SNP Shot: Genomic Insights

An epidermal nevus (plural: nevi) is a harmless, non-cancerous skin growth. It appears as an unusual skin patch due to an excessive amount of cells in the skin's outer layer, called the epidermis. These nevi typically appear at birth or during early childhood. Individuals affected by this condition may have one or more nevi that differ in size.

Epidermal nevi are classified into several types depending on which epidermal cell is affected. Keratinocytes, a specific type of cell, are the primary component of the epidermis. Keratinocytic or nonorganoid epidermal nevi are a group of epidermal nevi that involve only keratinocytes. Commonly found on the torso or limbs, these nevi can present as flat, tan or brown patches or raised, velvety areas. As people age, these nevi can thicken, darken, and develop a wart-like (verrucous) texture. Often, keratinocytic epidermal nevi follow a specific pattern on the skin known as the lines of Blaschko. These lines, normally invisible, are believed to represent the pathways of cell migration during skin development before birth. Keratinocytic epidermal nevi are also known as linear epidermal nevi or verrucous epidermal nevi, terms which describe their appearance.

Other types of epidermal nevi involve different kinds of epidermal cells, such as those found in hair follicles, sweat glands, or sebaceous glands (skin glands that produce protective oil). These are classified as organoid epidermal nevi. A common type of organoid epidermal nevus is nevus sebaceous. These nevi appear as waxy, yellow-orange patches, usually on the scalp or face. The affected area is often hairless, leading to a bald spot (alopecia). Similar to keratinocytic epidermal nevi, nevus sebaceous can thicken and become more verrucous over time. In approximately 25% of individuals with nevus sebaceous, a tumor develops in the same area. While these tumors are usually benign, there is a rare chance they can be cancerous (malignant).

Some individuals only experience the epidermal nevus itself without any other health issues. However, in some cases, people with an epidermal nevus may also have problems in other organs and systems, such as the brain, eyes, or bones. When this occurs, the individual is diagnosed with an epidermal nevus syndrome. Several different epidermal nevus syndromes exist, each characterized by the specific type of epidermal nevus involved.

Inheritance:

This condition is generally not inherited. Instead, it arises from new mutations within the body's cells after conception, called somatic mutations. In rare instances, a somatic mutation in the FGFR3 gene can occur in a parent's reproductive cells (sperm or eggs) and be passed on to their child. When this happens, the gene mutation is present in every cell of the child's body, leading to skeletal abnormalities rather than an epidermal nevus.