Giant congenital nevus

Alternate names

GPHN; Giant pigmented hairy nevus; Giant pigmented nevus; Bathing trunk nevus; Large congenital melanocytic nevus; Congenital giant pigmented nevus; Giant hairy nevus; Congenital hairy nevus; Giant congenital melanocytic nevus

Definition

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.

Epidemiology

Giant congenital melanocytic nevus occurs in approximately 1 in 20,000 newborns worldwide.

Cause

• NRAS gene mutations cause most cases of giant congenital melanocytic nevus.
• Rarely, mutations in the BRAF gene are responsible for this condition.
• The proteins produced from these genes are involved in a process known as signal transduction by which signals are relayed from outside the cell to the cell's nucleus.

Gene mutations

• The NRAS or BRAF gene mutations responsible for giant congenital melanocytic nevus are somatic, meaning that they are acquired during a person's lifetime and are present only in certain cells.
• These mutations occur early in embryonic development during the growth and division (proliferation) of cells that develop into melanocytes.
• Somatic NRAS or BRAF gene mutations cause the altered protein in affected cells to be constantly turned on (constitutively active) and relaying signals.
• The overactive protein may contribute to the development of giant congenital melanocytic nevus by allowing cells that develop into melanocytes to grow and divide uncontrollably, starting before birth.

Inheritance

This condition is generally not inherited but arises from a mutation in the body's cells that occurs after conception. This alteration is called a somatic mutation.

Signs and symptoms

• 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).

Clinical presentation

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

80%-99% of people have these symptoms

• Congenital giant melanocytic nevus(Giant pigmented mole)

30%-79% of people have these symptoms

• Generalized hirsutism(Excessive hairiness over body)

5%-29% of people have these symptoms

• Cutaneous melanoma
• Hydrocephalus(Too much cerebrospinal fluid in the brain)
• Hypopigmented skin patches(Patchy loss of skin color)
• Pruritus(Itching)
• Rhabdomyosarcoma
• Seizure
• Subcutaneous nodule(Firm lump under the skin)

Diagnosis

Molecular Genetics Tests may include:

• Methylation analysis
• Sequence analysis of select exons
• Targeted variant analysis
• Deletion/duplication analysis
• Sequence analysis of the entire coding region

Treatment

• Treatment for giant congenital nevus depends on the age of the affected individual as well as the size, location, and thickness of the nevus.
• Surgery may be done to remove the nevus, particularly when there is a concern that it may develop into a melanoma.
• When small nevi are removed, the surrounding skin can often be pulled together with stitches.
• Larger nevi may need to be removed in several stages and full-thickness skin grafts may be needed to help the skin heal following surgery.
• When surgery is not possible, other treatment may include procedures such as curettage, dermabrasion, and ablative laser therapy which may be used for superficial skin imperfections, including reducing pigment and hair, but cannot completely remove the nevus.
• Affected individuals should self-monitor and continue to have regular skin examinations to check for benign or malignant tumors.
• Early awareness will allow their physicians to adjust treatment protocols accordingly.
• Children are most likely to show neurological signs before primary school and can respond well to a range of symptomatic therapies.

NIH genetic and rare disease info

• NIH info on Giant congenital nevus

Giant congenital nevus is a rare disease.

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