Pityriasis rubra pilaris is an uncommon skin disorder characterized by the appearance of keratotic follicular papules, well-demarcated salmon-colored erythematous plaques covered with fine powdery scales interspersed with distinct islands of uninvolved skin, and palmoplantar keratoderma. Most cases are sporadic, although up to 6.5% of PRP-affected individuals report a positive family history. The rare familial cases show autosomal dominant inheritance with incomplete penetrance and variable expression: the disorder is usually present at birth or appears during the first years of life and is characterized by prominent follicular hyperkeratosis, diffuse palmoplantar keratoderma, and erythema, with only a modest response to treatment (summary by Fuchs-Telem et al., 2012).

A rare autosomal recessive inherited syndrome. It is characterized by xeroderma pigmentosum, mental retardation, dwarfism, hypogonadism, and neurologic abnormalities.

The NSDHL-related disorders include: CHILD (congenital hemidysplasia with ichthyosiform nevus and limb defects) syndrome, an X-linked condition that is usually male lethal during gestation and thus predominantly affects females; and CK syndrome, an X-linked disorder that affects males. CHILD syndrome is characterized by unilateral distribution of ichthyosiform (yellow scaly) skin lesions and ipsilateral limb defects that range from shortening of the metacarpals and phalanges to absence of the entire limb. Intellect is usually normal. The ichthyosiform skin lesions are usually present at birth or in the first weeks of life; new lesions can develop in later life. Nail changes are also common. The heart, lung, and kidneys can also be involved. CK syndrome (named for the initials of the original proband) is characterized by mild to severe cognitive impairment and behavior problems (aggression, attention deficit hyperactivity disorder, and irritability). All affected males reported have developed seizures in infancy and have cerebral cortical malformations and microcephaly. All have distinctive facial features, a thin habitus, and relatively long, thin fingers and toes. Some have scoliosis and kyphosis. Strabismus is common. Optic atrophy is also reported.

A rare, genetic, chronic, recurrent, slowly progressive, epidermal disease characterized by small, sterile, pustular eruptions, involving the nails and surrounding skin of the fingers and/or toes, which coalesce and burst, leaving erythematous, atrophic skin where new pustules develop. Onychodystrophy is frequently associated and anonychia and osteolysis are reported in severe cases. Local expansion (to involve the hands, forearms and/or feet) and involvement of mucosal surfaces (e.g. conjunctiva, tongue, urethra) may be observed.

Porokeratosis is a rare skin disorder characterized by one or more annular plaques with a surrounding raised horny border that spreads centrifugally. Variants of porokeratosis have been described that differ in morphologic shapes, distribution, and clinical course (Schamroth et al., 1997). However, as noted by Sybert (2010), several families with expression of more than one variant of porokeratosis among members, and several individuals expressing more than one variant, have been reported, suggesting that the distinctions among these variants may be artificial. Mutations in the MVK gene have been found to cause multiple types of porokeratosis, which have been described as porokeratosis of Mibelli, porokeratoma, genital porokeratosis, hyperkeratotic porokeratosis, and linear porokeratosis. The preferred title of this entry was formerly 'Porokeratosis 1, Mibelli Type; POROK1.' Genetic Heterogeneity of Porokeratosis Also see porokeratosis-2 (POROK2; 175850), mapped to chromosome 12q24; POROK3 (175900), caused by mutation in the MVK gene (251170) on chromosome 12q24; POROK4 (607728), mapped to chromosome 15q25-q26; POROK5 (612293), mapped to chromosome 1p31; POROK6 (612353), mapped to chromosome 1p31; POROK7 (614714), caused by mutation in the MVD gene (603236) on chromosome 16q24; POROK8 (616063), caused by mutation in the SLC17A9 gene (612107) on chromosome 20q13; and POROK9 (616631), caused by mutation in the FDPS gene (134629) on chromosome 1q22. A palmoplantar form of punctate porokeratosis has also been described (PPKP2; 175860). Genotype/Phenotype Correlations Zhang et al. (2015) screened 12 isoprenoid genes in 134 Chinese probands with porokeratosis and identified mutations in the MVK, MVD, PMVK, and FDPS genes in 113 patients. The authors noted that giant plaque-type porokeratosis ptychotropica with lesion diameters of at least 5 cm appeared to be uniquely associated with mutation in MVK; it was observed in 19 (50%) of 38 MVK probands, but not in patients with mutations in any of the other 3 genes or in the 21 probands in whom no mutation was found. MVK patients also showed the widest range in terms of the number and size of lesions, as well as presence of porokeratosis subtypes. In patients with MVD mutations, the age of onset ranged from 5 to 70 years, and lesion diameters were generally less than 2 cm. In addition, 6 of the 62 MVD probands exhibited solar facial porokeratosis, which was not seen in any other patients. Localized genital porokeratosis and porokeratoma appeared to be uniquely associated with mutation in the PMVK gene, whereas patients with mutations in the FDPS gene had more than 500 lesions, all with diameters of 1 cm or less.

