Congenital disorders of glycosylation (CDGs) are metabolic deficiencies in glycoprotein biosynthesis that usually cause severe mental and psychomotor retardation. Different forms of CDGs can be recognized by altered isoelectric focusing (IEF) patterns of serum transferrin. For a general discussion of CDGs, see CDG Ia (212065) and CDG Ib (602579).

The Curth-Macklin type of ichthyosis hystrix (IHCM) is clinically characterized by severe fissuring and mutilating palmoplantar keratoderma. Affected individuals also exhibit extensive dark spiky or verrucous hyperkeratotic plaques over the large joints and trunk, which in some patients may cover almost the entire body. Structural and ultrastructural hallmarks include compact orthokeratotic hyperkeratosis, hypergranulosis with perinuclear edema, binucleated cells, and formation of perinuclear filamentous shells composed of feathery entangled keratin intermediate filaments (summary by Richardson et al., 2006 and Fonseca et al., 2013). The Lambert type of ichthyosis hystrix (IHL; 146600), in which palms and soles are spared, is caused by mutation in the KRT10 (148080) gene.

A rare clinical variant of epidermolytic ichthyosis, with manifestations of blistering phenotype at birth and the development from early infancy of annular polycyclic erythematous scales on the trunk and extremities. It has been reported in less than 10 families. The disease is caused by mutations in the KRT1 (12q11-q13) and KRT10 (17q21-q23) genes, encoding keratins 1 and 10 respectively. These mutations impair keratin filament formation and weaken the structural stability of the keratinocyte cytoskeleton. Transmission is autosomal dominant.

A group of rare autosomal recessive forms of ichthyosis with clinical characteristics of superficial, asymptomatic, spontaneous peeling of the skin and histologically by a shedding of the outer layers of the epidermis. Presents with either an acral or a generalised distribution.

Epidermolysis bullosa simplex (EBS) is characterized by fragility of the skin (and mucosal epithelia in some instances) that results in non-scarring blisters and erosions caused by minor mechanical trauma. EBS is distinguished from other types of epidermolysis bullosa (EB) or non-EB skin fragility syndromes by the location of the blistering in relation to the dermal-epidermal junction. In EBS, blistering occurs within basal keratinocytes. The severity of blistering ranges from limited to hands and feet to widespread involvement. Additional features can include hyperkeratosis of the palms and soles (keratoderma), nail dystrophy, milia, and hyper- and/or hypopigmentation. Rare EBS subtypes have been associated with additional clinical features including pyloric atresia, muscular dystrophy, cardiomyopathy, and/or nephropathy.

Immunodeficiency-41 is an autosomal recessive complex disorder of immune dysregulation. Affected individuals present in infancy with recurrent viral, fungal, and bacterial infections, lymphadenopathy, and variable autoimmune features, such as autoimmune enteropathy and eczematous skin lesions. Immunologic studies show a defect in T-cell regulation (summary by Goudy et al., 2013).

Ectodermal dysplasia/skin fragility syndrome (EDSFS) is an autosomal recessive genodermatosis characterized by widespread skin fragility, alopecia, nail dystrophy, and focal keratoderma with painful fissures. Hypohidrosis and cheilitis are sometimes present (summary by Ersoy-Evans et al., 2006).

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

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.

Most characteristically, Aicardi-Goutières syndrome (AGS) manifests as an early-onset encephalopathy that usually, but not always, results in severe intellectual and physical disability. A subgroup of infants with AGS present at birth with abnormal neurologic findings, hepatosplenomegaly, elevated liver enzymes, and thrombocytopenia, a picture highly suggestive of congenital infection. Otherwise, most affected infants present at variable times after the first few weeks of life, frequently after a period of apparently normal development. Typically, they demonstrate the subacute onset of a severe encephalopathy characterized by extreme irritability, intermittent sterile pyrexias, loss of skills, and slowing of head growth. Over time, as many as 40% develop chilblain skin lesions on the fingers, toes, and ears. It is becoming apparent that atypical, sometimes milder, cases of AGS exist, and thus the true extent of the phenotype associated with pathogenic variants in the AGS-related genes is not yet known.

