A port wine stain is a common type of birthmark, also known as nevus flammeus, appearing as a permanent skin discoloration. These marks present as a flat patch, ranging in color from pink to red or purplish, often resembling wine spilled on the skin. They are present at birth and affect approximately three out of every 1,000 babies. The presence of such a birthmark often prompts questions about its origin and whether it can be passed down through families.
Understanding Port Wine Stains
Port wine stains are classified as vascular birthmarks, specifically capillary malformations. They appear as smooth, flat patches with distinct borders, commonly found on the face, neck, or scalp, though they can occur anywhere on the body. As an individual grows, the birthmark grows in proportion to the body. Over time, the color of a port wine stain can deepen, and its texture may change, becoming thicker or developing a bumpy surface.
These birthmarks result from abnormally formed or dilated capillaries, tiny blood vessels just beneath the skin’s surface. These capillaries are wider than usual, causing blood to pool within them. This pooled blood causes the characteristic pink, red, or purple hue observed in port wine stains.
The Hereditary Question
For the majority of individuals, port wine stains are not hereditary. These birthmarks are sporadic, meaning they occur randomly and are not inherited from parents. The genetic change leading to a port wine stain is a somatic mutation. This mutation occurs after conception during early development.
A somatic mutation is present only in affected skin cells, not in germline cells (sperm or egg). Since the mutation is not in the germline, it cannot be passed to future generations. A specific somatic mutation in the GNAQ gene (R183Q) is responsible for a high percentage of isolated port wine stains. This mutation leads to an overactive protein, disrupting normal blood vessel development and function in the affected area.
Genetic Links and Syndromes
While most isolated port wine stains are not inherited, some can be a feature of more complex genetic syndromes. These syndromes often involve additional health issues beyond the skin manifestation.
One such condition is Sturge-Weber Syndrome (SWS), which includes a port wine stain as a symptom. SWS is a neurocutaneous disorder affecting blood vessels in the brain, skin, and eyes. The port wine stain associated with SWS typically appears on the face, frequently on the forehead or eyelid.
Like isolated port wine stains, SWS links to a GNAQ somatic mutation. However, in SWS, this mutation affects blood vessels in the brain and eyes, potentially leading to complications like glaucoma and seizures. Sturge-Weber Syndrome itself is generally not inherited.
Another condition featuring a port wine stain is Klippel-Trenaunay Syndrome (KTS). KTS features a port wine stain, often covering part of a limb, alongside abnormal development of blood vessels, soft tissues, and bones, leading to overgrowth of the affected limb. Like SWS, KTS is almost always sporadic, typically caused by somatic mutations, frequently in the PIK3CA gene, rather than being inherited. In rare instances, familial forms of port wine stains, distinct from typical cases, may occur due to germline mutations in genes like RASA1. These familial cases, however, represent a small exception to the general rule that port wine stains are not hereditary.