Types of Ichthyosis
Common and Distinctive Types of Ichthyosis
The types of ichthyosis descriptions listed here and throughout FIRST's website are not intended to be comprehensive nor to take the place of consultations with your own physician. The most common or distinctive types of ichthyosis and related disorders of keratinization are listed, and their most characteristic features are outlined. For those who want more complete (and generally more technical) information, links are provided to the Online Mendelian Inheritance in Man (OMIM), a database that lists all known inherited disorders.
Several general comments about the format and content of this page are important to note:
Ichthyosis currently is classified on the basis of clinical appearance and inheritance pattern. This system, which is used on the following pages and relies on few sophisticated tools and tests, has worked remarkably well for diagnosing and classifying most patients with ichthyosis.
This may change in the future for several reasons. First, many individuals with ichthyosis are the first or only members of their family with ichthyosis; in those cases, inheritance pattern cannot be directly confirmed. Second, clinical appearance is not always a reliable indicator of the cause of the ichthyosis. For example, no two people with the same disease look quite the same.
Disease severity can vary significantly among individuals who have been given the same diagnosis and who have mutations in the same gene.
By contrast, some people whose ichthyosis looks very similar actually have mutations in different genes and, thus, the cause of their ichthyosis is different. Lastly, some individuals have clinical features that do not permit easy assignment to existing categories or diagnoses. In the future, an individual's personal genetic makeup (their genetic diagnosis) will become increasingly important in the diagnosis, classification and prognostication for that individual.
Different names have been used over the years to describe individuals who we now believe had the same disease. Names commonly used in Europe are not always the same as the names used in the United States. We've chosen names that are commonly used in the United States. A list of other names for each diagnosis is included.
The forms of ichthyosis listed here are all thought to be inherited. Inheritance refers to the usual pattern of passing the particular form of ichthyosis from one generation to the next. Sometimes there may be only one affected person in the family. This can happen if the individual possesses a new or "founder" mutation, or if the gene for his/her disease is recessively inherited. Consult your doctor if you have questions about inheritance of a particular form of ichthyosis. Some people have late-onset, acquired ichthyosis that is not inherited and is a manifestation of other diseases or conditions. Information about acquired ichthyosis is not included here and can be obtained from your dermatologist.
Incidence figures are only best guesses, because all of these diseases are relatively rare. This number is the likelihood of seeing a particular form of ichthyosis in a given number of live births. If no number is given, the incidence is probably lower than one per million.
- Key Findings
All forms of ichthyosis include dry, rough, scaly skin. Key findings are the most characteristic and constant changes found in the skin. The presence and frequency of findings in other parts of the integument, such as hair or nails, are mentioned only when they are thought to have the same cause as the ichthyosis.
- Associated Findings
Most forms of ichthyosis have clinical findings limited to the skin. There are some types of ichthyosis, however, where there are associated findings in organ systems other than the skin. These findings are thought to be caused by the same genetic abnormality that is responsible for the ichthyosis. The nature and frequency of such associated findings is given in this section.
- Age at First Appearance
Each type of ichthyosis has a characteristic age at first appearance. Some forms of ichthyosis are present at birth, others appear later in childhood.
- Long Term Course
Sometimes an individual's ichthyosis will change over time. We use long term course to give information about whether the skin problem customarily improves or worsens and whether particular attention should be paid to the possible development of associated problems.
- Diagnostic Tests
Diagnostic tests include skin biopsies or blood tests that give an unequivocal diagnosis. They are available for some, but not all, types of ichthyosis.
- Abnormal Gene
A genetic abnormality is present in all types of ichthyosis, but the abnormal gene has not yet been identified for all forms of ichthyosis. When known, the name of the protein coded by the abnormal gene is given.