Epidermal naevi Epidermal naevi are due to an overgrowth of the epidermis (upper layers of the skin). Lesions are present at birth (50%) or develop during childhood (mostly in the first year of life). The abnormality arises from a defect in the ectoderm. This is the outer layer of the embryo that gives rise to epidermis and neural tissue. Types of epidermal naevi The skin lesions most often referred to as epidermal naevi are due to an overgrowth of keratinocytes (horny skin cells). Linear epidermal naevus Epidermolytic epidermal naevus Acantholytic epidermal naevus Linear porokeratosis Systematised epidermal naevus However, several other conditions are also characterised by benign overgrowth of the epidermis and its appendages (organoid naevi): Inflammatory linear verrucous epidermal naevus (ILVEN) Sebaceous naevus Sweat gland naevi Comedone naevus Becker naevus What causes epidermal naevi? There are two copies of every gene, one derived from the individuals mother and the other from their father. It is thought that there are two populations of skin cells, containing either the mothers genes or the fathers genes (mosaicism). If one of these populations of skin cells is abnormal it results in localised areas of thickened skin. Luckily, epidermal naevi very rarely affect more than one member of the family. Epidermal naevi are distributed along the lines of Blashko. These lines are the tracks taken by groups of genetically identical cells in the developing embryo. Skin cells that have the active abnormal gene spread out to form the epidermal naevus, whereas the remaining skin cells form the other areas of apparently normal skin.
Posted on: Tue, 21 Oct 2014 08:51:21 +0000
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