Medical Professionals
Welcome to the EDD “Decade of Discovery and Drug Development“
Four landmark articles have been published this year in the British Journal of Dermatology, in which top experts in ichthyosis from around the world propose a new way to name the various forms of ichthyosis and related skin types. The group working on the new classification system, called the Reclassifying Epidermal Differentiation Disorders Initiative (REDDI), included 15 expert physician-scientists and two affected individuals. Over more than two years, the team met virtually and in person to achieve these landmark papers.
The new names are meant to be more accurate in their grouping than the old names of “disorders of cornification” or “disorders of keratinization” for the entire group. In addition, the new names get rid of terms that have been hurtful to people with ichthyosis, like “vulgar” in ichthyosis vulgaris, “harlequin” referring to a clown, “hystrix” meaning porcupine, or even “ichthyosis” itself which means fish.
The new naming system discards the names of people whose names tell us nothing about the skin problem (for example, Netherton syndrome).
Historically, these conditions also used names based on what the skin looked like, which led to confusing or outdated terms.
The new classification follows trends in naming of genetic issues by including the underlying gene that is affected. It also groups the disorders based on function, with the goal to find new treatments based on understanding the gene affected and how that gene change causes disease in the skin.
The authors replace the word “ichthyosis” with “epidermal differentiation disorder” or EDD, which truly encompasses all of the different types. There are three main categories:
The new names are meant to be more accurate in their grouping than the old names of “disorders of cornification” or “disorders of keratinization” for the entire group. In addition, the new names get rid of terms that have been hurtful to people with ichthyosis, like “vulgar” in ichthyosis vulgaris, “harlequin” referring to a clown, “hystrix” meaning porcupine, or even “ichthyosis” itself which means fish.
The new naming system discards the names of people whose names tell us nothing about the skin problem (for example, Netherton syndrome).
Historically, these conditions also used names based on what the skin looked like, which led to confusing or outdated terms.
The new classification follows trends in naming of genetic issues by including the underlying gene that is affected. It also groups the disorders based on function, with the goal to find new treatments based on understanding the gene affected and how that gene change causes disease in the skin.
The authors replace the word “ichthyosis” with “epidermal differentiation disorder” or EDD, which truly encompasses all of the different types. There are three main categories:
- Nonsyndromic epidermal differentiation disorders (nEDDs) affecting just the skin, hair, nails, and/or sweat glands
- Syndromic epidermal differentiation disorders (sEDDs) affecting the skin and its structure plus at least one other body system (most often the nervous system or eyes)
- Palmoplantar epidermal differentiation disorders (pEDDs) affecting mainly the palms and soles
Some of the new names are shorter (like FLG-nEDD, formerly ichthyosis vulgaris), while other names will be longer or harder to remember. Other ones that affect many in FIRST with their new names are: STS-sEDD (X-linked ichthyosis); TGM1-nEDD (most with lamellar ichthyosis); ALOX12B-nEDD (most common form of CIE); ABCA12-nEDD (harlequin ichthyosis); KRT9-pEDD (epidermolytic palmoplantar keratoderma).
These names will be more scientific to help doctors understand what causes the disease at a molecular and functional level. By classifying these conditions by the gene that is affected, doctors will be better able to counsel families about prognosis and develop more precise treatments.
The articles include an introduction to this new concept and one article on each of the three different subtypes. Each article has detailed tables with old names and new names, key features and detailed descriptions of each of the almost 150 subtypes now listed, and many photographic images to help practitioners recognize these EDDs and plan the best treatment. As such, these articles will be the new encyclopedia for ichthyosis and other similar disorders.
Clearly, the old names will be around for a while as each person has a form with a label that becomes part of one’s identity. The same is true for FIRST itself as an organization.
But during the next decade, these names will likely transition, as getting a test that tells the gene causing EDDs becomes the norm, and new individuals born with EDDs are told the new names rather than “ichthyosis”. The FIRST-associated registry has long offered free testing to find genes for FIRST members – and all are encouraged to take advantage of this offer, which simply involves providing consent to registry personnel and sending a sample of saliva. Taken together, this is an opportunity to be part of a transition that focuses on what causes the skin scaling, thickening, and redness and that will accelerate discoveries towards treatment and cure.
These names will be more scientific to help doctors understand what causes the disease at a molecular and functional level. By classifying these conditions by the gene that is affected, doctors will be better able to counsel families about prognosis and develop more precise treatments.
The articles include an introduction to this new concept and one article on each of the three different subtypes. Each article has detailed tables with old names and new names, key features and detailed descriptions of each of the almost 150 subtypes now listed, and many photographic images to help practitioners recognize these EDDs and plan the best treatment. As such, these articles will be the new encyclopedia for ichthyosis and other similar disorders.
Clearly, the old names will be around for a while as each person has a form with a label that becomes part of one’s identity. The same is true for FIRST itself as an organization.
But during the next decade, these names will likely transition, as getting a test that tells the gene causing EDDs becomes the norm, and new individuals born with EDDs are told the new names rather than “ichthyosis”. The FIRST-associated registry has long offered free testing to find genes for FIRST members – and all are encouraged to take advantage of this offer, which simply involves providing consent to registry personnel and sending a sample of saliva. Taken together, this is an opportunity to be part of a transition that focuses on what causes the skin scaling, thickening, and redness and that will accelerate discoveries towards treatment and cure.
Reference
A proposal for a new pathogenesis-guided classification for inherited epidermal differentiation disorders. Hernández-Martín Á, Paller AS, Sprecher E, et al. Br J Dermatol. Published online March 28, 2025. doi:10.1093/bjd/ljaf065s.
Nonsyndromic epidermal differentiation disorders: New classification and nomenclature based on disease-associated genes leading to targeted therapy. Akiyama M, Choate K, Hernandez-Martin A, et al. Br J Dermatol. Published online May 1, 2025. doi:10.1093/bjd/ljaf154
Syndromic epidermal differentiation disorders: New classification towards pathogenesis-based therapy. Paller AS, Teng J, Mazereeuw-Hautier J, et al. Br J Dermatol. Published online April 4, 2025. doi:10.1093/bjd/ljaf123
Palmoplantar epidermal differentiation disorders: a new classification towards pathogenesis-based therapy. Sprecher E, Ishida-Yamamoto A, Schwartz J, et al. Br J Dermatol. Published online March 19, 2025. doi:10.1093/bjd/ljaf054
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