What would cause someone who has a large port-wine stain birthmark on their arm also have 2 and half inch difference in the girth of that but not normal arm?

Sturge-Weber syndrome (SWS), also known as encephalotrigeminal angiomatosis, is a rare neurocutaneous disorder characterized by a triad of symptoms:

- A facial port-wine stain birthmark, usually involving the upper eyelid and forehead.

- Seizures

- Developmental delays or intellectual disabilities.

Additional features of SWS can include:

- Glaucoma (increased pressure within the eye)

- Eyelid drooping (ptosis)

- Hemiparesis (weakness on one side of the body)

- Skin changes, such as thickening of the skin (cutis marmorata telangiectatica congenita) and angiomas

- Mental retardation

The cause of SWS is unknown, but it is thought to be caused by a genetic mutation that occurs early in embryonic development. SWS is a sporadic disorder, meaning that it is not typically inherited from parents.

Treatment for SWS focuses on managing the symptoms of the condition, such as seizures, eye problems, and developmental delays. There is no cure for SWS, but early diagnosis and treatment can help improve the quality of life for people with this condition.