Palmoplantar keratoderma (PPK) is a complex group of hereditary syndromes that have been classified into diffuse, punctate, and focal forms according to the pattern of hyperkeratosis on the palms and soles (Lucker et al., 1994). For a discussion of phenotypic and genetic heterogeneity of palmoplantar keratoderma, see epidermolytic PPK (144200).

A very rare complex ichthyosis syndrome with characteristics of scalp hypotrichosis, scarring alopecia, ichthyosis and sclerosing cholangitis. The ichthyosis presents with diffuse white scales sparing the skin folds and is accompanied by scalp hypotrichosis, cicatricial alopecia, and sparse eyelashes/eyebrows. Additional manifestations may include oligodontia, hypodontia and enamel dysplasia. All patients present with neonatal sclerosing cholangitis with jaundice and pruritus, hepatomegaly and biochemical cholestasis. Caused by a mutation in the CLDN1 gene on chromosome 3q28 coding for the tight junction protein claudin-1. Autosomal recessive pattern of inheritance.

Autosomal recessive congenital ichthyosis (ARCI) is a heterogeneous group of disorders of keratinization characterized primarily by abnormal skin scaling over the whole body. These disorders are limited to skin, with approximately two-thirds of patients presenting severe symptoms. The main skin phenotypes are lamellar ichthyosis (LI) and nonbullous congenital ichthyosiform erythroderma (NCIE), although phenotypic overlap within the same patient or among patients from the same family can occur (summary by Fischer, 2009). Neither histopathologic findings nor ultrastructural features clearly distinguish between NCIE and LI. In addition, mutations in several genes have been shown to cause both lamellar and nonbullous ichthyosiform erythrodermal phenotypes (Akiyama et al., 2003). At the First Ichthyosis Consensus Conference in Soreze in 2009, the term 'autosomal recessive congenital ichthyosis' (ARCI) was designated to encompass LI, NCIE, and harlequin ichthyosis (ARCI4B; 242500) (Oji et al., 2010). NCIE is characterized by prominent erythroderma and fine white, superficial, semiadherent scales. Most patients present with collodion membrane at birth and have palmoplantar keratoderma, often with painful fissures, digital contractures, and loss of pulp volume. In half of the cases, a nail dystrophy including ridging, subungual hyperkeratosis, or hypoplasia has been described. Ectropion, eclabium, scalp involvement, and loss of eyebrows and lashes seem to be more frequent in NCIE than in lamellar ichthyosis (summary by Fischer et al., 2000). In LI, the scales are large, adherent, dark, and pigmented with no skin erythema. Overlapping phenotypes may depend on the age of the patient and the region of the body. The terminal differentiation of the epidermis is perturbed in both forms, leading to a reduced barrier function and defects of lipid composition in the stratum corneum (summary by Lefevre et al., 2006). In later life, the skin in ARCI may have scales that cover the entire body surface, including the flexural folds, and the scales are highly variable in size and color. Erythema may be very mild and almost invisible. Some affected persons exhibit scarring alopecia, and many have secondary anhidrosis (summary by Eckl et al., 2005). For a general phenotypic description and discussion of genetic heterogeneity of autosomal recessive congenital ichthyosis, see ARCI1 (242300).

Variant Vohwinkel syndrome is a rare genodermatosis characterized by hyperkeratosis of the palms and soles, with a honeycomb appearance; constricting bands encircling the digits of the hands and feet, which frequently lead to autoamputation of the fifth digits; starfish-shaped, salmon-colored hyperkeratotic lesions, or knuckle pads, on the dorsal surface of the hands; and ichthyosiform dermatosis. The pathognomonic histologic finding is markedly thickened stratum corneum, hypergranulosis, and particularly, hyperkeratosis with round nuclei retained in the stratum corneum. Unlike classic Vohwinkel syndrome, hearing loss is not a feature (summary by Maestrini et al., 1996).

