Types of Ichthyosis

Common Ichthyosis

Common ichthyoses are, as the name suggests, the most frequent types of ichthyosis among the population. That is, they are those whose prevalence (appearance) is higher. Its diagnosis is mild.

In the case of vulgar or common ichthyosis, it is estimated that 1 in 250 people may have it. In fact, due to its high rate of occurrence, it is not considered a rare disease in Europe.

X-linked recessive ichthyosis (non-syndromic) is considered a rare disease because, although it appears more frequently than other types, only 1 in 2,000-6,000 people might have it.

Recessive Autosomal Ichthyosis

Autosomal Recessive Ichthyosis (also called ARCI by its English acronym) are a type of ichthyosis characterized by being inherited by offspring from parents, provided that two anomalous genes are present.
So, it is necessary that both parents have the damaged gene to transmit the disease. That is why the degree of prevalence is much lower than in the case of common ichthyosis.

In this variant there is no common clinical diagnosis. The ARCI includes very severe cases, such as harlequin ichthyosis, and mild cases such as the baby self-resolving collodion or acral self-resolving, two types that can have almost complete resolution during the first three months of life.

Despite this, all ARCIs are considered a rare disease due to the low rate of occurrence of cases.

Keratinopathic Ichthyosis

Keratinopathic ichthyosis are all rare diseases since, with the exception of epidermolytic ichthyosis, which has a somewhat higher frequency – 1 case per 250,000-350,000 births – the rest has a prevalence of 1 per million people.

Unlike Autosomal Recessive ichthyosis, keratinopathic ichthyosis does not require the parents to have an anomalous gene each, it is enough that one of them is dominant to transmit the disease, which is known as autosomal dominant inheritance.

Regarding the diagnosis, this is also very varied, the most severe of them all is epidermolytic ichthyosis.

Other forms

Erythroderma variabilis and congenital reticular ichthyosiform, loricrin keratoderma, and exfoliated skin and Klick syndromes are types of ichthyosis that cannot be included in the previous categories but that also belong to the family of non-syndromic ichthyosis, that is, ichthyosis that have no syndromes or pathologies associated with other organs of the body other than the skin.

All of them are rare diseases with a prevalence of 1 case per million births or even higher.

Although all of them usually appear from the moment of birth, their diagnosis and evolution is different in each of the types.

X-linked Syndromic Ichthyosis

X-linked syndromic ichthyosis are those types of ichthyosis that, in addition to having other associated pathologies that affect organs other than the skin, are transmitted through the mother’s genetic load (X gene) and usually affect mainly males.

Its diagnosis ranges from moderate to severe and its prevalence rate is very uneven.

Syndromic X-linked recessive ichthyosis has a prevalence of 1 in 2,000-6,000 births, while Conradi-Hünermann-Happle syndrome is 1 in 400,000, and IFAP is so rare that it is even unknown.

Autosomal Syndromic Ichthyosis

Autosomal ichthyosis encompasses more than 10 variants of the disease. All of them are characterized by two things:

  • They affect other organs besides the skin.
  • Its appearance is due to an autosomal recessive inheritance, that is, to present the disease it is necessary that both parents have an anomalous gene in their DNA.

Within the family of the autosomal recessive syndromic ichthyosis, we can divide them into:

  • Those that are linked to hair disorders, as the case of Netherton syndrome
  • Those that are linked to neurological disorders, such as Sjögren-Larrson syndrome
  • Those that due to their extreme severity are lethal (with a life expectancy of between 1 and 10 years).
  • Other types with a prevalence of less than 1 case per million births.

All of them are rare diseases.