Ichthyosis (plural ichthyoses) is a heterogeneous family of at least 28, generalized, mostly genetic skin disorders.
All types of ichthyosis have dry, thickened, scaly or flaky skin. In many types there is cracked skin, which is said to resemble the scales on a fish; the word ichthyosis comes from the Ancient Greek ἰχθύς (ichthys), meaning “fish.”
The severity of symptoms can vary enormously, from the mildest, most common, type such as ichthyosis vulgaris which may be mistaken for normal dry skin up to life-threatening conditions such as harlequin type ichthyosis. Ichtyosis vulgaris accounts for more than 95% of cases.
There are many types of ichthyoses and an exact diagnosis may be difficult. Types of ichthyoses are classified by their appearance and their genetic cause. Ichthyosis caused by the same gene can vary considerably in severity and symptoms. Some ichthyoses do not appear to fit exactly into any one type. Also different genes can produce ichthyoses with similar symptoms. Of note, X-linked ichthyosis is associated with Kallmann syndrome (close to KAL1 gene)