Any psoriasis in which the cause of the disease is a mutation in the CARD14 gene.

An inherited epidermal disorder with characteristics of palmoplantar keratoderma, linear hyperkeratotic papules on the flexural side of large joints (cord-like distribution around wrists, in antecubital and popliteal folds), hyperkeratotic plaques (on neck, axillae, elbows, wrists, and knees), mild ichthyosiform scaling, and sclerotic constrictions around fingers that present flexural deformities. The disease is caused by homozygous mutation in the POMP gene.

Porokeratosis is a rare skin disorder characterized by one or more annular plaques with a surrounding raised horny border that spreads centrifugally. Variants of porokeratosis have been described that differ in morphologic shapes, distribution, and clinical course (Schamroth et al., 1997). However, as noted by Sybert (2010), several families with expression of more than one variant of porokeratosis among members, and individuals expressing more than one variant, have been reported, suggesting that the distinctions among these variants may be artificial. Mutations in the MVK gene have been found to cause multiple types of porokeratosis, which have been described as disseminated superficial actinic porokeratosis (DSAP), nonactinic disseminated superficial porokeratosis (DSP), porokeratosis of Mibelli, giant plaque of porokeratosis ptychotropica, hyperkeratotic porokeratosis, and linear porokeratosis. The preferred title of this entry was formerly 'Porokeratosis 3, Disseminated Superficial Actinic Type; POROK3.' Disseminated superficial actinic porokeratosis is the most common subtype of porokeratosis. It is characterized by multiple small, annular, anhidrotic, keratotic lesions that are located predominantly on sun-exposed areas of the skin, such as the face, neck, and distal limbs. The lesions typically begin to develop in adolescence and reach near-complete penetrance by the third or fourth decade of life (summary by Wu et al., 2004 and Zhang et al., 2012). For a discussion of genetic heterogeneity of porokeratosis, see 175800.

Autosomal recessive congenital ichthyosis (ARCI) encompasses several forms of nonsyndromic ichthyosis. Although most neonates with ARCI are collodion babies, the clinical presentation and severity of ARCI may vary significantly, ranging from harlequin ichthyosis, the most severe and often fatal form, to lamellar ichthyosis (LI) and (nonbullous) congenital ichthyosiform erythroderma (CIE). These phenotypes are now recognized to fall on a continuum; however, the phenotypic descriptions are clinically useful for clarification of prognosis and management. Infants with harlequin ichthyosis are usually born prematurely and are encased in thick, hard, armor-like plates of cornified skin that severely restrict movement. Life-threatening complications in the immediate postnatal period include respiratory distress, feeding problems, and systemic infection. Collodion babies are born with a taut, shiny, translucent or opaque membrane that encases the entire body and lasts for days to weeks. LI and CIE are seemingly distinct phenotypes: classic, severe LI with dark brown, plate-like scale with no erythroderma and CIE with finer whiter scale and underlying generalized redness of the skin. Affected individuals with severe involvement can have ectropion, eclabium, scarring alopecia involving the scalp and eyebrows, and palmar and plantar keratoderma. Besides these major forms of nonsyndromic ichthyosis, a few rare subtypes have been recognized, such as bathing suit ichthyosis, self-improving collodion ichthyosis, or ichthyosis-prematurity syndrome.

Porokeratosis is a rare skin disorder characterized by one or more annular plaques with a surrounding raised horny border that spreads centrifugally. Variants of porokeratosis have been described that differ in morphologic shapes, distribution, and clinical course (Schamroth et al., 1997). However, as noted by Sybert (2010), several families with expression of more than one variant of porokeratosis among members, and individuals expressing more than one variant, have been reported, suggesting that the distinctions among these variants may be artificial. Mutations in the MVD gene have been found to cause multiple types of porokeratosis, which have been described as disseminated superficial actinic porokeratosis (DSAP), nonactinic disseminated superficial porokeratosis (DSP), solar facial porokeratosis, linear porokeratosis, and hyperkeratotic porokeratosis. The preferred title of this entry was formerly 'Porokeratosis 7, Disseminated Superficial Actinic Type; POROK7.' Disseminated superficial actinic porokeratosis (DSAP) is the most common subtype of porokeratosis. It is characterized by multiple small, annular, anhidrotic, keratotic lesions that are located predominantly on sun-exposed areas of the skin, such as the face, neck, and distal limbs. The lesions typically begin to develop in adolescence and reach near-complete penetrance by the third or fourth decade of life (summary by Wu et al., 2004 and Zhang et al., 2012). For a discussion of genetic heterogeneity of porokeratosis, see 175800.

