Large Congenital Melanocytic Nevus (GMN)

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MedlinePlus Genetics: ⁴² Giant congenital melanocytic nevus is a skin condition characterized by an abnormally dark, noncancerous skin patch (nevus) that is composed of pigment-producing cells called melanocytes. It is present from birth (congenital) or is noticeable soon after birth. The nevus may be small in infants, but it will usually grow at the same rate the body grows and will eventually be at least 40 cm (15.75 inches) across. The nevus can appear anywhere on the body, but it is more often found on the trunk or limbs. The color ranges from tan to black and can become darker or lighter over time. The surface of a nevus can be flat, rough, raised, thickened, or bumpy; the surface can vary in different regions of the nevus, and it can change over time. The skin of the nevus is often dry and prone to irritation and itching (dermatitis). Excessive hair growth (hypertrichosis) can occur within the nevus. There is often less fat tissue under the skin of the nevus; the skin may appear thinner there than over other areas of the body.People with giant congenital melanocytic nevus may have more than one nevus (plural: nevi). The other nevi are often smaller than the giant nevus. Affected individuals may have one or two additional nevi or multiple small nevi that are scattered over the skin; these are known as satellite or disseminated nevi.Affected individuals may feel anxiety or emotional stress due to the impact the nevus may have on their appearance and their health. Children with giant congenital melanocytic nevus can develop emotional or behavior problems.Some people with giant congenital melanocytic nevus develop a condition called neurocutaneous melanosis, which is the presence of pigment-producing skin cells (melanocytes) in the tissue that covers the brain and spinal cord. These melanocytes may be spread out or grouped together in clusters. Their growth can cause increased pressure in the brain, leading to headache, vomiting, irritability, seizures, and movement problems. Tumors in the brain may also develop.Individuals with giant congenital melanocytic nevus have an increased risk of developing an aggressive form of skin cancer called melanoma, which arises from melanocytes. Estimates vary, but it is generally thought that people with giant congenital melanocytic nevus have a 5 to 10 percent lifetime risk of developing melanoma. Melanoma commonly begins in the nevus, but it can develop when melanocytes that invade other tissues, such as those in the brain and spinal cord, become cancerous. When melanoma occurs in people with giant congenital melanocytic nevus, the survival rate is low.Other types of tumors can also develop in individuals with giant congenital melanocytic nevus, including soft tissue tumors (sarcomas), fatty tumors (lipomas), and tumors of the nerve cells (schwannomas).

MalaCards based summary: Large Congenital Melanocytic Nevus, also known as giant pigmented hairy nevus, is related to nevus, epidermal and eye disease. An important gene associated with Large Congenital Melanocytic Nevus is NRAS (NRAS Proto-Oncogene, GTPase), and among its related pathways/superpathways are Translation Translation regulation by Alpha-1 adrenergic receptors and MAP Kinase Signaling. Affiliated tissues include skin, spinal cord and brain, and related phenotypes are congenital giant melanocytic nevus and generalized hirsutism

GARD: ¹⁹ A Giant congenital nevus is a dark-colored, often hairy patch of skin that is present at birth (congenital). It grows proportionally to the child. A congenital pigmented nevus is considered giant if by adulthood it is larger than 20cm (about 8 inches) in diameter. Giant congenital nevi can occur in people of any racial or ethnic background and on any area of the body. They result from localized genetic changes in the fetus that lead to excessive growth of melanocytes, the cells in the skin that are responsible for skin color. People with giant congenital nevi may have no other symptoms or may have several symptoms such as fragile, dry, or itchy skin. In about 5% to 10% of the cases the Giant congenital nevus is associated with neurocutaneous melanocytosis (excess pigment cells in the brain or spinal cord) and is characterized by neurological symptoms. They also have an increased risk of developing malignant melanoma, a type of skin cancer, especially if the nevus is localized in the vertebral column or when there are multiple associated lesions (satellites).

Orphanet: ⁵⁸ A large, or giant, congenital melanocytic nevus (LCMN or GCMN) is a pigmented skin lesion of more than 20 cm - or 40 cm- respectively, projected adult diameter, composed of melanocytes, and presenting with an elevated risk of malignant transformation.

Disease Ontology: ¹¹ A skin disease characterized by the presence at birth of a pigmented skin lesion composed of melanocytes of more than 20 cm in projected adult diameter that has material basis in somatic mutation in NRAS on chromosome 11p15.5.

Search Clinical Trials, NIH Clinical Center for Large Congenital Melanocytic Nevus