You must be referring to an autistic savant. Basically, its an autistic person who has savant syndrome.

Savant syndrome is a condition where an individual has a mental condition like autism. Not only that, but they also have profound abilities or capabilities in excess of what is considered normal.

There is no servant syndrome, It is likely that you are thinking albeit with bad spelling of Savant Syndrome. and it is recessive

The symptoms of Savant Syndrome are not to be confused with autism. It is a form of autism, but the children seem to do well at one special skill, such as drawing or math, going into the exceptional category but other skills they are below average.

First, I suggest reading "Born on a Blue day" by Daniel Tammet. The author is Autistic Savant and the book is about his experience with the syndrome. A definition from MedicineNet.com is: Autistic savant: A person with autism who is exceptionally gifted in a specialized field. That field may, for example, be mathematics. The autistic savant may be able to do rapid, complex mental calculations. Or the field may be music. The autistic savant may be able to perform a entire piece of music after hearing it only once. The term "autistic savant" has replaced the old term "idiot savant," which is perjorative and imprecise. A savant (from the French savoir, to know) is a sage, a learned person.