X-linked Olmsted syndrome (OLMSX) is a rare keratinization disorder characterized by the combination of periorificial keratotic plaques and bilateral palmoplantar transgredient keratoderma. Other clinical manifestations include diffuse alopecia, leukokeratosis of the oral mucosa, onychodystrophy, hyperkeratotic linear streaks, follicular keratosis, and constriction of the digits (summary by Yaghoobi et al., 2007). For a general phenotypic description and a discussion of genetic heterogeneity of Olmsted disease, see OLMS1 (614594).

Multiple self-healing palmoplantar carcinoma (MSPC) is characterized by recurrent keratoacanthomas in palmoplantar skin as well as in conjunctival and corneal epithelia. In addition, patients experience a high susceptibility to malignant squamous cell carcinoma (summary by Zhong et al., 2016).

Keratoderma with woolly hair is a group of related conditions that affect the skin and hair and in many cases increase the risk of potentially life-threatening heart problems. People with these conditions have hair that is unusually coarse, dry, fine, and tightly curled. In some cases, the hair is also sparse. The woolly hair texture typically affects only scalp hair and is present from birth. Starting early in life, affected individuals also develop palmoplantar keratoderma, a condition that causes skin on the palms of the hands and the soles of the feet to become thick, scaly, and calloused.\n\nCardiomyopathy, which is a disease of the heart muscle, is a life-threatening health problem that can develop in people with keratoderma with woolly hair. Unlike the other features of this condition, signs and symptoms of cardiomyopathy may not appear until adolescence or later. Complications of cardiomyopathy can include an abnormal heartbeat (arrhythmia), heart failure, and sudden death.\n\nKeratoderma with woolly hair comprises several related conditions with overlapping signs and symptoms. Researchers have recently proposed classifying keratoderma with woolly hair into four types, based on the underlying genetic cause. Type I, also known as Naxos disease, is characterized by palmoplantar keratoderma, woolly hair, and a form of cardiomyopathy called arrhythmogenic right ventricular cardiomyopathy (ARVC). Type II, also known as Carvajal syndrome, has hair and skin abnormalities similar to type I but features a different form of cardiomyopathy, called dilated left ventricular cardiomyopathy. Type III also has signs and symptoms similar to those of type I, including ARVC, although the hair and skin abnormalities are often milder. Type IV is characterized by palmoplantar keratoderma and woolly and sparse hair, as well as abnormal fingernails and toenails. Type IV does not appear to cause cardiomyopathy.

Autosomal recessive congenital ichthyosis (ARCI) encompasses several forms of nonsyndromic ichthyosis. Although most neonates with ARCI are collodion babies, the clinical presentation and severity of ARCI may vary significantly, ranging from harlequin ichthyosis, the most severe and often fatal form, to lamellar ichthyosis (LI) and (nonbullous) congenital ichthyosiform erythroderma (CIE). These phenotypes are now recognized to fall on a continuum; however, the phenotypic descriptions are clinically useful for clarification of prognosis and management. Infants with harlequin ichthyosis are usually born prematurely and are encased in thick, hard, armor-like plates of cornified skin that severely restrict movement. Life-threatening complications in the immediate postnatal period include respiratory distress, feeding problems, and systemic infection. Collodion babies are born with a taut, shiny, translucent or opaque membrane that encases the entire body and lasts for days to weeks. LI and CIE are seemingly distinct phenotypes: classic, severe LI with dark brown, plate-like scale with no erythroderma and CIE with finer whiter scale and underlying generalized redness of the skin. Affected individuals with severe involvement can have ectropion, eclabium, scarring alopecia involving the scalp and eyebrows, and palmar and plantar keratoderma. Besides these major forms of nonsyndromic ichthyosis, a few rare subtypes have been recognized, such as bathing suit ichthyosis, self-improving collodion ichthyosis, or ichthyosis-prematurity syndrome.

