Ichthyosis is the term used for a family of skin conditions that are characterized by a thickened stratum corneum and/or visible scales covering most or all of the body surface. Most ichthyoses are inherited – yet paradoxically, often people with ichthyosis know of no one else in their families with their condition. This can happen if the genetic change that produces the skin condition began with them – that is, if it was a new mutation. It can also happen in those forms that have a recessive inheritance. Recessive conditions are those that require that both copies of a gene, (both copy of the gene inherited from the mother and the one from the father), to be mutated before the condition manifests.
The genetic forms of ichthysosis vary from relatively common (~1 in 250 persons) to rare. Many people who have severe dry skin may indeed have a form called ichthyosis vulgaris. And in some of the rarer inherited types, other organs of the body may be affected, as well. Sometimes ichthyosis is not inherited, but is ‘acquired’, meaning that it is due to some other medical condition, or is caused by a medication or a dietary deficiency. Most of the inherited forms of ichthyosis begin early in life, while those due to acquired causes may not appear until later on. A consultation with a dermatologist is recommended for those who think they may have one of these types of skin disorders.
The scaling in ichthyosis is often most prominent over the lower legs.Over 40 genes have been discovered that can cause ichthyosis. The study of these genes and what they do has been invaluable to our understanding of how skin normally sheds – the process of desquamation – and why dry skin looks ashy or flaky. They have also helped us to understand how the skin’s permeability barrier operates.