The Appearance of the Skin in Ichthyosis
Because of the multiplicity of genes involved in the ichthyoses, it is not surprising that there are differences
in outward appearance. Sometimes the entire body surface is involved (e.g., LI/CIE), while in others (IV, XLI) the face and folds of the body may not be involved. The scales tend to be dark and coarse in some (e.g., LI), while in others (e.g., CIE, IV) they may be finer and lighter in color. In EI (formerly called EHK) the scales often have a ridged or even spiny character, and this can be especially apparent in body folds or over joints. Skin fragility and formation of blisters can also occur in EHK. Sometimes the skin under the scales is very red (erythrodermic); this is especially common in Harlequin ichthyosis and CIE, but may also be seen in EI and Netherton syndrome, and others. The correlations between genetic causes and clinical results (genotype-phenotype  correlations) are still being worked out for several of the ichthyosis families, especially LI/CIE.
The appearance of the skin in a newborn infant with ichthyosis is often quite different from how the child will look later on. This is because the fetus is immersed in amniotic fluid, an environment that imposes different demands on the stratum corneum from those following exposure to a dry atmosphere at birth. Some infants are encased in very thick, constrictive scales (e.g., Harlequin ichthyosis), while others have a taut, shiny, “shellaced” appearance, the so-called “collodion baby”. In both instances the tight skin may pull the eyelids open (ectropion) and the lips outward (eclabion). During the first weeks of life these thickened scales or “membranes” are shed, and the mature pattern gradually develops. Many types of ichthyosis may begin as a collodion baby, but LI/CIE is most common. Other types of ichthyosis may begin with generalized erythroderma (e.g., Netherton syndrome), or with exaggerated peeling or desquamation shortly after birth (e.g., XLI, Sjögren-Larsson syndrome). IV typically is not present until later in infancy or childhood. In contrast to all of these, in EI the newborn often presents with widespread blistering and denuded skin, rather than scaling.
 Genotype is the term that refers to the specific genetic composition or mutation. Phenotype refers to the effect of that genotype on the individual, for example, the appearance of the skin in a person with ichthyosis.
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