest of its life. This is known as "self-healing collodion baby".

The remaining 15% of cases are caused by a variety of diseases involving keratinization disorders. Known causes of collodion baby include ichthyosis vulgaris and trichothiodystrophy. Less well documented causes include Sjögren-Larsson syndrome, Netherton syndrome, Gaucher disease type 2, congenital hypothyroidism, Conradi syndrome, Dorfman-Chanarin syndrome, ketoadipiaciduria, koraxitrachitic syndrome, ichthyosis variegata and palmoplantar keratoderma with anogenital leukokeratosis. Since many of these conditions have an autosomal recessive inheritance pattern, they are rare and can be associated with consanguinity.

Tests that can be used to find the cause of collodion baby include examination of the hairs, blood tests and a skin biopsy.

This condition is an autosomal recessive genetic disorder, which means the defective gene is located on an autosome, and both parents must carry one copy of the defective gene in order to have a child born with the disorder. Carriers of a recessive gene usually do not show any signs or symptoms of the disorder.

One form of ichthyosis lamellaris (LI1) is associated with a deficiency of the enzyme keratinocyte transglutaminase.

Genes involved include:

Ichthyosis en confetti, also known as ichthyosis with confetti, congenital reticular ichthyosiform erythroderma (CRIE) and ichthyosis variegata, is a very rare form of congenital ichthyosis in which healthy patches of normal skin co-exist within the abnormal skin areas. The condition is caused by a frameshift mutation in the keratin 10 gene (KRT10); mutant keratin 10 accumulates in the nucleolus, a sub-nuclear structure, rather than within cellular intermedite filaments like the wild-type protein. Children with the condition exhibit red, flaky skin; however, for reasons not yet totally clear, wild type clonal patches of skin start to appear, in place of the red, flaky skin. Due to the clonal nature of the growth of the normal skin cells, it appears the patient is covered with confetti, hence the name of the condition. It has been hypothesized that this is the result of a combination of mitotic recombination and natural selection within the skin.

IBS is an autosomal dominant genetic condition caused by a mutation in the gene for keratin 2e on chromosome 12.

This means an affected person has a 50% chance of passing the condition on to their child. Around half of cases of IBS, however, have no parent with the condition and have the genetic fault due to a spontaneous mutation.

Constant care is required to moisturise and protect the skin. The hard outer layer eventually peels off, leaving the vulnerable inner layers of the dermis exposed. Early complications result from infection due to fissuring of the hyperkeratotic plates and respiratory distress due to physical restriction of chest wall expansion.

Management includes supportive care and treatment of hyperkeratosis and skin barrier dysfunction. A humidified incubator is generally used. Intubation is often required until nares are patent. Nutritional support with tube feeds is essential until eclabium resolves and infants can begin nursing. Ophthalmology consultation is useful for the early management of ectropion, which is initially pronounced and resolves as scale is shed. Liberal application of petrolatum is needed multiple times a day. In addition, careful debridement of constrictive bands of hyperkeratosis should be performed to avoid digital ischemia. Cases of digital autoamputation or necrosis have been reported due to cutaneous constriction bands. Relaxation incisions have been used to prevent this morbid complication.

In the past, the disorder was nearly always fatal, whether due to dehydration, infection (sepsis), restricted breathing due to the plating, or other related causes. The most common cause of death was systemic infection and sufferers rarely survived for more than a few days. However, improved neonatal intensive care and early treatment with oral retinoids, such as the drug Isotretinoin (Isotrex), may improve survival. Early oral retinoid therapy has been shown to soften scales and encourage desquamation. After as little as two weeks of daily oral isotretinoin, fissures in the skin can heal, and plate-like scales can nearly resolve. Improvement in the eclabium and ectropion can also be seen in a matter of weeks. Children who survive the neonatal period usually evolve to a less severe phenotype, resembling a severe congenital ichthyosiform erythroderma. Patients continue to suffer from temperature dysregulation and may have heat and cold intolerance. Patients can also have generalized poor hair growth, scarring alopecia, contractures of digits, arthralgias, failure to thrive, hypothyroidism, and short stature. Some patients develop a rheumatoid factor-positive polyarthritis. Survivors can also develop fish-like scales and retention of a waxy, yellowish material in seborrheic areas, with ear adhered to the scalp.

