Birthmarks are common skin markings present at birth or appearing shortly afterward. They vary in color, size, and shape, representing an overgrowth of normal cells or tissues in a specific skin area. They are broadly categorized into vascular birthmarks, involving blood vessels, and pigmented birthmarks, involving pigment-producing cells.
Defining Rarity in Birthmarks
A birthmark’s rarity is determined by its incidence rate within the general population. While common moles or salmon patches are widespread, other birthmarks are statistically infrequent. Rarity can also be linked to unique characteristics, such as unusual size or location, or an association with underlying medical conditions or syndromes. Rare birthmarks occur in a very small percentage of newborns.
Exceptionally Rare Birthmark Types
Among exceptionally rare birthmarks, the Giant Congenital Melanocytic Nevus (GCMN) is notable. This dark-colored skin patch, composed of melanocytes, is present at birth or appears soon after. GCMNs vary from tan to black, with surfaces that can be flat, rough, raised, or bumpy, often featuring excessive hair growth. They are typically found on the trunk, limbs, or head and neck, growing to at least 40 centimeters (15.75 inches) across by adulthood. Individuals with GCMN may also have additional smaller nevi, known as satellite nevi, scattered over the skin.
Nevus of Ota is a blue, bluish-gray, or brown patch of pigmentation primarily affecting the face. It typically appears along the trigeminal nerve distribution, often involving the eye, forehead, nose, cheek, and temple. The sclera is involved in about two-thirds of cases, which can increase glaucoma risk. While often present at birth, it can also emerge during puberty.
Klippel-Trenaunay Syndrome (KTS) is a rare disorder characterized by a triad of features, including a distinct port-wine stain. This flat, red or purple birthmark results from an overgrowth of small blood vessels near the skin’s surface. In KTS, the port-wine stain typically covers part of one limb, and its color can vary or darken with age. The syndrome also involves malformations of veins and an overgrowth of soft tissues and bones, often affecting the same limb.
Sturge-Weber Syndrome (SWS) also features a port-wine birthmark, usually on the face, specifically the forehead, temple, or eyelid. This pink to deep purple birthmark results from dilated capillaries close to the skin’s surface. The mark is typically present at birth and often appears on one side of the face, though it can extend to both. Over time, the skin within the birthmark may darken and thicken.
The Underlying Causes of Rare Birthmarks
The development of rare birthmarks often stems from specific genetic or developmental anomalies during fetal growth. Giant Congenital Melanocytic Nevi (GCMN) are caused by somatic gene mutations, most commonly in the NRAS gene and sometimes in the BRAF gene. These mutations occur spontaneously during early embryonic development, leading to an uncontrolled proliferation of melanocytes, the pigment-producing cells, forming the characteristic large, dark lesions.
Nevus of Ota results from the entrapment or failed migration of melanocytes to the dermal layer of the skin during embryonic development. While the precise cause remains under investigation, some research suggests a GNAQ gene mutation may play a role. Hormonal factors have also been considered, as the birthmark can sometimes appear or darken during puberty or pregnancy.
Klippel-Trenaunay Syndrome (KTS) is almost always sporadic, meaning it is not inherited, and is primarily caused by somatic mutations in the PIK3CA gene. This gene provides instructions for a protein involved in cell growth and division. PIK3CA mutations lead to abnormal protein activity, resulting in the excessive growth of bones, soft tissues, and blood vessels that characterize the syndrome, including the port-wine stain.
Sturge-Weber Syndrome (SWS) is also a sporadic condition, caused by a somatic mosaic mutation in the GNAQ gene. This mutation occurs randomly during early fetal development. The GNAQ gene mutation results in abnormal development and growth of blood vessels, leading to the formation of the port-wine birthmark on the skin and vascular malformations in the brain and eyes.
When to Seek Medical Evaluation for Birthmarks
While many birthmarks are harmless, seek medical evaluation for any birthmark, especially those that are rare or exhibit concerning characteristics. A medical professional should assess any birthmark that changes in size, shape, color, or texture, or begins to itch, bleed, or cause pain. Large or unusually located birthmarks also warrant professional assessment. For rare birthmarks like GCMN, KTS, or SWS, early diagnosis is important due to potential associated health considerations beyond skin manifestations. A healthcare provider can provide an accurate diagnosis and discuss appropriate management or monitoring strategies.