ISQMR is a severe autosomal recessive disorder characterized by ichthyosis apparent from birth, profound psychomotor retardation with essentially no development, spastic quadriplegia, and seizures (summary by Aldahmesh et al., 2011).

Ichthyosis with confetti (IWC), also known as congenital reticular ichthyosiform erythroderma (CRIE), is a rare skin condition characterized by slowly enlarging islands of normal skin surrounded by erythematous ichthyotic patches in a reticulated pattern. The condition starts in infancy as a lamellar ichthyosis, with small islands of normal skin resembling confetti appearing in late childhood and at puberty. Histopathologic findings include band-like parakeratosis, psoriasiform acanthosis, and vacuolization of keratinocytes with binucleated cells in the upper epidermis, sometimes associated with amyloid deposition in the dermis. Ultrastructural abnormalities include perinuclear shells formed from a network of fine filaments in the upper epidermis (summary by Krunic et al., 2003).

A rare genetic skin disease characterized by generalized skin peeling, leukonychia, acral punctate keratoses coalescing into focal keratoderma on the weight-bearing areas, angular cheilitis and knuckle pads with multiple hyperkeratotic micropapules. The skin appears dry and scaly with superficial exfoliation and underlying erythema. Histopathologic examination of affected skin areas shows hyperkeratosis, acanthosis and intraepidermal clefting with irregular acantholysis. Additional systemic abnormalities are absent.

Any peeling skin syndrome in which the cause of the disease is a mutation in the CSTA gene.

Peeling skin syndrome-5 (PSS5) is characterized by superficial peeling of the dorsal and palmar skin of the hands and feet; the skin of the forearms and legs may also be involved. Some patients exhibit diffuse yellowish hyperkeratotic palmoplantar plaques (Pigors et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of peeling skin syndrome, see PSS1 (270300).

In all forms of PLCA, the abnormal patches of skin usually arise in mid-adulthood. They can remain for months to years and may recur after disappearing, either at the same location or elsewhere. Very rarely, nodular amyloidosis progresses to a life-threatening condition called systemic amyloidosis, in which amyloid deposits accumulate in tissues and organs throughout the body.\n\nIn some affected individuals, the patches have characteristics of both lichen and macular amyloidosis. These cases are called biphasic amyloidosis.\n\nNodular amyloidosis is characterized by firm, raised bumps (nodules) that are pink, red, or brown. These nodules often occur on the face, torso, limbs, or genitals and are typically not itchy.\n\nIn macular amyloidosis, the patches are flat and dark brown. The coloring can have a lacy (reticulated) or rippled appearance, although it is often uniform. Macular amyloidosis patches are most commonly found on the upper back, but they can also occur on other parts of the torso or on the limbs. These patches are mildly itchy.\n\nLichen amyloidosis is characterized by severely itchy patches of thickened skin with multiple small bumps. The patches are scaly and reddish brown in color. These patches usually occur on the shins but can also occur on the forearms, other parts of the legs, and elsewhere on the body.\n\nPrimary localized cutaneous amyloidosis (PLCA) is a condition in which clumps of abnormal proteins called amyloids build up in the skin, specifically in the wave-like projections (dermal papillae) between the top two layers of skin (the dermis and the epidermis). The primary feature of PLCA is patches of skin with abnormal texture or color. The appearance of these patches defines three forms of the condition: lichen amyloidosis, macular amyloidosis, and nodular amyloidosis.

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).

Immunodeficiency-58 is an autosomal recessive primary immunologic disorder characterized by early-onset skin lesions, including eczematous dermatitis, infectious abscesses, and warts, recurrent respiratory infections or allergies, and chronic persistent infections with candida, Molluscum contagiosum, mycobacteria, EBV, bacteria, and viruses. Some patients may have gastrointestinal involvement, including inflammatory bowel disease, EBV+ smooth muscle tumors, and esophagitis. Immunologic analysis shows defective T-cell function with decreased Treg cells and deficient CD3/CD28 costimulation responses in both CD4+ and CD8+ T cells. B-cell function may also be impaired (summary by Wang et al., 2016 and Alazami et al., 2018).