The oldest known survivor is Nusrit "Nelly" Shaheen, who was born in 1984 and is in relatively good health as of April 2016. Lifespan limitations have not yet been determined with the new treatments.

A study published in 2011 in the Archives of Dermatology concluded, "Harlequin ichthyosis should be regarded as a severe chronic disease that is not invariably fatal. With improved neonatal care and probably the early introduction of oral retinoids, the number of survivors is increasing."

Aside from the skin scaling, XLI is not typically associated with other major medical problems. Corneal opacities may be present but do not affect vision. Cryptorchidism is reported in some individuals. Some individuals can also be seen to have an intellectual disability, this is thought to be due to deletions encompassing neighboring genes in addition to "STS".

Female carriers generally do not experience any of these problems but rarely can have difficulty during childbirth, as the STS expressed in the placenta plays a role in normal labor. For this reason carriers should ensure their obstetrician is aware of the condition.

Large congenital nevi are caused by a mutation in the body's cells that occurs early in embryonic development, usually within the first twelve weeks of pregnancy. Mutations are sometimes found in genes that code for NRAS and KRAS proteins. There is no known method of prevention.

This is rare and is usually due to mutations in the R-spondin 4 (RSPO4) gene which is located on the short arm of chromosome 20 (20p13). Clinically it is manifest by the absence (anonychia) or hypoplasia (hyponuchia) of finger- and/or toenails.

Keratitis–ichthyosis–deafness syndrome (also known as "Erythrokeratodermia progressiva Burns," "Ichthyosiform erythroderma, corneal involvement, and deafness," and "KID syndrome,") presents at birth/infancy and is characterized by pregressive corneal opacification, either mild generalized hyperkeratosis or discrete erythematous plaques, and neurosensory deafness.

It is caused by a mutation in connexin 26.

Ichthyosis vulgaris is one of the most common genetic disorders caused by a single gene. The disorder is believed to be caused by mutations to the gene encoding profilaggrin (a protein which is converted to filaggrin which plays a vital role in the structure of the skin). Around 10% of the population have some detrimental mutations to the profilaggrin gene that is also linked to atopic dermatitis (another skin disorder that is often present with ichthyosis vulgaris). The exact mutation is only known for some cases of ichthyosis vulgaris.

It is generally considered to be an autosomal dominant condition, i.e., a single genetic mutation causes the disease and an affected person has a 50% chance of passing the condition on to their child. There is some research indicating it may be semi-dominant. This means that a single mutation would cause a mild case of ichthyosis vulgaris and mutations to both copies of the gene would produce a more severe case.

Sjögren–Larsson syndrome (SLS) is an autosomal recessive form of ichthyosis apparent at birth.

Sjögren–Larsson syndrome is a rare autosomal, recessive, neurocutaneous disease. This disease can be identified by a triad of medical disorders. The first is ichthyosis, which is a buildup of skin to form a scale-like covering that causes dry skin and other problems. The second identifier is spastic paraplegia which is characterized by leg spasms. The final identifier is intellectual delay.

The gene of SLS is found on chromosome 17. In order for a child to receive SLS both parents must be carriers of the SLS gene. If they are carriers their child has a ¼ chance of getting the disease. In 1957 Sjogren and Larsson proposed that the Swedes with the disease all descended from a common ancestor 600 years ago. Today only 30–40 persons in Sweden have this disease.

"Bamboo hair" is a rare autosomal recessive genodermatosis characterized by congenital ichthyosiform erythroderma, trichorrhexis invaginata, and atopic diathesis with failure to thrive. Chronic skin inflammation results in scaling and exfoliation, predisposing these patients to life-threatening infections, sepsis, and dehydration. The Netherton syndrome Mendelian Inheritance in Man is inherited as an autosomal recessive disorder due to mutations of both copies of the "SPINK5" gene (localized to band 5q31-32), which encodes the serine protease inhibitor LEKTI (lymphoepithelial Kazal-type-related inhibitor). LEKTI is expressed in epithelial and mucosal surfaces and in the thymus. Each "SPINK5" mutation leads to a different length of LEKTI protein, resulting in genotype/phenotype correlations in cutaneous severity, susceptibility to atopic dermatitis, growth retardation, skin infection, increased stratum corneum protease activities, and elevated kallikrein levels in the stratum corneum.