Peeling skin syndrome-6 (PSS6) is characterized by generalized ichthyotic dry skin and bullous peeling lesions on the trunk and limbs at sites of minor trauma. There is residual hyperpigmentation in areas of healing, but no scarring. Skin symptoms are exacerbated by warmth and humidity; however, the disorder improves markedly with age (Bolling et al., 2018; Mohamad et al., 2018). For a discussion of genetic heterogeneity of peeling skin syndrome, see PSS1 (270300).

Aside from the clinical features of infantile cataract, skin abnormalities, and impaired intellectual development, CASGID is characterized by strikingly high intracerebral and urinary glutamate excess with almost undetectable glutamine. A gain-of-function mutation in the GLS gene was found (see MOLECULAR GENETICS) (Rumping et al., 2019). GLS loss of function is implicated in developmental and epileptic encephalopathy-71 (DEE71; 618328) and a syndrome of global developmental delay and progressive ataxia (GDPAG; 618412).

EKVP6 is characterized by erythematous hyperkeratotic plaques that develop within the first year of life, beginning on distal extremities and progressing to involve the face, wrists, and ankles, with sparing of volar surfaces. Intrafamilial variation in severity has been observed, and most affected individuals experience slowly progressive spontaneous remission after puberty (Wang et al., 2019). For a general phenotypic description and discussion of genetic heterogeneity of EKVP, see EKVP1 (133200).

Ichthyotic keratoderma, spasticity, hypomyelination, and dysmorphic features (IKSHD) is characterized by epidermal hyperproliferation and increased keratinization, resulting in ichthyosis; hypomyelination of central white matter, causing spastic paraplegia and central nystagmus; and optic atrophy, resulting in reduction of peripheral vision and visual acuity (Mueller et al., 2019). In addition, patients exhibit mild facial dysmorphism (Kutkowska-Kazmierczak et al., 2018).

Olmsted syndrome-1 (OLMS1) is a rare congenital disorder characterized by bilateral mutilating palmoplantar keratoderma (PPK) and periorificial keratotic plaques with severe pruritus of lesions. Diffuse alopecia, constriction of digits, and onychodystrophy have also been reported. Infections and squamous cell carcinomas can arise on the keratotic areas (summary by Lin et al., 2012). The digital constriction ('pseudoainhum') may progress to autoamputation of fingers and toes (Olmsted, 1927). Genetic Heterogeneity of Olmsted Syndrome Olmsted syndrome-2 (OLMS2; 619208) is caused by mutation in the PERP gene (609301) on chromosome 6q23. An X-linked form of Olmsted syndrome (OLMSX; 300918) is caused by mutation in the MBTPS2 gene (300294) on chromosome Xp22.

Olmsted syndrome-2 (OLMS2) is characterized by mutilating hyperkeratotic skin lesions, primarily on the palms and soles, but also extending onto dorsal surfaces of the hands and feet and distal extremities. The lesions are progressive, becoming thicker with verrucous fissures on the palms and soles over time. In addition, affected individuals exhibit perioral hyperkeratosis, and may have lesions around other orifices as well, such as the nostrils, perineum, and anus. Most patients also have hyperkeratotic nails and light-colored woolly hair (Duchatelet et al., 2019). Some patients may experience flexion contractures of the digits due to the severity of the keratoderma, and intractable pruritus and alopecia universalis have been observed (Dai et al., 2020). For a general phenotypic description and discussion of genetic heterogeneity of Olmsted disease, see OLMS1 (614594).

Netherton syndrome (NETH) is a rare and severe autosomal recessive skin disorder characterized by congenital erythroderma, a specific hair-shaft abnormality, and atopic manifestations with high IgE levels. Generalized scaly erythroderma is apparent at or soon after birth and usually persists. Scalp hair is sparse and brittle with a characteristic 'bamboo' shape under light microscopic examination due to invagination of the distal part of the hair shaft to its proximal part. Atopic manifestations include eczema-like rashes, atopic dermatitis, pruritus, hay fever, angioedema, urticaria, high levels of IgE in the serum, and hypereosinophilia. Life-threatening complications are frequent during the neonatal period, including hypernatremic dehydration, hypothermia, extreme weight loss, bronchopneumonia, and sepsis. During childhood, failure to thrive is common as a result of malnutrition, metabolic disorders, chronic erythroderma, persistent cutaneous infections, or enteropathy (summary by Bitoun et al., 2002).