Ichthyosis

Ichthyosis (also named fish scale disease) is a family of genetic skin disorders characterised by dry, thickened, scaly skin. The more than 20 types of ichthyosis range in severity of symptoms, outward appearance, underlying genetic cause, and mode of inheritance (e.g., dominant, recessive, autosomal, or X-linked).

Signs and Symptoms

The severity of symptoms can vary enormously, from the mildest, most common types such as ichthyosis vulgaris, which may be mistaken for normal dry skin, up to life-threatening conditions such as harlequin-type ichthyosis. Ichthyosis vulgaris accounts for more than 95% of cases. In general, ichthyosis is characterised by generalised, scaly skin which may appear dry and thickened.

Types

Many types of ichthyosis exist, and an exact diagnosis may be difficult. Types of ichthyosis are classified by their appearance, syndromic or non-syndromic nature, and mode of inheritance. Some common or well-known types include:

• Ichthyosis vulgaris: Autosomal semi-dominant, associated with the FLG gene.
• X-linked recessive ichthyosis: Associated with the STS gene.
• Harlequin ichthyosis: Autosomal recessive, linked to the ABCA12 gene.
• Lamellar ichthyosis: Autosomal recessive, involving multiple genes such as TGM1, NIPAL4, ALOX12B, among others.

Additionally, ichthyosis can be syndromic, associated with other genetic disorders, or non-genetic, such as ichthyosis acquisita.

Diagnosis

A physician often can diagnose ichthyosis by examining the skin and taking a detailed family history to determine the mode of inheritance. In some cases, a skin biopsy is done to help confirm the diagnosis, while in others, genetic testing may be necessary. Ichthyosis is more common in certain ethnic groups, including Native American, Asian, and Mongolian populations. There is no known way to prevent ichthyosis, and it can be either isolated to the skin or associated with other symptoms, such as limb reduction defects seen in CHILD syndrome.

Treatments

Treatments for ichthyosis often involve the topical application of creams and emollient oils to hydrate the skin. Creams with high percentages of urea or lactic acid are particularly effective in some cases. Propylene glycol is another treatment method. Retinoids may also be used for certain conditions.

Sunlight exposure may improve or worsen the condition. In some cases, excess dead skin sloughs off better from wet tanned skin after bathing or swimming, though the risk of sun damage must be considered.

Ocular manifestations of ichthyosis, such as corneal and ocular surface diseases, may occur. Vascularizing keratitis, which is more commonly found in congenital keratitis-ichthyosis-deafness (KID), may worsen with isotretinoin therapy.

Ichthyosis in Other Animals

Ichthyosis or ichthyosis-like disorders are also documented in several types of animals, including cattle, chickens, llamas, mice, and dogs. In dogs, ichthyosis is prevalent in breeds such as Golden Retrievers, American bulldogs, Jack Russell terriers, and Cairn terriers.

---

Self-assessment MCQs (single best answer)

What is the defining feature of all forms of ichthyosis?

Ichthyosis vulgaris is associated with which gene?

Which type of ichthyosis is autosomal recessive and linked to the ABCA12 gene?

What percentage of ichthyosis cases does ichthyosis vulgaris account for?

Which of the following is not a common treatment for ichthyosis?

Which type of ichthyosis is associated with the STS gene?

Which ethnic groups are more commonly affected by ichthyosis?

What is another name for ichthyosis?

Which of the following animal breeds is not commonly affected by ichthyosis?

Which treatment is particularly effective in hydrating the skin for ichthyosis patients?