Trichorrhexis invaginata, or bamboo hair, is a hair shaft abnormality that occurs as a result of an intermittent keratinizing defect of the hair cortex. Incomplete conversion of the sulfhydryl –SH group onto S-S disulfide bonds in the protein of the cortical fibers leads to cortical softness and subsequent invagination of the fully keratinized distal hair shaft into the softer, abnormally keratinized proximal hair shaft. Intussusception of the distal hair shaft into the proximal hair shaft results in a distinctive ball-and-socket hair shaft deformity. The affected hairs are brittle and breakage is common, resulting in short hairs.

Migratory lesions of ichthyosis linearis circumflexa may be caused by a dermal influx of inflammatory cells that undergo phagocytosis and digestion by keratinocytes, resulting in disruption of keratinization.

Increased transepidermal water loss resulting from the disturbance of corneocyte barrier function in erythroderma may cause profound metabolic abnormalities and hypernatremia, particularly in neonates.

Approximately 200 cases of trichorrhexis invaginata (bamboo hair) have been reported in the literature, but the true incidence is not known. The incidence of trichorrhexis invaginata (bamboo hair) may be as high as 1 case in 50,000 population.

Girls are affected more often by trichorrhexis invaginata (bamboo hair) than boys, but is present in all races.

Sabinas brittle hair syndrome is inherited as an autosomal recessive genetic trait.

In a study by Howell et al. patients were located and studied by means of complete histories and physical examinations, analyses of serum trace metals, ceruloplasmin concentration, urine and serum amino acids, and routine metabolic urine screens. In addition, serum and urine luteinizing hormone (LH) and follicle-stimulating hormone (FSH) values were determined, and were interpreted in conjunction with total plasma estrogen, estradiol, and testosterone levels. Close examination demonstrated the scalp hairs were very brittle, coarse, wiry in texture, and broke off quite easily with mechanical trauma such as combing and brushing. Some hairs could be visualized in their follicles, which were broken off at the skin line. Most patients had accompanying hyperkeratosis (thickening of the skin) of moderate degree on exposed surfaces. Maxillary hypoplasia (midfacial retrusion) was significant in many patients. The brittle, short hair, reduced eyelashes, crowded teeth, and dull appearance created a characteristic facial appearance. Post-pubertal patients had development of secondary sexual characteristics consistent with their age, except for sparse pubic escutcheons. All cases studied demonstrated some degree of mental deficiency; I.Q.'s ranged between 50–60. A deficiency in eye–hand coordination was also noted.

Trichorrhexis invaginata (also known as "Bamboo hair" ) is a distinctive hair shaft abnormality that may occur sporadically, either in normal hair or with other hair shaft abnormalities, or regularly as a marker for Netherton's syndrome. The primary defect appears to be abnormal keratinization of the hair shaft in the keratogenous zone, allowing for intussusception of the fully keratinized and hard distal shaft into the incompletely keratinized and soft proximal portion of the shaft.

Hystrix-like ichthyosis–deafness syndrome (also known as "HID syndrome") is a cutaneous condition characterized by a keratoderma.

Ichthyosis bullosa of Siemens is a type of familial, autosomal dominant ichthyosis, a rare skin disorder. It is also known as bullous congenital ichthyosiform erythroderma of Siemens or ichthyosis exfoliativa. It is a genetic disorder with no known cure which is estimated to affect about 1 in 500,000 people.

CHILD syndrome is a rare disorder with only 60 recorded cases worldwide thus far in literature.

Harlequin-type ichthyosis is a genetic disorder which results in thickened skin over nearly the entire body at birth. The skin forms large, diamond-shaped plates that are separated by deep cracks. They affect the shape of the eyelids, nose, mouth, and ears, and limit movement of the arms and legs. Restricted movement of the chest can lead to breathing difficulties. These plates fall off over weeks. Other complications can include premature birth, infection, problems with body temperature, and dehydration.

Harlequin-type ichthyosis is due to mutations of the "ABCA12" genes. It is inherited from a person's parents in an autosomal recessive manner. Diagnosis is often based on appearance at birth and confirmed by genetic testing. Before birth amniocentesis or ultrasound may support the diagnosis.

There is no cure. Early in life constant supportive care is typically required. Treatments may include moisturizing cream, antibiotics, etretinate, or retinoids. It affects about 1 per 300,000 births. Both sexes are affected equally commonly. Long term problems are common. Death in the first month is relatively common. The condition was first documented in 1750.