CAPOK syndrome (CAPOK) is characterized by onset of symptoms in the first year of life, with the development of progressive alopecia, hypo- and hyperpigmented macular skin lesions, palmoplantar keratoderma, and nail dystrophy. Beginning in the third decade of life, patients develop recurrent squamous cell carcinomas. Some patients may have brittle teeth resulting in tooth loss, and multinodular goiter has been observed (Courcet et al., 2015).

Myoectodermal gonadal dysgenesis syndrome (MEGD) is characterized by 46,XY complete or partial gonadal dysgenesis, or 46,XX gonadal dysgenesis, in association with extragonadal anomalies, including low birth weight, typical facies, rod and cone dystrophy, sensorineural hearing loss, omphalocele, anal atresia, renal agenesis, skeletal abnormalities, dry and scaly skin, severe myopathy, and neuromotor delay. Dysmorphic facial features along with muscular habitus are the hallmarks of the syndrome. Abnormal hair patterning with frontal upsweep and additional whorls, eyebrow abnormalities comprising broad, arched, and sparse or thick eyebrows, underdeveloped alae nasi, smooth philtrum, and low-set ears with overfolded helices facilitate a gestalt diagnosis. (Guran et al., 2019; Altunoglu et al., 2022).

The IFAP/BRESHECK syndrome is an X-linked multiple congenital anomaly disorder with variable severity. The classic triad, which defines IFAP, is ichthyosis follicularis, atrichia, and photophobia. Some patients have additional features, including mental retardation, brain anomalies, Hirschsprung disease, corneal opacifications, kidney dysplasia, cryptorchidism, cleft palate, and skeletal malformations, particularly of the vertebrae, which constitutes BRESHECK syndrome (summary by Naiki et al., 2012). Genetic Heterogeneity of IFAP Syndrome IFAP syndrome-2 (IFAP2; 619016) is caused by heterozygous mutation in the SREBF1 gene (184756) on chromosome 17p11.

Neurodevelopmental disorder with hypotonia and dysmorphic facies (NEDHYDF) is characterized by global developmental delay and hypotonia apparent from birth. Affected individuals have variably impaired intellectual development, often with speech delay and delayed walking. Seizures are generally not observed, although some patients may have single seizures or late-onset epilepsy. Most patients have prominent dysmorphic facial features. Additional features may include congenital cardiac defects (without arrhythmia), nonspecific renal anomalies, joint contractures or joint hyperextensibility, dry skin, and cryptorchidism. There is significant phenotypic variability in both the neurologic and extraneurologic manifestations (summary by Tan et al., 2022).

A restrictive dermopathy that has material basis in homozygous or compound heterozygous mutation in the ZMPSTE24 gene on chromosome 1p34.

Annular epidermolytic ichthyosis-2 (AEI2) is characterized by erythema and blistering of skin at birth that improves without scarring, as well as palmoplantar keratoderma. Some patients experience intermittent severe flares of generalized annular and polycyclic erythematous scaling plaques (Sybert et al., 1999; Zaki et al., 2018). For a discussion of genetic heterogeneity of AEI, see AEI1 (607602).

Epidermolytic hyperkeratosis-1 (EHK1) is a rare autosomal dominant disorder of cornification. The disorder usually presents at birth with erythema and blistering and is characterized in adulthood by warty flexural hyperkeratosis with fewer erosions and blisters. Ultrastructural analysis reveals clumping of the intermediate filaments within keratinocytes of the spinous and granular layers (summary by Whittock et al., 2001). A form of epidermolytic hyperkeratosis that is limited to the palms and soles, designated palmoplantar keratoderma (EPPK; 144200), can also be caused by mutation in KRT1, as well KRT9 (607606). Genetic Heterogeneity of Epidermolytic Hyperkeratosis Mutation in the KRT10 gene (148080) results in both autosomal dominant (EHK2A; 620150) and autosomal recessive (EHK2B; 620707) forms of epidermolytic hyperkeratosis.

RECON progeroid syndrome (RECON) is a chromosomal instability disorder characterized by postnatal growth retardation, progeroid facial appearance, hypoplastic nose, prominent premaxilla, skin photosensitivity and xeroderma, muscle wasting with reduced subcutaneous fat, and slender elongated thumbs (Abu-Libdeh et al., 2022).