Ichthyosis vulgaris is a common, chronic skin condition characterized by dry, scaly skin. The name “ichthyosis” comes from the Greek word for fish, reflecting the fish-like scales that appear on the skin. It is the most common type of ichthyosis, affecting approximately 1 in 250 to 300 people globally. Many individuals with milder forms may perceive their condition as unusual dry skin, often leading to it going undiagnosed.
The Genetic Basis
The primary cause of inherited Ichthyosis Vulgaris lies in mutations within the filaggrin (FLG) gene. This gene provides instructions for creating a protein called profilaggrin, which is later processed into multiple filaggrin units. Filaggrin is a protein found in the outermost layer of the skin, the stratum corneum, where it binds keratin fibers to maintain a strong skin barrier and proper hydration.
Loss-of-function mutations in the FLG gene lead to defective or reduced production of filaggrin. This deficiency impairs the skin’s ability to form an effective barrier, compromising natural moisturizing factors and leading to excessive water loss. This results in the characteristic dryness and scaling observed in Ichthyosis Vulgaris.
How It Is Passed Down
The genetic form of Ichthyosis Vulgaris is inherited in an autosomal dominant pattern. This means a person only needs one copy of the mutated FLG gene from a single parent to develop the condition. Inheritance is often “semidominant,” where one mutated gene results in a milder form, while two mutated genes (one from each parent) can lead to more moderate to severe symptoms.
While inheritance from a parent is the most common way to acquire the genetic form, Ichthyosis Vulgaris can also arise from a spontaneous gene mutation. In such rare cases, the mutation occurs during fetal development, meaning neither parent carries the altered gene.
When It Is Not Inherited
Beyond the genetic forms, Ichthyosis Vulgaris can also develop later in life, a condition known as acquired ichthyosis vulgaris. This form is not due to inherited genetic mutations but appears as a symptom of an underlying medical condition or a side effect of certain medications. The onset typically occurs in adulthood.
Various systemic diseases can trigger acquired ichthyosis. These include certain types of cancer, such as Hodgkin lymphoma, non-Hodgkin lymphoma, multiple myeloma, and carcinomas of the lung, breast, and liver. Other medical conditions associated with acquired ichthyosis include HIV infection, sarcoidosis, hypothyroidism, chronic kidney failure, and autoimmune disorders like systemic lupus erythematosus. Additionally, some medications, such as nicotinic acid, cimetidine, allopurinol, and hydroxyurea, have been reported to induce acquired ichthyosis. The skin changes may even appear before other signs of the underlying disease, prompting further medical investigation.
The Skin’s Barrier Dysfunction
The causes of Ichthyosis Vulgaris, whether genetic or acquired, ultimately lead to a compromised skin barrier. This epidermal barrier, the outermost protective layer, normally prevents excessive water loss and blocks environmental irritants.
When the skin barrier is defective, it results in increased transepidermal water loss (TEWL), leading to skin dehydration. The impaired barrier function also causes skin cells to not shed normally, leading to an accumulation of dead skin cells. This abnormal shedding and retention of corneocytes contribute to the characteristic dry, scaly, and sometimes thickened appearance of the skin in Ichthyosis Vulgaris.