At the family medicine clinic, a 17 year old male named Heath came in because of lower back pain. Clinical examination reveals lots of small growths on the face, light flat patches throughout his body, and a darker raised patch on his forehead. Heath was adopted early in his life and his family history is unknown. Abdominal ultrasound reveals an angiomyolipoma of the left kidney. Next to Heath, there’s an 8 year old child named Sylvia. Sylvia complains of difficulty seeing what the teacher is writing in school. She also has a purple mark that covers the forehead and her right upper eyelid. Eye examination reveals increased intraocular pressure in the right eye. Her medical history includes an episode of seizure when she was 5 years old. A brain MRI is ordered and reveals brain atrophy. Finally, there’s a 45 year old male named Austin who came in because of a ringing sound in his ears and a gradual loss of hearing. Brain MRI reveals bilateral masses on the cerebellopontine angle.
Okay, so all of them have a neurocutaneous syndrome. Neurocutaneous syndromes primarily affect the nervous system and the skin. They include Sturge-Weber syndrome, tuberous sclerosis, neurofibromatosis type I and II, and Von Hippel-Lindau disease. For the exams remember that Sturge-Weber occurs due to sporadic mutations, while tuberous sclerosis, neurofibromatosis type I and II, and Von Hippel-Lindau disease are autosomal dominant conditions.
Alright, now let’s take a closer look at these different disorders, starting with Sturge-Weber syndrome, which is also known as encephalotrigeminal angiomatosis. During week 6 of development, as the cephalic portion of the neural tube grows, a network of tiny blood vessels called a vascular plexus develops. There’s a gene called the GNAQ gene which codes for a guanine nucleotide-binding protein that is involved in the development of that plexus. Normally, around week 9, the GNAQ gene stops getting expressed, leading to the regression of the vascular plexus. But in Sturge-Weber syndrome, a sporadic mutation occurs that let some cells keep making GNAQ proteins. The mutated cell then replicates over and over, so all of the cells that descend from it have the mutation.