Superficial Epidermolytic Ichthyosis
|Disease group||Keratinization disorder|
|DISEASE NAME||SUPERFICIAL EPIDERMOLYTIC ICHTHYOSIS|
|Synonymous||Ichthyosis Bullosa of Siemens, Ichthyosis exfoliativa|
|Estimated prevalence||< 1 / 1 000 000|
|Gene (s)||KRT2 (600194)|
In a consensus conference in 2009, a new classification system and terminology has been established for ichthyoses . Ichthyoses are determined as Mendelian disorders of cornification (MeDOC) that are characterized by universal scaling of the skin. In two main categories, non-syndromic forms (phenotype restricted to the skin) are distinguished from syndromic forms (involvement of other organs). A further distinction is made between common and rare forms. Within the non-syndromic forms the term keratinopathic ichthyosis is used to describe all forms of ichthyosis that are based on mutations in keratin genes. They manifest at birth and sometimes involve blistering [2, 3].
Superficial epidermolytic ichthyosis (SEI), formerly know as Ichthyosis bullosa of Siemens (IBS), is a rare keratinization disorder with superficial peeling. Although hyperkeratotic, the skin is unusually fragile and has tendency to shed the outer layers of the epidermis, producing localized denuded areas.
The clinical features of SEI are similar but milder to that of epidermolytic ichthyosis (EI) (formerly known as “Brocq). SEI infants are born with erythema and widespread blistering which persists during infancy or early childhood in response to trauma, heat or excessive sweating. Blistering improves with increasing age, becoming more localized to the acral extremities, leading to superficial erosions with peripheral scales. Superficial peeling of the skin, described by Siemens in 1937 as "mauserung" or "moulting effect" is characteristic . Grey or brown hyperkeratosis appears on arms and legs, and when improving with age, hyperkeratosis and lichenification becomes limited to flexural areas. Although erythema are seen in infancy, erythroderma had never been observed in any of the affected patients. Skin lesions are localized especially at the extensor surfaces of the arms and legs (wrist, elbows, knee, ankle) as well as the periumbilical region, buttocks and palms and soles [5, 6].
Mutations in the KRT2 gene at locus 12q13.13 are made responsible for SEI [7, 8] (According to HGCN, the abbreviation “KRT2E” should not be used any more). The majority of mutations affect the helix termination motif of KRT2, and hot spot mutations in the 1A and 2B domain of KRT2 have been identified molecularly [8, 9]. Expression of KRT2 is restricted to the upper epidermis, more prominent in the skin of palms and soles and extensor surfaces, consistent with the clinical distribution of the disease. As with other keratin defects, the formation of the keratin cytoskeleton is impaired, resulting in structural fragility.
In general, differential diagnosis of MeDOC should include the following clinical criteria: 1) the type of scaling and hyperkeratosis; 2) the onset and evolution of skin changes over time; 3) other dermatologic features and the involvement of other organ systems; 4) the family history/mode of inheritance .
In the case of SEI, the diagnosis is based on the association of hyperkeratosis with superficial blistering. Patients typically show dark, gray hyperkeratotic lesions with superficial denuded areas. SEI closely resembles EI. It should also be differentiated from ichthyosis hystrix of Curth-Macklin, in which hyperkeratosis is more verrucous and lacks epidermal fragility. Ultrastructural analysis in SEI shows aggregates of keratin filament bundles in the granular and the upper spinous layers .
Treatment is symptomatic. Keratolytics and emollients can be used to treat hyperkeratosis. Low dose oral retinoids can be helpful, but should be used with caution.
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Rothnagel JA, Traupe H, Wojcik S, Huber M, Hohl D, Pittelkow MR, Saeki H, Ishibashi Y, Roop DR. (1994) Mutations in the rod domain of keratin 2e in patients with ichthyosis bullosa of Siemens. Nat Genet 7:485-490.
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