Linear Nevus Sebaceous Syndrome: The Syndrome
For some people who have a sebaceous nevus, other problems occur as well: seizures, cognitive and other developmental delays, ocular (eye) disorders, skeletal and other abnormalities. This combination of the nevus and additional symptoms constitutes a diagnosis of Linear Nevus Sebaceous Syndrome. The syndrome is a neurocutaneous disorder (neuro=nervous system; cutaneous=skin-related).
The so-called classic triad of an LNSS diagnosis includes the sebaceous nevus, seizures, and intellectual disability (otherwise known as mental retardation). However, other combinations of symptoms may receive the diagnosis as well, generally if the nevus and one other of the classic triad are present.
Other organ systems commonly involved in LNSS are the ocular system (eyes), skeletal system (bones), cardiovascular system (heart & blood vessels), and genitourinary system. There can also be other nervous system symptoms beyond the epilepsy and cognitive delays. As more case studies continue to be published, the variety of recognizably related symptoms has grown over the years.
Since LNSS is often studied together with other epidermal nevus syndromes, articles often combine the two when they make lists of symptoms. A list that includes symptoms not only of LNSS but also other epidermal nevus syndromes can be found at The Doctor's Doctor. The symptoms in the chart are listed alphabetically within organ systems and not in order of frequency. The chart also does not tell which symptoms are associated with which variety of epidermal nevus syndrome.
How Many People Have LNSS?
One textbook claims that of people born with sebaceous nevi, 1.7% are born with additional syndrome symptoms, and up to 10% will develop syndrome issues as children. [Rook 15.26] However, these numbers may not be accurate; the references supporting them are considerably outdated.
I have not been able to find an estimate of how many people in the world are affected. LNSS is listed with the National Organization for Rare Disorders, which defines rare as affecting "fewer than 200,000 people in the United States."
What Causes LNSS?
LNSS is a genetic disorder that is not inherited. For many years it was suspected to involve mosaicism [Harper, p.1139], in which the genetic difference does not occur system-wide. Recent research has now shown that suspicion to be true. In 2011, genetic sequencing research was able to identify mutations in two genes that are now thought to be the cause of both nevus sebaceous and linear nevus sebaceous syndrome. The mutations happen during pregnancy and are present in the nevi but not in surrounding tissues. [Groesser 783] Only two patients with LNSS were studied in this research; the other 65 patients had only the nevus without further syndrome symptoms. The same mutations, however, were found in nevus tissue both when the syndrome was present, and when it was not.
LNSS diagnosis is still made by observing symptoms.
How is LNSS Treated?
Since LNSS can involve so many combinations of symptoms, there is no single treatment. A variety of symptoms may require a variety of specialists: dermatologist for the nevus, neurologist for epilepsy, opthalmologist for ocular problems, and so forth. It can also be helpful to work with a geneticist for a broader view of the condition, and for coordination of care.